TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES
938 Aurora Boulevard, Cubao, Quezon City
COLLEGE OF ENGINEERING AND ARCHITECTURE
Civil Engineering Department
CE 506
CE Design Projects 1
DESIGN OF STORMWATER MANAGEMENT SYSTEM OF GRACELAND SUBDIVISION
IN AMPID II, SAN MATEO, RIZAL
PREPARED BY:
BAYSA, PETERSON R.
GAVIN, JUDITH CLAIRE O.
PAGULAYAN, STEPHANIE LOUISE DL.
PARAISO, JOYCE ANN E.
(GROUP 9)
CE51FC1
SUBMITTED TO:
ENGR. MICO P. CRUZADO
Instructor
March 2019
1
ACKNOWLEDGEMENT
The designers wished to express their thoughtful appreciation and gratitude to the people who made this
design possible.
All praises, honor, glory and thanks to God and our Lord Jesus Christ for giving the designers the gift of
knowledge and wisdom to in the light of making this research possible.
The designers would like to thank their instructor, Engr. Mico P. Cruzado for the guidance in assessing and
completing the design. He provided assistance, valuable suggestions, trust and encouragement for the
improvements of this study. The designers would also like to thank Engr. John Pepard M. Rinchon, who
helped the designers as their internal adviser assisting them in the design and in relation to Water Resource
Engineering.
The designers would like to thank friends, classmates and family who contribute to be major part of their lives
– their support, encouragement, criticism, ideas, and loyalty help the designers in everything we did. Our
relationship with them helps make this design possible.
2
TABLE OF CONTENTS
ACKNOWLEDGEMENT
2
LIST OF FIGURES
5
LIST OF TABLES
6
LIST OF EQUATIONS
6
CHAPTER 1: INTRODUCTION
7
1.1
Project Background
7
1.2
The Project
7
1.3
Project Location
8
1.4
Project Client
9
1.5
Project Objectives
9
1.5.1
General Objectives
9
1.5.2
Specific Objectives
9
1.6
Scope and Limitation
9
1.6.1
Scope
9
1.6.2
Limitation
9
1.7
Project Development
CHAPTER 2: DESIGN CRITERIA
2.1
Design Data
10
13
13
2.1.1
Design Storm
13
2.1.2
Tributary Area
14
2.1.3
Existing Drainage System
15
2.1.4
Land Use and Runoff Coefficient
16
2.1.5
Time of concentration
17
2.1.6
Critical Rainfall Intensity
18
2.1.7
Peak Flow Rate
19
2.1.8
Design Criteria
20
2.2
Review of Related Literature
21
2.2.1
Local Literature
21
2.2.2
Foreign Literature
21
Review of Related Studies
22
2.3
2.3.1
Local Studies
22
3
2.3.2
Foreign Studies
CHAPTER 3: CONSTRAINTS, TRADE-OFFS, AND STANDARDS
3.1
Design Constraints
22
24
24
3.1.1
Quantitative Constraints
24
3.1.2
Qualitative Constraint
25
3.2
Trade-off Strategy
26
3.3
Design Trade-offs
26
3.3.1
Water Resources Trade-offs
27
3.3.2
Structural Trade-offs
28
3.4
Initial Estimates of Trade-offs (Water Resources)
30
3.4.1
Economic Constraint (Project Cost)
30
3.4.2
Constructability Constraint (Constructability Cost)
31
3.4.3
Sustainability (Life Span)
32
3.4.4
Risk Assessment Constraint (Level of Hazard)
33
3.4.5
Initial Summary of Designer’s Raw Ranking for Water Resources Trade-offs
35
3.4.6
Conclusion of Water Resources Trade-offs
35
3.5
Initial Estimates of Trade-offs (Structural)
35
3.5.1
Economic Constraint (Project Cost)
35
3.5.2
Constructability Constraint (Constructability Cost)
36
3.5.3
Sustainability (Life Span)
37
3.5.4
Risk Assessment Constraint (Level of Hazard)
38
3.5.5
Initial Summary of Designer’s Raw Ranking for Structural Trade-offs
40
3.5.6
Conclusion of Structural Trade-offs
40
3.6
Trade-off Assessment (Water Resources and Structural)
40
3.6.1
Economic Constraint Assessment
40
3.6.2
Constructability Constraint Assessment
40
3.6.3
Sustainability Constraint Assessment
40
3.6.4
Risk Assessment
41
3.6.5
Over-all Assessment of Trade-offs
41
3.7
Design Standards
41
REFERENCES
43
APPENDIX A: INITIAL ESTIMATED ECONOMIC COST OF TRADE-OFFS
44
APPENDIX B: INITIAL ESTIMATED CONSTRUCTABILITY COST OF TRADE-OFFS
47
4
LIST OF FIGURES
Figure 1- 1. Ampid River Near Graceland Subdivision .................................................................................. 7
Figure 1- 2: Satellite View of Project Location ............................................................................................... 8
Figure 1- 3: Five-Year Flood Hazard Map of Project Location ....................................................................... 8
Figure 1- 4: Project Development Flowchart ................................................................................................ 11
Figure 2- 1: Total Catchment Area of the Subdivision ................................................................................. 14
Figure 2- 2: Topographical View of Project Location ................................................................................... 14
Figure 2- 3: Existing Drainage System of Graceland Subdivision ................................................................ 15
Figure 3- 1: Ranking Scale .......................................................................................................................... 26
Figure 3- 2: Example of Stormwater Detention Pond ................................................................................... 27
Figure 3- 3: Example of Dry Well ................................................................................................................. 28
Figure 3- 4: Example of Enhanced Drainage System .................................................................................. 28
Figure 3- 5: Example of a Winch Floodgate ................................................................................................. 29
Figure 3- 6: Tidal Floodgate......................................................................................................................... 29
Figure 3- 7: Sluice Gate, Nagor River .......................................................................................................... 30
Figure 3- 8: Initial Economic Ranking of Dry Well vs. Detention Pond......................................................... 30
Figure 3- 9: Initial Economic Ranking of Dry Well vs. Enhanced Drainage System ..................................... 31
Figure 3- 10: Initial Constructability Ranking of Dry Well vs. Detention Pond .............................................. 31
Figure 3- 11: Initial Constructability Ranking of Dry Well vs. Enhanced Drainage System .......................... 32
Figure 3- 12: Initial Sustainability Ranking of Enhanced Drainage System vs. Detention Pond .................. 33
Figure 3- 13: Initial Sustainability Ranking of Enhanced Drainage System vs. Dry Well ............................. 33
Figure 3- 14: Initial Risk Assessment Ranking of Enhanced Drainage System vs. Detention Pond ............ 34
Figure 3- 15: Initial Risk Assessment Ranking of Enhanced Drainage System vs. Dry Well ....................... 34
Figure 3- 16: Economic Ranking of Tidal Floodgate vs. Winch Floodgate ................................................... 36
Figure 3- 17: Economic Ranking of Tidal Floodgate vs. Sluice Gate ........................................................... 36
Figure 3- 18: Constructability Ranking of Tidal Floodgate vs. Winch Floodgate .......................................... 37
Figure 3- 19: Constructability Ranking of Tidal Floodgate vs. Sluice Gate .................................................. 37
Figure 3- 20: Sustainability Ranking of Winch Floodgate vs. Tidal Floodgate ............................................. 38
Figure 3- 21: Sustainability Ranking of Winch Floodgate vs. Sluice Gate ................................................... 38
Figure 3- 22: Initial Risk Assessment Ranking of Tidal Floodgate vs. Winch Floodgate ............................. 39
Figure 3- 23: Initial Risk Assessment Ranking of Tidal Floodgate vs. Sluice Gate ..................................... 39
5
LIST OF TABLES
Table 2- 1: Design Storm Return Period According to the Type of Location ................................................ 13
Table 2- 2: Values of ‘C’ Recommended for Rational Formula .................................................................... 16
Table 2- 3: Time of Entry ............................................................................................................................. 17
Table 3- 1: Daily Rate of Workers ................................................................................................................ 25
Table 3- 2: Summary of Initial Estimated Economic Cost for Water Resources Trade-offs ......................... 30
Table 3- 3: Summary of Initial Estimated Constructability Cost for Water Resources Trade-offs ................ 31
Table 3- 4: Summary of Initial Estimated Life Span for Water Resources Trade-offs .................................. 32
Table 3- 5: Summary of Initial Estimated Risk for Water Resource Trade-offs ............................................ 34
Table 3- 6: Initial Ranking of Water Trade-offs ............................................................................................ 35
Table 3- 7: Summary of Initial Estimated Economic Cost for Structural Trade-offs ..................................... 35
Table 3- 8: Summary of Initial Estimated Constructability Cost for Structural Trade-offs ............................. 36
Table 3- 9: Summary of Initial Estimate Life Span for Sustainability Constraint........................................... 37
Table 3- 10: Summary of Initial Estimated Risk for Structural Trade-offs .................................................... 39
Table 3- 11: Initial Ranking of Structural Trade-offs.................................................................................... 40
Table A- 1: Initial Estimated Economic Cost for Detention Pond ................................................................. 44
Table A- 2: Initial Estimated Economic Cost for Dry Well ............................................................................ 44
Table A- 3: Initial Estimated Economic Cost for Enhanced Drainage System ............................................. 45
Table A- 4: Initial Estimated Economic Cost for Winch Floodgate ............................................................... 45
Table A- 5: Initial Estimated Economic Cost for Tidal Floodgate ................................................................. 46
Table A- 6: Initial Estimated Economic Cost for Sluice ................................................................................ 46
Table B- 1: Initial Estimated Constructability Cost for Detention Pond ........................................................ 47
Table B- 2: Initial Estimated Constructability Cost for Dry Well ................................................................... 48
Table B- 3: Initial Estimated Constructability Cost for Enhanced Drainage System ..................................... 49
Table B- 4: Initial Estimated Constructability Cost for Winch Floodgate ...................................................... 50
Table B- 5: Initial Estimated Constructability Cost for Tidal Floodgate ........................................................ 50
Table B- 6: Initial Estimated Constructability Cost for Sluice Floodgate ...................................................... 51
LIST OF EQUATIONS
Equation 1: Percentage of Imperviousness Equation .................................................................................. 16
Equation 2: Time of Concentration Formula ................................................................................................ 17
Equation 3: Inlet Time Equation ................................................................................................................... 17
Equation 4: Flow Time Formula ................................................................................................................... 18
Equation 5: Critical Rainfall Intensity Formula ............................................................................................. 19
Equation 7: Peak Flow Rate Equation ......................................................................................................... 19
6
CHAPTER 1: INTRODUCTION
1.1 Project Background
Ampid II being one of the many barangays in the municipality of San Mateo, has been likely to experience
frequent flooding from heavy rains or hurricanes that may or had occurred throughout. The barangay had
been known and reported to have undergone chest-high flood after monsoon rains inundated large portions
of Luzon last August 2018. The municipality has many residential areas sectioned all throughout and are
reachable through small roads. This makes most of the municipality congested. Noting the barangay,
Graceland subdivision has been one of the sections to experience shoulder-height floods.
