How to Successfully Design a Drainage System for
Compliance with the New Urban Stormwater
Management Manual by D.I.D.
Workshop No. 3How to Design Detention/Sediment Basins and Culverts
for Compliance with the
“Urban Stormwater Management Manual for Malaysia” by D.I.D.
A 2-Day Hands-On Training Workshop* Organised By:
Dr. Quek & Associates
http://www.msmam.com
7th Workshop
26 – 27 June 2008
Venue: Universiti Teknologi Malaysia, Kuala Lumpur
* This is an BEM (Board of Engineers Malaysia) endorsed course. The BEM CPD (Continuing Professional Development) policy
requires all registered engineers to undertake a minimum of 50 hours of CPD per year. Attendance at this seminar attracts
valuable CPD hours towards your total. This workshop is accredited with 16 CPD hours by BEM.
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
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TABLE OF CONTENTS
INTRODUCTION TO THE WORKSHOP .............................................................. 1
What Can You Gain from the Workshop? .................................................................... 1
Objectives of the Workshop and this Publication .......................................................... 3
Target Audience/Prerequisite .......................................................................................... 4
Content of the Workshop ................................................................................................. 4
Chief Course Instructor and Biodata.............................................................................. 4
Author, Publisher and Copyright.................................................................................... 5
Contact Details .................................................................................................................. 5
Request for Login Name and Password to MEMBERS ONLY area ........................... 6
Free eCourse ...................................................................................................................... 6
Training Certificate .......................................................................................................... 6
BEM/CPD Accreditation .................................................................................................. 6
Notations Used in this Publication................................................................................... 7
1
INTRODUCTION ........................................................................................ 8
1.1
General ................................................................................................................... 8
1.2
Design for Water Quantity and Quality Control ............................................... 8
1.3
Design for Quantity Control ................................................................................ 9
1.3.1
Major and Minor Systems ............................................................................... 9
1.3.2
Major and Minor Storms ............................................................................... 12
1.3.3
Major and Minor Systems Design Concepts ................................................ 12
1.3.4
Devices for Quantity Control ........................................................................ 13
1.3.4.1 Detention Storage.................................................................................. 13
1.3.4.2
Retention Storage .................................................................................. 14
1.4
Design for Quality Control ................................................................................. 15
1.4.1
Quality control criteria .................................................................................. 15
1.4.2
Differences between design for Quantity and Quality Control .................... 15
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1.4.3
Devices for Quality Control .......................................................................... 16
1.4.3.1 Post-Construction Stage ........................................................................ 16
1.4.3.2
During Construction Stage .................................................................... 17
1.5
Changes from the Planning and Design Procedure No. 1 ............................... 18
1.6
Relevant sections in MSMAM ........................................................................... 19
1.7
Summary Sheet ................................................................................................... 19
2.
DESIGN OF DETENTION BASIN ............................................................ 21
2.1
Review of Level Pool Routing Procedure ......................................................... 21
2.1.1
Storage Routing Method ............................................................................... 21
2.1.2
Worked Example 2.1- Level Pool Routing Through A Reservoir................ 25
2.1.3
Notes about the Spreadsheet Computation ................................................... 29
2.1.4
Changes from the Planning and Design Procedure No. 1 ............................. 30
2.1.5
Relevant Sections in MSMAM ...................................................................... 30
2.2
Detention Basin Routing..................................................................................... 31
2.2.1
Theory ........................................................................................................... 31
2.2.2
Worked Example 2.2 .................................................................................... 31
2.2.2.1 Problem................................................................................................. 31
Determine design storm criteria for the basin .................................... 32
2.2.2.3
Determine the permissible outflow from basin ................................... 32
2.2.2.4
Compute the basin inflow hydrograph ................................................ 34
2.2.2.5
Preliminary estimate of the required storage volume ......................... 35
2.2.2.6
Develop a basin grading plan .............................................................. 37
2.2.2.7
Compute the stage-storage relationship .............................................. 38
2.2.2.8
Sizing of the minor design storm primary outlet ................................ 38
2.2.2.9
Sizing of the major design storm primary outlet ................................. 39
2.2.2.10
Sizing of the secondary spillway outlet............................................... 40
2.2.3
2.2.4
2.2.2.2
2.3
Worked Example 2.3 .................................................................................... 51
Worked Example 2.4 .................................................................................... 51
Summary Sheet ................................................................................................... 52
Appendix 2A Computation of Design Storm ................................................................ 54
2.1
Design Rainfall .................................................................................................... 54
2.1.1
Computation of Design Rainfall ................................................................... 54
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Derivation of IDF Curves using MSMAM ........................................................... 54
Work Example 2.1- Derive IDF Curve for Ipoh ........................................................... 56
2.1.2.1 Derivation of IDF curves ...................................................................... 56
2 .......................................................................................................................... 57
2.1.2.2 How to Create the Spreadsheet ............................................................. 59
2.1.3.1
How to Use the Spreadsheet ................................................................. 59
Appendix 2B Rational Method ...................................................................................... 60
2.4
Design Discharge ................................................................................................. 60
2.4.1
Methods of computing peak discharges ........................................................ 60
2.4.1.1 Methods in MSMAM ............................................................................ 60
2.4.2
Rational Method of MSMAM ........................................................................ 62
2.4.2.1 Theory ................................................................................................... 62
2.4.2.2
Worked Example 2.3- Rational Method for a minor drainage system in
Ipoh
67
2.4.2.3
How to Create a Spreadsheet ................................................................ 70
3.
DESIGN OF SEDIMENT BASIN .............................................................. 71
3.1
Definition ............................................................................................................. 71
3.2
General Criteria for Installation of Sediment Basins ...................................... 71
3.3
Criteria for Sizing of Sediment Basins .............................................................. 72
3.4
Design of Dry Sediment Basins .......................................................................... 72
3.5
Design of Wet Sediment Basins ......................................................................... 73
3.6
Worked Example 3.1- Design of A Dry Sediment Basin ................................. 75
3.6.2.1 Settling Zone ......................................................................................... 76
3.6.2.2
Sediment Storage Zone ......................................................................... 77
3.6.2.3
Overall Basin Dimensions .................................................................... 78
3.7
Worked Example 3.2- Design of A Dry Sediment Basin (Ipoh) ..................... 81
3.8
Worked Example 3.3- Design of A Wet Sediment Basin ................................. 83
3.8.2.1 Settling Zone ......................................................................................... 84
3.8.2.2
Sediment Storage Zone ......................................................................... 85
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3.8.2.3
Overall Basin Dimensions .................................................................... 85
3.9
Worked Example 3.4- Design of A Wet Sediment Basin (Melaka) ................ 88
3.10
Worked Example 3.5- Design of A Dry Sediment Basin (Kuching) ............... 88
3.11
Worked Example 3.6- Design of A Wet Sediment Basin (Kuching) .............. 89
Appendix 3.1- Design of Silt Trap Using the Planning and Design Procedure No. 1Incorporating an Overflow Weir and Bypass Channel ............................................... 92
4.
DESIGN OF CULVERTS ....................................................................... 114
4.1
Inlet Control ...................................................................................................... 114
4.2
Outlet Control ................................................................................................... 114
4.2.1
Theory ......................................................................................................... 115
4.2.1.1 Velocity head (Hv) ...................................................................................... 115
4.2.1.2 Entrance loss (He) ....................................................................................... 115
4.2.1.3 Friction loss (Hf) ......................................................................................... 116
4.2.1.4 Total Energy Head (H)................................................................................ 116
4.2.1.5 Determining Headwater (HW) .................................................................... 117
4.3
Work Example 4.1 (Concrete Box Culvert) ................................................... 118
4.3.1
Case Study .................................................................................................. 118
4.3.2
Design for 50 years ARI ............................................................................. 118
4.3.3
Design for 100 years ARI ........................................................................... 120
4.3.4
Spreadsheet Computation ........................................................................... 122
4.4
Work Example 4.2 (Concrete Box Culvert) ................................................... 123
4.5
Work Example 4.3 (Concrete Pipe Culvert)................................................... 123
4.6
Work Example 4.4 (Rating Curve).................................................................. 124
4.7
Work Example 4.5 (Peak Discharges) ............................................................. 124
5.
REFERENCES: ..................................................................................... 126
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
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How to Successfully Design a Drainage
System for Compliance with the New Urban
Stormwater Management Manual by D.I.D.
Workshop No. 3How to Design Detention & Sediment Basins and Culverts for
Compliance with the “Urban Stormwater Management
Manual for Malaysia” by D.I.D.
INTRODUCTION TO THE WORKSHOP
What Can You Gain from the Workshop?
As an engineer, do you have problem understanding all the requirements of the new
urban drainage design procedure gazetted by the Federal Government in 2001- the
“Urban Stormwater Management Manual for Malaysia” (“Manual Saliran Mesra
Alam Malaysia” or abbreviated as MSMAM) published by the Department of Irrigation
and Drainage (D.I.D.)?
If the answer is yes, then the following section contains some important information for
you.
Before 2001, engineers in Malaysia applied the “Planning and Design Procedure No. 1”
published by D.I.D. in 1975 for all their drainage design. This is a relatively simple
document to use- with only 242 pages covering ten chapters. But this has changed with
the implementation of MSMAM by the Government in 2001.
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It is a fact that the new Manual is much more thorough in its coverage of subject matters
compared to the old procedure. It contains 48 chapters spanning more than 1,100 pagesabout five times thicker compared to the “Planning and Design Procedure No. 1.”
The new MSMAM is an impressive document by any standards. Its content reflects the
latest advances in the field of stormwater quantity and quality management from around
the world, with many major changes in approaches and procedures. The preparation of
MSMAM was a task involving a large team of local and foreign experts, costing million
of Ringgits and took years to complete.
Not surprisingly, because of above, many engineers are still not familiar with the
requirements of MSMAM.
By attending the Workshop, you will learn:
1. How to solve drainage problems using the new “control-at-source” approach,
instead of the old approach of “rapid-disposal”,
2. What are the water quality issues you must considered- in addition to the drainage
issues when solving a drainage problem,
3. What are the new computer modelling techniques recommended, and
4. What are the major changes in design procedures and recommendations for
solving urban drainage and water quality issues.
The 2-Day Workshop will cover both the theoretical and practical aspects of urban
drainage design based on MSMAM. The theoretical aspect will give the students a broad
understanding of the principles behind various design procedures, while the practical
aspect will include many worked examples to ensure that the students can put theories
into practice.
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The Workshop will highlight the major differences between MSMAM and the Planning
and Design Procedure No. 1. It will also introduce participants to the tools, software and
resources available for application of the new design procedures.
Following are benefits of attending the Workshop:
1. You will be guided by a qualified lecturer with more than 20 years of industrial
experience in the fields of hydrology, hydraulic and water quality modelling, and
has extensive experience in applying the HEC-HMS and HEC-RAS Models.
2. You will benefit from the lecturer’s past involvement in the review process of
MSMAM and his experience in conducting courses on the “Workshop Series on
MSMAM.”
3. You will receive hands-on training using a PC with broadband internet connection
in a modern PC laboratory.
4. You will get a set of specially prepared course note which covers both theories
and step-by-step worked examples.
5. You will be taught the new requirements of MSMAM and the major changes from
the Planning and Design Procedure No. 1.
6. You can download many free computer programs for use with MSMAM. Note
these programs are extremely useful and can be used for your work, without
having to spend a lot of time rewriting them yourself.
7. You will get free lifetime access to the website http://www.msmam.com to
download new updated programs/software and course material.
8. You will be entitled to free lifetime technical support for material covered in the
course by email/phone and through the website. Email: webmaster@msmam.com
9. This workshop is endorsed by BEM for its Continuing Professional Development
(CPD) programme. You can gain valuable CPD hours by attending the workshop.
Objectives of the Workshop and this Publication
The objective of the workshop is to introduce the procedures for urban drainage design
for compliance with the “Urban Stormwater Management Manual for Malaysia.”
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The objectives of this publication are as follows:

To provide the workshop material for the 2-Day Workshop

To provide a resource material in urban drainage design for all participants of the
Workshop.
Target Audience/Prerequisite
The course is suitable for engineers/graduates in civil/environmental engineering. The
basic requirement is a degree in the above disciplines.
There is no prerequisite for Workshop No. 1 and 2. However, the prerequisite for
Workshop No. 3 is Workshop No. 1.
Content of the Workshop
Following are the major topics covered in this Workshop:
1. Design concept for quantity and quality control.
2. Design of detention basin.
3. Design of dry and wet sediment basins.
4. Design of culvert.
Chief Course Instructor and Biodata
The chief course instructor is Ir. Dr. Quek Keng Hong, who is a consulting engineer by
practice and the principal of Dr. Quek & Associates. He obtained his Civil Engineering,
Master of Engineering Science and Ph.D. degrees from the University of NSW, Australia.
He has over 20 years of post-graduate experience mainly in consultancy work. He
specialises in the field of water resources including hydrologic and hydraulic modelling
and environmental management.
Dr. Quek is a regular contributor of engineering journals, seminars and conferences, with
more than 30 publications to his credit. He has conducted regular workshops, seminars
and talks in his fields of expertise.
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Dr. Quek was the reviewer representing IEM in the review process of MSMAM
organised by D.I.D. He was the former Chairman of the Water Resources Technical
Division of IEM.
Dr. Quek has conducted a 4-day workshop entitled “Advanced Course On Urban
Drainage Design For Compliance With The New ‘Urban Stormwater Management
Manual For Malaysia’ By D.I.D.” jointly organised by the Water Resources Technical
Division and IEM Training Centre between 20 and 23 August, 2002.
Between 2002 and 2003, he has also conducted three 2-day workshops on MSMAM in
association with IEM training Centre in Petaling Jaya and Penang.
He was one of the presenters of the 2-day course entitled “Introduction to MSMAM”
conducted by the Water Resources Technical Division of IEM in conjunction with the
following State D.I.D’s in 2000 and 2001: Selangor, Wilayah Persekutuan, Pahang,
Trengganu, Melaka and Negeri Sembilan.
Over the years, Dr. Quek has also conducted numerous talks and seminars on MSMAM
at IEM HQ and other states.
Author, Publisher and Copyright
This Manual is prepared by Ir. Dr. Quek Keng Hong and published by Dr. Quek &
Associates.
The copyrights of all software referred to in this manual belong to their respective
owners. All rights reserved. No part of this manual may be reproduced, in any form or by
any means, without permission in writing from the publisher.
Contact Details
Office: No. 11-1A, Jalan Bandar 10, Pusat Bandar Puchong, 47100 Puchong, Selangor
Darul Ehsan, Malaysia. Phone: (603) 5882 2085 Facsimile: (603) 5882 1603.
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To contact the author send email to: webmaster@msmam.com. For free software and
information on upcoming courses, visit the course website at:
http://www.msmam.com. All software and worked examples in this manual are available
for download from the above site.
Request for Login Name and Password to MEMBERS ONLY area
You must have your own login name and password (i.e., membership) to access the
MEMBERS ONLY area of http://www.msmam.com to download the FULL versions of
the spreadsheet software and worked examples.
To request for your membership, you must send an email to membership@msmam.com
giving full details of your name, email address, dates of attendance, company address and
contact phone numbers for verification purpose.
Note the membership is given only to participants of the workshop. Sharing of your login
name and password with others may result in withdrawal of your membership without
notice.
Free eCourse
You can subscribe to the Free eCourse at http://www.msmam.com. You can also invite
your friends and colleagues to do the same. The eCourse contains useful reference
material, sent to you at 2-day intervals in a number of installments.
Training Certificate
All participants who successfully completed the Workshop will receive a Training
Certificate.
BEM/CPD Accreditation
This is an BEM (Board of Engineers Malaysia) endorsed course. The BEM CPD
(Continuing Professional Development) policy requires all registered engineers to
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undertake a minimum of 50 hours of CPD per year. Attendance at this seminar attracts
valuable CPD hours towards your total.
Dr. Quek & Associates is an Accredited Training Provider for the BEM CPD
programme. You will gain 16 CPD hr by attending any one of Workshop 1, 2 or 3 i.e., 1
CPD hour for every hour of attendance.
You may keep a copy of the receipt and certificate as proof of attendance required by
BEM. Please note, however, that you must attend the workshop daily and sign the
attendance sheet each day before you will receive your certificate. Payment alone cannot
be accepted as proof of your attendance.
Notations Used in this Publication
In this publication, there are numerous references to figures, tables and appendices in
MSMAM and other publications. These are underlined in order to differentiate them from
the same references used in this publication. The convention adopted is as follows:
If the reference is not underlined e.g., Table 4.1, it refers to a table in this publication.
If the reference is underlined e.g., Table 4.1, it refers to a table in MSMAM.
If the table is taken from a publication other than MSMAM, then the source is stated after
the table reference e.g., Table 1 of HP11.
The above apply to tables, figures, appendices and etc.
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1 INTRODUCTION
1.1
General
Workshop 3 covers the following:

Design concept for quantity and quality control.

