i
DEVELOPMENT OF A PC-BASED TANK MODEL REAL-TIME FLOOD
FORECASTING SYSTEM.
CHEOK HOU SENG
A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Masters of Civil Engineering (Civil - Hydraulic and Hydrology)
Faculty of Civil Engineering,
Universiti Teknologi Malaysia
NOVEMBER 2005
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS υ
JUDUL : DEVELOPMENT OF A PC-BASED TANK MODEL REAL-TIME
FLOOD FORECASTING SYSTEM.
SESI PENGAJIAN:
Saya
2005/ 2006
CHEOK HOU SENG
(HURUF BESAR)
mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan
Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut :
1. Tesis adalah hakmilik Universiti Teknologi Malaysia.
2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan
pengajian sahaja.
3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengajian tinggi.
4. **Sila tandakan (9)
SULIT
9
TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau
kepentingan Malaysia seperti yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah
ditentukan oleh organisasi/badan di mana penyelidikan
TIDAK TERHAD
(TANDATANGAN PENULIS)
Disahkan oleh
(TANDATANGAN PENYELIA)
Alamat Tetap:
107, JALAN SS24/1,
TAMAN MEGAH,
47301 PETALING JAYA.
Tarikh: 07 – NOV - 2005
P.M. DR. SOBRI HARUN
Nama Penyelia
Tarikh: 07 – NOV - 2005
CATATAN: * Potong yang tidak berkenaan.
** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/
organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu
dikelaskan sebagai SULIT atau TERHAD.
υ Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara
penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan,
atau Laporan Projek Sarjana Muda (PSM).
Date: _ 07-nov-2005__
Librarian
Perpustakaan Sultanah Zanaria
UTM, Skudai
Johor
Sir,
CLASSIFICATION OF THESIS AS RESTRICTED
“DEVELOPMENT OF A PC-BASED TANK MODEL REAL-TIME FLOOD
FORECASTING SYSTEM”
By CHEOK HOU SENG
Please be informed that the above mentioned project report entitled
“DEVELOPMENT OF A PC-BASED TANK MODEL REAL-TIME FLOOD
FORECASTING SYSTEM.” be classified as RESTRICTED for a period of three
(3) years from the date of this letter. The reasons for this classification are
(i)
(ii)
(iii)
The project has potential for commercialization
“I/We* hereby declare that I/we* have read this project report and in my/our*
opinion this project report is sufficient in terms of scope and quality for the
award of the degree of Master of Civil Engineering
(Civil - Hydraulics and Hydrology)”
Signature
:
…………………………………..
Name of Supervisor 1
:
…………………………………..
Date
:
…………………………………..
Signature
:
…………………………………..
Name of Supervisor 2
:
…………………………………..
Date
:
…………………………………..
ii
I declare that this project report entitled “Development of a PC-based Tank Model
Real-Time Flood Forecasting System” is the result of my own research except as in
cited references. The project report has not been accepted for any degree and
is not concurrently submitted in candidature of any other degree.
Signature
:
………………………..
Name of Candidate
:
Cheok Hou Seng
Date
:
………………………..
iii
This project is dedicated to my family, my supervisors and
to those who had given me tremendous support to contribute to
the betterment of the society.
iv
ACKNOWLEDGEMENT
My deepest and most heartfelt gratitude goes to my supervisor, Associate
Professor Dr. Sobri Harun & Ir. Chong Sun Fatt, for their constant ideas and
enthusiasm. Their continuous guidance, patience and support have enabled me to
approach my work positively, and make even the impossible seem possible.
I would also like to thank all personnel of the Jabatan Pengairan dan Saliran
Malaysia and Dr. Nik & Associates Sendirian Berhad who had provided me much
assistance in the data acquisition process. It is only with their help can this project be
completed successfully.
My sincerest gratitude also goes to Ng Boon Chong and his previous work in
applying the Tank Model for Sungai Kuantan. He had given me much guidance and
inspiration to further develop the Tank Model into a complete real-time flood
forecasting system. I would also like to thank everyone who has contributed whether
directly or indirectly to this project.