The extreme typhoon that the subdivision had gone through is Typhoon Ondoy last September 26, 2009.
According to GMA news report (2009), a family got stuck in the neighbor’s 3 rd floor in Lot 4, Block 7 in
Graceland Subdivision for more than 16 hours due to eighty percent (80%) of San Mateo being submerged
in muddy water. Based from the interviews of the residents, the overflow of the river contributes the
subdivision to experience sudden flooding. Graceland Subdivision is one of the 100 prone areas in Metro
Manila that has been identified by the Metropolitan Manila Development Authority (M.M.D.A.).
Graceland Subdivision's drainage system is shown in the Chapter 2 of this paper. The current system was
designed to hold up to 5 years of return period only. In able to expand the capacity, the designers will add
stormwater management system or enhance the current drainage system of the said subdivision.
1.2 The Project
The approximate 1.62-hectare area of Graceland Subdivision is one of the catch basins of Ampid River in
San Mateo, Rizal. The subdivision is near the Ampid River where the stormwater is supposed to be
discharged. The designers, upon request of the client, will design an efficient and adequate stormwater
management system for the benefit of Graceland subdivision to mitigate the flooding within the area. The
designers will focus on temporary holding areas for amount of flood that will help regulate the flow of runoff
through the river. Using Environmental Protection Agency (E.P.A.)’s software Storm Water Management
Model, or EPA-SWMM, and HEC-RAS, the designers will provide, design and test six (6) trade-offs. The
target area encompasses the different streets and available vacant lots of Graceland subdivision.
Figure 1- 1. Ampid River Near Graceland Subdivision
7
1.3 Project Location
The proposed project is located underneath the encompassing land of Graceland Subdivision from Ampid II
in the municipality of San Mateo, province of Rizal in the region of IV-A CALABARZON. It lies at West of
Paraiso Memorial Park, at East of St. Matthew College. It is bounded on the south by the Ampid River, on
the east by the GSIS Road, on the north by Ampid 2 Barangay hall and other residential areas, and on the
west by uninhabited land. The area is also located nearby General Luna Avenue. In addition, Figure 1-5
Graceland Subdivision have high hazard in flooding.
Figure 1- 2: Satellite View of Project Location
Source: Google Map
Figure 1- 3: Five-Year Flood Hazard Map of Project Location
Source: LiPAD, DOST
8
1.4 Project Client
The client of the project is the local government of San Mateo, Rizal thru C.S. Ramos Developer with an
estimated budget of 15 million Philippine peso for the project with a target duration of 1 year. The budget is
broken down into two components: economic cost and constructability cost. For the economic cost, their
budget is 10 million Philippine peso and for the constructability cost, their budget is 5 million. C.S. Ramos
Developer is an engineering and construction management company, focused on delivering quality
infrastructure consulting services, with an emphasis on public related projects that serve the needs of our
communities. It is the developer who is responsible in the construction and who also developed the said
subdivision.
1.5 Project Objectives
1.5.1 General Objectives
The main objective of the project is to provide a design with the most efficient management of stormwater
flow of the area, while applying all acquired knowledge, skills, techniques, and principles in Water Resource
Engineering.
1.5.2
Specific Objectives
1. To design an adequate stormwater management system efficient and consistent enough to reduce
project location’s flooding problems.
2. To provide and design water and structural trade-offs for management of stormwater flood flow and
runoff.
3. To weigh-in the trade-offs and evaluate each to determine the most economic and most adequate
choice for the client and the area.
4. To design a project in accordance with the standards and codes respected to the different trade-offs.
1.6 Scope and Limitation
1.6.1 Scope
The following are the scope of the project:
1. The designers will gather primary data and information needed for the design input upon assessing
the trade-offs to be chosen.
2. The designers will focus on the analysis and design of water resources and structural trade-offs.
3. The designers will perform quantitative and qualitative design constraints to rank the different tradeoffs with respect to their sustainability, economic consideration and constructability.
4. The designers will provide the most sustainable, economical, and constructable water resources and
structural trade-offs.
5. The designers will design and test the trade-offs chosen on the respective software application with
respect to the standards and codes needed for the following trade-off.
1.6.2
Limitation
The limitations of the project are the following:
9
1. The project will only focus on designing a stormwater management system in the said area of
Graceland Subdivision in Ampid II, San Mateo, Rizal.
2. The designers will not provide other alternative designs not included in the trade-offs.
3. The designers will only provide cost for equipment, materials and labor of each trade-offs needed for
the evaluation of constraints.
4. The designers will only design and test the trade-offs using HECRAS and EPA-SWMM.
5. Any form of obstruction will not be considered by the designers.
1.7 Project Development
The designers will gather data from Graceland Subdivision through observation of the physical aspects of
the subdivision and inquiry from residing locals of the existing problems that contribute to flooding in that
area. The designers will also request for existing drainage system data from the developer of the subdivision,
C.S. Ramos Dev’t Corp, to further analyse the root of the problem of flooding within the area. After a deliberate
study of the data gathered, the designers shall produce and present six design trade-offs to help address the
problem and regulate a more effective stormwater management system. Deliberation and evaluation of the
trade-offs will be met based on the criteria and qualitative and quantitative design constraints to limit and
control the project with respect to its scope and the provisions of the client. Results of the design proper shall
be presented in accordial manner and be chosen to be implemented in the area. The following steps in a
methodical order are:
1. Identification of the Problem – the designers identified the problem by looking for news reports
about flooding in Ampid II, San Mateo. Also, the designers visited the subdivision to observe the real
situation of the area.
2. Data Gathering and Approach – through data gathering, the designers identified the real problem
and through conceptualization, they decided that stormwater management system is the best solution.
3. Project Constraints – the designers identified the possible hindrances to reduce the number of
constraints during early development of the design. Each possible constraint and standard are
considered in order to formulate solutions.
4. Producing Trade-offs – based on the review related to mitigation of flood, the designer will provide
conceivable choices to solve the identified problem considering the constraints.
5. Design Proper – the designers will design each trade-off including information for each of their
advantages and disadvantages.
6. Evaluation of Results – After rating each trade-off with their features; results will be compared
and evaluated in order to come up with the most efficient tradeoff for the area.
7. Final Design – The final design is based on the most efficient and effective result evaluated by the
designers. The final design will be suggested to be able to lessen the flooding in Graceland
Subdivision through the specified constraints.
10
1
1
1
1
1
1
1
1
1
1
Figure 1- 4: Project Development Flowchart
11
The figure above shows the project development flow chart consisting of steps that the designers will follow
from start of the design up to the end. First, the designers will identify the existing problems in the area. As
the problems are being identified, the designers will gather the needed data from the municipality of San
Mateo and from the developer of the subdivision to be used in constraints and standards and use them as a
bases to produce trade–offs. In choosing the best solution, the designers will present and evaluate six(6)
trade-offs for the improvement of stormwater management system in the area. The designers will design
each trade-off and rank the most economic, constructible and most efficient trade-off for the project with
respect to the constraints presented. After the evaluation, the final design is chosen and is suggested to be
implemented in the area.
12
CHAPTER 2: DESIGN CRITERIA
2.1 Design Data
Designing a stormwater management system duly requires data and consideration to justify the needs of the
enhancing and refurbishing a system. A set of standards and codes are each provided to different designs,
whether it may be structural, geotechnical, highway or water system of classification. These are equipped to
guide the designers in modelling their systems or structures with the extent and limitations of values. These
help ensure safety and qualify the success of the system. The data gathered in a study acts as key factors
in considering design improvement of the new system as to align with the limits and constraints. This study
of designing the storm water management system considers the data and computation of the design storm,
tributary area, the land use and runoff coefficient and such more to consider adequacy. The listed data will
be used as a parameters to design the system effectively and efficiently as possible given that amount of
rainfall may be the cause and flood be the effect and part of the problem.