Design of detention basin

Design of dry and wet sediment basin

Design of culvert
It is strongly recommended that participant attend Workshop No. 1 before
attending Workshop No. 3 as the fundamentals of design storm computation, timearea method and reservoir routing are covered in the former.
1.2
Design for Water Quantity and Quality Control
Topics to be covered are divided into two broad areas as follows:

Design for Quantity Control, and

Design for Quality Control.
Design for Quantity Control covers the following topics:
1. Major and Minor Systems
2. Major and Minor Storms
3. Major and Minor Systems Design concepts
4. Devices for Quantity Control
Design for Quality Control covers the following topics:
1. Quality control criteria
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2. Differences between design for Quantity and Quality Control
3. Devices for Quality Control
1.3
Design for Quantity Control
1.3.1 Major and Minor Systems
Design concepts for the major and minor systems are illustrated diagrammatically
in Figure 1.1.
The basic concepts of major and minor systems are discussed below:
Minor system is designed to convey runoff from a minor storm, which occurs
relatively frequently, and would result in inconvenience and nuisance flooding.
Examples: kerbs, gutters, inlets, open drains and pipes.
Major system is designed to convey runoff from a major storm, which comprises
the many planned and unplanned drainage routes that convey runoff to waterways
and rivers. It is designed to protect the community from the consequences of large
and rare events which could cause severe flood damage, injury and loss of life.
Differences between the design objectives of Major and Minor System are
summarised in Table 1.1.
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FIGURE 1.1 MAJOR AND MINOR SYSTEM DESIGN CONCEPTS (DID, 2000)
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The choice of design standards for both major and minor storms should be made
by economic analysis, considering the tangible and intangible costs and benefits
of different levels of protection.
AN ILLUSTRATION OF DESIGN FOR QUANTITY CONTROL
Design for Quantity Control
Rare major
storm, severe
damage and
loss of life
Frequent minor
storm, nuisance
flooding
Major System
(Major drains or planned
drainage routes)
Minor System
(Kerbs, gutters, inlets,
open drains and pipes)
TABLE 1.1 MAJOR AND MINOR SYSTEM DESIGN OBJECTIVES (DID, 2000)
MAJOR SYSTEM
MINOR SYSTEM
Reduced injury and loss of life
Improved aesthetics
Reduced disruption to normal business
Reduction in minor traffic accidents
activities
Reduced damage to infrastructure services Reduced health hazards (mosquitoes, flies)
Reduced emergency services costs
Reduced personal inconvenience
Reduced flood damage
Reduced roadway maintenance
Reduced loss of production
Reduced clean-up costs
Increased feeling of security
Increased land values
Improved aesthetics and recreational
opportunities
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1.3.2 Major and Minor Storms
Major and minor storms- Table 4.1 shows the design storm ARIs for urban
stormwater systems.
It can be seen that the ARI for minor system ranges from 1, 2, 5 to 10 years
depending on the types of development. The ARI for major system, however,
ranges up to 100 years for all types of development.
1.3.3 Major and Minor Systems Design Concepts
There are major differences in approach on the design for minor and major
systems. These are presented in Figure 1.2 and discussed as follows:
Community facilities are major drainage structures for larger areas which
combine different landuse areas. Quantity design based on hydrograph approach
using larger storms of up to 100 years ARI.
On-site facilities are minor drainage structures provided for individual housing
and industrial sites. Quantity design for ARI of 2 and 10 years.
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FIGURE 1.2 GENERAL DESIGN CONCEPT FOR MAJOR AND MINOR
SYSTEMS (DID, 2000)
1.3.4 Devices for Quantity Control
The main devices for stormwater quantity control are as follows:

Detention Storage- either Onsite Detention (OSD), Community Detention or
Regional Detention (Chapters 19 and 20 of MSMAM).

Retention Storage- either Onsite Retention, Community Retention or Regional
Retention (Chapters 21 and 22 of MSMAM).
1.3.4.1 Detention Storage
The basic concept of providing detention storage is to limit the peak outflow rate
for a specific range of flood frequencies to that which existed before
development.
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The primary function of detention facilities is to reduce peak discharge by the
temporary storage and gradual release of stormwater runoff by way of an outlet
control structure.
Examples of Onsite Detention include: car park, surface and underground tanks,
rooftop and landscaped area. See Figure 18.2.
Community and Regional Detention facilities are larger facilities than OSD which
are provided in public areas outside private properties. These are commonly
formed by the construction of an embankment across a stream and/or the
excavation of a basin storage area.
Two main types: dry and wet basins.
Examples of dry basins include public parks and playing fields.
Examples of wet basins include: ponds and lakes.
1.3.4.2 Retention Storage
True retention facilities reduce runoff volume and peak discharge by the
temporary storage of stormwater runoff, which is subsequently released via
evaporation and infiltration only.
Examples of Onsite and Community Retention include: infiltration trench,
soakaway pit, porous pavement and infiltration basin. See Figure 18.2.
Examples of Regional Retention include: basin method, Ditch and Furrow
Method, flooding method, irrigation method and recharge well method (refer
Chapter 18).
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1.4
Design for Quality Control
1.4.1 Quality control criteria
Criteria for sizing for sediment retention (Chapter 4):
3 month ARI for construction project taking < 2 years
6 month ARI for construction project taking > 2 years
1.4.2 Differences between design for Quantity and Quality Control
Table 1.2 summarises the major differences between design for quantity and
quality control. It is important to understand the differences in approach.
Quality control mainly concerns control of sediment, as many pollutants are
attached to sediment particles.
TABLE 1.2 GENERAL HYDROLOGIC DESIGN CONSIDERATIONS
(DID, 2000)
Quantity
Quality
Runoff peak
Runoff volume
Landuse % imperviousness
Landuse activities
Management of infrequent storms
Management of frequent storms
Multi storm ARI design approach
Single storm ARI design approach
(major/minor)
Detention/retention may not perform in
Ponds may not be efficient in infrequent
repeated/multiple storms
storms
Event and continuous (retention only)
modeling
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AN ILLUSTRATION OF DIFFERENCES BETWEEN
QUANTITY AND QUALITY CONTROL
Differences Between Quantity and
Quality Control
Runoff Peak, Infrequent
Storm, Major/Minor
ARI, Event Modelling
Runoff Volume, Frequent
Storms, Single ARI,
Annual Average Load
Modelling
Quantity Control
Quality Control
1.4.3 Devices for Quality Control
1.4.3.1 Post-Construction Stage
Following are the main runoff quality control devices at the post-construction
stage:

Filtration- Examples: Biofiltration swales and vegetated filter strip. Main
processes include: sedimentation, filtration, infiltration, soil adsorption and
biological uptake by plants.

Infiltration- Examples: Infiltration trench, infiltration basin and porous
pavement.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________

Gross Pollutant Trap- Remove coarse sediment (and other pollutants e.g.,
nutrients and metals attached to sediment), litter and debris. Examples:
booms, in-pit devices, trash rack and litter control devices, sediment traps,
SBTR (Sediment Basin and Trash Rack) traps, proprietary devices. Do not
provide flow attenuation.

Constructed Ponds and Wetlands- function both for water quality control and
flood control. Only remove fine sediment. Not suitable for coarse sediment.
Provide temporary flood storage to reduce downstream flow peaks. Improve
water quality by sedimentation and biological processes.
1.4.3.2 During Construction Stage
During the construction stage, the main runoff quality control methods are as
follows:

Erosion and Sediment Control Measures- These are Best Management
Practices (BMP). Examples:site planning considerations, vegetative
stabilization, physical stabilization, diversion of runoff, flow velocity
reduction, sediment trapping and filtering.

Erosion and Sediment Control Plans- Preparation of a ESCP before start of
project detailing types of erosion control measures.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
AN ILLUSTRATION OF DESIGN FOR QUALITY CONTROL
Design for Quality Control
3 mth ARI for construction project < 2 yrs
6 mth ARI for construction project > 2 yrs
During Construction Stage
(BMP, ESCP)
1.5
Post Construction Stage
(Filtration, infiltration,
GPT, SBTR, Ponds and
Wetlands)
Changes from the Planning and Design Procedure No. 1
Following are the major changes from P&DP No. 1:
1. Change from “rapid disposal” to “Control-at-source.”
2. Method of computing design rainfall
3. Design ARI for major and minor systems
4. Computation of peak discharge- empirical and rainfall-runoff model (time-area,
RORB, HEC-HMS, etc)
5. Water quality consideration
6. Use of hydraulic model HEC-RAS
7. More detention, retention and water quality control devices.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
1.6
Relevant sections in MSMAM
Following are the relevant sections of the MSMAM manual referred to in this
Section:
Chapter 4- design criteria
Chapter 11- Hydrologic design concepts
Chapters 19 and 20- Detention Storage
Chapters 21 and 22- Retention Storage
1.7
Summary Sheet
1. The major changes in MSMAM include:

A shift from the old approach of conveyance-based, “rapid-disposal”
approach to the new “control-at-source” approach,

Greater emphasis on water quality management- in addition to water
quantity management,

Greater emphasis on the use of computational models including computer
software,

Changes in design procedures for various drainage components, and

More thorough coverage of subject matters.
2. Topics covered are divided into two broad areas as follows:

Design for Quantity Control, and

Design for Quality Control.
3. Design for Quantity Control covers the following topics:

Major and Minor Systems

Major and Minor Storms

Major and Minor Systems Design concepts

Devices for Quantity Control
4. Design for Quality Control covers the following topics:
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________

Quality control criteria

Differences between design for Quantity and Quality Control

Devices for Quality Control
5. Major differences in approach on the design of detention storage for minor
and major systems:

Onsite Stormwater Detention Facilities (OSD)- minor drainage structures
for individual housing and industrial sites, designed for minor storm, can
use rational methods.

Community or Regional Detention- major drainage structures for larger
areas which combine different landuse areas, designed for both major and
minor storms, located in public lands, hydrograph methods required.
.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
2.
DESIGN OF DETENTION BASIN
2.1 Review of Level Pool Routing Procedure
2.1.1 Storage Routing Method
The sizing of detention basins can be done using a reservoir routing method such
as the Level-Pool Routing Procedure, which computes storage routing by solving
the continuity equation and the storage function.
The continuity equation or the equation of conservation of mass simply expresses
the condition that the rate of inflow less the rate of outflow at any instance in time
is equal to the rate of change in storage in the basin as follows:
I Q 
S
t
(2.1)
where
I
is the instantaneous inflow rate of discharge to the basin (m3/s)
Q
is the instantaneous outflow rate of discharge from the basin (m3/s)
S
is the volume of temporary storage in the basin (m3)
The above equation may be expressed in finite difference form as follows:
I
j
 I j 1 
2

Q
j
 Q j 1 
2

S j 1  S j
t
(2.2)
where
j, j+1 are time steps j and j+1, respectively.
t
is the time interval defining the finite difference approximation of
the continuity equation.
The above equation can be rearranged such that all known variables are placed on
the left side of the equation and all unknown variables on the right as follows:
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
AN ILLUSTRATION OF RESERVOIR ROUTING
Inflow Hydrograph
Hydrograph Method
Initial
Conditions
Si & Qi
Continuity Equation
Storage Function Q=f(S)
S
t
I Q 
 Rating curve: Q=f(H)
 Storage curve: H=f(S)
Outflow Hydrograph
Qp
Qp
t
t
Qp
t
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
AN ILLUSTRATION OF APPLICATION OF DESIGN STORM +
HYDROGRAPH METHOD + RESERVOIR ROUTING METHODS
Design Storm
Calculate IDF data
I
t
Hydrograph Method
Time Area Method or
Runoff Routing Method
Reservoir Routing
Level Pool Routing
Through Detention Storage
Detention Basin
Calculate Water Level
(Workshop 2)
Use HEC-RAS model to
calculate water level in drain
EOpen Drain
Qp
t
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
I
j
2Sj
  2  S j 1

 I j 1   
 Q j   
 Q j 1 
 t
  t

(2.3)
It is evident from the above equation that a second equation is necessary to solve
the two unknown variables of Qj+1 and Sj+1. This second equation is referred to as
the storage function, which expresses the relationship between the storage in the
basin and the discharge from the basin in the form of Q = f(S).
The storage function represents the combined effect of:
1. The discharge characteristics or the “rating curve” as represented by Q=f(H)
2. The topography of the site i.e., the geometric properties as represented by the
storage curve or H versus S data of the storage facility, expressed as H= f(S).
By combining Q=f(H) and H= f(S), the storage-discharge relationship for the
basin or the storage function can be derived as Q = f(S).
The discharge characteristics for a basin with spillway outlet can be represented
by the following spillway discharge equation:
Q s  cL( H  H s ) 3 / 2
(2.4)
where
Qs
is the spillway discharge in m3/s.
c
is the weir coefficient for the spillway (ranging from 1.45 m0.5/s for a
broad crested weir to 2.15 m0.5/s for an ogee crested weir)
L
is the effective length of the spillway (m)
H
is the water level (m)
Hs
is the spillway crest elevation (m)
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
A level pool routing can be carried out using either one of the following
approaches:

a spreadsheet like MS Excel (see Work Example 2.1)

a simple computer program (Fortran Program: resrot1z.zip- a bonus
program given to participants of the Workshop)
2.1.2 Worked Example 2.1- Level Pool Routing Through A Reservoir
This is a worked example using a spreadsheet to perform level pool routing
through a reservoir.
Following are the data required for the solution of Equation 2.3:
1. Time step.
2. Stage-Storage relationship- usually derived from topographic maps.
3. Stage-Discharge relationship- can be based on formula such as Equation 2.4
for spillway or other appropriate formula.
4. The inflow hydrograph.
5. Initial values of storage and discharge.
Excel Filename: DrQuekLevelPoolRouting1a.zip.
Equation 2.3 can be solved using the spreadsheet below as follows:
 2  S j 1

 Q j 1  which is
 t

1. At time j+1, compute the RHS of Equation 2.3 ie, 
equal to the LHS of the equation or the sum of I j  I j 1  and
2Sj



 t  Q j  which are all known. (Col. 4+Col. 5= Col. 6)- See purple cells.


2. Prepare a table of Stage-Discharge-Storage data as referred to above and
 2S

 Q  . (See Col. 9, 10, 11, 12.)- See light blue cells.
compute 
 t

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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
 2  S j 1

 Q j 1  compute the value of Qj+1 and
 t

3. For a particular value of 
water level (which is the sum of stage and the basin elevation at zero stage) by
interpolating the table in (2). (Interpolate Col. 6, 7 & 8 from Col. 12, 10 & 9.)
 2  S j 1