To my family and friends, I cannot thank you enough for your support and
faith in me.
v
ABSTRACT
The Upper Klang catchment has been under-going rapid development which
instigated many flash flood occurrences within the catchment, especially at the Kuala
Lumpur City. A reliable and timely flood forecasting system is necessary to provide
early warning to minimize the destruction caused by flash floods. Utilizing the
publicly available online hydrological data combined with the most recent
programming technologies, a PC-based a real-time flood forecasting system is
developed for this purpose. The Tank Model is used as the hydrological model to
simulate the catchment discharge while the Standard Step Method applied as the
hydraulic model to simulate the water level profile of Klang River starting from the
confluence of Klang and Ampang River to Jambatan Tun Perak. Integration of both
models into a complete real-time hydro-dynamic flood forecasting system is
programmed using the Microsoft Excel and Visual Basic For Application.
Calibration and Verification of the model has proven that forecast generated by the
system is highly reliable with an average Model Efficiency of 89.37% and a Mean
Absolute Error of 0.23m. The system acquires real-time hydrological data from the
Infobanjir server maintained by Department of Irrigation and Drainage Malaysia at 5
minutes intervals and is therefore able to provide a reliable and timely warning at 40
minutes before the flood peak reaches the city center.
vi
ABSTRAK
Proses urbanisasi yang berlaku dengan pesat di kawasan tadahan Upper
Klang telah menyebabkan kejadian banjir kilat melanda pusat bandar Kuala Lumpur
yang terletak di bahagian hilir kawasan tadahan tersebut. Untuk mengurangkan
kemysnahan akibat banjir kilat yang berlaku, satu sistem peramalan banjir “realtime” berasaskan computer peribadi harus dibangunkan untuk memberi amaran awal
tentang kejadian banjir kepada penduduk-penduduk di kawasan pusat bandar.
Dengan gabungan teknologi aturcara dan data hydrologi on-line yang disediakan oleh
Jabatan Pengairan dan Saliran (JPS), suatu sistem peramalan banjir telah
dibangunkan bagi tujuan tersebut. Dalam sistem yang dibangunkan, Model Tangki
telah digunakan sebagai model hidrologi untuk meramalkan hidrograf discas dari
kawasan kajian. Kaedah “Standard Step” pula digunakan untuk mensimulasikan aras
air bagi sungai kajian iaitu Sungai Klang, bermula dari pertemuan Sungai Klang dan
Sungai Ampang ke pertemuan Sungai Klang dan Sungai Gombak. Kedua-dua model
ini kemudian diintegrasikan menjadi satu sistem peramalan banjir yang lengkap
dengan menggunakan Microsoft Excel dan Aturcara Visual Basic For Application.
Kalibrasi dan verifikasi model tersebut telah membuktikan bahawa ketepatan
ramalan yang dihasilkan oleh sistem ini adalah memuaskan, dengan keberkesanan
model sebanyak 89.67% dan purata perbezaan mutlak sebanyak 0.23mm. Sistem
peramalan ini akan mengambil data hidrologi melalui internet pada sela masa setiap
5 minit dari server Infobanjir yang disediakan oleh JPS. Maka sistem ini boleh
memberi ramalan banjir yang memuaskan 40 minit sebelum puncak banjir hidrograf
sampai ke pusat bandar Kuala Lumpur.
vii
TABLE OF CONTENT
CONTENTS
PAGE
TITLE
i
STATEMENT
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF SYMBOLS/ABBREVIATIONS
xiv
LIST OF APPENDICES
xv
CHAPTER
1
2
TITLE
PAGE
INTRODUCTION
1.1
Background of Study
1
1.2
Statement of Problem
4
1.3
Objective of Study
4
1.4
Scope and Limitation of Study
5
1.5
Importance of Study
6
LITERATURE REVIEW
7
2.1
Introduction
7
2.1
Hydrological and Hydraulic Model Selection
8
2.2
Hydrological Tank Model
10
viii
TABLE OF CONTENTS
CHAPTER
3
4
TITLE
PAGE
2.3
Standard Step Method
14
2.4
Software and Internet Programming Techonologies
17
2.4.1 HTTP Web Request
17
2.4.2
Ms Excel Web Query
19
2.4.3
Microsoft Visual Basic for Application
22
2.4.4
Microsoft Office Automation
23
2.4.5
ActiveX Controls
24
2.4.6
Windows API
24
RESEARCH METHODOLOGY
27
3.1
Project Design and Approach
27
3.2
The Upper Klang Study Catchment
28
3.3
Subjects and Data Sources
30
3.4
Model Calibration and Verification
32
3.5
System Architecture
34
3.6
Automated Flood Forecasting Operation
37
RESULTS ANALYSIS AND DISCUSSION
40
4.1
Tank Model Calibration Results
40
4.2
Tank Model Accuracy
45
4.3
Verification of Tank Model
46
4.4
Hydraulic Model Results Analysis
47
CONCLUSIONS
48
5.1
Model Accuracy
48
5.2
Assumptions and Limitations
49
5.3
Advantages of the System
51
5.4
Overall Flood Forecasting System
52
5
ix
CONTENTS
CHAPTER
TITLE
5.5
PAGE
Recommendations for Future Improvements
52
REFERENCES
Reference and Bibliography
54
APPENDIX A
Detail Calculation of the Standard Step Method in
56
th
Simulating th Water Level Profiles for the 10 July
2005 Storm Event
APPENDIX B
Example of the Tank Model Worksheet Used to
58
Simulate the Discharge Hydrograph of the Upper
Klang Catchment.