2.1.1
Design Storm
The design storm determines the level of safety and protection a drainage system can provide against
flooding and heavy rainfalls. In some practices, the design storm return period is calculated and based upon
the damage costs by flooding, but mostly a design storm periods of 1 or 2 years are used for most systems
but more recently a return period of 30 years is being adapted as it can withstand more storms, prevent more
flooding and sustain a longer life. Also, for combined sewer, flooding can be more hazardous than flooding
just from storm runoff, and this can affect the choice of the more fitting return period.
The table below shows the recommended design frequencies or return period by the relevant European
Standard (BS EN 752, 2017). This standard has been adapted due to the fact that the Philippines doesn’t
have a recommended design frequency for its inhabitants, specifically in the Rizal Area.
Table 2- 1: Design Storm Return Period According to the Type of Location
Location
Design Storm
Design Flooding
Return Period (yr) Return Period (yr)
Rural Areas
1
10
Residential Areas
2
20
City Centers/Industrial/Commercial Areas
● With flooding check
2
30
● Without flooding check
5
Underground Railways/Underpasses
10
50
Source: European Standard (BS EN 752, 2017)
Based from Table 2-1, the designers can say that the type of area of the Graceland Subdivision falls under
the residential area which has a design return period of 20 years. The chosen design period will be used for
the computation of the design rainfall intensity.
𝑇 = 20 𝑦𝑒𝑎𝑟𝑠
13
2.1.2 Tributary Area
The physical properties of the catchment, such as the slope, the type of soil, the usage of the land and more,
are integral to the prediction of a reasonable storm water runoff. The project location is shown in Figure 2-1
which is at Graceland Subdivision in Ampid II in San Mateo, Rizal with an area of 16,164 m2 or approximately
1.62 hectares.
Figure 2- 1: Total Catchment Area of the Subdivision
Source: Google Map
Figure 2- 2: Topographical View of Project Location
Source: OpenStreetMap
14
Figure 2-2 shows the topographical view of the project location. The highest elevation of the area where the
inlet is located is 24 meters while the lowest elevation is 20 meters. The elevation gathered shows that the
design of the storm water drainage of the area is driven fully by gravity.
2.1.3 Existing Drainage System
The existing drainage system is an essential data that the designers collected since it will be the basis for
the identification of the problem and for generating trade-offs. The plot of the existing drainage system is
shown in Figure 2-3 where the inlet pipe is located in the upper part of the Subdivision with an elevation of
24 meters and the outlet pipe discharges the storm water into the Ampid River. There are a total of 20 pipes
in the existing drainage system.
1.1
1.2
2.4
1.3
1.4
1.8
1.5
2.0
2.5
2.2
1.9
2.1
1.6
2.6
2.3
2.7
1.7
2.8
3.0
2.9
Figure 2- 3: Existing Drainage System of Graceland Subdivision
Source: C.S. Ramos Development Corporation
15
2.1.4 Land Use and Runoff Coefficient
Stormwater runoff is not only regulated through lift stations and piping system via drainage systems but is
also discharged through different ways. Runoff may be discharged to natural water forms like rivers and
ponds, or will undergo infiltration on soil or vegetation and possibly through evaporation. The runoff coefficient
(C) is used to account for these losses by reducing the total amount to be discharged into the drainage
system.
To identify the runoff coefficient, the designers first need to know the percentage imperviousness (PIMP) of
the area and the formula by (Butler & Davie, 20111) will be used.
𝑷𝑰𝑴𝑷 = 𝟔. 𝟒√𝑱
Equation 1: Percentage of Imperviousness Equation
Where: J = housing density (dwellings/ha) and the value of J must be between 10 and 40
The estimated total number of dwellings in the subdivision is 126 dwellings. By dividing the estimated number
of dwellings by 1.6164 ha, the value of J will be equal to 77.951. Substituting the computed J into the previous
formula will give us the value for PIMP:
𝐏𝐈𝐌𝐏 = 𝟔. 𝟒√𝟕𝟕. 𝟗𝟓𝟏 = 𝟓𝟔. 𝟓𝟎𝟓𝟓𝟏
The runoff coefficient is not automatically equal to the percentage of imperviousness but is related to it.
According to the Volume 3 standard by DPWH, impervious surface, such as asphalt pavements and roofs of
buildings will produce nearly 100% runoff after the surface become thoroughly wet, regardless of the slope.
The value of runoff coefficient is assumed using Table 2.2 which is the general guidance on potential runoff
coefficient and can be adopted for the design. The table is also provided in the Volume 3 of the DPWH
standard. The area of Graceland Subdivision can be classified into residential area – densely built. The
designers choose the maximum value which is 0.75.
Table 2- 2: Values of ‘C’ Recommended for Rational Formula
Land Use
Residential Area – Densely built
Residential Area – Not densely built
City Business District
Light Industrial Areas
Heavy Industrial Areas
Parks, Playgrounds, Cemeteries, unpaved open spaces and vacant lots
Concrete or Asphalt Pavement
Gravel Surfaced Road and Shoulder
Rocky Surface
Bare Clay Surface (faces of slips, etc.)
Forested Land (sandy to clay)
Flattish Cultivated Areas (not flooded) / Farmland
Steep or Rolling Grasses Areas / Steep gullies not heavily timbered
Minimu
m
0.50
0.30
0.70
0.50
0.60
0.20
0.90
0.30
0.70
0.70
0.30
0.30
0.50
Maximu
m
0.75
0.55
0.95
0.80
0.90
0.30
1.00
0.60
0.90
0.90
0.50
0.50
0.70
16
Flooded or Wet Paddies
0.70
0.80
Source: Volume 3, DPWH Standard
2.1.5 Time of concentration
There are a number of methods for calculating the time of concentration. The time of concentration is the
time needed for the water to flow from the most remote point in a watershed to the watershed outlet. It is
composed of two components namely the time of entry (𝑡𝑒) and the time of flow (𝑡𝑓).
𝑡c = 𝑡i + 𝑡𝑓
Equation 2: Time of Concentration Formula
The time of entry is the amount of time it takes for the storm water runoff to reach the inlets of the drainage
system. We can obtain the value for the time of entry from the table below. (Department of Environment,
1981).
2.1.5.1 Inlet Time
The computation of the inlet time can also be found in the DPWH standards and can be computed as follows:
● Find the inlet point. If the estimated inlet catchment area is over 2 km2, the inlet time is t = 30 min
● When the catchment area (A) of the farthest point of the channel is clearly judged to be less than 2
km2, compute the inlet time (min.) from A (km2) using the equation below.
𝒕𝒊 =
𝟑𝟎√𝑨
√𝟐
Equation 3: Inlet Time Equation
The time of entry is the amount it takes for the storm water runoff to reach the inlets of the drainage system.
Since the designers does not have yet the total catchment area in the subdivision. The table from the (Design
and Analysis of Urban Drainage System (Vol.1), 1981) will be used.
Table 2- 3: Time of Entry
Rainfall Return Period (yr)
1
2
5
Time of Entry (min.)
4-8
4-7
3-6
Source: Vol. 1 Design and Analysis of Urban Drainage System, 1981
Since the rainfall return period is 25 years, the time of entry that the designers would be using would range
between 4-7 mins. Getting the average of the maximum and minimum values we get the time of entry of 5.5
minutes.
𝑡𝑒 = 5.5 𝑚𝑖𝑛𝑠
17
2.1.5.2 Flow Time
To compute for the time of flow we need to find the pipe network that is farthest from the outlet or the one
that provides the longest distance the runoff will travel through the pipes. Based on the drainage network
diagram we could see that the pipeline with the longest distance with a distance of 153.75 m.
𝐿 = 153.75 𝑚
Besides the distance travelled we also need to determine the design velocity to compute for the time of flow.
Since we don't have the value of the area of the pipes we could only assume our design velocity but it should
still be within the minimum permissible velocity. Therefore, we could assume that our design velocity would
be 1.5 m/s as 0.6m/s is enough for the pipes to cleanse itself and even though there is no limit required for
the maximum velocity a higher value means there are higher energy losses on curves or intersections, higher
chances of cavitation which reduces the structural integrity of the design and other possible safety hazards,
thus 1.5 m/s is suitable for the design.
𝑣 = 1.5 𝑚/𝑠
Once done, we can compute for the time of flow by dividing the distance travelled by the velocity. Therefore
we use the formula:
𝐋
𝐭𝐟 = 𝐕
Equation 4: Flow Time Formula
Where: L = length of flow in meters
V = flow velocity in m/s
Substituting the designers gathered data to compute the time of flow and converting it to minutes:
𝑡𝑓 =
153.75 𝑚
𝑚
1.5
𝑠
= 102.5 𝑠 𝑥
1 𝑚𝑖𝑛𝑢𝑡𝑒
60 𝑠
𝑡𝑓 = 1.70833 𝑚𝑖𝑛𝑢𝑡𝑒𝑠
When the time of entry (𝑡𝑒) and the time of flow (𝑡𝑓) are obtained we can finally compute for the time of
concentration by adding up their values which leaves us with:
𝑡𝑐 = 𝑡𝑒 + 𝑡𝑓 = 5.5 𝑚𝑖𝑛𝑠. +1.70833 𝑚𝑖𝑛𝑠.