4. Compute the value of 
 Q j 1  which is equal to
 t

 2  S j 1


 Q j 1  minus 2 x Qj+1. (Col. 5= Col. 6 - 2 x Col. 7)- see green
 t

cells.
5. The above process is repeated for each subsequent time steps until the outflow
becomes zero.
TABLE 2.1 LEVEL POOL ROUTING USING SPREADSHEET
1
2
3
4
t
T (min) I
Ij+I(j+1)
(min)
J
12
0 0.0000
j+1
13 0.4375 0.4375
j+2
14 0.875 1.3125
j+3
15 1.3125 2.1875
j+4
16 1.75 3.0625
j+5
17 2.1875 3.9375
j+6
18 2.625 4.8125
j+7
19 3.0625 5.6875
j+8
20
3.5 6.5625
j+9
21 4.14 7.6400
j+10
22 4.78 8.9200
j+11
23 5.42 10.2000
j+12
24 6.06 11.4800
j+13
25
6.7 12.7600
j+14
26 7.34 14.0400
j+15
27 7.98 15.3200
j+16
28 8.62 16.6000
j+17
29 9.26 17.8800
j+18
30
9.9 19.1600
j+19
31 10.45 20.3500
j+20
32
11 21.4500
j+21
33 11.55 22.5500
j+22
34 12.1 23.6500
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5
6
7
8
9
10
11
12
(2Sj/dt) (2S(j+1)/dt) Q(j+1)
WL(mRL)=H H (m)
Q (m3/s) S (m3)
(2S/dt)+Q
-Qj
+Q(j+1)
+Datum
0
0
0
99.5
0.00
0.00
0
0.000
0.2335
0.4375
0.102
99.55
0.025
0.051
4.500
0.201
0.832
1.546
0.357
99.675
0.050
0.102
9.000
0.402
1.8115
3.0195
0.604
99.775
0.075
0.153
13.500
0.603
3.102
4.874
0.886
99.85
0.100
0.204
18.000
0.804
4.5155
7.0395
1.262
99.95
0.125
0.255
22.500
1.005
6.186
9.328
1.571
100.025
0.150
0.306
27.000
1.206
8.0055
11.8735
1.934
100.1
0.175
0.357
31.500
1.407
9.974
14.568
2.297
100.175
0.200
0.408
36.000
1.608
12.294
17.614
2.66
100.25
0.225
0.459
40.500
1.809
15.41
21.214
2.902
100.3
0.25
0.51
45
2.010
19.08
25.61
3.265
100.375
0.275
0.604
59.500
2.587
23.062
30.56
3.749
100.475
0.300
0.698
74.000
3.165
27.888
35.822
3.967
100.525
0.325
0.792
88.500
3.742
33.412
41.928
4.258
100.6
0.350
0.886
103.000
4.319
39.828
48.732
4.452
100.65
0.375
0.980
117.500
4.897
46.942
56.428
4.743
100.725
0.400
1.074
132.000
5.474
54.948
64.822
4.937
100.775
0.425
1.168
146.500
6.051
63.846
74.108
5.131
100.825
0.450
1.262
161.000
6.629
73.352
84.196
5.422
100.9
0.475
1.356
175.500
7.206
83.57
94.802
5.616
100.95
0.50
1.45
190
7.783
94.5
106.12
5.81
101
0.525
1.571
215.400
8.751
106.15
118.15
6
101.05
0.550
1.692
240.800
9.719
Free software
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26
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
j+23
j+24
j+25
j+26
j+27
j+28
j+29
j+30
j+31
j+32
j+33
j+34
j+35
j+36
j+37
j+38
j+39
j+40
j+41
j+42
j+43
j+44
j+45
j+46
j+47
j+48
j+49
j+50
j+51
j+52
j+53
j+54
j+55
j+56
j+57
j+58
j+59
j+60
j+61
j+62
j+63
j+64
j+65
j+66
j+67
j+68
j+69
j+70
j+71
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
12.65
13.2
13.75
14.3
14.85
15.4
14.62
13.84
13.06
12.28
11.5
10.72
9.94
9.16
8.38
7.6
7.16
6.72
6.28
5.84
5.4
4.96
4.52
4.08
3.64
3.2
2.98
2.76
2.54
2.32
2.1
1.88
1.66
1.44
1.22
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
24.7500
25.8500
26.9500
28.0500
29.1500
30.2500
30.0200
28.4600
26.9000
25.3400
23.7800
22.2200
20.6600
19.1000
17.5400
15.9800
14.7600
13.8800
13.0000
12.1200
11.2400
10.3600
9.4800
8.6000
7.7200
6.8400
6.1800
5.7400
5.3000
4.8600
4.4200
3.9800
3.5400
3.1000
2.6600
2.2200
1.9000
1.7000
1.5000
1.3000
1.1000
0.9000
0.7000
0.5000
0.3000
0.1000
106746216 (2/16/16)
118.52
131.61
145.42
159.95
175.466
191.854
207.784
222.04
234.508
245.302
254.422
261.872
267.762
272.092
274.752
275.852
275.732
274.732
272.962
270.312
266.782
262.372
257.192
251.132
244.306
236.714
228.576
220.112
211.322
202.206
192.764
182.996
172.902
162.482
151.812
141.082
130.412
119.732
109.232
98.722
88.396
78.258
68.502
58.934
49.554
40.556
130.9
144.37
158.56
173.47
189.1
205.716
221.874
236.244
248.94
259.848
269.082
276.642
282.532
286.862
289.632
290.732
290.612
289.612
287.732
285.082
281.552
277.142
271.852
265.792
258.852
251.146
242.894
234.316
225.412
216.182
206.626
196.744
186.536
176.002
165.142
154.032
142.982
132.112
121.232
110.532
99.822
89.296
78.958
69.002
59.234
49.654
6.19
6.38
6.57
6.76
6.817
6.931
7.045
7.102
7.216
7.273
7.33
7.385
7.385
7.385
7.44
7.44
7.44
7.44
7.385
7.385
7.385
7.385
7.33
7.33
7.273
7.216
7.159
7.102
7.045
6.988
6.931
6.874
6.817
6.76
6.665
6.475
6.285
6.19
6
5.905
5.713
5.519
5.228
5.034
4.84
4.549
101.1
101.15
101.2
101.25
101.275
101.325
101.375
101.4
101.45
101.475
101.5
101.525
101.525
101.525
101.55
101.55
101.55
101.55
101.525
101.525
101.525
101.525
101.5
101.5
101.475
101.45
101.425
101.4
101.375
101.35
101.325
101.3
101.275
101.25
101.225
101.175
101.125
101.1
101.05
101.025
100.975
100.925
100.85
100.8
100.75
100.675
0.575
0.600
0.625
0.650
0.675
0.700
0.725
0.75
0.775
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.00
1.025
1.050
1.075
1.100
1.125
1.150
1.175
1.200
1.225
1.25
1.275
1.300
1.325
1.350
1.375
1.400
1.425
1.450
1.475
1.50
1.525
1.550
1.575
1.600
1.625
1.650
1.675
1.700
1.725
1.75
1.775
Free software
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27
1.813
1.934
2.055
2.176
2.297
2.418
2.539
2.66
2.781
2.902
3.023
3.144
3.265
3.386
3.507
3.628
3.749
3.87
3.967
4.064
4.161
4.258
4.355
4.452
4.549
4.646
4.743
4.84
4.937
5.034
5.131
5.228
5.325
5.422
5.519
5.616
5.713
5.81
5.905
6.000
6.095
6.190
6.285
6.380
6.475
6.570
6.665
6.76
6.817
266.200
291.600
317.000
342.400
367.800
393.200
418.600
444
482.900
521.800
560.700
599.600
638.500
677.400
716.300
755.200
794.100
833
905.900
978.800
1051.700
1124.600
1197.500
1270.400
1343.300
1416.200
1489.100
1562
1694.500
1827.000
1959.500
2092.000
2224.500
2357.000
2489.500
2622.000
2754.500
2887
3091.000
3295.000
3499.000
3703.000
3907.000
4111.000
4315.000
4519.000
4723.000
4927
5206.500
10.686
11.654
12.622
13.589
14.557
15.525
16.492
17.460
18.878
20.295
21.713
23.131
24.548
25.966
27.384
28.801
30.219
31.637
34.164
36.691
39.218
41.745
44.272
46.799
49.326
51.853
54.380
56.907
61.420
65.934
70.448
74.961
79.475
83.989
88.502
93.016
97.530
102.043
108.938
115.833
122.728
129.623
136.518
143.413
150.308
157.203
164.098
170.993
180.367
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
j+72
j+73
j+74
j+75
j+76
j+77
j+78
j+79
j+80
j+81
j+82
j+83
84
85
86
87
88
89
90
91
92
93
94
95
106746216 (2/16/16)
1.800
1.825
1.850
1.875
1.900
1.925
1.950
1.975
2.00
2.025
2.050
2.075
2.100
2.125
2.150
2.175
2.200
2.225
2.25
2.275
2.300
2.325
2.350
2.375
2.400
2.425
2.450
2.475
2.50
2.525
2.550
2.575
2.600
2.625
2.650
2.675
2.700
2.725
2.75
2.775
2.800
2.825
2.850
2.875
2.900
2.925
2.950
2.975
3.00
Free software
at http://www.msmam.com
28
6.874
6.931
6.988
7.045
7.102
7.159
7.216
7.273
7.33
7.385
7.440
7.495
7.550
7.605
7.660
7.715
7.770
7.825
7.88
7.932
7.984
8.036
8.088
8.140
8.192
8.244
8.296
8.348
8.40
8.451
8.502
8.553
8.604
8.655
8.706
8.757
8.808
8.859
8.91
8.958
9.006
9.054
9.102
9.150
9.198
9.246
9.294
9.342
9.39
5486.000
5765.500
6045.000
6324.500
6604.000
6883.500
7163.000
7442.500
7722
8069.900
8417.800
8765.700
9113.600
9461.500
9809.400
10157.300
10505.200
10853.100
11201
11594.900
11988.800
12382.700
12776.600
13170.500
13564.400
13958.300
14352.200
14746.100
15140
15558.400
15976.800
16395.200
16813.600
17232.000
17650.400
18068.800
18487.200
18905.600
19324
19757.900
20191.800
20625.700
21059.600
21493.500
21927.400
22361.300
22795.200
23229.100
23663
189.741
199.114
208.488
217.862
227.235
236.609
245.983
255.356
264.730
276.382
288.033
299.685
311.337
322.988
334.640
346.292
357.943
369.595
381.247
394.429
407.611
420.793
433.975
447.157
460.339
473.521
486.703
499.885
513.067
527.064
541.062
555.060
569.057
583.055
597.053
611.050
625.048
639.046
653.043
667.555
682.066
696.577
711.089
725.600
740.111
754.623
769.134
783.645
798.157
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
3.025
3.050
3.075
3.100
3.125
3.150
3.175
3.200
3.225
3.25
3.275
3.300
3.325
3.350
3.375
3.400
3.425
3.450
3.475
3.50
9.437
9.484
9.531
9.578
9.625
9.672
9.719
9.766
9.813
9.86
9.906
9.952
9.998
10.044
10.090
10.136
10.182
10.228
10.274
10.32
24116.500
24570.000
25023.500
25477.000
25930.500
26384.000
26837.500
27291.000
27744.500
28198
28699.500
29201.000
29702.500
30204.000
30705.500
31207.000
31708.500
32210.000
32711.500
33213
2.1.3 Notes about the Spreadsheet Computation

The initial time j is taken as 12 min in the computation.

The inflow hydrograph is computed using either Time-Area Method or the
Runoff-Routing Model.

Water level WL (m RL) is equal to Water Depth (m) + datum (RL).

The function VLOOKUP() automatically takes the lower value in the
iteration. But this is not a problem as the result is still within the required
order of accuracy.

The outflow hydrograph has the highest peak discharge of 7.44 m3/s at 101.55
m RL.

The highest peak discharge is compared to and found to be less than the predevelopment peak.

The highest water level of 101.55 m RL is found to be lower than the top of
the reservoir, thus will not cause overtopping of the reservoir.

Refer to the downloaded spreadsheet for details.
106746216 (2/16/16)
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29
813.320
828.484
843.648
858.811
873.975
889.139
904.302
919.466
934.630
949.793
966.556
983.319
1000.081
1016.844
1033.607
1050.369
1067.132
1083.895
1100.657
1117.420
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________

Two worksheets are included: SHORTHSQ (with a shorter H-S-Q table) and
LONGHSQ (with a longer H-S-Q table). Notice both give identical answer.
So a short H-S-Q is good enough in this case.
2.1.4 Changes from the Planning and Design Procedure No. 1

Based on the Modified Rational Method to compute the inflow hydrograph.
The cumulative inflow and the outflow hydrographs are plotted and the largest
differential storage is taken as the required storage of the detention basin. The
ARI is 100 years.
2.1.5 Relevant Sections in MSMAM
Refer Appendix 20.B of MSMAM.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
2.2 Detention Basin Routing
2.2.1 Theory
This section provides guidelines for the design of the community/regional based
stormwater detention facilities. Some of the requirements for the design of a dry
detention basin are as follows:

The primary outlets for detention basins shall be designed to reduce the
post-development peak flows to below the pre-development peak flows
for both the minor and major system design storm ARI.

The sizing of a detention basin requires the following data:
o Inflow hydrograph
o Stage-storage curve
o Stage-discharge curve
2.2.2 Worked Example 2.2
2.2.2.1 Problem
Design a dry detention basin for a catchment as follows:

Location= Ipoh

Flow will be directed to the basin via a grassed floodway along the
alignment of an existing stream.

A low flow pipe system with a capacity of 2.1 m3/s will bypass the basin
and combine with the basin outflow in the downstream floodway.
Excel filename: DrQuekDetention1a.xls
The worksheets in the above file are are summarised as follows:
106746216 (2/16/16)
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
No.
Worksheet Name
Purpose
1
2
ShortDuration
IDF
3
100yr15min, 100yr30min, 100yr60min
4
50yr15min, 50yr30min, 50yr60min
5
5yr15min, 5yr30min, 5yr60min
6
5yr30minPreDev, 50yr30minPreDev
7
Compute
8
culvert1
9
culvert2, culvert2a, culvert2b
10
Spillway
11
rout5yr30min, rout50yr30min,
rout100yr30min
For computing 15 min short duration storm
Compute IDF data for input to time-area
method
Time-area method for 100 year 15, 30 and 60
min duration storm for post development
case.
Time-area method for 50 year 15, 30 and 60
min duration storm for post development
case.
Time-area method for 5 year 15, 30 and 60
min duration storm for post development
case.
Time-area method for 5 and 50 year 30 min
duration storm for pre-development case.
Summary of all time-area method results and
determination of net inflow to basin after
subtracting low flow.
Culvert sizing and computation of stagedischarge curve for Q5 minor flow
Culvert sizing and computation of stagedischarge curve for Q50 major flow
Spillway sizing and computation of stagedischarge curve for Q100 major flow
Level-pool routing procedure for 5, 50 and
100 year basin inflow of 30 min duration
2.2.2.2 Determine design storm criteria for the basin
The aim is to reduce the post-development peak flows for the minor and major
system ARI to less than or equal to the pre-development peaks.
The major and minor system design storms are 5 year and 50 years ARI,
respectively in accordance with Table 4.1.
The design storm for the secondary outlet spillway is 100 year ARI.
2.2.2.3 Determine the permissible outflow from basin
The time of concentration for the catchment is 30 minutes.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Permissible basin outflow= Pre Development Peak- Bypass flow.
As shown in Table 2.3, the permissible basin outflows are:

4 m3/s for 5 year flow

6.25 m3/s for 50 year flow
TABLE 2.2 PRE AND POST DEVELOPMENT TOTAL FLOW HYDROGRAPH
M3/S
Time
(min)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
Pre
Development
Pre
Pre
Dev
Dev
5 yr
50 yr
30
30
min
min
0.00
0.00
0.00
0.12
0.36
0.58
0.78
1.33
1.44
2.77
4.12
6.17
6.14
8.35
4.79
6.33
2.96
3.90
1.78
2.35
0.77
1.01
0.15
0.19
0.00
0.00
106746216 (2/16/16)
Post Development
Post
Dev
5 yr
15
min
0.00
0.55
1.42
2.53
6.74
11.01
8.86
3.55
0.57
0.00
0.00
0.00
0.00
Post
Dev
5 yr
30
min
0.00
0.33
0.89
2.15
4.86
8.84
10.87
8.00
4.94
2.97
1.28
0.25
0.00
Post Development
Post
Dev
5 yr
60
min
0.00
0.06
0.27
0.86
1.81
4.30
7.03
8.42
9.49
8.02
5.69
3.94
2.93
2.11
1.57
1.04
0.45
0.09
0.00
Post
Dev
50 yr
15
min
0.00
0.75
1.90
3.40
9.08
14.72
11.79
4.70
0.76
0.00
0.00
0.00
0.00
Post
Dev
50 yr
30
min
0.00
0.46
1.19
2.88
6.54
11.76
14.35
10.54
6.50
3.91
1.69
0.32
0.00
Post Development
Post
Dev
50 yr
60
min
0.00
0.10
0.37
1.17
2.50
5.73
9.24
11.02
12.43
10.49
7.45
5.16
3.84
2.77
2.05
1.37
0.58
0.12
0.00
Post
Dev
100 yr
15
min
0.00
0.83
2.09
3.75
10.01
16.18
12.95
5.16
0.84
0.00
0.00
0.00
0.00
Free software
at http://www.msmam.com
33
Post
Dev
100 yr
30
min
0.00
0.50
1.30
3.16
7.20
12.89
15.70
11.53
7.11
4.28
1.84
0.35
0.00
Post
Dev
100 yr
60
min
0.00
0.11
0.41
1.29
2.78
6.29
10.10
12.04
13.57
11.46
8.13
5.63
4.19
3.02
2.24
1.49
0.64
0.13
0.00
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
TABLE 2.3 BASIN INFLOW HYDROGRAPHS
M3/S
Time
(min)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
Pre
Development
subtract low
flow
5 yr
50 yr
30
30
min
min
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.67
2.02
4.07
4.04
6.25
2.69
4.23
0.86
1.80
0.00
0.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Post Development
Post Development
Post Development
subtract low flow
subtract low flow
subtract low flow
5 yr
15
min
0.00
0.00
0.00
0.43
4.64
8.91
6.76
1.45
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
5 yr
30
min
0.00
0.00
0.00
0.05
2.76
6.74
8.77
5.90
2.84
0.87
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
5 yr
60
min
0.00
0.00
0.00
0.00
0.00
2.20
4.93
6.32
7.39
5.92
3.59
1.84
0.83
0.01
0.00
0.00
0.00
0.00
0.00
50 yr
15
min
0.00
0.00
0.00
1.30
6.98
12.62
9.69
2.60
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
50 yr
30
min
0.00
0.00
0.00
0.78
4.44
9.66
12.25
8.44
4.40
1.81
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
50 yr
60
min
0.00
0.00
0.00
0.00
0.40
3.63
7.14
8.92
10.33
8.39
5.35
3.06
1.74
0.67
0.00
0.00
0.00
0.00
0.00
100 yr
15
min
0.00
0.00
0.00
1.65
7.91
14.08
10.85
3.06
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
100 yr
30
min
0.00
0.00
0.00
1.06
5.10
10.79
13.60
9.43
5.01
2.18
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
100 yr
60
min
0.00
0.00
0.00
0.00
0.68
4.19
8.00
9.94
11.47
9.36
6.03
3.53
2.09
0.92
0.14
0.00
0.00
0.00
0.00
2.2.2.4 Compute the basin inflow hydrograph
The basin inflow hydrographs were computed using the Time-Area method for
the following events:
Post Development- 100 year ARI storm, Duration=15, 30 and 60 minutes.
Post Development- 50 year ARI storm, Duration=15, 30 and 60 minutes.
Post Development- 5 year ARI storm, Duration=15, 30 and 60 minutes.
Pre Development- 50 year ARI storm, Duration=15, 30 and 60 minutes.
Pre Development- 5 year ARI storm, Duration=15, 30 and 60 minutes.
The basin inflow hydrographs are summarised as shown in Table 2.3. These are
obtained as follows:
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Flows in Table 2.3= Flows in Table 2.2 - Bypass flow.
2.2.2.5 Preliminary estimate of the required storage volume
A preliminary estimate of the required basin volume can be made using the
following equation (Equation 20.13) for the major design storm ARI.
Vs  1.291  Vi  (1 
Qo 0.753 t i 0.411
)
( )
Qi
tp
(2.5)
where
V
V
s
= estimated storage volume (m3)
i
= inflow hydrograph runoff volume (m3)
Q
i
= inflow hydrograph peak flow rate (m3/s)
Q
o
= allowable peak outflow rate (m3/s)
t
t
i
= time base of the inflow hydrograph (min)
p
= time to peak of the inflow hydrograph (min)
The basin volume is estimated for each basin inflow hydrographs as shown in
Table 2.4 and the largest value selected.
TABLE 2.4 PRELIMINARY DETERMINATION OF CRITICAL STORM
50 yr ARI
Parameter
Vi (m3)
Qi (m3/s)
Qo (m3/s)
ti (min)
tp (min)
Vs/Vi
Prelim Vs (m3)
106746216 (2/16/16)
Storm duration (min)
15
30
9961
12536
12.62
12.25
6.25
6.25
40
50
25
30
0.636
0.612
6338.0
7666.9
60
14889
10.33
6.25
70
40
0.510
7590.6
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35
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
FIGURE 2.1 PRELIMINARY DETERMINATION OF CRITICAL STORM
Est Pond Volume (m3)
Preliminary Determination of Critical Storm
10000
8000
6000
Series1
4000
2000
0
0
20
40
60
80
Storm Duration (min)
TABLE 2.5 BASIN STAGE STORAGE DISCHARGE DATA
106746216 (2/16/16)
H (m)
S (m3)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
3.25
3.50
0
45
190
444
833
1562
2887
4927
7722
11201
15140
19324
23663
28198
33213
5 YR
Q
(m3/s)
0.000
0.725
1.418
2.081
2.714
3.316
3.887
4.427
4.937
5.416
5.864
6.282
6.669
7.025
7.351
50 YR
Q
(m3/s)
0.00
0.72
1.42
2.08
2.71
3.32
3.89
5.59
7.21
8.74
10.18
11.53
12.79
13.97
15.06
100 YR
Q (m3/s)
0.00
0.72
1.42
2.08
2.71
3.32
3.89
5.59
7.21
9.13
11.49
14.08
16.82
19.69
22.65
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36
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
2.2.2.6 Develop a basin grading plan
The location and grading of the basin embankment and storage area is selected by
trial and error.
Initially, it is recommended to provide the estimated 7,666 m3 as a start to cater
for the 50 year ARI design storm.
The floor of the basin is graded at 1% toward the primary outlet.
Basin and floodway side slopes are 6(H): 1(V).
The preliminary grading plan is shown in Figure 2.2.
FIGURE 2.2 PRELIMINARY GRADING PLAN AT DETENTION BASIN SITE
103
102
101
100
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
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2.2.2.7 Compute the stage-storage relationship
Based on the grading plan developed earlier, the water surface area is calculated
at 0.25 m intervals of basin depth.
The individual storage volume between successive stages is calculated using
Equation 20.1 to determine the total stage-storage relationship as shown in Table
2.5:
V1, 2  (
A1  A2
)  d
2
(2.6)
where
V
A
A
1,2
= storage volume between elevations 1 and 2 (m3)
1
= surface area at elevation 1 (m2)
2
= surface area at elevation 2 (m2)
∆d= change in elevations between layer 1 and 2 (m)
2.2.2.8 Sizing of the minor design storm primary outlet
Sizing is carried out by trial and error to produce a maximum basin outflow that is
less than or equal to the permissible 5 year minor flow.
Steps involved:

Selecting outlet structure arrangement and size by trial and error

Compute the stage discharge relationship.

