UNIVERSITI PUTRA MALAYSIA
APPLICATION OF RORB RAINFALL-RUNOFF MODEL TO URBAN AND RURAL CATCHMENTS
CHOO EE LI.
FK 2004 18
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APPLICATION OF RORB RAINFALL-RUNOFF MODEL TO URBAN AND RURAL CATCHMENTS
BY CHOO EE LI
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science
March 2004
DEDICATION
To my beloved family especially my parents, for their continual support, patience, love and care, which finally make this happened.
To GOD, fiom the bottom of my heart thank you for your love and blessings of perseverance and patience..
.
Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirements for the degree of Master of Science
APPLICATION OF RORB RAINFALL-RUNOFF MODEL TO URBAN AND RURAL CATCHMENTS
CHOO EE LI March 2004
Chairman : Faculty
Abdul Halim bin Ghazali, Ph.D.
Engineering
Over the years, many have realised the growing importance of water and its resources to sustain industrial and community development and most importantly life in all forms. However, excess of uncontrolled surface runoff could lead to flooding and potential damages in properties and loss of life. As a result, the field of hydrology and hydraulic has become a growing importance. With the current technology, various software programs are developed to assist in the analysis and study of water resources management and flood mitigation. Amongst them is the Rainfall-Runoff Routing Model which was widely used in Australia. It has also been used in some of the catchments' studies and flood mitigation projects in Malaysia, mostly to perform flood routing and estimation.
The primary aim of the study is to assess the suitability of RORB model for application to catchments in Malaysia. It is used to simulate the rainfall-runoff routing process of two characteristically different catchments namely Sg Klang Basin at. Tun Perak Bridge and Sg Bernam Basin at South Kinta Consolidated
Bridge. The former is highly urbanised and located in Wilayah Persekutuan while the latter is considerably rural and encompasses both Perak and Selangor states.
The setting up of the model begins with subdividing the catchment into various subcatchments based on catchment topography, river system and drainage divides which are then modelled by a series of links and nodes, which represent the reaches of flow and subcatchments respectively. Next, the various input parameters such as subcatchment area and landuse condition, channel type, length and slope, fraction imperviousness, rainfall and streamflow data are defined and determined. All these are compiled in an input data file which is written in Fortran language following a specific sequence of command codes for running of the model simulations.
The catchment modelling is performed up to the calibration and verification stage using 4 storm events; 2 each for calibration and verification respectively. These events are identified based on available past 3 to 40 years of rainfall and streamflow records collected from Department of Irrigation and Drainage Malaysia. The best fit model parameters, m and
b,
are determined and the results of the generated runoff hydrographs are compared to the observed hydrographs.The model is areally distributed, nonlinear, and has a linear or non-linear storage relationship between storage S and outflow discharge Q which is given as:
S = kckrQm
where kc and m are the catchment parameters determined by trial and error fitting while kr is relative delay applicable to individual reach storage calculated based on any unit of indicator of storage delay time. Two units of indicator, namely flow
length and flow time, are adopted separately in 1" Model Setup and 2nd Model Setup to ascertain the sensitivity of these two units to the model and its results.
This study concludes that the application of RORB model is relatively user friendly.
Also, the model is less complicated in its application as it does not involve too many input parameters leading to less assumption to be made. This is an advantage in view of the inherent problem of data inadequacy and poor quality of recorded data.
In addition, there are only two model parameters, m and k,, to determine because of the simplified approach to the rainfall-runoff process.
The study also showed that R O D model is applicable to both urban and rural catchments. The overall results indicated variations of less than 10% between the generated and observed runoff discharges and volumes, which is of acceptable limitation. However, it is also shown SKC catchment has a higher variation than Tun Perak catchment. This is most possibly due to the fact that SKC catchment has a very much bigger catchment area about 10 times greater than Tun Perak catchment. This results in larger propagated errors or discrepancies in the modelling. But overall, the peak times and shape of the runoff hydrographs are generally matching between the observed and generated. Finally, the model is also not sensitive to the types of indicator used for relative storage delay time as the maximum variations in the results between the two model setups are 2%.
In conclusion, RORB is an acceptable model which provides a reasonably good simulation of the rainfall-runoff process in a catchment.
Abstrak tesis dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk Ijazah Master Sains APPLIKASI MODEL HUJAN-LAFUAN RORB KE ATAS KAWASAN-KAWASAN TADAHAN BANDAR DAN DESA.
Oleh CHOO EE LI
Mac 2004
Pengerusi : Fakulti
Abdul Halim bin Ghazali, Ph.D.