𝑡𝑐 = 7.20833 𝑚𝑖𝑛𝑢𝑡𝑒𝑠
2.1.6 Critical Rainfall Intensity
Critical Rainfall Intensity (�) determines the amount of rainfall runoff to be introduced to the drainage system
for an amount of time. To compute for the rainfall intensity we use the formula provided by (Solomon):
18
𝐢=
𝟏
𝐚 − 𝐛 𝐥𝐧 𝐥𝐧 [− 𝐥𝐧 𝐥𝐧 (𝟏 − 𝐓) ]
(𝐃 + 𝐊)𝐍
Equation 5: Critical Rainfall Intensity Formula
Where: i = Rainfall intensity (mm/hr)
𝑇 = Return period (years)
𝐷 = Duration or time of concentration (minutes)
a,b,K and N = constants
The formula above is derived from the Rainfall Intensity Duration Frequency curve for the Philippines by the
Water Cycle Integrator (WCI) Hydrology Experts. With this equation, we incorporate the previous values that
were computed. a, b, N, and K, are constants from the process of derivation and varies according to rainfall
stations positioned all around the Philippines. The nearest station available to the catchment area being
designed is the Science Garden Station in Quezon City which has these values:
𝑎 = 473.5958
𝑏 = 256.9070
𝑁 = 0.5596
𝐾=6
Inserting these values to the formula, will yield:
𝑖=
473.5958 − 256.9070 𝑙𝑛 𝑙𝑛 [− 𝑙𝑛 𝑙𝑛 (1 −
1
)]
25
(7.20833 + 6)0.5596
The value that we obtain for our rainfall intensity is:
𝑖 = 298.09496 m𝑚/ℎ𝑟
2.1.7 Peak Flow Rate
Once the rainfall intensity is calculated, the rate of flow can be obtained. The flow rate is the amount of water
flowing through the pipes in a set of amount of time and is also the depth of rainfall in a set amount of time
falling over a catchment area while also considering the area’s imperviousness which gives the formula”
𝐐 = 𝑪𝒊𝑨
Equation 6: Peak Flow Rate Equation
Where: Q = design peak flow rate (m3/s)
C = runoff coefficient
i = rainfall intensity (mm/hr)
A = area in m2
When we substitute the values we obtained earlier in the chapter we would obtain the flow rate as:
19
𝑄 = 0.75𝑥298.09496
𝑚𝑚
1𝑚
1 ℎ𝑟
𝑥16,164 𝑚2 𝑥
𝑥
ℎ𝑟
1000𝑚𝑚 3600𝑠
𝑄 = 1.00383
𝑚3
𝑠
The computed flowrate will be the flowrate to be considered for the design of the pipes for the drainage
system.
2.1.8 Design Criteria
The designers adopted the (Design Guidelines, Criteria, and Standards (Vol.3), 2015). The said standard
provides the basic requirements and essential tools in the design preparation of water engineering projects
specifically for urban drainage infrastructures. In addition, it is important to follow a set of standards because
it is composed of specifications and procedures which provides an organized process for the designers to
follow.
2.1.8.1 Minimum Size
It is essential to know the minimum size of the pipe which should be 910 mm in order to allow the passage
of debris and minimize the risk of blockage.
2.1.8.2 Minimum Velocity
In order to encourage self-cleaning, and minimize sediment build up, pipes should be designed to ensure a
minimum flow velocity of 0.8 m/s at pipe full.
2.1.8.3 Maximum Velocity
The maximum velocity is the limiting velocity to be implemented for piped drainage systems which is 5 m/s.
2.1.8.4 Cover
The cover refers to the distance from the top of the pipe to the surface. A minimum cover of 600 mm should
typically be adopted. For pipes under highways, or heavily trafficked areas, a cover of 900 mm should be
adopted. A cover depth of 450mm may be adopted on private property or under open space that experiences
only occasional traffic.
2.1.8.5 Alignment
Pipes should run straight between pits wherever possible. Where curves in the pipe are absolutely required,
standard curved pipes from suppliers should be adopted. Deflecting joints to achieve curvature is not
recommended.
2.1.8.6 Capacity
The capacity of a pipe flowing full, but not under pressure, should be calculated using Manning’s equation,
as discussed in Section 4.5. It is generally recommended to avoid pipes flowing under pressure in drainage
applications, although this may not always be possible.
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2.2 Review of Related Literature
2.2.1 Local Literature
2.2.1.1 How do we solve our flooding problem?
Most people blamed the poor drainage system, and clogged sewer lines in the area but if all of these were
fixed the Metro Manila would still not be flood-free. In a commentary by (Lasco, 2017), he stated three ways
on how to solve the flooding in Metro Manila. The first one is about having a reliable flood forecasting system
since there are still areas that does not have a flood map. Next is the interoperability between forecasters
and local government units. Lastly, the data must be readily available to the public. There are a lot of
researchers as well as students who would like to study about the flooding occurrences in the Philippines but
is hindered because of the lack of data.
2.2.1.2 Welcoming Water (Part 3): Is An Open Stormwater System Applicable In The Philippines?
In an article by (Amillah, 2011), she stated that building an open storm water management system is definitely
worth trying out in the Philippines. She also added that there may already areas which seems to have this
kind of system like the University of the Philippines Campus in Diliman where most of the storm water in the
campus drains to a central creek way and lagoon surrounded by a park. Still, there are many factors to be
considered such as the amount of rainfall, cost, health and safety issues, and the amount of space needed
for the system.
2.2.1.3 Boracay Rebuilds Drainage System with Latest Technology
With the latest upbringing of Boracay having to be tourist crowded, it had accumulated more that percentage
of waste in the past year which resulted to poor waste management and clogged drainage systems. The year
2018, the province of Boracay has assessed on rebuilding their drainage system with latest technology, as
per reported via news by (UNTV News, 2018), the Boracay's drainage system adapted the German
technology by using a high density polyethylene (HDPE) plastic pipes with a width of 1.2 meters. The said
pipes have a lifespan of 100 years in which its sizes are doubled compared to the traditional one used by the
DPWH. In addition, the pipe also has the capacity to contain man-made chemicals and solid waste to prevent
leakage and contamination. With the said reassessment and enhancing of their drainage system.
2.2.2 Foreign Literature
2.2.2.1 WEF Stormwater and Green Infrastructure Symposium 2019
As reported by the Water Environment Federator (October 2018), effective stormwater management requires
collaboration among design and construction engineers, inspection and maintenance professionals,
landscape architects, municipal stormwater program managers, environmental scientists, water resources
managers, economists, communications specialists, decision makers and the public. Often, stormwater is
perceived as a nuisance and addressed as a regulatory burden rather than a valuable resource. The effects
from extreme weather events (drought, flood, heat) highlight that we must strive for a flexible and multidimensional approach to stormwater management while leveraging the strengths of differing design and
operation of stormwater infrastructure types — green, grey, and blue.
2.2.2.2 New Floodgates Will Enable Faster Response Times
A news from the (New Zealand Government, 2018) stated that the Waikato Regional Council will install new
mechanised floodgates which will provide full protection to the community faster. The said project will include
putting of footings over that will allow the gates to open and shut at the flick of a switch. During power outages,
the gates will be opened and closed using a winch. The installation of the floodgates will affect the pedestrians
as well as motorist but the council will provide an alternative access way while the construction is ongoing.
21
More community in the said area will benefit from this project and there will also be more field staff assigned
to different locations during flood.
2.2.2.3 Flooding Blamed on Subdivision Construction
The construction of a high-end subdivision in the barangay Guadalupe is at risk if proven that defective works
caused the flooding in the area. Based from the news report by (Philstar, 2018), the said city had to stop the
development until they could build adequate retention ponds to prevent construction materials from sliding
down the site. In addition, another city which is Monterrazas de Cebu was hit by the storm but due to the
construction of four detention ponds with capacities in excess of city requirements there were no reports of
flooding within its immediate vicinity except for the one reported in Sitio Dakit.
2.3 Review of Related Studies
2.3.1 Local Studies
2.3.1.1 Hydraulic Modelling of the New and Old Drainage System in Brgy. Pansol, Calamba, Laguna
A study conducted by Constantino (July 2017), before having the design of the enhanced drainage system
he had stated that the old drainage system must duly be conducted of its effectivity and efficiency rate first
as to compare and conduct any preparations and simulations of the system lacking thereof. Results of both
old and enhanced drainage systems must include determination of location flooding as to refer from
topography of the location, maximum depth of flood and conduit surcharging. Standard hydraulic simulations
should also be evident to further support system’s efficiency and effectivity. Having his study’s location to
have experience continuous simulation, it is referred to use daily rainfall data as per discrete simulations only
to use hyetograph.
2.3.1.2 Hydraulic Modelling of Possible Flood Mitigation Strategies in Brgy. Pansol, Calamba, Laguna
With the study conducted by Apuntar (May 2018), this precedes what Constantino had solved in his study of
Hydraulic Modelling in Pansol, Calamba Laguna. Apuntar had presented the different flood mitigation
strategies as per recommended by Constantino’s study. His study include model of detention basin,
stormwater lift station, as well as the base model and the enhanced drainage system to compare the each
strategy’s efficiency and improvement contribution. Both studies have used EPA-SWMM to design and run
all model simulations. Results of his study showed adequacy in enhancement of drainage network, adequacy
of detention basin and adequacy of stormwater lift station.