Routing the basin inflow hydrograph through the basin to determine the
maximum outflow and water level produced.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Results:

Using a time step of 1 minute in level-pool routing procedure, the critical
duration storm for 5 year ARI was found to be 30 min. Thus the
hydrograph associated with this duration is analysed further.

After a number of trial and error, selected box culvert of 2 m by 0.75 m
situated at Stage of 0 (100 m RL) (See worksheet “culvert1” for trials
involved.) Follow the steps:
o Step 1- Using culvert spreadsheet, compute the Stage-Discharge
Curve for a range of culvert sizes. Derive the best-fit formula.
o Step 2- Using reservoir routing spreadsheet, enter the best-fit
formula and inflow hydrograph into the table and rout it through.
o Step 3- Repeat until the computed outflow from Step 2 is less than
the permissible flow.

The stage discharge relationship is summarised in Table 2.5 and plotted in
Figure 2.7a.

Maximum discharge of 3.9 m3/s with water level at 101.5 m RL (stage=
1.5 m) from the routing results summarised in Table 2.6.

The above is less than the permissible 4 m3/s for 5 year minor flow.

The basin inflow and outflow hydrographs for 5 year storm of duration 30
minutes are shown in Figure 2.3.
2.2.2.9 Sizing of the major design storm primary outlet
Sizing is carried out by trial and error to produce a maximum basin outflow that is
less than or equal to the permissible 50 year major flow.
Steps involved:

Selecting outlet structure arrangement and size by trial and error

Compute the stage discharge relationship.

Routing the basin inflow hydrograph through the basin to determine the
maximum outflow and water level produced.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Results:

Using a time step of 1 minute in the level-pool routing procedure, the
critical duration storm for 50 year ARI was found to be 30 min. Thus the
hydrograph associated with this duration is analysed further.

After trial and error, a box culvert of 4 m by 0.5 m situated at Stage of 1.5
m (101.50 m RL) (5 year minor flow maximum water level) was found to
be optimum. (See worksheet “culvert2”, “culvert2a”, “culvert2b” for trials
involved.) Follow the steps:
o Step 1- Using culvert spreadsheet, compute the Stage-Discharge
Curve for a range of culvert sizes. Derive the best-fit formula.
o Step 2- Using reservoir routing spreadsheet, enter the best-fit
formula and inflow hydrograph into the table and rout it through.
o Step 3- Repeat until the computed outflow from Step 2 is less than
the permissible flow.

The stage discharge relationship is the sum of minor and major culvert
capacities as summarised in Table 2.5.

Maximum discharge of 5.6 m3/s with water level at 101.75 m RL (1.75 m)
from the routing results summarised in Table 2.7.

The above is less than the permissible 6.25 m3/s for 50 year major flow.

The basin inflow and outflow hydrographs for 50 year storm of duration
30 minutes are shown in Figure 2.4.
2.2.2.10
Sizing of the secondary spillway outlet
Sizing of the secondary outlet is to minimise the overall height of the
embankment and avoid having an excessively large secondary outlet.
Steps involved:

Selecting outlet structure arrangement and size by trial and error

Compute the stage discharge relationship.
106746216 (2/16/16)
Free software
at http://www.msmam.com
40
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________

Routing the basin inflow hydrograph through the basin to determine the
maximum outflow and water level produced.
Results:

Using a time step of 1 minute in the level-pool routing procedure, the
critical duration storm for 100 year ARI was found to be 30 min. Thus the
hydrograph associated with this duration is analysed further.

After trial and error, selected a 3 m wide broad-crested spillway with
3(H): 1 (V) side slopes as the secondary outlet. (See worksheet “spillway”
for trials involved.)

The spillway formula is used to compute the stage-discharge curve
assuming a broad crested weir with c=1.45, length= 3m.

The spillway is set at an elevation of 50 year maximum water level + 0.3
m freeboard= 101.75 + 0.3= 102.05 m RL, stage= 2.05 m.

The stage discharge relationship is the sum of minor and major culvert
plus spillway capacities are summarised in Table 2.5 and plotted in Figure
2.7b.

Maximum discharge of 5.6 m3/s with water level at 101.75 m RL from the
routing results summarised in Table 2.8. Note there is no change between
the Q50 and Q100 maximum outflow and water level due to low 100 year
storm intensity and hence basin inflow for this particular locality.

Nevertheless the embankment crest is determined by adding 0.3 m for
wave action to the above maximum 100 year water level ie, 102.35 m RL
(2.35 m)

The basin inflow and outflow hydrographs for 100 year storm of duration
30 minutes are shown in Figure 2.5.
TABLE 2.6 RESULT OF ROUTING THROUGH THE DETENTION BASIN
(5 YEAR ARI, 30 MIN)
t
(min)
j
t
(min)
0
I
Ij+I(j+1)
0.00
0.000
106746216 (2/16/16)
(2Sj/dt)Qj
0.000
(2S(j+1)/dt)+Q(j+1)
Q
0.000
0.000
W.L.
(m RL)
100.000
H
(m)
0.00
Free software
at http://www.msmam.com
41
Q
(m3/s)
0.000
S
(m3)
0
(2S/dt)+Q
0.00
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
j+1
j+2
j+3
j+4
j+5
j+6
j+7
j+8
j+9
j+10
j+11
j+12
j+13
j+14
j+15
j+16
j+17
j+18
j+19
j+20
j+21
j+22
j+23
j+24
j+25
j+26
j+27
j+28
j+29
j+30
j+31
j+32
j+33
j+34
j+35
j+36
j+37
j+38
j+39
j+40
j+41
j+42
j+43
j+44
j+45
j+46
j+47
j+48
j+49
j+50
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.01
0.02
0.03
0.04
0.05
0.59
1.13
1.68
2.22
2.76
3.56
4.35
5.15
5.95
6.74
7.15
7.55
7.96
8.36
8.77
8.19
7.62
7.05
6.47
5.90
5.29
4.68
4.06
3.45
2.84
2.44
2.05
1.66
1.26
0.87
0.69
0.52
0.35
0.17
0.00
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.010
0.029
0.049
0.068
0.088
0.640
1.725
2.809
3.894
4.978
6.317
7.909
9.502
11.095
12.688
13.889
14.698
15.508
16.317
17.127
16.959
15.813
14.668
13.522
12.377
11.191
9.965
8.739
7.513
6.287
5.281
4.493
3.705
2.918
2.130
1.563
1.215
0.868
0.521
0.174
106746216 (2/16/16)
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.010
0.039
0.088
0.157
0.245
0.885
1.160
2.520
4.965
7.106
10.586
14.333
19.672
25.339
32.599
41.060
49.127
58.003
67.689
78.185
88.512
96.552
103.447
109.196
113.799
117.217
119.409
120.374
120.114
118.628
116.135
112.855
108.787
103.931
98.288
93.219
87.803
82.040
75.930
69.472
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.010
0.039
0.088
0.157
0.245
0.885
2.609
3.969
6.414
9.943
13.423
18.496
23.835
30.767
38.027
46.488
55.758
64.634
74.320
84.816
95.143
104.326
111.220
116.969
121.572
124.990
127.182
128.148
127.888
126.402
123.909
120.628
116.560
111.704
106.061
99.850
94.434
88.671
82.561
76.103
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.725
0.725
0.725
1.418
1.418
2.081
2.081
2.714
2.714
2.714
3.316
3.316
3.316
3.316
3.316
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.316
3.316
3.316
3.316
3.316
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.250
100.250
100.250
100.500
100.500
100.750
100.750
101.000
101.000
101.000
101.250
101.250
101.250
101.250
101.250
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.250
101.250
101.250
101.250
101.250
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
3.25
3.50
Free software
at http://www.msmam.com
42
0.725
1.418
2.081
2.714
3.316
3.887
4.427
4.937
5.416
5.864
6.282
6.669
7.025
7.351
45
190
444
833
1562
2887
4927
7722
11201
15140
19324
23663
28198
33213
2.22
7.75
16.88
30.48
55.38
100.12
168.66
262.34
378.78
510.53
650.42
795.44
946.96
1114.45
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
j+51
j+52
j+53
j+54
j+55
j+56
j+57
j+58
j+59
j+60
j+61
j+62
j+63
j+64
j+65
j+66
j+67
j+68
j+69
j+70
j+71
j+72
j+73
j+74
j+75
j+76
j+77
j+78
j+79
j+80
j+81
j+82
j+83
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
106746216 (2/16/16)
62.841
56.209
49.578
44.150
38.722
33.295
27.867
23.704
19.541
15.378
12.541
9.705
6.868
5.419
3.970
2.521
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
69.472
62.841
56.209
49.578
44.150
38.722
33.295
27.867
23.704
19.541
15.378
12.541
9.705
6.868
5.419
3.970
2.521
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
1.072
Outflow Qp=
3.316
3.316
3.316
2.714
2.714
2.714
2.714
2.081
2.081
2.081
1.418
1.418
1.418
0.725
0.725
0.725
0.725
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
3.886725
101.250
101.250
101.250
101.000
101.000
101.000
101.000
100.750
100.750
100.750
100.500
100.500
100.500
100.250
100.250
100.250
100.250
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
101.5
Free software
at http://www.msmam.com
43
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
TABLE 2.7 RESULT OF ROUTING THROUGH THE DETENTION BASIN
(50 YEAR ARI, 30 MIN)
t
(min)
j
j+1
j+2
j+3
j+4
j+5
j+6
j+7
j+8
j+9
j+10
j+11
j+12
j+13
j+14
j+15
j+16
j+17
j+18
j+19
j+20
j+21
j+22
j+23
j+24
j+25
j+26
j+27
j+28
j+29
j+30
j+31
j+32
j+33
j+34
j+35
j+36
j+37
j+38
j+39
j+40
j+41
j+42
j+43
j+44
t
(min)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
I
Ij+I(j+1)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.16
0.31
0.47
0.62
0.78
1.51
2.24
2.98
3.71
4.44
5.49
6.53
7.57
8.61
9.66
10.18
10.69
11.21
11.73
12.25
11.49
10.73
9.97
9.20
8.44
7.64
6.83
6.02
5.21
4.40
3.89
3.37
2.85
2.33
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.156
0.467
0.779
1.091
1.402
2.291
3.756
5.222
6.688
8.154
9.929
12.015
14.101
16.186
18.272
19.833
20.869
21.905
22.942
23.978
23.735
22.213
20.691
19.169
17.647
16.079
14.463
12.848
11.233
9.618
8.291
7.253
6.216
5.178
106746216 (2/16/16)
(2Sj/dt)Qj
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.156
0.623
1.402
1.044
0.997
1.838
4.146
6.531
10.383
14.373
20.140
26.727
35.400
46.158
57.799
71.000
85.238
99.370
114.538
130.743
146.704
161.144
170.653
178.640
185.105
190.002
193.283
194.949
194.999
193.435
190.543
186.615
181.648
175.644
(2S(j+1)/dt)+Q(j+1)
Q
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.156
0.623
1.402
2.493
2.446
3.287
5.595
9.368
13.219
18.536
24.303
32.155
40.828
51.586
64.430
77.632
91.870
107.144
122.312
138.516
154.478
168.917
181.835
189.822
196.287
201.184
204.465
206.131
206.182
204.617
201.726
197.797
192.830
186.826
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.725
0.725
0.725
0.725
1.418
1.418
2.081
2.081
2.714
2.714
2.714
3.316
3.316
3.316
3.887
3.887
3.887
3.887
3.887
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
W.L.
(m RL)
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.250
100.250
100.250
100.250
100.500
100.500
100.750
100.750
101.000
101.000
101.000
101.250
101.250
101.250
101.500
101.500
101.500
101.500
101.500
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
H
(m)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
3.25
3.50
Free software
at http://www.msmam.com
44
Q
(m3/s)
0.00
0.72
1.42
2.08
2.71
3.32
3.89
5.59
7.21
8.74
10.18
11.53
12.79
13.97
15.06
S
(m3)
0
45
190
444
833
1562
2887
4927
7722
11201
15140
19324
23663
28198
33213
(2S/dt)+Q
0.00
2.22
7.75
16.88
30.48
55.38
100.12
169.82
264.61
382.10
514.84
655.66
801.56
953.90
1122.16
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
j+45
j+46
j+47
j+48
j+49
j+50
j+51
j+52
j+53
j+54
j+55
j+56
j+57
j+58
j+59
j+60
j+61
j+62
j+63
j+64
j+65
j+66
j+67
j+68
j+69
j+70
j+71
j+72
j+73
j+74
j+75
j+76
j+77
j+78
j+79
j+80
j+81
j+82
j+83
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
1.81
1.45
1.09
0.72
0.36
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4.140
3.259
2.535
1.811
1.086
0.362
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
106746216 (2/16/16)
168.602
160.679
155.440
149.478
142.791
135.379
127.606
119.832
112.059
104.286
96.512
89.881
83.250
76.618
69.987
63.356
56.724
50.093
44.665
39.237
33.810
28.382
24.219
20.056
15.893
13.056
10.220
7.383
5.934
4.485
3.036
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
179.784
171.861
163.214
157.251
150.564
143.153
135.379
127.606
119.832
112.059
104.286
96.512
89.881
83.250
76.618
69.987
63.356
56.724
50.093
44.665
39.237
33.810
28.382
24.219
20.056
15.893
13.056
10.220
7.383
5.934
4.485
3.036
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
1.587
Outflow Qp=
5.591
5.591
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.316
3.316
3.316
3.316
3.316
3.316
3.316
2.714
2.714
2.714
2.714
2.081
2.081
2.081
1.418
1.418
1.418
0.725
0.725
0.725
0.725
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
5.59
101.750
101.750
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.250
101.250
101.250
101.250
101.250
101.250
101.250
101.000
101.000
101.000
101.000
100.750
100.750
100.750
100.500
100.500
100.500
100.250
100.250
100.250
100.250
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
101.75
Free software
at http://www.msmam.com
45
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
TABLE 2.8 RESULT OF ROUTING THROUGH THE DETENTION BASIN
(100 YEAR ARI, 30 MIN)
t
(min)
j
j+1
j+2
j+3
j+4
j+5
j+6
j+7
j+8
j+9
j+10
j+11
j+12
j+13
j+14
j+15
j+16
j+17
j+18
j+19
j+20
j+21
j+22
j+23
j+24
j+25
j+26
j+27
j+28
j+29
j+30
j+31
j+32
j+33
j+34
j+35
j+36
j+37
j+38
j+39
j+40
j+41
j+42
j+43
j+44
t
(min)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
I
Ij+I(j+1)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.21
0.42
0.64
0.85
1.06
1.87
2.68
3.48
4.29
5.10
6.24
7.37
8.51
9.65
10.79
11.35
11.91
12.48
13.04
13.60
12.77
11.93
11.10
10.26
9.43
8.55
7.66
6.78
5.90
5.01
4.45
3.88
3.31
2.74
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.212
0.637
1.062
1.487
1.912
2.931
4.545
6.159
7.773
9.386
11.332
13.609
15.886
18.163
20.440
22.140
23.265
24.389
25.513
26.637
26.365
24.697
23.029
21.361
19.693
17.976
16.210
14.443
12.677
10.910
9.460
8.325
7.190
6.055
106746216 (2/16/16)
(2Sj/dt)Qj
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.212
0.850
1.912
1.950
2.414
3.896
5.605
8.927
13.863
19.086
26.255
34.436
44.894
56.425
70.233
85.742
101.233
117.849
135.588
154.452
169.635
183.150
194.997
205.176
213.687
220.481
225.508
228.769
230.263
229.991
228.269
225.412
221.419
216.293
(2S(j+1)/dt)+Q(j+1)
Q
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.212
0.850
1.912
3.399
3.863
5.345
8.441
11.763
16.699
23.249
30.418
39.863
50.321
63.056
76.865
92.374
109.007
125.622
143.362
162.225
180.817
194.332
206.179
216.358
224.869
231.663
236.690
239.951
241.446
241.174
239.451
236.594
232.602
227.475
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.725
0.725
0.725
1.418
1.418
1.418
2.081
2.081
2.714
2.714
3.316
3.316
3.316
3.887
3.887
3.887
3.887
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
5.591
W.L.
(m RL)
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.250
100.250
100.250
100.500
100.500
100.500
100.750
100.750
101.000
101.000
101.250
101.250
101.250
101.500
101.500
101.500
101.500
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
101.750
H
(m)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
3.25
3.50
Free software
at http://www.msmam.com
46
Q
(m3/s)
0.00
0.72
1.42
2.08
2.71
3.32
3.89
5.59
7.21
9.13
11.49
14.08
16.82
19.69
22.65
S
(m3)
0
45
190
444
833
1562
2887
4927
7722
11201
15140
19324
23663
28198
33213
(2S/dt)+Q
0.00
2.22
7.75
16.88
30.48
55.38
100.12
169.82
264.61
382.49
516.16
658.21
805.59
959.62
1129.75
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
j+45
j+46
j+47
j+48
j+49
j+50
j+51
j+52
j+53
j+54
j+55
j+56
j+57
j+58
j+59
j+60
j+61
j+62
j+63
j+64
j+65
j+66
j+67
j+68
j+69
j+70
j+71
j+72
j+73
j+74
j+75
j+76
j+77
j+78
j+79
j+80
j+81
j+82
j+83
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
2.18
1.74
1.31
0.87
0.44
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4.921
3.918
3.047
2.177
1.306
0.435
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
106746216 (2/16/16)
210.031
202.767
194.632
185.626
175.750
165.003
157.229
149.456
141.682
133.909
126.135
118.362
110.589
102.815
95.042
88.410
81.779
75.148
68.516
61.885
55.254
49.826
44.398
38.970
33.543
28.115
23.952
19.789
15.626
12.789
9.953
7.116
5.667
4.218
2.769
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
221.213
213.949
205.814
196.808
186.932
176.185
165.003
157.229
149.456
141.682
133.909
126.135
118.362
110.589
102.815
95.042
88.410
81.779
75.148
68.516
61.885
55.254
49.826
44.398
38.970
33.543
28.115
23.952
19.789
15.626
12.789
9.953
7.116
5.667
4.218
2.769
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
1.320
Outflow Qp=
5.591
5.591
5.591
5.591
5.591
5.591
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.887
3.316
3.316
3.316
3.316
3.316
3.316
2.714
2.714
2.714
2.714
2.714
2.081
2.081
2.081
1.418
1.418
1.418
0.725
0.725
0.725
0.725
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
5.591119
101.750
101.750
101.750
101.750
101.750
101.750
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.500
101.250
101.250
101.250
101.250
101.250
101.250
101.000
101.000
101.000
101.000
101.000
100.750
100.750
100.750
100.500
100.500
100.500
100.250
100.250
100.250
100.250
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
100.000
101.75
Free software
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47
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
FIGURE 2.3 BASIN INFLOW AND OUTFLOW HYDROGRAPHS FOR THE
CRITICAL 5 YEAR ARI 30 MINUTE STORM
5 year ARI- 30 minute
10
9
8
Flow (m3/s)
7
6
Inflow
5
Outflow
4
3
2
1
0
0
20
40
60
80
100
Tim e (m in)
FIGURE 2.4 BASIN INFLOW AND OUTFLOW HYDROGRAPHS FOR THE
CRITICAL 50 YEAR ARI 30 MINUTE STORM
50 year ARI- 30 min
14
Flow (m3/s)
12
10
8
Inflow
6
Outflow
4
2
0
0
20
40
60
80
100
Tim e (m in)
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
FIGURE 2.5 BASIN INFLOW AND OUTFLOW HYDROGRAPHS FOR THE
CRITICAL 100 YEAR ARI 30 MINUTE STORM
100 year ARI- 30 min
16
14
Flow (m3/s)
12
10
Inflow
8
Outflow
6
4
2
0
0
20
40
60
80
100
Tim e (m in)
FIGURE 2.6 DETENTION BASIN SCHEMATIC
103
102
Downstream
Floodway
101
Secondary Outlet
(100 year ARI)
3 m broad crested weir
100
Primary Outlet
(5 year ARI)
2m x 0.75m Box Culvert
Primary Outlet
(50 year ARI)
4m x 0.5m Box Culvert
Basin Embankment
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_______________________________________________________________________
FIGURE 2.7A & B- STAGE-DISCHARGE CURVE FOR OUTLET 1, 2 AND 3
Note:
Q1: 5 yr minor (2 x 0.75 m box culvert)
Q2: 50 yr major (4 x 0.5 m box culvert)
Q3: 100 yr major (3 m broad crested spillway)
FIGURE 2.7 A
Q1+Q2
16
DISCHARGE (M3/S)
14
12
10
Q1
8
Q2+ Q1
6
4
2
0
0
0.5
1
1.5
2
2.5
3
3.5
4
STAGE (M)
FIGURE 2.7 B
Q1+Q2+Q3
25
DISCHARGE (M3/S)
20
15
10
5
0
0
0.5
1
1.5
2
2.5
3
3.5
STAGE (M)
Q2+Q1
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Q3+Q2+Q1
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4
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
FIGURE 2.8 SCHEMATIC OUTLET ARRANGEMENT
Embankment crest @ 102.35 m RL
Spillway @ 102.05 m RL
Wave Freeboard= 0.3 m
50 yr WL= 101.75 m RL
4 m x 0.5 m BC
101.50 m RL
2 m X 0.75 m BC
Datum= 100 m RL
2.2.3 Worked Example 2.3
Design a dry detention basin for a catchment as follows:

Location= Kuala Lumpur

A low flow pipe system with a capacity of 2 m3/s will bypass the basin
and combine with the basin outflow in the downstream floodway.

The time area curve is as follows: 50000, 60000, 90000, 112000, 69000,
70000.
2.2.4 Worked Example 2.4
Design a dry detention basin for the catchment in Kuching as described in
Worked Example 2.9 in Workshop No. 1.

A low flow pipe system with a capacity of 2 m3/s will bypass the basin
and combine with the basin outflow in the downstream floodway.
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_______________________________________________________________________
2.3 Summary Sheet
1. The sizing of detention basins can be done using a reservoir routing method
such as the Level-Pool Routing Procedure, which computes storage routing by
solving the continuity equation and the storage function.
2. The continuity equation or the equation of conservation of mass simply
expresses the condition that the rate of inflow less the rate of outflow at any
instance in time is equal to the rate of change in storage in the basin as
follows:
I Q 
S
t
where
I
is the instantaneous inflow rate of discharge to the basin (m3/s)
Q
is the instantaneous outflow rate of discharge from the basin (m3/s)
S
is the volume of temporary storage in the basin (m3)
3. The above equation may be expressed in finite difference form as follows:
I
j
 I j 1 
2

Q
j
 Q j 1 
2

S j 1  S j
t
where
j, j+1 are time steps j and j+1, respectively.
t
is the time interval defining the finite difference approximation of
the continuity equation.
4. The above equation can be rearranged such that all known variables are placed
on the left side of the equation and all unknown variables on the right as
follows:
I
j
2Sj
  2  S j 1

 I j 1   
 Q j   
 Q j 1 
 t
  t

5. For solution of the above equation, we need a second equation- the storage
function, which expresses the relationship between the storage in the basin
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
and the discharge from the basin in the form of Q = f(S) which combines the
effect of:

The discharge characteristics or the “rating curve” as represented by
Q=f(H)

The topography of the site i.e., the geometric properties as represented by
the storage curve or H versus S data of the storage facility, expressed as
H= f(S).
6. Worked Example 2.1- Level Pool Routing Through A Reservoir- Excel
Filename: DrQuekLevelPoolRouting1a.zip
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Appendix 2A Computation of Design Storm
2.1
Design Rainfall
2.1.1 Computation of Design Rainfall
Chapter 13 of MSMAM supersedes HP1 (DID, 1982) for design rainfall
computation.
Derivation of IDF Curves using MSMAM
The following polynomial equation (Equation 13.2 in MSMAM) has been fitted to
the published IDF curves for the 35 major urban centres in Malaysia:
ln( RI t )  a  b  ln( t )  c  (ln( t )) 2  d  (ln( t ))3 (2.1)
where
R
It = the average rainfall intensity (mm/hr) for ARI R and duration t
R = average return interval (years)
t
= duration (minutes)
a to d are fitting constants dependent on ARI.
The fitted coefficients for the IDF curves for all the major cities are given in
Appendix 13.A of MSMAM.
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AN ILLUSTRATION OF DESIGN RAINFALL COMPUTATION
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Work Example 2.1- Derive IDF Curve for Ipoh
2.1.2.1 Derivation of IDF curves
In this work example, the rainfall intensity-frequency-duration data are computed
for Ipoh based on Equation 2.1 for ARI of 2, 5 10, 20, 50 and 100 years.
The fitted coefficients for the IFD curves are taken from Appendix 13.A of
MSMAM for Ipoh.
The computations can be easily done using a spreadsheet as shown in Table 2.2.
The resulting set of IFD curves are plotted as shown in Figure 2.2.
Log in to the MEMBERS ONLY area for Workshop 1, and click the following
file to download (You must have the WINZIP software to unzip the file- a free
copy can be downloaded at http://www.msmam.com):
Excel Filename: DrQuekIFD1a.zip
After you download the file, you need to unzip it before you can use it.
If you do not have your login name and password, you must send an email to
membership@msmam.com giving the following details:

your name,

email address,

dates of attendance,

company name and address, and

contact phone numbers for verification purpose.
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WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
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TABLE 2.2 RAINFALL IDF DATA FOR IPOH DERIVED USING
“URBAN STORMWATER MANAGEMENT MANUAL FOR MALAYSIA” (DID, 2000)
ARI A
HOUR
b
C
D
30 min 60
0.5 hr 1.0
90
1.5
120
2.0
150
2.5
180
3.0
200
3.3
250
4.2
300
5.0
360
6.0
480
8.0
600
10.0
720
12.0
1080 1440 2880 4320
18.0 24.0 48.0 72.0
LN (T)
3.4012 4.0943 4.4998 4.7875 5.0106 5.1930 5.2983 5.5215 5.7038 5.8861 6.1738 6.3969 6.5793 6.9847 7.2724 7.9655 8.3710
2
5.2244 0.3853 -0.1970 0.0100 104.5 65.8 48.4 38.5 32.0 27.5 25.1 20.7 17.6 15.0 11.6 9.4
8.0
5.5
4.3
2.3
1.7
5
5.0007 0.6149 -0.2406 0.0127 122.5 78.0 57.6 45.8 38.0 32.6 29.8 24.5 20.8 17.7 13.7 11.2 9.5
6.6
5.1
2.9
2.1
10
5.0707 0.6515 -0.2522 0.0138 135.9 86.3 63.6 50.6 42.1 36.1 33.0 27.2 23.2 19.7 15.3 12.6 10.7 7.5
5.9
3.4
2.6
20
5.1150 0.6895 -0.2631 0.0147 147.7 93.4 68.7 54.5 45.3 38.8 35.5 29.2 24.9 21.2 16.5 13.6 11.6 8.2
6.5
3.8
2.9
50
4.9627 0.8489 -0.2966 0.0169 161.4 102.1 74.9 59.3 49.2 42.1 38.4 31.6 26.9 22.9 17.7 14.6 12.5 8.9
7.0
4.2
3.3
100 5.1068 0.8168 -0.2905 0.0165 176.5 111.5 81.7 64.7 53.6 45.8 41.8 34.4 29.3 24.9 19.3 15.9 13.5 9.6
7.6
4.6
3.5
2
Note: MS Excel spreadsheet filename: ipohIDF.xls (can be downloaded from Quek, 2002)
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FIGURE 2.2 IFD CURVE FOR IPOH DERIVED USING MSMAM
IFD CURVE FOR IPOH (1951-1990)
1000
INTENSITY (MM/HR)
100
10
1
10
100
1000
DURATION (MINUTES
2
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10
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20
50
100
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2.1.2.2 How to Create the Spreadsheet
Following are the steps involved in creating and using the spreadsheet:
1. Open the spreadsheet DrQuekIFD1a.zip.
2. Enter values of coefficients: a, b, c, d from Appendix 13.A for ARI of 2, 5,
10, 20, 50 and 100 years for Ipoh- the cells are highlighted in yellow.
3. Row 2- calculate the LN of 30, 60, 90 to 4320 minutes- e.g.,
LN(30)=3.4012.
4. Cell F3 to V8 is the solution of the equation
ln( RI t )  a  b  ln( t )  c  (ln( t )) 2  d  (ln( t ))3
5. Solving the above equation by expressing it as:
R
I t  exp( a  b  ln( t )  c  (ln( t )) 2  d  (ln( t )) 3 )
6. Plot the Rainfall Intensity-Frequency-Duration Curve as shown.
2.1.3.1 How to Use the Spreadsheet
Following are the steps involved:
1. Open the spreadsheet DrQuekIFD1a.zip.
2. Change the values of coefficients: a, b, c, d from Appendix 13.A for ARI of
2, 5, 10, 20, 50 and 100 years for Penang- the cells are highlighted in yellow.
3. The intensities will automatically changed- there is no need to change the
formulas in Cell F3 to V8.
4. The Rainfall Intensity-Frequency-Duration Curve will change automatically.
But remember to change the title of the graph.
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Appendix 2B Rational Method
2.4 Design Discharge
2.4.1 Methods of computing peak discharges
2.4.1.1 Methods in MSMAM
MSMAM provides two basic approaches of computing stormwater flows from
rainfall as follows:
1. Rational Method
2. Hydrograph Method
The Rational Method is based on the Rational Formula which converts average
rainfall intensity on a catchment area into peak discharge of the same ARI
through a runoff coefficient. It differs from the Modified Rational Method of
P&DP No. 1 (DID, 1975) in the following aspects:
1. The value of the runoff coefficient is related to rainfall intensity and the types
of ground cover, instead of just on the types of landuse as in DID (1975).
2. It is not recommended for catchment area greater than 0.8 km2 compared to
the limit of 52 km2 (20 mi2) in P&DP No. 1.
3. The absence of a storage coefficient to account for channel storage.
The Hydrograph Method, on the other hand, computes a flow hydrograph from a
rainfall hyetograph after subtracting losses and temporary storage effects. There
are many methods available and those of practical importance to this course on
urban drainage design are discussed as follows:
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AN ILLUSTRATION OF THE COMPUTION OF PEAK DISCHARGE AND
HYDROGRAPH IN MSMAM
To compute peak discharge
using MSMAM
Area < 0.8 km2
Area > 0.8 km2
Rational Method
(Workshop 1)
Gives peak discharge
only, no hydrograph





Only applicable to area <
0.8 km2
For design only, not for
analysis
Not suitable if
hydrograph required eg.,
for routing through a
detention storage.
Simple empirical
formula.
Limited application.
Hydrograph Methods
Gives peak discharge + hydrograph
Time-Area Method
(Workshop 1)





Convolution of rainfall excess
hyetograph with time-area
diagram.
Suitable for design only, not
for analysis.
Not recommended for large
catchment, very complicated if
too many isochrones.
Must fully understand the
theory in order to solve
equations using spreadsheet.
Cannot route the hydrograph
through a detention storage.
Need separate software for
reservoir routing.
Runoff-Routing Method
(Workshop 2)









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Many computer models in the
market eg., HEC-HMS.
Suitable for design and
analysis.
Suitable for any catchment
size including area < 0.8 km2
Calibrate using historical
rainfall and streamflow data.
Predictive, can model future
landuse changes.
Can route a hydrograph
through a detention storage
using build-in reservoir routing
procedure.
Good graphical user interface
(GUI)- intuitive.
Can interface with a hydraulic
model eg., HEC-RAS to
calculate water level.
Free software available.
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2.4.2 Rational Method of MSMAM
2.4.2.1 Theory
MSMAM relates the peak discharge to the rainfall intensity and catchment area via
the Rational Method:
C y I t  A
Qy 
360
(2.4)
where
Qy
is the y year ARI peak discharge (m3/s)
C
is the dimensionless runoff coefficient
y
is the average intensity of the design rainstorm of duration equal to the time
It
of concentration tc and of ARI of y year (mm/hr)
A
is the drainage area (ha)
The time of concentration, tc, in hours is the sum of the overland flow time, to, and
the time of flow in the stormwater conveyance system, td, as follows:
tc  to  td
(2.5)
The overland flow time to can be estimated using Friend’s Formula below or using
the Nomograph in Design Chart 14.1:
107  n  L1 / 3
to 
S 0 .2
(2.6)
where
to
= Overland sheet flow travel time (minutes)
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AN ILLUSTRATION OF RATIONAL METHOD IN MSMAM
Calculate Tc
tc  to  td
Calculate I
tc>30 min IDF formula
tc<30 min short duration
Calculate C
Design Chart 14.3 & 14.4
(urban & rural)
depends on I & soil conditions
Calculate Qp
C y I t  A
Qy 
360
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L
= Overland sheet flow path length (m)
n
= Manning’s roughness value for the surface (refer Table 14.2 of MSMAM)
S
= Slope of overland surface (%)
And td, the total time of flow in the stormwater conveyance system, is given by:
t d  t r  t g  t ch  t p
(2.7)
tr
= Roof flow time
tg
= Kerbed Gutter flow time (Design Chart 14.2)
tch
= Channel flow time
tp
= Pipe flow time
The time of flow in open channel can be determined by dividing the length of the
channel by the average flow velocity which can be calculated from normal hydraulic
formula such as Manning’s Formula, given the channel cross section, length,
roughness and slope.
t ch 
nL
60  R 2 / 3  S 1 / 2 (2.8)
where
n
= Manning’s roughness coefficient.
R
= Hydraulic radius (m)
S
= Friction slope (m/m)
L
= Length of reach (m)
tch
= Travel time on the channel (minutes)
For natural catchments and mixed flow paths, the time of concentration can be found
by using the Bransby-Williams’ Equation which includes the time of overland flow
and channel flow:
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tc 
F L
A  S 1 / 5 (2.9)
c
1 / 10
where
tc
= Time of concentration (minutes)
Fc
= Conversion factor=92.5
L
= Length of flow path from catchment divide to outlet (km)
A
= Catchment area (ha)
S
= Slope of stream flow path (m/km)
For small catchments up to 0.4 ha in area, the time of concentration can be assumed
to be 10 min instead of performing detailed calculation (refer Table 14.3 of
MSMAM.)
The runoff coefficient is a function of the ground cover and the rainfall intensity.
During a storm the actual runoff coefficient increases as the soil become saturated.
The greater the rainfall intensity, the greater is the runoff coefficient due to the
reducing relative amount of rainfall losses.
Recommended values of C may be obtained from Design Chart 14.3 for urban areas
and Design Chart 14.4 for rural areas.
The Rational Method is not recommended for catchment area greater than 80 ha (0.8
km2) and in situations where significant storage occurs in the catchment.
Assumptions inherent in the Rational Method are as follows:
1. The peak flow occurs when the entire catchment is contributing to the flow.
2. The rainfall intensity is the same over the entire catchment area.
3. The rainfall intensity is uniform over a time duration equal to the time of
concentration, tc.
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4. The ARI of the computed peak flow is the same as that of the rainfall
intensity.
FIGURE 2.4 GENERAL PROCEDURE FOR ESTIMATING PEAK FLOW
FOR A SINGLE SUB-CATCHMENT USING THE RATIONAL METHOD
(AFTER MSMAM)
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2.4.2.2 Worked Example 2.3- Rational Method for a minor drainage system in Ipoh
The objective of this worked example is to compute the design flow for a minor
drainage system of a residential area in Ipoh using the Rational Method in
MSMAM. Figure 2.5 shows a map of the catchment area.
Other information are as follows:

Area= 30 hectares.