APPENDIX C
Example of Infobanjir HTML web Page Displaying
59
Real-time Hydrological Data for Jambatan Tun Perak
Station.
APPENDIX D
Example of the Real-Time Data Acquisition
60
Worksheet Used to Acquire Hydrological Data from
Infobanjir at Every 5 Minutes Interval.
APPENDIX E
Example of Thiessen Polygon Analysis to Obtain the
61
Mean Areal Rainfall for the Upper Klang Catchment
APPENDIX F
Example of the Cross Sectional Plot Showing the
Current Water Level and the 45 Minutes Lead Time
Forecasted Water Level
62
x
LIST OF TABLES
TABLE NO.
4.1
TITLE
PAGE
Calibrated parameters of the Tank Model for the Upper
41
Klang catchment.
4.2
Mean absolute error and model efficiency for all
historical storm events used for model calibration
45
xi
LIST OF FIGURES
FIGURE NO.
1.1
TITLE
PAGE
Flash Flood Occurrence in the Kuala Lumpur City Center
2
due to a Heavy Downpour on the 26th April 2001.
1.2
Photos showing the damage caused by the 10th June 2003
2
Flash flood event at the Kuala Lumpur City Center.
1.3
Budget allocated for flood mitigation projects by the
3
government for past Malaysian Plans.
2.1
Concept of the Tank Model to simulate the physical
11
hydrological processes using a series of storage tanks.
2.2
Typical configuration of a Tank model.
13
2.3
Definition sketch of the energy grade line used to determine
15
the flow depth at a specified location.
2.4
HTTP request-response between a client computer and the
18
web server.
2.5
Screen shot showing the use of web query in acquiring
20
real-time rainfall data from JPS Ampang station which is used
as input for the Tank-SStep Model
2.6
Screen shot showing the option settings for the web query used
21
for the real-time data acquisition module of the Tank-SStep
Flood Forecasting system.
2.7
Screen shot showing the built-in Visual Basic editor used to
program macros for automating the real-time data acquisition
module.
22
xii
LIST OF FIGURES
FIGURE NO.
2.8
TITLE
PAGE
Project break-down of the development of a real-time
28
PC-based flood forecasting system for the Upper Klang
catchment.
3.2
Catchment map showing the Upper Klang catchment.
29
3.3
Rainfall and water level used for the development of the
31
Tank-SStep Flood Forecasting System for the Upper Klang
Catchment.
3.4
Rating curve for Klang River at Jambatan Tun Perak
32
3.5
System architecture fot the Tank-SStep Flood Forecasting
34
System.
3.6
Each module in the Tank-SStep system is programmed as an
35
individual Excel worksheet. All the modules are contained
within the same Excel workbook.
3.7
Automated processes involved in the operation of the
38
Tank-SStep PC-bassed, real-time flood forecasting system.
4.1
Observed and simulated water level hydrograph for the 02
41
July 2005 storm event.
4.1
Observed and simulated water level hydrograph for the 02
41
July 2005 storm event.
4.2
Observed and simulated water level hydrograph for the 28
42
April 2005 storm event.
4.3
Observed and simulated water level hydrograph for the 23
March 2005 storm event.
42
xiii
LIST OF FIGURES
FIGURE NO.