3.1.1.1
2.3.1.3 The proposed new drainage system in Cebu Technological University – Main Campus
As studied by the students of Cebu Technological University (Tejeto R., Carulasa K.J., Lapas C.J., Maluya
D.M., Punzalan D.J., Sabellano E. and Ylaya R. 2013 March), drainage system is a system of natural or
artificial channel through which water flows or drains for carrying off excess water. A drainage system is
designed that the water flows away quickly, smoothly and is disposed of in a surface watercourse. To prevent
flooding, an efficient drainage system is therefore essential to allow water to flow off and away from the
ground as quickly as possible. Water is the most valuable natural resources essential for human and animal
life, industry and agriculture. One of the means developed by humans to minimize flooding was through
directing water to an outlet, hence, the drainage system.
2.3.2 Foreign Studies
2.3.2.1 Design on Evaluation of Red River Flooding in Caddo Parish Regions, Northwest Louisiana
As studied by Christman, J., Fields, K., et.al. (May 2018), with the Red River Flooring flooding in Northwest
Louisiana the solution recommended to flooding is to work to build more resilient cities in areas that are floodprone. Solutions range from reducing impervious surfaces, managing rainfall, improving infrastructure,
22
improving flood water removal systems, and designing more green space to better absorb excess water.
Additionally, physical solutions for flood management include levees, reservoirs, and pumps have been
implemented to keep the floodwaters away from the area. These are several of the possible solutions to help
mitigate the damage of urban flooding.
2.3.2.2 An Automatic Control System for Sluice Gate in Salinity and Flood Control in Open Channel
According to (Dharshana, 2017), they stated that the Sluice Gates are helpful for controlling the flow of water
on canals and open channels. These gates are opened manually in to achieve the desired level of water in
open channel and it is time consuming. So they began to research on how to operate it automatically. In their
study the put sensors to determine the rise of floodwater in order to put proper algorithms that will match the
need to adjust the opening of the gates. By making the Sluice Gate automatic we raise its function to mitigate
the floods in the location.
2.3.2.3 Tide Gates in the North Pacific West and Floodgate Management
In order to control more effectively the water to prevent flood is the controlled opening of floodgates during
non-flood periods. These gates are made of steel and can also withstand strong currents from floods. This
gate is used to prevent the passing of water from river to overflow to nearby houses and ensure safety of the
people living (NSW Government). Tidal gates can be also helpful on mitigating floods by conveying storm
water and prevent them from being stagnant. He also stated the function of its parts that is involved on
controlling the movements of water. These tide gates can also withstand strong currents of water and can
also have longer life span. As a country that is often experiencing floods it is good to have these gates that
can last for long to mitigate floods from storms (Douglas, 2001),
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CHAPTER 3: CONSTRAINTS, TRADE-OFFS, AND STANDARDS
3.1
Design Constraints
The design constraints serve as the qualification and criteria for evaluating the different trade-offs. These
constraints help control and set boundaries that limit the design and performance of a project. In order to
meet and acquire these conditions, the project should be designed with respect to provisions given by the
client and also measured with respect to the different codes and standards each trade-off is specified into.
Constraints will be set for each of the trade-offs given and will help measure the most applicable trade-off for
the project. The following are the established constraints for the project:
3.1.1 Quantitative Constraints
3.1.1.1 Economic Constraint (Project Cost)
Project cost is one of the most discerning considerations in the construction of the project. It is known that
budget is always a factor on the client’s capacity to pay. This is a limiting factor for it affects the design of the
project as well as the construction materials’ quantity and quality. Having to estimate the project cost before
the project starts helps the client and the designers in considering the most economic trade-off. Poor
construction materials may lead to the poor performance of the system to be built. Summation of the cost of
each trade-off will be ranked having the least price cost to be most economic.
Limitation:
The constraint only composes of the estimated materials and equipment cost with respect to the proper
process of designing and construction of the different trade-offs. This constraint is limited to an amount of 10
million Philippine peso for the project.
3.1.1.2
Constructability Constraint (Labor Cost)
The designers considers the cost of labor per worker involved in design and construction of each trade-off
with respect to the duration of project per traded-off. The table below indicates the average daily rate of the
laborers and engineers needed for the duration and completion of any project as per trade-off. The duration
of the project promotes the project’s efficiency when it comes to cost. The total labor cost of all involved of
the project is directly proportional to the duration of the project. Vice Versa. The longer process of the project
construction, the more expense it yields. Given that the project needs to be timely, well-organized and ready
for the situation it was designed for. The required number of laborers also affects the cost of the total design
which disturbs the assessment of the other constraints as well.
Limitation:
This constraint will be evaluated and be composed of construction activities with its respective cost and
manpower. Allowable duration of the project as expected by the client can only be within a year. Daily rate
for the initial estimation only applies to an eight (8) hours a day of work, without overtime pay yet. This
constraint is limited to an amount of 5 million Philippine peso for the project.
24
Table 3- 1: Daily Rate of Workers
Source: Payscale Philippines
3.1.1.3
Sustainability Constraint (Life Span)
The lifespan of a system serves as a restriction that sets the project in using energy and resources without
compromising the natural environment and the future generation’s resources. How long the system can last
without external factors but when only left on itself is a component that is also considered when designing.
The longer the longevity of the system the better it is for the design but it also comes with a price which can
affect the whole design.
Limitation:
The designers purely base the lifespan of each trade-off from research. The life span must be at least 30
years.
3.1.1.4
Risk Assessment (Level of Hazard)
Risk constraint includes the identification of the hazards and risk factors in the designs based from the
designer’s assessment and research. The qualitative risks stated by sources for each trade-off is given
equivalent value based from the degree of risk. The designers will scale the given risks by which ten (10) is
given if the said risk is very minor, five (5) for minor and one (1) for major.
Limitation:
The risk assessment for water resources will be broken down into three components: pollution hazards, public
safety hazards, and natural environment hazards. For the risk assessment of the structural trade-offs, the
designers will include only two main risks which is operator and mechanical failure according to the research
of NSW Fisheries and NSW Agriculture on the north coast of NSW (2003). The average for the risk
assessment should be 6 and below.
3.1.2 Qualitative Constraint
3.1.2.1 Ergonomics
This design considered the efficiency of the workers. A strong safety culture boosts productivity, employee
morale and employee retention. With this constraint, it can make the workplace safer and reduce costs. It
can also provide an outcome of great quality for the design.
25
3.1.2.2
Functionality
Making sure that the system will live up to its expected purpose is an important aspect when selecting the
optimal design. It is necessary to understand that the system will serve a specific type of event to fulfill its
purpose.
3.1.2.3
Legal Consideration
Obtaining the necessary contracts and permissions prior to the construction of the design is imperative as to
not be in any run-in with the law. Knowing that the project is safe to proceed and secured from any legal
actions can eliminate any unnecessary postponement of the project.
3.2 Trade-off Strategy
The designers have different trade-offs or possible solutions offered which is to be evaluated by ranking their
constraints based on their level of importance. The trade-off strategy method by (Otto & Antonsson, 1991)
will be used for the quantification of each trade-off’s constraints. It is commonly used for comparing different
design alternatives even if they have vastly different physical forms or parameters. The designers will scale
the constraints from 0 to 10 to give more accurate ranking and as a guide for design decisions.
The formula by (Otto & Antonsson, 1991) shown below will be used to determine the computation for the
ranking of each constraint:
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝐻𝑖𝑔ℎ𝑒𝑟 𝑉𝑎𝑙𝑢𝑒 − 𝐿𝑜𝑤𝑒𝑟 𝑉𝑎𝑙𝑢𝑒
𝐻𝑖𝑔ℎ𝑒𝑟 𝑉𝑎𝑙𝑢𝑒
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 𝐺𝑜𝑣𝑒𝑟𝑛𝑖𝑛𝑔 𝑅𝑎𝑛𝑘 − (% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 ∗ 10)
Figure 3- 1: Ranking Scale
To determine the trade-off that will give us the greatest value, the subordinate rank and percent difference
will be computed. The governing rank is the highest possible value in the scale. The subordinate rank is the
variable rank that shows how the trade-off is able to satisfy the importance criterion shown by the percent
difference in distance by the governing rank in the ranking scale. After summing up and comparing each
trade-off, the greatest value will be declared as the leading trade-off for the design.
3.3 Design Trade-offs
Trade-offs are the variable medium for the design to be assessed with the constraints listed. The trade-offs
to be presented are also enumerated based on they specialization. They are the possible methods of
stormwater management system, designing the structures for the improvement of the storm water runoff and
26
methods for the stability of the soil. Each specialization have different trade-offs that are to be evaluated to
arrive for the best possible design for the project.
3.3.1 Water Resources Trade-offs
3.3.1.1 Detention Pond
Stormwater detention ponds are designed to be catch basins for developed areas. Stormwater ponds collect
stormwater runoff that runs over impermeable surfaces such as parking lots, roads, and buildings. In
undeveloped areas rainwater can be absorbed into the soil, taken up by trees and plants or flow into rivers,
streams or wetlands naturally. (Finerfronk, K., 2009)
The daily activities of people cause pollutants to collect on impermeable surfaces and get washed into
waterways during rain events. These pollutants include dirt, oil, fertilizers, yard waste and litter. Pollutants
can be harmful to habitats and wildlife downstream if they are allowed into the ecosystem. With stormwater
ponds in place, rainwater can collect, sediment and pollutants can settle out before being released back into
the watershed. A stormwater management pond can be evident in the management system of Graceland
Subdivision, whereas an open land area North of that is available of use for area of design, government
owned.