Length of Overland flow= 100 m (A) & 60 m (B)

Slope= 0.3%, paved surface.

Length of Open Drain= 600 m (A) & 680 m (B)
Step 1- Calculate Tc
Overland flow time (To) is estimated using Friend’s Formula:
to 
107  n  L1 / 3
S 0 .2
where
n= 0.011 from Table 14.2 for paved surface
S= 0.3%
L= Overland sheet flow path length in m (295 m for A, and 150 m for B).
Applying the Friend’s Formula, To= 9.97 min for A and 7.96 min for B.
Average velocity in the open drain is assessed using Manning’s Equation (Equation
2.8) where V is found to be 1 m/s.
For A, Td=L/V= 600/1= 600 s= 10 min.
For B, Td=L/V= 680/1= 680 s= 11.3 min.
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ECatchment Area= 30 hectares
Residential, Paved, Medium Density
EOpen Drain Length (from here to the
Outlet)= 680 m
A
B
EOpen Drain Length (from here
to the Outlet)= 600m
ERiv
er
FIGURE 2.5 CATCHMENT MAP
Hence,
Tc= To + Td = 9.97+10 = 19.97min = 20.0 min for A (governs)
Tc= To + Td = 7.96+11.3 = 19.26 min = 19.3 min for B
Note Tc should be based on the larger for A and B. In this case, the Tc for A
governs as it is the larger of the two. The reason for this is because in the Rational
Method, the peak discharge is based on the Tc value when the whole catchment
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area is contributing. And this occurs only when a drop of water from the most
remote point of the catchment area enters the open drain and travels to the outlet
of the catchment. This affects the magnitude of the calculated peak discharge.
Step 2- Calculate I
The values of the coefficients for a, b, c and d in Table 13.A1 for ARI of 5 years
for Ipoh are as follows:
a= 5.0007, b= 0.6149, c= -0.2406, d= 0.0127
Substituting the above coefficients into:
ln( RI t )  a  b  ln( t )  c  (ln( t )) 2  d  (ln( t ))3
For t= 30 min, 5I30= 122.5 mm/hr
For t= 60 min, 5I60= 78.0 mm/hr
Convert to rainfall depths,
5
P30= 122.5/2 = 61.25 mm
5
P60= 78.0/1 = 78.0 mm
Step 3- Calculate C
According to MSMAM, the design rainfall depth Pd for a short duration d (min) is
given by:
Pd  P30  FD  ( P60  P30 )
(2.10)
where
P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from
the published polynomial curves.
FD is the adjustment factor for storm duration based on Table 13.3.
Hence 5P20= 61.25-0.47*(78-61.25)= 53.4 mm
Therefore 5I20= 160 mm/hr
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From Design Chart 14.3, for Category 3,
C= 0.86
Step 4- Calculate Qp
The peak discharge for ARI=5 years is computed using the Rational Method:
C y I t  A
Qy 
360
Qp= 0.86*160*30/360 = 11.5 m3/s
2.4.2.3 How to Create a Spreadsheet
Following are the steps for solving the Rational Method using a spreadsheet
(Filename: DrQuekRational1a.zip):
1. Open the spreadsheet for IDF curve computation for Ipoh: DrQuekIFD1a.zip.
2. To the right hand side of the spreadsheet add the columns below for ARI=5
years.
3. Calculate To using Friend’s Formula.
4. Calculate Td using length of drain divided by velocity.
5. Calculate Tc = To +Td
6. Convert the intensities into depth: P30 and P60
7. Enter the value of FD
8. Calculate the value of Pd from:
Pd  P30  FD  ( P60  P30 )
9. Convert to intensity Id.
10. Enter C by reading Design Chart 14.3
11. Calculate Q using the Rational Method.
Qy 
C y I t  A
360
12. Save the file as DrQuekRational1a.zip.
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3.
DESIGN OF SEDIMENT BASIN
3.1
Definition
A sediment basin is a structure formed by excavation and/or construction of an
embankment across a waterway or other suitable location.
The purpose of a sediment basin is to collect and store sediment from sites cleared
during construction for extended periods of time before re-establishment of
permanent vegetation and/or construction of permanent drainage structures.
A sediment basin is designed to trap sediment before it leaves the construction
site. It is a temporary structure with a life span of 1 to 2 years.
3.2
General Criteria for Installation of Sediment Basins
Following are the important installation or application criteria for sediment basin:

Sediment basin is required at the outlet of all disturbed catchment areas
greater than 2 hectares, or smaller area if necessary.

Sediment basin should be located at future permanent detention basins or
water quality control structures.

Sediment basin should be constructed before clearing and grading work
begins.

Sediment basin must not be located in a stream.

Basins should be located where failure of the structure would not result in
loss of life or damage to roads and properties.

Large basins may be subject to Federal Dam Safety requirements.

Sediment basins may be dangerous to children whose access must be
restricted by adequate fencing.

An emergency spillway must be installed to safely convey flows of up to
and including 10 years ARI.
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3.3

Basin length to settling depth ratio should be less than 200:1.

Basin length to width ratio should be greater than 2:1.

Side slopes should not be steeper than 2(H): 1 (V). to prevent sloughing.
Criteria for Sizing of Sediment Basins
Following are the sizing criteria for sediment basin:

Table 3.1 (Table 39.4) lists the three different soil types and the design
considerations which apply to sediment basin design and operation for
each soil type.

The design capacity of a sediment basin is the sum of two components:
o A settling zone at least 0.6 m deep to contain runoff and allow
suspended sediment to settle.
o A sediment storage zone at least 0.3 m deep to store settled
sediment until the basin is cleaned out.
TABLE 3.1 SEDIMENT BASIN TYPES AND DESIGN CONSIDERATIONS
Soil Description
Soil
Type
C
Coarse-grained sand, sandy loam: less
than 33%<0.02 mm
Fine-grained loam, clay: more than
F
33%<0.02 mm
Dispersible fine-grained clays as per type D
F, more than 10% of dispersible material.
3.4
Basin
Type
Dry
Wet
Wet
Design Considerations
Settling velocity, sediment
storage.
Storm impoundment, sediment
storage.
Storm impoundment, sediment
storage, assisted flocculation.
Design of Dry Sediment Basins
Following are the criteria for the design of dry sediment basins:

Dry Sediment basins should be used on Type C soil (Table 3.1)- which is
characterized by a high percentage of coarse particles, where less than
one-third of particles are less than 0.02 mm in size.
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
For most construction situations, the design storm should be the 3 month
ARI event.

If the construction site is upstream of an environmentally sensitive area, or
if the construction time is more than 2 years, the 6 month ARI is
recommended.

Peak flow to be estimated using methods including the Rational Method.

An overall particle removal target of 85% is adopted.

Volume of the settling zone and sediment storage zones should each be
half of the total basin volume.

For areas of high soil erodibility, the sediment storage volume should be
able to retain 2 month of soil loss from the catchment- calculated using the
Modified Universal Soil Loss Equation.

Dry sediment basin should drain naturally after heavy rain through the
emabankment or outlet riser.

Table 3.2 (Table 39.5) summarises the dry sediment basin sizing
guidelines.

For dry sediment basins, the embankment or outlet structure must be
designed such that the basin will completely empty within 24 hours after a
storm event.
TABLE 3.2 DRY SEDIMENT BASIN SIZING GUIDELINES
(BASED ON TABLE 39.5)
Parameter
Design Storm Time of Concentration of Basin Catchment (min)
(mth ARI)
10
20
30
45
60
Surface Area 3
333
250
200
158
121
2
(m /ha)
6
n/a
500
400
300
250
Total Volume 3
400
300
240
190
145
(m3/ha)
6
n/a
600
480
360
300
3.5
Design of Wet Sediment Basins
Following are the design criteria for wet sediment basins:
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
Wet sediment basins should be used on Type F or Type D soils.

The approach adopted is based on “storm containment”, fully impounding
runoff from a nominated design event- due to observation that traditional
approaches to settling fine sediments, particularly dispersible clays, have
been ineffective.

The design event is selected using a risk-based approach. The rainfall and
predicted runoff from that design event is used to size the “settling” zone
of the basin.

The duration of the design event should be 5 days- time needed to achieve
effective flocculation, settling and pumpout of the stormwater.

The 75th percentile 5-day rainfall event should be used as the design event.
Refer Table 3.4 for Malaysia.

The 80th percentile 5-day event should be used if the construction site is
upstream of an environmentally sensitive area, or if the construction
period is more than 2 years.

The total volume consists of one-third as sediment storage volume and
two-thirds as settling zone volume.

For areas of high soil erodibility, the sediment storage volume should be
able to retain 2 month of soil loss from the catchment- calculated using the
Modified Universal Soil Loss Equation.

The captured stormwater in the settling zone should be drained or pumped
out within the five day period following rainfall.

Target water quality should be Class II Standard according to the Interim
National Water Quality Standards for Malaysia where the TSS < 50mg/L.

Sizing guidelines for wet sediment basins for normal situations are given
in Table 3.3 (Table 39.6)
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TABLE 3.3 WET SEDIMENT BASIN SIZING GUIDELINES
(BASED ON TABLE 39.6)
Parameter
Magnitude of Design Storm Event in mm
20
30
40
50
60
Settling Zone Volume Moderate-high runoff 70
127
200
290
380
(m3/ha)
Very high runoff
100
167
260
340
440
Total Volume
Moderate-high runoff 105
190
300
435
570
3
(m /ha)
Very high runoff
150
250
390
510
660
3.6
Site Runoff Potential
Worked Example 3.1- Design of A Dry Sediment Basin
This worked example uses a spreadsheet to size a dry sediment basin.
Excel Filename: DrQuekDrySedBasin1a.xls
Problem: To design a dry sediment basin and outlet structures required for a
construction site in Kuala Lumpur.
Relevant data are as follows:

Basin type= earth embankment and perforated outlet as shown in
SD I-16(c) in (Appendix 39.B)

Soil type= sandy loam. Type C.

Construction period less than 2 years, design storm= 3 month ARI.

Area= 7.8 ha.

Compute overland flow time using Friend’s Formula where n=0.011, Lo=
50 m, S=0.3%.

Compute drain flow time for a Ld= 270 m and V=1 m/s.
3.6.1 Determine Tc
Overland flow time (To) is estimated using Friend’s Formula:
to 
107  n  L1 / 3
S 0 .2
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where
n= 0.011 from Table 14.2 for paved surface
S= 0.3%
L (Overland sheet flow path length) = 50 m.
Applying the Friend’s Formula, To= 5.5 min.
Td=L/V= 270/1= 270 s= 4.5 min.
Hence, Tc = To + Td = 5.5+4.5 = 10 min
3.6.2 Sizing of Sediment Basin
From Table 3.1 (Table 39.4), Soil Type= C
Construction time < 2 years
Design storm= 3 mth ARI
From Table 3.2 (Table 39.5), for the above Tc,
Required surface area= 333 m2/ha
Required total volume = 400 m3/ha
Catchment area= 7.8 ha
Surface area required= 333 x 7.8= 2596.8 m2
Total volume required= 400 x 7.8= 3119.3 m3
3.6.2.1 Settling Zone
According to Table 39.5, the required settling volume is half the total volume,
and the settling zone depth, y1= 0.6 m.
Hence the required settling zone volume, V1= 0.5 x 3119.3= 1559.6 m3
Try settling zone average width, W1= 25 m
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The required settling zone average length, L1 = V1/(W1 y1)= 1559.6/(25 x 0.6)=
104.0 m
Design surface area= 104 x 25= 2599.3 m2 >
2596.7 m2 (OK)
Check settling zone dimensions,
L1/y1= 104/0.6= 173.3 <200 (OK)
L1/W1=104/25= 4.16 >2
(OK)
3.6.2.2 Sediment Storage Zone
Similarly, the required sediment storage zone volume is half the total volume.
Hence the required sediment storage zone volume, V2 = 0.5 x 3119.3= 1559.6 m3
Side slope (H/V), z = 2
Dimension at the top of the sediment storage zone:
W2 = W1-2 (y1/2) z= 25 - 0.6 x 2= 23.8 m
L2 = L1-2 (y1/2) z= 104 - 0.6 x 2= 102.8 m
The required depth for the sediment storage zone (y2) can be calculated from the
following formula:
V2  (W2  z.  y2 )( L2  z  y2 )  y2
 z 2  y23  z  y22 ( L2  W2 )  W2 L2 y2
Try y2 (m)=
0.69
V2 (m3)=
1568.5 > 1559.6 m3 OK
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3.6.2.3 Overall Basin Dimensions
At top water level:
Wtwl = W1+ 2 (y1/2) z= 26 m
Ltwl = L1 + 2 (y1/2) z= 105 m
Base:
Wb = W1 - 2 (y1/2 + y2) z = 21 m
Lb = L1 - 2 (y1/2 + y2) z = 100 m
Depth:
Settling zone, y1 = 0.6 m
Sediment storage zone, y2=
0.69 m
Side slope, z= 2
3.6.3 Sizing of Outlet Pipe
Outlet riser diameter= 900 mm
Use perforated MS pipe
Pipe provided with orifice openings to ensure the basin will completely drain after
filling.
Time for completely draining the basin= 24 hr
Orifice size, D= 25 mm
Area of each orifice= pi D2 / 4 = 0.000490874
m2
Cd=0.6 for orifice diameter < 50 mm (Equation 19.3)
Ave surface area, Aav= (Wtwl Ltwl + Wb Lb)/2 = 2430 m2
From Equation 19.5,
Atotal 

2  Aav  y
t  Cd  2g
2  2430  0.6  0.69
24  60  60  0.6  2  9.81
 0.024038614 m 2
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Total no. of orifices required=0.024038614/0.000490874= 49
Try 5 rows of 10 orifices @ 0.258 m spacing
Adopt 5 rows of 10 x 25 mm orifices evenly spaced around the pipe at height
increment of 250 mm, starting at the bottom of the pipe.
3.6.4 Sizing of Emergency Spillway
The emergency spillway is designed for a 10 yr ARI flood (Q10).
Assume riser pipe flow is orifice flow through the top of the pipe only and riser
pipe head is 300 mm (height between the top of the pipe and the spillway crest
level).
Calculate Q10
Calculate I
The values of the coefficients for a, b, c and d in Table 13.A1 for ARI of 10 years
for Kuala Lumpur are as follows:
a=4.9696, b=0.6796, c= -0.2584, d= 0.0147
Substituting the above coefficients into:
ln( RI t )  a  b  ln( t )  c  (ln( t )) 2  d  (ln( t ))3
For t= 30 min, 10I30= 130.4 mm/hr
For t= 60 min, 10I60= 83.9 mm/hr
Convert to rainfall depths,
10
P30= 130.4/2 = 65.18 mm
10
P60= 83.9/1 = 83.9 mm
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Calculate C
According to MSMAM, the design rainfall depth Pd for a short duration d (min) is
given by:
Pd  P30  FD  ( P60  P30 )
where
P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from
the published polynomial curves.
FD is the adjustment factor for storm duration based on Table 13.3.
Hence 10P10= 65.18-1.28*(83.9-65.18)= 41.2 mm
Therefore 10I10= 247.2 mm/hr
From Design Chart 14.3, for Category 3,
C= 0.84
Calculate Qp
The peak discharge for ARI=10 years is computed using the Rational Method:
C y I t  A
Qy 
360
Qp= 0.84*247.2*7.8/360 = 4.5 m3/s
Calculate Qriser:
Assume riser pipe head= 0.3 m
Qriser  C o  Ao 2  g  H o
pi * 0.9 2
 2  9.81  0.3
4
 0.93m 3 / s
 0.6 
Qspillway=Q10-Qriser =4.5-0.93=3.57 m3/s
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Calculate Qspillway (check):
Try spillway basewidth, B = 6.5 m
Try effective spillway head, Hp = 0.5 m
Csp (Spillway discharge coeff from Design Chart 20.2)=1.65
Qspillway  C sp  B  H 1p.5
 1.65  6.5  0.51.5
 3.79m 3 / s
> 3.57 m3/s
In summary,
Settling depth=0.6 m
Sediment storage depth=0.69 m
Riser head= 0.3 m
Spillway head=0.5 m
Total basin depth including the spillway is= 2.09 m
3.7
Worked Example 3.2- Design of A Dry Sediment Basin (Ipoh)
Problem: To design a dry sediment basin and outlet structures required for a
construction site in Ipoh.
Relevant data are as follows:

Basin type= earth embankment and perforated outlet as shown in
SD I-16(c) in (Appendix 39.B)

Soil type= sandy loam. Type C.

Construction period less than 2 years, design storm= 3 month ARI.

Area= 9.2 ha.

Compute overland flow time using Friend’s Formula where n=0.01, Lo=
57.5 m, S=0.4%.

Compute drain flow time for a Ld= 450 m and V=1.1 m/s.