4.4
TITLE
Observed and simulated water level hydrograph for the 13
PAGE
43
February 2005 storm event.
4.5
Observed and simulated water level hydrograph for the 25
43
February 2004 storm event.
4.6
Observed and simulated water level hydrograph for the 02
44
November 2003 storm event.
4.7
Observed and simulated water level hydrograph for the 17
44
March 2003 storm event.
4.8
Water level time series at Jambatan Tun Perak for the 10th
46
July 2005 storm event.
4.9
Longitudinal water level profile for the study channel on 10th
47
July 2005 at 7:22pm
5.1
Figure showing the lag time between the simulated water
level and the observed water level captured at Jambatan Tun
Perak.
49
xiv
LIST OF SYMBOLS/ABBREVIATIONS
DID
-
Department of Irrigaion and Drainage, Malaysia
JPS
-
Jabatan Pengairan dan Saliran, Malaysia
RF
-
Rainfall
Q
-
Flood Discharge
WL
-
Water Level
m R.L.
-
Meters Reduced Level
Ms Excel
-
Microsoft Excel
VB
-
Visual Basic
BASIC
-
Beginner’s All-Purpose Symbolic Instruction Code
GVF
-
Gradually Varied Flow
HTTP
-
HyperText Transfer Protocol
URL
-
Uniform Resource Locator
RFC
-
Request for Comments
PC
-
Personal Computer
WWW
-
World Wide Web
HTML
-
HyperText Marked-up Language
VBA
-
Microsoft Visual Basic for Application
GUI
-
Graphical User Interface
GIF
-
Graphic Interchange Format
API
-
Application Programming Interface
xv
LIST OF APPENDICES
APPENDIX
APPENDIX A
TITLE
Detail Calculation of the Standard Step Method in
PAGE
56
Simulating th Water Level Profiles for the 10th July
2005 Storm Event
APPENDIX B
Example of the Tank Model Worksheet Used to
58
Simulate the Discharge Hydrograph of the Upper
Klang Catchment.
APPENDIX C
Example of Infobanjir HTML web Page Displaying
59
Real-time Hydrological Data for Jambatan Tun Perak
Station.
APPENDIX D
Example of the Real-Time Data Acquisition
60
Worksheet Used to Acquire Hydrological Data from
Infobanjir at Every 5 Minutes Interval.
APPENDIX E
Example of Thiessen Polygon Analysis to Obtain the
61
Mean Areal Rainfall for the Upper Klang Catchment
APPENDIX F
Example of the Cross Sectional Plot Showing the
Current Water Level and the 45 Minutes Lead Time
Forecasted Water Level
62
CHAPTER 1
INTRODUCTION
1.1
Background of Study
The Upper Klang Catchment covers a total area of 108km2 (excluding the
Klang Gate catchment), which extends from the tip of Klang River until the
confluence of Klang and Gombak River. The downstream of the catchment, which
includes part of the Kuala Lumpur City Center is fully developed while the upstream
part like Taman Melati, Wangsa Maju and Ulu Klang are being rapidly developed to
accommodate the drastic increase in the capital’s population.
With the rapid development, many areas have been paved impervious by
roads and building which eventually reduces the amount of rainfall infiltrated into
the ground and caused an increase in surface runoff (MASMA, 2000). Besides that,
impervious areas like roads and concrete pavements have smoother surfaces
compared to the undeveloped vegetation. This causes the reduction in the time of
concentration of the catchment, which literally means that the rainfall will discharge
much faster into the river, causing the water level in the river system to rise
drastically during storm events. The combined effects due to the rapid development
has contributed to an increase in the river discharge and thus caused many flash flood
occurrences in the catchment for the past few years (refer Figure 1.1 and Figure 1.2).
2
Figure 1.1
flash flood occurrence in the Kuala Lumpur City Center due to a
heavy downpour on the 26th April 2001
Figure 1.2
Photos showing the damages caused by the 10th June 2003 flash flood
event at the Kuala Lumpur City Center.
3
These flash floods nuisance have forced the government to allocate a total of
RM 2.7 billion from the Eighth Malaysian Plan to mitigate the problem (refer Figure
1.3). According to a study by The Drainage & Flood Mitigation Division of Drainage
and Irrigation Department (DID) Malaysia in 2003, the flood mitigation projects
implemented has successfully reduced the flood damages from RM1356 million to
RM915 million. However most of these mitigation measures are structural river
improvement works. In order to further reduce the flood damages caused, a timely
and reliable flood forecasting system is important to provide early warning to
evacuate people and properties from the flood-prone areas.