Figure 3- 2: Example of Stormwater Detention Pond
Source: Richmont Hill Stormwater Management
3.3.1.2 Dry Well
A lift or pump station is designed to receive or store stormwater through a collection system. Its effectivity is
evident in sections simply cannot be drained by gravity. CDOT (2017)’s Drainage Design Manual specifies
that the design considerations should be met upon before considering namely: location, hydrologic factors,
collection systems, station types, pump types, drainage system and others. Stormwater can discharge into a
retention pond, wetland, other waterway, or to treatment. Depending on the point of discharge, stormwater
must be handled in different ways. It so happens that in Graceland Subdivision of Ampid II, a creek surrounds
the area.
Stormwater pump stations are designed to handle storm events with potentially high flows, but the rest of the
year there might be rain that produces very low flows of stormwater. This low flow is frequently referred to as
nuisance flow. Nuisance flow can cause a variety of maintenance concerns for pump stations if it is not
handled in the system design. The best way to handle nuisance flow is by adding a small pump to the system.
This pump is often called a jockey pump, and it can handle nuisance flow until a storm event requires the
larger pumps to take over operation. (ROMTEC Utilities, 2019)
27
Figure 3- 3: Example of Dry Well
Source: Romtec Utilities
3.3.1.3 Enhanced Drainage System
The common structural measure for flood protection in lowland or flood-prone areas is the building of dikes
along rivers or major channels (de Bruin, 2009). If water accumulates, because of heavy precipitation, where
drains are lacking or their discharge capacity is exceeded, flooding may occur due to water overtopping dikes
to produce widespread flood damage over lowlands. To manage flood hazards, it is vital to implement an
effective flood risk management concept. Although flooding cannot be eliminated completely, the
consequences of flooding can be mitigated by appropriate actions in the broader context of integrated river
basin management.
A systematic approach to flood risk management is to use the flood-prone lowlands efficiently. This leads to
flood defense prioritisation for protecting people and property, and also creating space for water storage and
channel cross-section modification. Overall, implementation of appropriate actions to enhance flood security
is both possible and necessary to reduce the exposure and vulnerability of people and property to flood
hazards. Flow models for drainage and inundation simulation have been developed and applied to evaluate
the feasibility of various technical solutions in the planning of flood management (Majewski 2013).
Figure 3- 4: Example of Enhanced Drainage System
Source: Prefabricated Vertical Drains for Enhanced In Situ Remediation
3.3.2 Structural Trade-offs
3.3.2.1 Winch Floodgate
We can open floodgates and let river water into the drain a worm drive mechanism that opens the gates
vertically. Vertical lift gates have good water level control and can be set in any position, from fully closed to
28
fully open. Winch gates can allow large, rapid inflows of river water and can be fully raised to assist outflow
after flooding. These gates require intensive manual operation and manual closure in the event of flooding.
Horizontal winch gates have a greater risk of causing overtopping when open. Large forces can be involved
in winch and cable system. Vertical winch gates can experience closing difficulties due to friction.
Figure 3- 5: Example of a Winch Floodgate
Source: Google Image
3.3.2.2 Tidal Floodgate
Various designs exist. They usually consist of an aperture within the existing floodgate with another smaller
floodgate attached. A floating arm opens the gate and allows water exchange with each tide. The gate opens
on the low tide and closes with the rising tide. Water control is very good as the float arm can be adjusted to
stop inflow at the desired water level. Automatic operation of the gate by the tide. Excellent water level
control. The amount of exchange and maximum height of tidal influence on the inside water level can be
adjusted. This design is flood secure and automatically closes as outside water level rises. There is a minor
risk of being jammed open (as with normal gates). May require a new gate to be made in some cases.
Figure 3- 6: Tidal Floodgate
Source: Google Image
3.3.2.3 Sluice Gate
Sluice consist of an aperture within existing floodgate with a sliding plate cover that can be opened to varying
degrees. This opening can be vertical, horizontal or rotational in design. The aperture size can be adjusted
to vary the amount of inflow to suit site conditions so water level control is good. The position of the aperture
in the floodgate can also be varied and will affect water level control. The variable aperture size means sluice
gates provide excellent water level control. The simple design is low cost and low maintenance and requires
manual operation and manual closure in floods.
29
Figure 3- 7: Sluice Gate, Nagor River
Source: Google Image
3.4 Initial Estimates of Trade-offs (Water Resources)
3.4.1 Economic Constraint (Project Cost)
Table 3- 2: Summary of Initial Estimated Economic Cost for Water Resources Trade-offs
Trade-offs
1. Detention Pond
2. Dry Well
3. Enhanced Drainage System
Initial Estimate Cost
(Php)
3,995,550.00
816,588.05
5,823,510.64
Subordinate
Rank
2.00
10.00
1.50
Solution for Economic Constraint:
Dry well has the lowest initial estimated economic cost, the designers gave it a scale of ten (10).
Dry Well vs. Detention Pond
3,995,550 − 816,588.05
3,995,550
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.80
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.80 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 2.00
Figure 3- 8: Initial Economic Ranking of Dry Well vs. Detention Pond
Dry Well vs. Enhanced Drainage System
5,823,510.64 − 816,588.05
5,823,510.64
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.85
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
30
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.85 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =1.50
Figure 3- 9: Initial Economic Ranking of Dry Well vs. Enhanced Drainage System
3.4.2
Constructability Constraint (Constructability Cost)
Table 3- 3: Summary of Initial Estimated Constructability Cost for Water Resources Trade-offs
Trade-offs
1. Detention Pond
2. Dry Well
3. Enhanced Drainage System
Initial Estimated Labor
Cost (Php)
2, 910, 460.00
2, 843, 768.00
10, 090, 568.00
Subordinate
Rank
9.80
10.00
2.80
Solution for Constructability Constraint:
The dry well has the lowest initial estimated cost, the designers gave it a scale of ten (10).
Dry Well vs. Detention Pond
2,910,460.00 − 2, 843,768.00
2,910,460.00
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.02
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.02 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =9.80
Figure 3- 10: Initial Constructability Ranking of Dry Well vs. Detention Pond
Dry Well vs. Enhanced Drainage System
10, 090, 568.00 − 2, 843,768.00
10, 090, 568.00
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.72
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.72 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =2.80
31
Figure 3- 11: Initial Constructability Ranking of Dry Well vs. Enhanced Drainage System
3.4.3 Sustainability (Life Span)
The designers considers the lifespan of each stormwater management systems based purely on research
and accumulation of data.
Detention Pond
According to (Institute for Environmental Analytics, 2016) , detention pond’s life span is up to 50 years
considering it is regularly maintained such as clearing inlets and outlets.
Dry Well
Based from an article by (Breeze, 2015), a dry well can work effectively for more than 30 years of it is properly
maintained. The best way to maintain a dry well is to inspect it four times a year, as well as after every storm
with accumulated rainfall over an inch.
Enhanced Drainage System
As stated by (Clinehens, 2015), the U.S. Army Corps of Engineers suggests a design life of 70-100 years for
reinforced concrete pipes. Many concrete pipes have been documented to remain sound for far longer than
100 years so the designer choose a lifespan of 100 years for the input value in sustainability.
Table 3- 4: Summary of Initial Estimated Life Span for Water Resources Trade-offs
Trade-offs
1. Detention Pond
2. Dry Well
3. Enhanced Drainage System
Initial Estimate Life Span
(Years)
50
30
100
Subordinate Rank
5.00
3.00
10.00
Solution for Sustainability Constraint:
The enhanced drainage system is the one having the highest life span, the designers gave it a rank scale of
ten (10).
Enhanced Drainage System vs. Detention Pond
100 − 50
100
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.50
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.50 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 5.00
32
Figure 3- 12: Initial Sustainability Ranking of Enhanced Drainage System vs. Detention Pond
Enhanced Drainage System vs. Dry Well
100 − 30
100
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.70
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.70 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 3.00
Figure 3- 13: Initial Sustainability Ranking of Enhanced Drainage System vs. Dry Well
3.4.4 Risk Assessment Constraint (Level of Hazard)
The designers scaled the given risk by which ten (10) is given if the said risk is very minor, five (5) for minor
and one (1) for major.
Detention Pond
According to the city of Everett (201), insects and microorganisms living in the pond’s mud help remove
pollutants from the stormwater have grown, mosquitoes and algae may become a problem. As the plants
grow and fill the water, they remove the extra nutrients that cause algae. Eventually other kinds of organisms
that eat mosquito larvae move into the pond. Usually, these ponds attract frogs, dragonflies and red-winged
blackbirds.
Dry Well
Based from the article by Mr. Rooter Plumbing (2017), the possible risks of dry well includes collapsing of
the structure, injury of laborers and potential fatality if someone falls in to one of these systems. In addition,
older site-built systems that were often made of dry-stacked stone or concrete block are not protected by a
very secure cover. Moreover, buildup of leaves, sediment and other assorted materials inhibit or prevent the
function of a dry well, and that is when it becomes worse in the form of flooding, damage, standing water,
foul smells and even dangerous bacteria.
Enhanced Drainage System
Being the enhanced system of the existing drainage system, the designers likely designed this to have more
effectivity in prevention of risk and lesses possibility of possible risks. Therefore, ranked highest with higher
preventive risk, with only occurrence of minor risks.