Kejuruteraan
Sejak kebelangkangan ini, ramai telah menyedari kepentinganan air dan sumber air untuk menampung pembangunan industri dan masyarakat, serta semua jenis kehidupan. Walaubagaimanapun, kelebihan air permukaan yang tak terkawal akibat hujan lebat mungkin mengakibatkan banjir and seterusnya kerosakan harta dan kehilangan nyawa. Dengan ini kepentingan bidang hidrologi dan hidraul kian meningkat. Kemajuan teknologi kini membolehkan banyak program perisian dihasilkan untuk membantu dalam analisis dan kajian pengurusan sumber air dan tebatan banjir. Antaranya ialah model RORB, iaitu satu program penyaluran hujan- air larian, yang digunakan dengan meluas di Australia. Ia juga telah digunakan untuk penyaluran dan penganggaran luahan banjir dalam beberapa kajian lembangan sungai dan tebatan banjir di Malaysia. Tujuan utama kajian ini adalah untuk mengesahkan kesesuaian model RORB untuk applikasi ke atas kawasan-kawasan tadahan sungai di Malaysia. Ia digunakan untuk simulasi proses penyaluran hujan- air larian bagi dua kawasan tadahan iaitu lembangan Sg Klang di Jambatan Tun Perak dan Sg Bernam di Jambatan Kinta Selatan. Lembangan pertarna terletak di
dalam Wilayah Persekutuan manakala lembangan kedua merentasi negeri Perak dan Selangor.
Penyediaan model bennula dengan pembahagian kawasan tadahan kepada beberapa subtadahan berdasarkan topografi kawasan, sistem sungai dan pembahagian saliran dan kemudian dimodelkan sebagai satu siri kait dan nod yang masing-masing mewakili rangkaian aliran dan subtadahan. Kemudian parameter input seperti luas kawasan subtadahan dan keadaan gunatanah, jenis, panjang dan cerun saluran, turutan operasi penyalwan, pecahan kawasan tak telus, data hujan dan aliran sungai ditentukan. Kesemua data tersebut disusun dalam satu fail data input yang ditulis menggunakan bahasa Fortran dan mengikuti jujukan kod arahan yang tertentu untuk simulasi model.
Kawasan tadahan dimodelkan hingga tahap penentukuran dan pengesahan model berdasarkan 4 kejadian hujan yang lepas. Kejadian-kejadian tersebut dikenalpasti daripada 3 hingga 40 tahun rekod hujan dan aliran sungai yang sediada dan terkurnpul daripada Jabatan Pengairan dan Saliran Malaysia. Pasangan parameter penyaluran, k, dan m, yang paling padan ditentukan dan keputusan hasil hidrograf air larian dibandingkan dengan cerapan hidrograf air larian. Model ini berdasarkan luas teragih, bukan linear dan mempunyai hubungan storan linear atau tak linear antara storan S dan luahan Q seperti berikut:
di mana kc and m adalah parameter tadahan yang perlu ditentukan melalui proses padan cuba dan silap manakala k, ialah masa lengah relatif bagi storan jangkauan individu berdasarkan sebarang unit penunjuk masa lengah storan. Dua unit
vii
penunjuk, panjang saluran aliran dan masa lengah, telah digunakan dalam 'lSt Model Setup7 dan '2" Model Setup' masing-masing untuk mengkaji kepekaan kedua-dua penunjuk ke atas model dan keputusannya.
Kesimpulan kajian ini menunjukkan bahawa model RORB adalah mudah diguna dan kurang rurnit dalam aplikasinya kerana ia tidak melibatkan terlalu banyak parameter input. Maka, kurang andaian perlu dibuat dalam penentuan input data.
Ini merupakan kebaikan memandangkan ketidaklengkapan dan kekurangan data yang sediaada. Tambahan, hanya dua parameter penyaluran, m dan kc yang perlu diselaraskan disebabkan konsep proses hujan-air larian yang dipermudahkan.
Kajian ini juga mengesahkan bahawa RORB sesuai digunakan untuk kawasan tadahan berkeadaan bandar dan desa. Secara keseluruhannya, variasi keputusan yang kurang daripada 10% dalam perbandingan keputusan luahan dan isipadu air larian yang dihasilkan dengan rekod yang sediaada adalah boleh diterima. Namun, variasi bagi kawasan tadahan SKC adalah lebih tinggi daripada di Tun Perak. Ini disebabkan luas kawasan tadahan SKC yang 10 kali lebih besar daripada Tun Perak mungkin mengakibatkan perambatan variasi yang lebih tinggi. Pada keseluruhannya, masa puncak dan bentuk hidrograf air larian adalah padan secara amnya di antara hidrograf yang terhasil dan direkodkan. Akhirnya, adalah didapati bahawa model adalah tidak sensitif kepada unit penunjuk bagi masa relatif lengah storan kerana variasi maksimum keputusan antara dua jenis siapan model hanya 2%.