Figure 1.3
Budget allocated for flood mitigation projects by the government for
past Malysian Plans.
4
1.2
Statement of Problem
There are currently 2 flood forecasting models setup for Kuala Lumpur,
namely the FloodWatch System and a Unit Hydrograph Model. However both
models require cumbersome maintenance and are still being evaluated in their
capability to provide reliable real-time flood warnings. Taking advantage of the
online hydrological data for the Klang River Basin and utilizing the various
programming technologies available, it is time to research into the development of a
new personal computer-based flood forecasting model to provide timely and reliable
flood forecast to prevent loss of lives and properties within the Kuala Lumpur City
Center.
1.3
Objective of Study
The main objectives of the project are:
1.
To develop and setup a hydrological Tank Model to simulate the discharge
hydrograph of the Upper Klang catchment at Jambatan Tun Perak.
2.
To develop and setup a hydraulic model, using the Standard Step Method to
simulate the water level profile for Klang River starting from the confluence
of Klang and Ampang River until Jambatan Tun Perak.
3.
To develop a real-time PC-Based flood forecasting system with user-friendly
graphical user interface (GUI) for easy model updating, calibration and flood
forecasting operations.
5
1.4
Scope and Limitation of Study
1.
To obtain and process relevant hydrological data of various historical storms
which are used for calibration and verification purposes of the developed
models.
2.
To calibrate the Tank Model based on historical flood events to provide
reliable simulation of flood discharges at Jambatan Tun Perak.
3.
To obtain and process all relevant hydraulic data which are used for the
Standard Step Method Model to simulate the water level profile within the
study channel.
4.
To develop a PC-based system to integrate both the Tank Model and the
Hydraulic Model into a complete Hydro-dynamic model for the Upper-Klang
catchment.
5.
To develop a software module to acquire hydrological data at 5 minutes
interval from the Infobanjir web site to be inputted into the PC-based
forecasting system to provide real-time flood forecast at Jambatan Tun Perak.
6.
The main limitation of the study is the availability of reliable and error-free
hydrological data. Therefore the scope of the study is only limited to the
Upper Klang catchment because of the inadequacy of well-established on-line
hydrological data in other catchments.
7.
The scope of the hydraulic model development is limited to the determination
of water level profile for a river channel with one inflow and one outflow.
Modelling of complicated river networks with lateral inflow is not covered in
this study.
8.
The hydraulic model can model river channel without any flow control
structures. The modeling of water level profiles regulated by flow control
structures are not covered in this study.
6
1.5
Importance of Study
The developed system synergizes the most recent engineering modeling
techniques with the technologies in software and the internet programming in order
to achieve the objective of providing an accurate and timely flood forecast to the
masses. The developed system, given the name Tank-SStep Model uses the
hydrological Tank Model to simulate the catchment discharge hydrograph while the
water level profile within the Klang River is generated using the Standard Step
Method. It also includes a data acquisition module to continuously acquire rainfall
and water level data from the Infobanjir web server as input to the model. The
generated output of flood forecast warnings can then be disseminated using various
communication technologies like through the internet, cell phones and other wireless
devices.
CHAPTER 2
THEORETICAL BACKGROUND
2.1
INTRODUCTION
The project of developing a real-time PC-based flood forecasting system
requires a sound knowledge in hydrology and hydraulic engineering and the
manipulation of the latest programming technology. Hydrology modeling allows us
to simulate the discharge hydrograph generated by the study catchment in response
to a rainfall event while hydraulic modeling is capable of simulating the water level
profile along the river channel. Utilizing the programming technologies available for
internet and PC-based programming, we can setup an automated real-time flood
forecasting system to provide early flood warning to the citizens in the Kuala
Lumpur City Center.
The advancement in Information Technology has caused the proliferation of
various modeling and programming techniques which can be applied in the study.
However deliberate study is critical in selecting the most suitable hydrological and
hydraulic model, as well as the programming technologies to be adopted in order to
effectively achieve the objectives of the project. This chapter outlines the
8
fundamental concepts and theoretical background for the modeling techniques and
programming technologies applied in the course of the study.