33
Table 3- 5: Summary of Initial Estimated Risk for Water Resource Trade-offs
Trade-offs
1. Detention Pond
2. Dry Well
3. Enhanced Drainage
System
Pollution
Hazards
Public Safety
Hazards
Natural
Environment
Hazards
Average
of Risks
Subordinate
Risk
5.00
10.00
5.00
5.00
1.00
10.00
10.00
5.00
10.00
6.67
5.33
8.33
8.00
6.40
10.00
Solution for Risk Assessment Constraint:
Enhanced drainage system has the very minor risks, with a scale of ten (10).
Enhanced Drainage System vs. Detention Pond
8.33 − 6.67
8.33
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.20
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.20 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 8.00
Figure 3- 14: Initial Risk Assessment Ranking of Enhanced Drainage System vs. Detention Pond
Enhanced Drainage System vs. Dry Well
8.33 − 5.33
8.33
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.36
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.36 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 6.40
Figure 3- 15: Initial Risk Assessment Ranking of Enhanced Drainage System vs. Dry Well
34
3.4.5
Initial Summary of Designer’s Raw Ranking for Water Resources Trade-offs
Table 3- 6: Initial Ranking of Water Trade-offs
CONSTRAINTS
1.
2.
3.
4.
CRITERION
IMPORTANCE
Economic
10.00
Constructability
10.00
Sustainability
10.00
Risk Assessment
10.00
TOTAL RANKING
EFFECTIVITY ORDER
TRADE-OFFS
Detention Pond
Dry Well
2.00
9.80
5.00
8.00
24.80
2nd
10.00
10.00
3.00
6.40
29.40
1st
Enhanced Drainage
System
1.50
2.80
10.00
10.00
24.30
3rd
3.4.6 Conclusion of Water Resources Trade-offs
With respect to the criteria and the trade-offs’ importance to the designers, it has seemed that the design of
the dry well is estimated to be the first choice considering the given constraints such as economical,
constructability, sustainability and risk assessment for the management of stormwater in the area garnering
a 29.40 total ranking. The detention pond came second place in terms of the total ranking even though it
does not have any highest value in the given constraints. The lowest total ranking accumulation for all of the
constraints came down to designing of enhanced drainage system. Though it may seem well effective and a
proper trade-off for a stormwater management system, it had resulted to low economic and constructability
constraints comparing only to the other two water trade-offs. Thus it is best to design a dry well, and detention
pond and enhanced drainage system won’t be ignored as to depend only on the budget, project duration,
and specifications of the client with respect to the project.
3.5 Initial Estimates of Trade-offs (Structural)
3.5.1 Economic Constraint (Project Cost)
Table 3- 7: Summary of Initial Estimated Economic Cost for Structural Trade-offs
Initial Estimate Cost
(Php)
221, 527.98
196, 897.00
602, 940.66
Trade-offs
1. Winch Floodgate
2. Tidal Floodgate
3. Sluice Gate
Subordinate
Rank
8.90
10.00
3.30
Solution for Economic Constraint:
The tidal floodgate has the lowest initial estimate cost, the designers gave it a scale of ten (10).
Tidal Floodgate vs. Winch Floodgate
221, 527.98 − 196,897.00
221, 527.98
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.11
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.11 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 8.90
35
Figure 3- 16: Economic Ranking of Tidal Floodgate vs. Winch Floodgate
Tidal Floodgate vs. Sluice Gate
602, 940.66 − 196,897.00
602, 940.66
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.67
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.67 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 3.30
Figure 3- 17: Economic Ranking of Tidal Floodgate vs. Sluice Gate
3.5.2
Constructability Constraint (Constructability Cost)
Table 3- 8: Summary of Initial Estimated Constructability Cost for Structural Trade-offs
Initial Cost Labor
Estimate (Php)
4, 971, 430.00
3, 190, 762.00
5, 214, 172.00
Trade-offs
1. Winch Floodgate
2. Tidal Floodgate
3. Sluice Gate
Subordinate
Rank
6.40
10.00
6.10
Solution for Constructability Constraint:
The tidal floodgate has the least constructability cost, the designers gave it a scale of ten (10).
Tidal Floodgate vs. Winch Floodgate
4, 971, 430.00 − 3,190,762.00
4, 971, 430.00
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.36
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.36 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 6.40
36
Figure 3- 18: Constructability Ranking of Tidal Floodgate vs. Winch Floodgate
Tidal Floodgate vs. Sluice Gate
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
5, 214, 172.00 − 3,190,762.00
5, 214, 172.00
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.39
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.39 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 6.10
Figure 3- 19: Constructability Ranking of Tidal Floodgate vs. Sluice Gate
3.5.3 Sustainability (Life Span)
The designers considers the lifespan of each stormwater management systems based purely on research
and accumulation of data.
Winch Floodgate
According to (Smith, 2017), the maximum lifespan for a Winch floodgate is 40 years.
Tidal Floodgate
According to (Bloore, 2003), they designed the tidal floodgates with the estimated return period of 37 years.
Sluice Gate
According to the journal (Shammaa, 2005), the lifespan of a Sluice floodgate is 30 years.
Table 3- 9: Summary of Initial Estimate Life Span for Sustainability Constraint
Trade-offs
1. Winch Floodgate
2. Tidal Floodgate
3. Sluice Gate
Initial Estimate Life Span
(Years)
40
37
30
Subordinate Rank
10.00
9.20
7.50
Solution for Sustainability Constraint:
The most sustainable is the Winch floodgate which have the greatest lifespan, the designers gave it a scale
of ten (10).
37
Winch Floodgate vs. Tidal Floodgate
40 − 37
40
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.08
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.08 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =9.20
Figure 3- 20: Sustainability Ranking of Winch Floodgate vs. Tidal Floodgate
Winch Floodgate vs. Sluice Gate
40 − 30
40
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.25
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.25 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =7.50
Figure 3- 21: Sustainability Ranking of Winch Floodgate vs. Sluice Gate
3.5.4 Risk Assessment Constraint (Level of Hazard)
The designers scaled the given risk by which ten (10) is given if the said risk is very minor, five (5) for minor
and one (1) for major.
Winch Floodgate
According to the research of NSW Fisheries and NSW Agriculture on the north coast of NSW (2003) the two
main risks of failing floodgates result from operator failure and mechanical failure. Manual floodgate opening
devices, like winch gates, require a person to close them. If this fails to occur during high river water levels,
flooding can result. All mechanisms which allow for the opening of floodgates, including existing flap gate
hinges, can be jammed open by debris in the drain or river. Winch gates require intensive manual operation
and manual closure in the event of flooding. And as vertical winch gates can experience closing difficulties
due to friction.
Sluice Gates
Sluice Gates are also considered as a manual floodgate opening device according to the research of NSW
Fisheries and NSW Agriculture on the north coast of NSW (2003) because of this it is also made to be prone
to the same main risks of failing floodgates, operator failure and mechanical failure. Devices with a fixed
38
aperture size, such as sluice gates, are less prone to jamming. A regular maintenance and inspection routine
can help avoid unwanted device failure in both winch and sluice gates.
Tidal Floodgates
Also according to the research of NSW Fisheries and NSW Agriculture on the north coast of NSW (2003)
the risks of being jammed open(as with normal gates) is a minor risk; however, the gates have proven to be
self-cleaning at trial sites in the Clarence, Hastings and Hunter rivers.
Table 3- 10: Summary of Initial Estimated Risk for Structural Trade-offs
Trade-offs
1. Winch Floodgate
2. Tidal Floodgate
3. Sluice Gate
Human Error
Risk
1.00
10.00
1.00
Mechanical
Failure
1.00
5.00
10.00
Average of Risks
1.00
7.50
5.50
Subordinate
Rank
1.33
10
7.33
Solution for Risk Assessment Constraints:
The tidal floodgate shows the very minor risks, with a scale of ten (10).
Tidal Floodgate vs. Winch Floodgate
7.50 − 1.00
7.50
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =0.867
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.867 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =1.33
Figure 3- 22: Initial Risk Assessment Ranking of Tidal Floodgate vs. Winch Floodgate
Tidal Floodgate vs. Sluice Gate
7.50 − 5.50
7.50
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 0.267
% 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 = 10 − (0.267 ∗ 10)
𝑆𝑢𝑏𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑅𝑎𝑛𝑘 =7.33
Figure 3- 23: Initial Risk Assessment Ranking of Tidal Floodgate vs. Sluice Gate
39
3.5.5
Initial Summary of Designer’s Raw Ranking for Structural Trade-offs
Table 3- 11: Initial Ranking of Structural Trade-offs
CONSTRAINTS
1.
2.
3.
4.
CRITERION
IMPORTANCE
Economic
10.00
Constructability
10.00
Sustainability
10.00
Risk Assessment
10.00
TOTAL RANKING:
EFFECTIVITY ORDER:
TRADE-OFFS
Winch Floodgate
Tidal Floodgate
Sluice Gate
8.90
6.40
10.00
1.33
26.63
2nd
10.00
10.00
9.20
10
39.20
1st
3.30
6.10
7.50
7.33
24.23
3rd
3.5.6 Conclusion of Structural Trade-offs
The design of structural trade-offs all are a variety of floodgates but with the constraints and criteria given by
the designers, a difference in the value and importance became evident. With the initial ranking of the different
floodgates namely Winch, tidal and sluice, it has shown that tidal floodgate outstand amongst others. With a
close ranking average of 39.20, it had initially proved itself to be far more economical, constructive, and
sustainable and contains very minor risks compare closely to winch floodgate and sluice gate. On the other
hand, it had seemed that the winch floodgate has shown the longest lifespan sustainability than the two other
trade-offs. Nonetheless, winch floodgate and sluice gate are seen also adequate for designing for the
stormwater management system in the area as to their average rankings also lie close to one another.