Kesimpulannya, RORB adalah model yang boleh diterima dan dapat memberikan hasil simulasi proses hujan-larian suatu kawasan tadahan yang memuaskan.
. . .
V l l l
ACKNOWLEDGEMENTS
In the course of the Study, many individuals and organisation have lent their time and support to ensure the success of this study. The author thus would like to thank her supervisor Assoc. Prof. Dr. Abdul Halim bin Ghazali for his never-ending patience and guidance throughout the course of this study. Appreciation is also extended to the other supervising committee members, Assoc. Prof. Kwok Chee Yan and Mdm. Badronnisa bin Yusuf for their understanding and support.
The author would also like to express her gratitude to Assoc. Prof. Dr. Aziz F.
Eloubaidy, without whom the author would not have the courage to undertake the course of study. His encouragement and advice is highly treasured by the author.
Her gratitude also goes out to the Department of Irrigation and Drainage at Ampang for supplying the necessary hydrological data required for the study and its staff under the Unit of Information Management for their kind assistance and helpfulness.
Last but not least, the author would like to convey her heartfelt gratitude to her family and dear fiends for their continual advice and support that has carried her through the completion of the project.
I certify that an Examination Committee met on 1 9 ~ ~ March 2004 to conduct the final examination of Choo Ee Li on her Master of Science thesis entitled
"Application of RORB Rainfall-Runoff Model to Urban and Rural Catchments" in accordance with the Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 198 1. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:
THAMER AHMED MOHAMMED, Ph.D.
Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)
ABDUL HALIM BIN GHAZALI, Ph.D.
Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)
KWOK CHEE YAN Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)
BADRONNISA BIN YUSUF Lecturer
Faculty of Engineering Universiti Putra Malaysia (Member)
~ r o f e s s o r / ~ e ~ u t ~ ~ e a d School of Graduate Studies Universiti Putra Malaysia Date :
2 1 (q 4 ' 6
This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirements for the degree of Master of Science. The members of the Supervisory Committee are as follow:
ABDUL HALIM BIN GHAZALI, Ph.D.
Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)
KWOK CHEE YAN Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)
BADRONNISA BIN YUSUF Lecturer
Faculty of Engineering Universiti Putra Malaysia (Member)
AINI IDERIS, Ph.D.
ProfessorIDean
School of Graduate Studies Universiti Putra Malaysia
DECLARATION
I hereby declare that the thesis is based on my original work except for quotations and citations which have been acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.
CHOO EE LI Date: 19 March 2004
xii
TABLE OF CONTENTS
Page DEDICATION
...
ABSTRACT
...
...
AB S TRAK
ACKNOWLEDGEMENTS
...
...
APPROVAL
DECLARATION
...
LIST OF TABLES
...
LIST OF FIGURES
...
LIST OF ABBREVIATIONS
...
CHAPTER
...
INTRODUCTION
...
1.1 General Background
...
1.2 Statement of Problem
1.3 Objectives of The Study
...
...
1.4 Scope of Study
...
LITERATURE REVIEW
...
2.1 General
2.2 Classification of Models
...
2.3 Watershed Simulation Models
...
2.3.1 Stanford Watershed Model IV
...
2.3.2 Boughton Model
...
2.3.3 Huggins and Monke (HM) Model
...
...
2.3.4 SCS TR-20 Model
2.3.5 Watershed Hydrology Simulation (WAHS) Model
...
2.3.6 HYMO Model
...
2.3.7 GAWSER Model
...
2.3.8 SSARR Model
2.3.9 Lag and Route Model
...
2.3.10 Kalinin-Milyukov Model
...
2.3.1 1 HYRROM Model
...
...
2.3.12 RORB Model
...
2.3.1 3 HEC-HMS Model
...
RORB MODEL
...
3.1 Introduction
...
3.2 The Model
3.3 Historical Development of Program
...
...
3.4 Functions of Program
...
3.5 Modeling Procedure
3.5.1 Stream Channel Network Representation
...
3 S . 2 Reach Storage Representation
...
vi ix
X
xii xv xvii
XX
X l l l ...
3.5.3 Routing Method
...