Spillway basewidth, B = 6.5 m
Use Design Chart 14.3, assume Category 3.
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FIGURE 3.1 SCHEMATIC DIAGRAM OF A SEDIMENT BASIN
Ltwl, Wtwl
y1 /2
Settling zone
z
z
1
y1
L1, W1
L2, W2
Storage zone
z
z
y2
Lb, Wb
FIGURE 3.2 SCHEMATIC DIAGRAM OF A DRY SEDIMENT BASIN
Q 10
Spillway Head
Q Riser
Riser Head
Q Spillway
Settling Zone
Storage Zone
Q10=Q Riser + Q Spillway
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3.8
Worked Example 3.3- Design of A Wet Sediment Basin
This worked example uses a spreadsheet to size a wet sediment basin in Ipoh.
Excel Filename: DrQuekWetSedBasin1a.xls
Problem: To design a wet sediment basin and outlet structures required for a
construction site in Ipoh.
Relevant data are as follows:

Basin type= earth embankment and perforated outlet as shown in
SD I-16(d) in (Appendix 39.B)

Soil type= sandy loam. Type F.

Construction period less than 2 years.

Area= 8 ha.

Compute overland flow time using Friend’s Formula where n=0.01, Lo=
47 m, S=0.4%.

Compute drain flow time for a Ld= 570 m and V=1 m/s.
3.8.1 Determine Tc
Overland flow time (To) is estimated using Friend’s Formula:
107  n  L1 / 3
to 
S 0 .2
where
n= 0.01 from Table 14.2 for paved surface
S= 0.4%
L (Overland sheet flow path length) = 47 m.
Applying the Friend’s Formula, To= 4.6 min.
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Td=L/V= 570/1= 270 s= 9.5 min.
Hence, Tc= To + Td = 4.6 + 9.5 = 14.1 min
3.8.2 Sizing of Sediment Basin
From Table 3.3 (Table 39.6), Soil Type= F
Construction time < 2 years
The 75th percentile 5-day storm for Ipoh is 36.75 mm (Refer Table 3.4 for other
locations in Malaysia)
From Table 3.3, for the above 75th percentile 5-day storm,
Required settling zone volume= 176 m3/ha
Required total volume = 264 m3/ha
Catchment area= 8 ha
Settling zone volume required= 176 x 8= 1410 m3
Total volume required= 264 x 8= 2114 m3
3.8.2.1 Settling Zone
According to Table 3.3, the settling zone depth, y1= 0.6 m.
Try settling zone average width, W1= 30 m
The required settling zone average length, L1 = V1/(W1 y1)= 1410/(30 x 0.6)=
78.3 m
Check settling zone dimensions,
L1/y1= 78.3/0.6= 130.6
<200 (OK)
L1/W1=78.3/30= 2.61
>2
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3.8.2.2 Sediment Storage Zone
Hence the required sediment storage zone volume,
V2 = V-V1= 2114-1410.2=703.8 m3
Side slope (H/V), z = 2
Dimension at the top of the sediment storage zone:
W2 = W1-2 (y1/2) z= 30 - 0.6 x 2= 28.8 m
L2 = L1-2 (y1/2) z= 78.3 - 0.6 x 2= 77.1 m
The required depth for the sediment storage zone (y2) can be calculated from the
following formula:
V2  (W2  z.  y2 )( L2  z  y2 )  y2
 z 2  y23  z  y22 ( L2  W2 )  W2 L2 y2
Try y2 (m)=
0.35
> 0.3 m OK
V2 (m3)=
751
> 703 m3 OK
3.8.2.3 Overall Basin Dimensions
At top water level:
Wtwl = W1+ 2 (y1/2) z= 31 m
Ltwl = L1 + 2 (y1/2) z= 80 m
Base:
Wb = W1 - 2 (y1/2 + y2) z = 27 m
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Lb = L1 - 2 (y1/2 + y2) z = 76 m
Depth:
Settling zone, y1 = 0.6 m
Sediment storage zone, y2=
0.35 m
Side slope, z= 2
3.8.3 Sizing of Emergency Spillway
The emergency spillway is designed for a 10 yr ARI flood (Q10).
Calculate Q10
Calculate I
The values of the coefficients for a, b, c and d in Table 13.A1 for ARI of 10 years
for Ipoh are as follows:
a=5.0707, b=0.6515, c= -0.2522, d= 0.0138
Substituting the above coefficients into:
ln( RI t )  a  b  ln( t )  c  (ln( t )) 2  d  (ln( t ))3
For t= 30 min, 10I30= 135.9 mm/hr
For t= 60 min, 10I60= 86.3 mm/hr
Convert to rainfall depths,
10
P30= 135.9/2 = 67.96 mm
10
P60= 86.3/1 = 86.3 mm
Calculate C
According to MSMAM, the design rainfall depth Pd for a short duration d (min) is
given by:
Pd  P30  FD  ( P60  P30 )
where
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P30 and P60 are the 30 min and 60 min rainfall depths, respectively, obtained from
the published polynomial curves.
FD is the adjustment factor for storm duration based on Table 13.3.
Hence 10P14= 67.96-0.8*(86.3-67.96)= 53.3 mm
Therefore 10I14= 226.3 mm/hr
From Design Chart 14.3, for Category 3,
C= 0.88
Calculate Qp
The peak discharge for ARI=5 years is computed using the Rational Method:
C y I t  A
Qy 
360
Q10= 0.88*226.3*8/360 = 3.82 m3/s
Qspillway=Q10 =3.82 m3/s
Calculate Qspillway:
Try spillway basewidth, B = 7 m
Try effective spillway head, Hp = 0.5 m
Csp (Spillway discharge coeff from Design Chart 20.2)= 1.65
Qspillway  C sp  B  H 1p.5
 1.65  7  0.51.5
 4.08m 3 / s
> 3.82 m3/s OK
In summary,
Settling depth=0.6 m
Sediment storage depth=0.35 m
Spillway head=0.5 m
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Total basin depth including the spillway is= 1.45 m
3.9
Worked Example 3.4- Design of A Wet Sediment Basin (Melaka)
Problem: To design a wet sediment basin and outlet structures required for a
construction site in Melaka.
Relevant data are as follows:

Basin type= earth embankment and perforated outlet as shown in
SD I-16(d) in (Appendix 39.B)

Soil type= sandy loam. Type F.

Construction period less than 2 years.

Area= 8 ha.

Compute overland flow time using Friend’s Formula where n=0.015, Lo=
66 m, S=0.38%.

Compute drain flow time for a Ld= 422 m and V=1.0 m/s.

Refer Table 3.4 for the 75th percentile 5-day storm for Melaka.
Use Design Chart 14.3, assume Category 3.
3.10
Worked Example 3.5- Design of A Dry Sediment Basin (Kuching)
Problem: To design a dry sediment basin and outlet structures required for a
construction site in Kuching.
Relevant data are as follows:

Basin type= earth embankment and perforated outlet as shown in
SD I-16(c) in (Appendix 39.B)

Soil type= sandy loam. Type C.

Construction period less than 2 years, design storm= 3 month ARI.

Area= 5.0 ha.
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
Compute overland flow time using Friend’s Formula where n=0.015, Lo=
77 m, S=0.5%.
3.11

Compute drain flow time for a Ld= 640 m and V=1.2 m/s.

Spillway basewidth, B = 10 m
Worked Example 3.6- Design of A Wet Sediment Basin (Kuching)
Problem: To design a wet sediment basin and outlet structures required for a
construction site in Kuching.
Relevant data are as follows:

Basin type= earth embankment and perforated outlet as shown in
SD I-16(d) in (Appendix 39.B)

Soil type= sandy loam. Type D.

Construction period less than 2 years.

Area= 5 ha.

Compute overland flow time using Friend’s Formula where n=0.015, Lo=
70 m, S=0.5%.

Compute drain flow time for a Ld= 511 m and V=1.1 m/s.
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FIGURE 3.3 SCHEMATIC DIAGRAM OF A WET SEDIMENT BASIN
Q 10
Spillway Head
Q Spillway
Settling Zone
Storage Zone
Q10=Q Spillway
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TABLE 3.4 5-DAY CUMULATIVE RAINFALL DEPTHS (MM)
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Appendix 3.1- Design of Silt Trap Using the Planning and Design Procedure
No. 1- Incorporating an Overflow Weir and Bypass Channel
THE DESIGN AND MAINTENANCE OF EFFECTIVE SILT TRAP
(Based on Planning and Design Procedure No. 1, 1975)
(Paper Presented at ½ day Seminar On Environmental Management in the Property
Development and Construction Sectors, 10th July 1999)
By
Ir. Dr. Quek Keng Hong BE (Civil), MEngSc, Ph.D. (NSW), MIEM1
1.
INTRODUCTION
94
2
EXISTING PROCEDURES AND GUIDELINES FOR THE DESIGN OF
SILT TRAP 96
2.1
Introduction .............................................................................................................. 96
2.2
Silt Trap Storage Volume ........................................................................................ 96
2.3
Maintenance Requirement of Silt Trap .................................................................. 96
2.4
Design Discharge....................................................................................................... 96
2.5
Rate of Erosion from Construction Site ................................................................. 96
3
WORK EXAMPLE 98
3.1
Introduction .............................................................................................................. 98
3.2
Design Flows .............................................................................................................. 99
3.3
Outlet Pipe Design .................................................................................................... 99
3.4
Riser Design............................................................................................................. 104
1
Principal, Dr. Quek & Associates
Emails: quek@pop.jaring.my
Website URL: http://wrec.cjb.net
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3.5
Inlet Pipe Design ..................................................................................................... 105
3.6
Sediment Basin Design ........................................................................................... 106
3.7
Overflow Weir......................................................................................................... 111
3.8
Bypass Channel ....................................................................................................... 112
3.9
Maintenance Requirement..................................................................................... 113
4
REFERENCES
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1.
INTRODUCTION
(Comment by the Author: This paper was prepared in 1999- before the
introduction of MSMAM. Although it is based on the old procedure (PDP1), it
contains some useful reference on alternative design of Sediment BasinDr. Quek).
A silt trap is a device for controlling excessive siltation by the trapping and
storing of sediments which enter a stream from upstream catchment area and
deposited in downstream area. It is usually constructed either by the building of a
barrier or dam across a stream, or by excavation of a basin, or a combination of
both. The silt trap described here is a temporary structure during construction
stage and must be removed upon completion of the construction work.
Currently, the Planning and Design Procedure No. 1 (JPS, 1975) provides some
simplified guidelines for the design of silt trap. The approach is to design the
capacity of the silt trap based on a certain storage volume per unit catchment area
(126.5 m3 per hectare or 67 yd3 per acre of drainage area). The procedure
recommends desilting to be carried out when the storage capacity is reduced by
sedimentation to 40% of its design storage capacity (i.e., 51 m3 per hectare or 27
yd3 per acre of drainage area).
The limitations in the JPS (1975) approach are as follows:
1. The storage volume is not sized based on the design peak discharge from the
contributing catchment area. Hence it is not possible to relate the storage
volume which is dependent on the volume of runoff to the following factors:
land use, slope, stream length, time of concentration, catchment area, and
spatial variability of storm in different parts of the country.
2. The sizing of the silt trap does not take into account the size of sediment
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particle to be removed. Hence it is not possible to correlate the storage volume
required with the size of sediment to be removed to give an indication of
whether the effluent standard can meet the stipulated water quality criteria.
3. The sediment basin is not hydraulically designed to take into account the need
to limit excessive horizontal velocity to prevent scouring and resuspension of
settled sediment, and the optimum proportioning of depth, length and width.
This paper presents the design principles and approach for silt traps. This includes
the selection of recurrence intervals, hydrologic computation of design inflows,
hydraulic calculations for the principal and emergency spillways, freeboard
allowance, sizing of storage volume, proportioning of basin dimensions, and
desilting or maintenance requirement.
Section 2 of this paper provides a brief review of the existing procedures and
guidelines for the design of silt trap.
Section 3 covers a step-by-step worked example for the design of a typical silt
trap.
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2
EXISTING PROCEDURES AND GUIDELINES FOR THE
DESIGN OF SILT TRAP
2.1
Introduction
This section provides a brief review of the existing procedures and guidelines for
the design of silt trap.
2.2
Silt Trap Storage Volume
The Planning and Design Procedure No. 1 (JPS, 1975) recommends a storage
capacity of at least 126.5 m3 per hectare of drainage area (or 67 yd3 per acre of
drainage area). This requirement applies to all locations in Peninsular Malaysia.
2.3
Maintenance Requirement of Silt Trap
The JPS procedure recommends that sedimentation basin should be cleaned out
when the storage capacity is reduced by sedimentation to 51 m3 per hectare of
drainage area (or 27 yd3 per acre of drainage area). This translates to about 40%
of the design storage volume as discussed in Section 2.2.
2.4
Design Discharge
The procedure states that the runoff computations shall be based on the Modified
Rational Method, using the soil cover conditions expected to prevail in the
contributing drainage area during the anticipated lifespan of the structure. The
combined capacities of the principal and emergency spillways shall be sufficient
to pass the peak rate of runoff from a 10 year frequency storm.
2.5
Rate of Erosion from Construction Site
To determine the frequency of desilting, it is necessary to know the rate of erosion
from a project site. The rate of erosion from a project site varies considerably over
time and within an area, depending on terrain, geology, hydrogeology, soil types,
climate and landuse.
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The publication by JAS entitled “Guidelines for Prevention and Control of Soil
Erosion and Siltation in Malaysia” (JAS, 1996) provides examples of erosion
rates for various landuses and terrain types in Malaysia.
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3
WORK EXAMPLE
3.1
Introduction
A silt trap is proposed as shown in Figure 3.1 downstream of a construction site.
A worked example showing step-by-step calculations for the sizing of the silt trap
is given below.
FIGURE 3.1 PROJECT SITE
Construction
Site
River
Silt Trap
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3.2
Design Flows
The peak discharges can be calculated using the Modified Rational Method as
given in JPS (1975). The steps of calculation will not be covered here. Following
are the computed minor and major flows for an Average Recurrence Interval
(ARI) of 10 and 100 years, respectively:
Minor flow:
Q10= 2.8 m3/s
Major flow:
Q100= 4.7 m3/s
Note that the minor flow is the flow that will be routed through the silt trap. The
portion of the flow which is greater than the minor flow, but less than the major
flow will be diverted through a bypass channel.
3.3
Outlet Pipe Design
The schematic layout of the silt trap used for this work example is shown in
Figure 3.2.
The first component of the silt trap to be designed is the outlet pipe. This section
computes the head required to discharge Q10 through the 1.5 m diameter outlet
pipe flowing with outlet control with a maximum downstream water level of 21.5
m RL. This will determine the water level in the basin. By allowing for freeboard,
the minimum embankment height can be determined to ensure no overtopping of
the embankment.
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FIGURE 3.2 SILT TRAP LAYOUT
Q
major
EQ
minor
C
Overflow Weir
Q major – Q
minor
B
L
B
A
Inle
t
Pipe
Sediment Basin
Rip-Rap
Protection
To Suit
Outle
t
Pipe
A
Bypass Channel
C
W
Ground
Level
D
W
SECTION AA
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Q major Level
22.4 m
RL
22.1 m RL
Q minor
Level
Channel
Bypass Channel
Overflow Weir
Pipe Inlet To
Sedimentation
Basin
SECTION BB
2mx2m
Square Box Riser
Overflow
Weir
22.1 m
RL
22.7 m
RL
1.5 m
dia
20.1 m RL
21.9 m RL
22.5 m RL
21.5 m RL
20 m RL
19.7 m
RL
Lw
1.5 m
dia
L
SECTION CC
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21.5 m
RL RL
18.5 m
RL
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The parameters adopted for a concrete pipe outlet are as follows:
n=0.014
L=60 m
S=0.02 m/m
D=1.5 m
ke=0.5
Q10=2.8 m3/s
Try 1 pipe,
A=1.778 m2
P=4.71 m
Outlet invert level = 18.5 m RL
V = Q/A = 1.6 m/s (no special energy dissipation structure required at outfall to
the downstream channel, provide rip-rap on foreshore extending 4 m downstream
of outfall)
The head (H in m) required to pass Q10 through the pipe flowing full with outlet
control is the sum of the velocity head (Hv), the entrance loss (He) and the friction
loss (Hf). Assuming an entrance loss coefficient (ke) of 0.5, the head H can be
expressed as follows:
H  Hv  He  H f

29  n 2  L  v 2
 1  k e 
4
  2g
3
R


3.1
2
 Q 
 Q  n  P 23
A

 1.5 

5

2g
3
 A
 0.19  0.11  0.30
2

 L


where
Q
is the flow rate in culvert barrel (m3/s)
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n
is the Manning’s roughness coefficient
A
is the area of flow for full cross section (m2)
P
is the wetted perimeter (m)
R
is the hydraulic radius (m)
L
is the length of culvert barrel (m)
g
acceleration due to gravity (m/s2)
For outlet control type of flow, the depth of headwater (HW) is determined as
follows:
HW  TW  H  S o  L
3.2
 3  0.3  0.02  60  2.1 m
where
TW
is the tailwater (m RL)
So
is slope of the flow line (m/m)
Note that HW is equal to the depth of the basin at the outlet.
The associated HW level is therefore 21.5 + 0.3 = 21.8 m RL which is the
maximum water level in the basin to discharge Q10 through the outlet pipe based
on available head.
Hence adopt 1.5 m diameter outlet pipe.
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3.4
Riser Design
Assuming a 2 m by 2 m box shaped riser inlet. The inlet level is fixed at the
maximum downstream water level of 21.5 m RL to prevent backflow. The
calculation for rise in water level associated with the riser is as follows:
L= 4*2 = 8 m
c= 1.4
Substituting the above into the weir equation:
Qs  c  L  H
3
3.3
2
H=0.40 m
Taking into account the 0.4 m rise in water level in the basin associated with the
riser, the maximum water level in the basin is 21.5 + 0.4 = 21.9 m RL (>21.8 m
RL based on available head consideration).
Allowing a freeboard of 0.6 m, the minimum embankment height is 21.9 + 0.6 =
22.5 m RL.
Hence adopt a 2 m by 2 m box riser with grate inlet.
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3.5
Inlet Pipe Design
Based on the maximum water level (21.9 m RL) in the basin as determined above,
it is necessary to check the upstream water level to ensure no flooding upstream
of the inlet pipe.
The parameters adopted for a concrete pipe inlet are as follows:
n=0.014
L=30 m
S=0.002 m/m
D=1.5 m
ke=0.5
Q10=2.8 m3/s
Try 1 pipe,
A=1.778 m2
P=4.71 m
V=1.6 m/s (no scouring protection required)
Outlet invert level = 20.0 m RL
The head required to pass Q10 through the pipe flowing full with outlet control is:
2
 Q 
 Q  n  P 23
A