3.6
Trade-off Assessment (Water Resources and Structural)
3.6.1 Economic Constraint Assessment
The trade-off assessment for the economic constraint yields that using the tidal floodgate in terms of structural
trade-off and dry well in terms of water resources trade-off in the design of the stormwater management
system are the most economical choices. The compact structure of dry well considering that it only have
minimal space requirements resulted to its low economic cost. The tidal floodgate yielded to be the most
economical in the structural trade-offs because of the low cost of materials that are going to be included in
its construction.
3.6.2 Constructability Constraint Assessment
In this assessment, the results still yielded the use of dry well and tidal floodgate since they have minimum
initial constructability cost. Considering the total duration of construction and the manpower required still the
dry well and tidal floodgates both give a low constructability cost for in the project.
3.6.3 Sustainability Constraint Assessment
Enhanced drainage system and winch floodgate protrude as the best trade-off when it comes to having the
longest design life. The longevity of the said trade-offs are purely based on research. The enhanced drainage
system can give a longevity of 100 years which is really greater than the other water resources trade-offs.
The lifespan of the winch floodgates the longest longevity even though the lifespan of the other trade-offs
have small differences in years compared to winch.
40
3.6.4 Risk Assessment
Tidal floodgate and enhanced drainage system are the best choice when it comes to having minimum risks
considering different factors for water resources and structural trade-offs. The tidal floodgate have a very
minor risk considering human error risk and have minor risk in terms of mechanical failure which resulted for
the said trade-off to have the least risk compared to the other structural trade-offs. In water resources tradeoffs, the enhanced drainage system yielded to have the lowest risk considering pollution hazards, public
safety hazards, and natural environment hazards. The public safety hazard and natural environment hazards
both have a very minor risk scale which resulted for the said trade-off to be recommended by the designers
in terms of risk.
3.6.5 Over-all Assessment of Trade-offs
From the overall assessment, it can be concluded that the dry well for the water resources trade-offs and the
tidal floodgates from the structural trade-offs are the best options among trade-offs for having the highest
total ranking. The tidal floodgates obviously outstands the other structural trade-offs in the economic,
constructability and risk assessment constraints. While the dry well outstands the other trade-offs in the
economic and constructability constraints. All the trade-offs presented by the designers are within the budget
and target duration of the client. Based on this assessment using the quantitative constraints, the designers
recommend the use the dry well and tidal floodgate as the best stormwater management system for the area
of Graceland Subdivision.
3.7 Design Standards
Design standards are needed because it is composed of specifications and procedures which provides an
organized process for the designers to follow. Moreover, the use of standards ensures that the design and
methods are appropriate and for the intended use of the designers. The list of standards shown below will be
used by the designers as an aid to make the designing process more effective and systematic.
● DPWH Design Guidelines, Criteria & Standards (DGCS) 2015, Vol.3 : Water Engineering Projects
● ASCE Manuals and Reports of Engineering Practice No. 77, WEF Manual of Practice FD-20. Design
and Construction of Urban Stormwater Management Systems
● National Plumbing Code of the Philippines
DPWH Design Guidelines, Criteria & Standards (DGCS) 2015, Vol.3: Water Engineering Projects
The set of guidelines provides the necessary requirements and tools for the design preparation of water
engineering projects, specifically for flood control, water supply, coastal facilities and urban drainage
infrastructures.




Rainfall Analysis: DGCS Section 3.3
Runoff Analysis: DGCS Section 3.4
Time of Concentration: DGCS Section 3.4.1.4
Rainfall Intensity: DGCS Section 3.4.1.5
ASCE Manuals and Reports of Engineering Practice No. 77, WEF Manual of Practice FD-20. Design
and Construction of Urban Stormwater Management Systems
This manual is an update version of the ASCE/WPCF Manual of Practice No. 37 (Design and Construction
of Sanitary and Storm Sewers) which is necessary due to the use of microcomputers and the need to control
the quality of runoff, as well as the quantity. The manual presents a summary of currently accepted
41
procedures such as financial services, regulations, surveys and investigations, design concepts and master
planning, hydrology and water quality, storm drainage hydraulics, and computer modeling.
National Plumbing Code of the Philippines
The National Plumbing Code of the Philippines includes the latest provisions of the plumbing and
environmental laws. It provides the different specifications and requirements to be used by the designers for
the effectiveness and protection for the water resources. The code also includes a list of principles for the
design, construction, and maintenance to safeguard against fouling, deposit of solids, and clogging.




Connections to Plumbing System Required: NPC Section 304
Damage to Drainage System or Public Sewer 306
Prohibited Fittings and Practices: NPC Section 311
Independent System: NPC Section 312
42
REFERENCES
Lasco, J. D. (2017). How do we solve our flooding problem? Inquirer.
Chang, H., Tan, Y., Lai, J., Pan, T., Liu, T., & Tung, C. (2013). 2.1.1.1 Improvement of a Drainage System
for Flood Management with Assessment of the Potential Effects of Climate Change. Hydrological
Sciences Journal, 58.
Shane, S., & Mahmood, B. (2017). A hybrid stormwater management system for a residential development:
an experience.
Burns, M. J., Fletcher, T. D., Walsh, C. J., Ladson, A. R., & Hatt, B. E. (2012). Hydrologic shortcomings of
conventional urban stormwater management and opportunities for reform. ScienceDirect, 230-240.
Amillah. (2011, September 5). Welcoming Water (Part 3): Is an Open Stormwater System Applicable in the
Philippines? Urban Report.
Design Guidelines, Criteria, and Standards (Vol.3). (2015). Department of Public Works and Highways.
Design and Analysis of Urban Drainage System (Vol.1). (1981). Department of Environment.
UNTV News. (2018). Boracay Rebuilds Drainage System with Latest Technology. UNTV News and Rescue.
Turner, G. (2018). Detroit City Council Approves Stormwater Management Ordinance for Developers.
Detroit's Premier Business Journal.
Water Environment Federator (October 2018). Abstracts Due for the WEF Stormwater and Green
Infrastructure Symposium 2019.
International Journal of Earth and Science. (April 2015)
Boracay Rebuilds Drainage System With Latest Technology (2018, August 2nd). UNTV News.
Clark, G. (2018, August 13th). The Crisis Lurking in Australia’s Stormwater Drains. Australia Government
News
Tejeto R., Carulasa K.J., Lapas C.J., Maluya D.M., Punzalan D.J., Sabellano E. and Ylaya R. (March 2012)
The proposed new drainage system in Cebu Technological University – Main Campus
https://www.researchgate.net/publication/320880849_AN_AUTOMATIC_CONTROL_SYSTEM_FOR_SLUI
CE_GATE_IN_SALINITY_AND_FLOOD_CONTROL_IN_OPEN_CANAL
https://seagrant.oregonstate.edu/sites/seagrant.oregonstate.edu/files/sgpubs/onlinepubs/t05001.pdf
https://www.dpi.nsw.gov.au/fishing/habitat/rehabilitating/floodgate
NSW Fisheries and NSW Agriculture on the north coast of NSW (2003) Restoring the balance : guidelines
for managing floodgates and drainage systems on coastal floodplains
Everett (2013 March) What is Detension Pond?
Jones J., Guo J., Urbonas B., Pittinger R. Safety Detention and Retention Ponds
Mr. Rooter Plumbing (2017 February) Guide to Residential Catch Basins and Dry Well
https://www.philstar.com/cebu-news/2008/04/15/56044/flooding-blamed-subdivisionconstruction#FZPLoOrqWCfrm9WF.99
43
APPENDIX A: INITIAL ESTIMATED ECONOMIC COST OF TRADE-OFFS
Water Resources Trade-offs
● Detention Pond
Table A- 1: Initial Estimated Economic Cost for Detention Pond
● Dry Well
Table A- 2: Initial Estimated Economic Cost for Dry Well
44
● Enhanced Drainage System
Table A- 3: Initial Estimated Economic Cost for Enhanced Drainage System
Structural Trade-offs
● Winch Floodgate
Table A- 4: Initial Estimated Economic Cost for Winch Floodgate
45
● Tidal Floodgate
Table A- 5: Initial Estimated Economic Cost for Tidal Floodgate
● Sluice
Table A- 6: Initial Estimated Economic Cost for Sluice
46
APPENDIX B: INITIAL ESTIMATED CONSTRUCTABILITY COST OF TRADE-OFFS
Water Resources Trade-offs
● Detention Pond
Table B- 1: Initial Estimated Constructability Cost for Detention Pond
47
● Dry Well
Table B- 2: Initial Estimated Constructability Cost for Dry Well
48
● Enhanced Drainage System
Table B- 3: Initial Estimated Constructability Cost for Enhanced Drainage System
49
Structural Trade-offs
● Winch Floodgate
Table B- 4: Initial Estimated Constructability Cost for Winch Floodgate
● Tidal Floodgate
Table B- 5: Initial Estimated Constructability Cost for Tidal Floodgate
50
● Sluice Gate
Table B- 6: Initial Estimated Constructability Cost for Sluice Floodgate
51