...
3.5.4 Representation of Rainfall-Runoff Events
3.5.5 Rainfall Effective Area
...
3 S.6 Loss Modeling
...
3 S.7 Direct Runoff
...
...
3 S.8 Calibration and Verification of Model
3 S.9 Input and Output Data
...
METHODOLOGY
...
4.1 Introduction
...
4.2 Background of Selected Catchments
...
4.2.1 Sg Klang Basin at Tun Perak Bridge
...
4.2.2 Sg Bemam Basin at South Kinta Consolidated Bridge
...
4.3 General Climate
4.4 Data Collection
...
4.4.1 Topographical Maps
...
...
4.4.2 Aerial Photographs and Satellite Imageries
...
4.4.3 Hydrological Records
4.5 Model Simulation
...
...
4.6 Model of Sg Klang Basin at Tun Perak Bridge
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4.6.1 Catchment and Stream Channel Representation 4.6.2 Input Parameters
...
4.7 Model of Sg Bemam Basin at South Kinta Consolidated Bridge
...
4.7.1 Catchment and Stream Channel Representation 4.7.2 Input Parameters
...
4.8 Model Calibration and Verification
...
4.9 Evaluation of the Modelling Results and RORB Model
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RESULTS AND DISCUSSION
...
5.1 Introduction
...
5.2 Model Calibration and Verification of Tun Perak Catchment 5.2.1 Model Calibration
...
5.2.2 Model Verification
...
5.3 Model Calibration and Verification of SKC Catchment
...
...
5.3.1 Model Calibration
5.3.2 Model Verification
...
5.4 Simulation Trends Between Generated Hydrographs and
...
Observed Hydrographs
5.5 Comparison of Results Between Different Model Setups
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5.6 Limitations in The Study
...
...
CONCLUSION
6.1 Applicability and Limitations of Model
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6.2 Recommendations
...
REFERENCES
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APPENDICES
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BIODATA OF THE AUTHOR
...
xiv
LIST OF TABLES
Table Page
2.1 The Parameters used in HYRROM Model (Source: I.H.U.K., 1989)
3.1 Types of Run for RORB Model (Source: Laurenson and Mein, 1988) 47 3.2 Model Reach Types (Source: Laurenson and Mein, 1988)
3.3 Units for Various Input and Output Data (Source: Laurenson and Mein, 198 8)
4.1 Physiographical Details of Tun Perak Catchment 4.2 Characteristics of Rivers in Tun Perak Catchment
4.3 Physiographical Details of SKC Catchment 74
4.4 Characteristics of Rivers in SKC Catchment 74 4.5 List of Rainfall and Streamflow Stations in Tun Perak Catchment 77 4.6 List of Rainfall and Streamflow Stations in SKC Catchment 77 4.7 Subcatchment Properties for lSt Model Setup of Tun Perak Catchment 85 4.8 Reach Properties for 1" Model Setup of Tun Perak Catchment 86 4.9 Subcatchment Properties for 2nd Model Setup of Tun Perak Catchment 87 4.10 Channel Properties for 2nd Model Setup of Tun Perak Catchment 8 8 4.1 1 Subcatchment Properties for 1" Model Setup of SKC Catchment 94 4.12 Reach Properties for 1" Model Setup of SKC Catchment 95 4.13 Subcatchment Properties for 2nd Model Setup of SKC Catchment 96 4.14 Channel Properties for 2nd Model Setup of SKC Catchment 97 5.1 Rainfall Data of Storm Events in Tun Perak Catchment for Calibration 102 5.2 Surface Runoff of Storm Events in Tun Perak Catchment for Calibration 103 5.3 Summary of Calibration Results for Tun Perak Catchment 104 5.4 Rainfall Data of Storm Events in Tun Perak Catchment for Verification 105
Table Page
5.5 Surface Runoff of Storm Events in Tun Perak Catchment for Verification
5.6 Summary of Verification Results for Tun Perak Catchment 5.7 Rainfall Data of Storm Events in SKC Catchment for Calibration 5.8 Surface Runoff of Storm Events in SKC Catchment for Calibration 5.9 Summary of Calibration Results for SKC Catchment
5.10 Rainfall Data of Storm Events in SKC Catchment for Verification 5.11 Surface Runoff of Storm Events in SKC Catchment for Verification 5.12 Summary of Verification Results for SKC Catchment