H  1.5 

5

2g
3
 A
 0.19  0.05  0.24 m
2

 L


The depth of headwater (HW) is therefore:
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HW  TW  H  S o  L
 1.9  0.24  0.002  30  2.1 m
The HW level reached is 21.9 + 0.24 = 22.1 m RL (check against the upstream
permissible tail water level)
Hence adopt 1 no concrete pipe @ 1.5 m diameter.
3.6
OK
Sediment Basin Design
The sediment basin is designed for the removal of coarse sand with diameter
above 500 m (0.5 mm). For particles of this size with low concentration, it is
reasonable to assume ideal settling of discrete particles in a horizontal flow
rectangular sedimentation basin (see Figure 3.3) as proposed by Hazen in 1904.
According to Hazen Theory, for complete removal of the slowest settling particle,
its settling velocity Vp must be equal to the surface overflow rate Qp/A. This
relationship can be expressed as follows:
Vp 
Qp
3.4
A
where
Qp
is the peak discharge (m3/s)
Vp
is the settling velocity for coarse sand (m/s)
A
is the horizontal surface area of basin (m2)
It follows from the above reasoning that all particles with settling velocities equal
to or greater than the overflow rate will be completely removed from the basin.
Also any particle with settling velocity Vp’ which is less than Vp will be removed
in the ratio of Vp’/ Vp.
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Equation 3.4 applies if the settling in the basin follows ideal settling behavior.
However, this is difficult to achieve in practice. In order to account for the effect
of non-ideal conditions including turbulence, a factor of 1.2 is applied to the
design discharge after rearranging as follows (note that the factor varies according
to the hydraulic design of the basin):
A  1 .2 
Qp
Vp
The settling of coarse sand can be determined from Figure 3.4, Vp=0.053 m/s
Hence A=63.4 m2
Assume basin depth D= 2 m
To prevent resuspension, the horizontal flow velocity (Vh) should be kept to
below 0.36 m/s which is the resuspension velocity of coarse sand. The width of
the basin is therefore determined as follows:
W

1.2  Q p
3.5
Vh  D
1.2  2.8
 4.6 m
0.36  2
Hence the length of the basin is
A
W
63.4

 13.8 m
4.6
L
3.6
L/W = 3 (Value of L/W should be kept to within 3 to 6 for optimum behavior of
settling basin.)
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The detention time can be computed as follows:
T

L W  D
Qp
3.7
13.8  4.6  2
 45 s
2.8
Hence adopt sediment basin with dimension of 2 m (D), 4.6 m (W) and 13.8 m
(L) with a storage volume of 127 m3.
OK
Note that for fine sand with a settling velocity of 0.011 m/s, the above procedure
gives the following values of area and volume:
A=305.5 m2
V=611 m3
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FIGURE 3.3 IDEAL SETTLING IN RECTANGULAR HORIZONTAL
FLOW SEDIMENTATION BASIN
INLET
Vh
D
Vp
OUTLE
T
EL
LONGITUDINAL SECTION
W
PLAN VIEW
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FIGURE 3.4 SETTLING VELOCITY OF SEDIMENT PARTICLES
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3.7
Overflow Weir
The aim of the overflow weir is to divert the major flow away from the sediment
basin which is designed only to cater for the minor flow. Just upstream from the
inlet to the basin, a diversion weir structure is provided such that any flow above
the minor flow will be diverted into the channel which is designed to cater up to
the capacity of the major flow. Hence the design flow for the overflow weir is
Q100 - Q10.
Assuming flow over a broad crested weir, the weir equation is given by:
Qs  c  Lw  H
3
3.8
2
By rearranging the above equation, the length of the weir can be determined as
follows:
Lw 
Qs
c  H
3
2
Where
Lw
is the length of the overflow weir
Qs
is the flow over the weir
The overflow weir level is fixed at 22.1 m RL which is the maximum HW level
upstream of the inlet for Q10.
Maximum permissible level over weir H = 0.3 m
Qs= Q100 - Q10 = 4.7-2.8 = 1.9
Hence Lw= 7.7 m (say 8 m)
Adopt 8 m wide broad crested weir.
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3.8
Bypass Channel
The bypass channel is sized based on Mannings equation to discharge Q100 - Q10.
Q
2
1
1
 A R 3  S 2
n
3.9
where
Q
is the flow rate (m3/s)
n
is the Manning’s roughness coefficient
A
is the cross sectional area (m2)
R
is the hydraulic radius (m)
S
is the channel slope (m/m)
Assuming rectangular shaped grass lined channel, the parameters are:
n=0.03 (grass lined channel)
S=0.001 m/m
Q= Q100 - Q10 = 4.7-2.8=1.9 m3/s
Using trial and error, the above Q requires a channel width (w) of 2.7 m and depth
(D) of 1 m:
W=2.7 m
D= 1 m
A=2.7 m2
P= 4.7 m
R= A/P= 0.57 m
Q100  Q10
A
1 .9

 0 .7 m / s
2 .7
V 
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3.9
which is less than the scouring velocity of 2 m/s.
OK
VD= 0.7 < 1
OK
Maintenance Requirement
Refer the earlier secton.
4
REFERENCES
Drainage and Irrigation Department (1975). Urban Drainage Design Standards and
Procedures for Peninsular Malaysia. Ministry of Agriculture, Malaysia.
Drainage and Irrigation Department (1976). Flood Estimation for Urban Areas in
Peninsular Malaysia. Hydrological Procedure No. 16. Ministry of Agriculture,
Malaysia.
Drainage and Irrigation Department (1982). Estimation of the Design Rainstorm in
Peninsular Malaysia (Revised and Updated). Hydrological Procedure No. 1.
Ministry of Agriculture, Malaysia.
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4.
4.1
DESIGN OF CULVERTS
Inlet Control
The major factors affecting culverts flowing under inlet control are:
1. Entrance conditions including type, headwalls and wingwalls.
2. Projection of the culvert into the headwater.
Following factors do not determine culvert capacity for culverts flowing under
inlet control:
1. Roughness of culvert.
2. Length of culvert.
3. Outlet conditions including depth of tailwater.
The figures below show three different types of culverts flowing under inlet
control (see Figure 27.6):
1. Unsubmerged inlet of projecting end
2. Submerged inlet of projecting end
3. Submerged inlet of mitred end
4.2
Outlet Control
Culverts flowing with outlet control can flow either with the culvert cell full, or
with the cell part full for all of the culvert length.
The following figures show different types of culverts flowing under outlet
control (see Figure 27.7):
1. Both inlet and outlet submerged
2. Inlet submerged but not the outlet
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3. Inlet submerged and the cell part full over part of its length
4. Inlet and outlet not submerged and flowing part full over its entire length.
Theory
The head (H in m) required for a flow discharging full through the entire length of
a culvert with outlet control is the sum of:

the velocity head (Hv),

the entrance loss (He) and

the friction loss (Hf)
The above can be expressed as follows:
H  H v  H e  H f (4.1)
4.2.1.1
Velocity head (Hv)
The velocity head (Hv) is given by:
Hv 
v2
(4.2)
2g
where
v= mean velocity.
g= acceleration due to gravity.
4.2.1.2
Entrance loss (He)
The entrance loss (He) is expressed as:
H e  ke 
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The entrance loss coefficient Ke depends on the inlet geometry due to its effect on
the contraction of the flow.
Their values are determined from experiment and are given in Design Chart 27.2.
4.2.1.3
Friction loss (Hf)
The friction head (Hf) is the energy required to overcome the roughness of the
culvert barrel.
It can be expressed in several ways and the following expression is based on
Manning’s n.
 29  n 2  L  v 2

Hf 
4

 2 g (4.4)
3
 R

4.2.1.4
Total Energy Head (H)
Substituting the above into the Total Head equation (Equation 4.1) and after
simplification, the head H can be expressed as follows (see Figure 27.8 for
graphical representation of terms in the equation):
H  Hv  He  H f

29  n 2  L  v 2

 1  ke 
4

R 3  2g

(4.5)
2
 Q 
2
A   Q  n  P 3

 (1  ke ) 

 A53
2g

2

 L


where
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Q
is the flow rate in culvert barrel (m3/s)
n
is the Manning’s roughness coefficient
A
is the area of flow for full cross section in m2
P
is the wetted perimeter in m
R
is the hydraulic radius (m)
L
is the length of culvert barrel (m)
g
acceleration due to gravity (= 9.8 m/s2)
4.2.1.5
Determining Headwater (HW)
For outlet control type of flow, finding the value of H is not the complete solution
for the Headwater (HW) which is dependent on factors such as slope of the
culvert barrel and outlet conditions.
The headwater (HW) can be defined as follows:
HWo  H  ho  S o  L
(4.6)
where
ho
is the greater of TW and hc  D  / 2 where hc<or = D
So
is slope of the flow line (m/m)
Refer Figure 27.10 for the determination of ho.
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Work Example 4.1 (Concrete Box Culvert)
4.3.1
Case Study
It is proposed to lay a drainage box culvert under a main road in Bandar
MSMAM. The peak discharges at this location are as follows:
Q50 = 11.00 m3/s
Q100 = 12.40 m3/s
Estimated area A= Q50/V where V= 2 m/s
A= 11/2= 5.5 m2
Try 1 x 3000 (B) x 1500 (D) box culvert (Type 1).
Excel filename= DrQuekCulvert1a.xls
4.3.2
1.
Design for 50 years ARI
Inlet Contro1
Assuming inlet control, from Design Chart 27.4,
Q/NB= 11/3= 3.67
HW/D= 1.20
HW= 1.8 m
2.
Outlet Control
ke= 0.2
L= 30 m
n= 0.012
A= 4.5 m2
From Design Chart 27.11, H= 0.44
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Or using the following equation:
H  Hv  He  H f
2
 Q 
 Q  n  P 23
 A
 (1  k e ) 

5

2g
A 3

 0.366  0.065  0.431
2

 L


From Design Chart 27.9,
hc= 1.1
Or using equation:
 Q 
hc  0.467  

 NB 
2/3
 1.11
Hence ho= (hc+D)/2= 1.3
S= 0.005 m/m
HW o  H  ho  S o  L
 1.59
(compared to 1.59 using equation)
HWi  HW o
Hence Inlet Control governs.
3
Outlet Velocity
Check outlet velocity.
Area of flow= 3 x 1.5 = 4.50 m2.
V= 2.4 m/s
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4.
Froude Number
F
V
gD
 0.64
F<1 so flow is subcritical.
4.3.3
1.
Design for 100 years ARI
Inlet Control
Assuming inlet control, from Design Chart 27.4,
Q/NB= 12.4/3= 4.1
HW/D= 1.35
HW= 2.03 m
2.
Outlet Control
ke= 0.2
L= 30 m
n= 0.012
A= 4.5 m2
From Design Chart 27.11, H= 0.59
Or using the following equation:
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H  Hv  He  H f
2
 Q 
 Q  n  P 23
 A
 (1  k e ) 

5

2g
A 3

 0.465  0.0826  0.547
2

 L


From Design Chart 27.9,
hc= 1.2
Or using equation:
 Q 
hc  0.467  

 NB 
2/3
 1.2
Hence ho= (hc+D)/2= 1.35
S= 0.005 m/m
HW o  H  ho  S o  L
 1.79
(compared to 1.75 using equation)
HWi  HW o
Hence Inlet Control governs.
3.
Outlet Velocity
Check outlet velocity.
Area of flow= 3 x 1.5 = 4.50 m2.
V= 2.76 m/s
4.
Froude Number
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F
V
gD
 0.72
F<1 so flow is subcritical.
Therefore adopt 1 x 3000 x 1500 box culvert (after checking to make sure that the
HWi of 2.03 m will not caused flooding upstream).
4.3.4
Spreadsheet Computation
The above computation can be easily programmed using a spreadsheet e.g., MS
Excel.
Table 4.1 is an example of the computation using the spreadsheet software. This
is similar to Design Chart 27.1.
Note the only input required for the above spreadsheet is the value of HW/D for
inlet control culvert. All the other parameters can be programmed using the above
equations.
The main advantage of using a spreadsheet is the ease to try out different culvert
sizes without re-reading the nomographs.
Culvert C1 is a box culvert while Culvert C2 is a pipe culvert.
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Work Example 4.2 (Concrete Box Culvert)
Design another concrete box culvert using the following data:
Q50 = 22.00 m3/s
Q100 = 25.40 m3/s
L= 15 m
S= 0.003 m/m
Inlet Type= 45o wingwall flare
Ke= 0.5
HW<3 M
Work Example 4.3 (Concrete Pipe Culvert)
Design a third crossing in Bandar MSMAM using concrete pipe culvert. The peak
discharges at this location are as follows:
Q50 = 7.00 m3/s
Q100 = 8.20 m3/s
L= 22 m
S= 0.002 m/m
Inlet Type= Headwall with square edge
Ke= 0.2.
HW<2 M
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Work Example 4.4 (Rating Curve)
Compute the rating curve for concrete box culverts designed for the following
peak discharges:
Q50 = 25.5 m3/s
Q100 = 52.0 m3/s
L= 33 m
S= 0.001 m/m
Inlet Type= 90o wingwall flare
Ke= 0.4.
Work Example 4.5 (Peak Discharges)
Compute the peak discharges of the following pipe culverts:
Diameter= 2 m
L= 67 m
S= 0.002 m/m
Inlet Type= Headwall with square edge
Ke= 0.4
HW<3.0 m
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TABLE 4.1 DESIGN COMPUTATION OF CULVERT (CULVERT 1- BOX CULVERT, CULVERT 2- PIPE CULVERT)
CATCHMENT
CULVERT
NO.
Q50/Q100
(m3/s)
1
C1
2
C2
11.00
12.40
7.70
8.60
NO. OF
CELLS,
N
1
1
2
2
B
(M)
D
(M)
3.0
3.0
1.5
1.5
1.5
1.5
INLET CONTROL:
Q/NB
HW/D HW
(M3/S/M)
(M)
3.7
4.1
3.9
4.3
1.20
1.35
1.10
1.21
1.80
2.03
1.65
1.82
ke
OUTLET CONTROL: (H)
L
n
A
P
(M)
(M2) (M)
0.2
0.2
0.2
0.2
30
30
30
30
0.012
0.012
0.012
0.012
4.5
4.5
3.53
3.53
9
9
9.42
9.42
H1
(M)
H2
(M)
H
(M)
(hc)
hc
(M)
(hc+D)/2
0.366
0.465
0.291
0.363
0.065
0.083
0.076
0.095
0.431
0.548
0.367
0.457
1.11
1.20
0.95
1.05
1.31
1.35
1.23
1.28
Continued from above
CHECK OUTLET VELOCITY:
d
Ae (M2)
V (M/S)
1.50
4.50
2.44
1.50
4.50
2.76
1.44
3.53
2.18
1.50
3.53
2.43
CHECK FROUDE NO:
F
SUPER/SUBCRITICAL
0.64
SUBCRITICAL
0.72
SUBCRITICAL
0.57
SUBCRITICAL
0.63
SUBCRITICAL
CRI A (100 YR WL)
0.300
0.525
0.150
0.315
NOTE: Culvert C1- Box culvert and Culvert C2- pipe culvert.
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125
EMBANKMENT LEVEL:
CRI B (50 YR WL + 0.3M) CRI C (+ 1M)
0.600
1.000
0.450
1.000
GOVERNS
1.000
1.000
(HW)
S
HW
(M/M) (M)
0.005
0.005
0.005
0.005
1.59
1.75
1.44
1.58
CONTROL
INLET
INLET
INLET
INLET
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
5.
REFERENCES:
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of Agriculture, Malaysia.
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software at http://www.msmam.com
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
Drainage and Irrigation Department (1987) Magnitude and Frequency of Floods in
Peninsular Malaysia. Hydrological Procedure No. 4. Ministry of Agriculture, Malaysia.
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Program- User Manua” Department of Civil Engineering, Monash University,
Melbourne.
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software at http://www.msmam.com
ANNUAL MAXIMUM DISCHARGES (M3/S)
180
WORKSHOP NO. 3- DETENTION / SEDIMENT BASIN & CULVERT DESIGN
_______________________________________________________________________
160
Perbadanan Putrajaya (1998). “Putrajaya Stormwater Management Design
140
Guidelines,” Edited by T. H. F. Wong, Angkasa GHD Engineers Sdn Bhd.
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Quek, K.H. (1993) "Assessment of flood Estimation Techniques for Urbanizing
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in Urban Development, organised by Water Resources Technical Division, the
60
Institution of Engineers Malaysia, Regent Hotel, Kuala Lumpur, 18th January.
40
Quek K. H. (1999) “Water Quality Modelling of Wetlands and Lake” Journal of the
20
Institution of Engineers Malaysia, Vol. 60, No. 3, September 1999, pp 11-19.
0
-2
-1
0
1
2
3
Quek K. H. and Carroll D. (1999) “Flood Hydrology Study of Multi-Cell Multi-Stage
REDUCED VARIATE
Wetlands and
YR: 0.3665, 5 YR: 1.4999, 10 YR: 2.2504, 20 YR: 2.9702, 50 YR: 3.9019, 100 YR:
Lake(ARI
in2Putrajaya”
Journal of the Institution of Engineers Malaysia,
4.6001)
Vol 60, No. 1, March.
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Manual” Version 2.2, US Army Corps of Engineers, September.
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software at http://www.msmam.com
4