2.2
Hydrological and Hydraulic Model Selection
Many different flood forecasting models, ranging from simple stage
regression techniques to sophisticated physically-based distributed hydrologic
models have been developed and used to forecast floods. A flood forecasting model
is one specific type of hydrologic model developed to simulate catchment responses
to precipitation and generate forecasts of the water level and stream flow. Generally
flood forecasting model can be categorized into three types:
1.
Distributed physics-based models (e.g. SHE, TOP-model)
2.
Lumped conceptual models (e.g. Sacramento, Tank, CLS)
3.
Black box models (e.g. stage-regression, Unit Hydrograph, LTF)
From the various types of models available, the selection of a suitable flood
forecasting model has to be carried out with caution depending on the catchment
characteristics especially due to urbanization and the balance between the model
complexities versus the accuracy of the forecast required. According to Pilgrim
(1987), the factors which need to be considered in the choice of flood estimation
method are:
i.
The form and structure of available methods, the factors they consider, their
theoretical basis, and their accuracies.
ii.
The data available for calibration. The amount and range of the data on which
the relationships in the methods are based, and their applicability to the
design catchment.
iii.
The type and importance of the work for which the design is required, the
cost of the structure, and the design risk of surcharge. These affect the desired
9
accuracy and the type of information required, such as whether a peak
discharge is adequate or a complete hydrograph is needed.
iv.
The time that can be spent on obtaining an estimate.
v.
The expertise available. The more complex methods generally require more
expertise for their valid use and interpretation.
Answering these factors, the Tank Model has been identified as the best
solution to model the hydrological processes of the Upper Klang Catchment due to
the advantages below:
1.
The structure of the model using a series of storage tanks can reliably depict
the physical hydrological processes such as infiltration, base flow, river
discharge, evaporation, tank storages etc.
2.
The available data for this study is the online rainfall and water level data
provided by the Infobanjir server, maintained by the DID. No soil
investigation study has been carried out for the catchment. Because the Tank
Model only requires the rainfall data as input and historical water level data
for model calibration purposes, it is adequate for the model to simulate the
hydrological processes with the available data.
3.
For flood forecasting purposes, the progression of the flood against time is
very important especially in determining the available lag time for an early
warning and the inundation period of the flood if the banks are over spilled.
With a complete rainfall hyetograph, the Tank Model is able to simulate the
complete discharge hydrograph of the catchment.
4.
The tank model uses simple mathematical equations which can be easily
programmed and calculated with an electronic spreadsheet such as Microsoft
Excel. Therefore the forecast can be calculated within less than one second
after the rainfall data is inputted into the system.
5.
Because of its simple model structure and minimal input parameters, it can be
easily understood, operated and maintained by flood operating personnel with
a fundamental knowledge in hydrology and flood forecasting.
10
For the hydraulic model, the Standard Step Method has been identified as the
suitable model for the study channel based on the following reasons:
1.
The study river has a mild slope without any regulating control structures
along the channel, making it a channel with a gradually varying flow.
Therefore all assumptions for a gradually varied flow are valid and the
Standard Step Method can be applied to simulate the water levels within the
study channel.
2.
The method can be applied to nonprismatic channels and is best suited to
computations for natural channels (Lejeune, 1994). With the cross section
data collected for the channel stretch, the flow depth at all of the cross
sections can be calculated iteratively by a trial and error process.
3.
The Standard Step Method be is an iterative computation that can be easily
tabulated and programmed into an electronic spreadsheet (Chaudry, 1993).
2.3
Hydrological Tank Model
For the purpose of this study, the TANK model by Sugawara (1979) is
proposed due to its various advantages over other models. It is a linear conceptual
model which uses a series of storage tank configuration to simulate the hydrological
processes that occur in a catchment. It is simple to use but at the same time, capable
of depicting the physical hydrological processes like evaporation, groundwater
infiltration, precipitation, and stream flow to a considerable accuracy (Chong, 1998).
Each storage tank literally represents one soil layer. The upper-most tank is
used to model the hydrological processes occurring in the top soil layer including
rainfall precipitation, evaporation, surface runoff and also infiltration and exfiltration
between the top soil and the sub soil layer. Because most of the discharge in the river
is contributed by the surface runoff, the first tank has the most influence in the
simulated discharge. Similarly, the subsequent tanks in the vertical tank series is used