5.13 Overall Summary of the Results
5.14 Summary of Results for Different Model Setups
xvi
LIST OF FIGURES
Figure Page
2.1 A Flow Diagram of The Hydrologic System Within Typical Catchment Area (Source: Singh, 1988)
2.2 Model Classification (Source: Haan, Johnson & Brakensiek, 1982) 2.3 General Form of Stanford Watershed Model IV, showing
Principal Storages and Flows (Source: Singh, 1989) 2.4 Boughton Model Structure (Source: Fleming, 1975)
2.5 Huggins and Monke Model Structure (Source: Fleming, 1975) 2.6 General Structure of SSARR Watershed Model
(Source: Mohammed, 1989)
2.7 A Block Diagram Representation of Lag and Route Model (Source: Singh, 1988)
2.8 The IUH of The Lag and Route Model (Source: Sngh, 1988) 2.9 A Block Diagram Representation of The Kalinin-Milyukov Model
(Source: Singh, 1988)
2.10 The
IUH
of The Kalinin-Milyukov Model (Source: Singh, 1988) 2.1 1 HYRROM Representation of the Hydrological Processes(Source: I.H.U.K., 1989)
2.12 General Concept of RORB Model (Source: Laurenson and Mein, 1988) 35 2.13 Rainfall-Runoff Process of a Catchment in HEC-HMS Model
(Source: Scharffenberg, 2001)
3.1 Global Movement of Moisture (Source: Ayoade, 1988) 3.2 Movement of Moisture in The Earth System
3.3 Overall Runoff-Routing Model (Source: Laurenson and Mein, 198 8)
3.4 Functional Arrangement of Program (Source: Laurenson and Mein, 1988) 45 3.5 Stream Channel Network Representation
(Source: Laurenson and Mein, 1988)
xvii
Figure Page
3.6 Rainfall Effective Area Based on Thiessen Polygon Method 3.7 Direct Runoff Estimation Based On Simple Baseflow Separation
(Source: Linsley, Kohler and Paulhus, 1988) 4.1 Plan of Sg Klang Basin at Tun Perak Bridge
4.2 Plan of Sg Bernam Basin at South Kinta Consolidated Bridge 4.3 Model Sub-Division of Tun Perak Catchment
4.4 Node - Link Schematisation for lSt Model Setup of Tun Perak Catchment
4.5 Node - Link Schematisation for 2nd Model Setup of Tun Perak Catchment
4.6 Model Sub-Division of SKC Catchment
4.7 Node-Link Schematisation for 1" Model Setup of SKC Catchment 4.8 Node-Link Schematisation for 2nd Model Setup of SKC Catchment 5.1 Calibration of 1" Model Setup of Tun Perak Catchment
Based on 3 1" December 2000 Storm Event
5.2 Calibration of 1" Model Setup of Tun Perak Catchment Based on 26th April 2001 Storm Event
5.3 Calibration of 2nd Model Setup of Tun Perak Catchment Based on 31St December 2000 Storm Event
5.4 Calibration of 2nd Model Setup of Tun Perak Catchment Based on 26th April 2001 Storm Event
5.5 Verification of lSt Model Setup of Tun Perak Catchment Based on 2gth October 2001 Storm Event
5.6 Verification of lSt Model Setup of Tun Perak Catchment Based on 1 lth June 2002 Storm Event
5.7 Verification of 2nd Model Setup of Tun Perak Catchment Based on 2gth October 2001 Storm Event
5.8 Verification of 2nd Model Setup of Tun Perak Catchment Based on 11 th June 2002 Storm Event
xviii
Figure Page
5.9 Calibration of lSt Model Setup of SKC Catchment Based on 4th - gth December 1973 Storm Event 5.10 Calibration of 1'' Model Setup of SKC Catchment
Based on lSt
-
1 3 ~ ~ October 1977 Storm Event 5.1 1 Calibration of 2nd Model Setup of SKC CatchmentBased on 4th - 9th December 1973 Storm Event 5.12 Calibration of 2nd Model Setup of SKC Catchment
Based on lSt - October 1977 Storm Event
5.13 Verification of lSt Based on 25th November Model Setu of SKC Catchment - 2" December 1982 Storm Event
d?
5.14 Verification of lSt Model Setup of SKC Catchment Based on 1 4 ~ ~ - 21St September 1988 Storm Event 5.15 Verification of 2nd Model Setup of SKC Catchment
Based on 25th November - 2nd December 1982 Storm Event 5.16 Verification of 2nd Model Setup of SKC Catchment
Based on 1 4 ' ~ - 21S' September 1988 Storm Event
xix
LIST OF ABBREVIATIONS
DCM DEM DID DR F
Continuing Loss
Deterministic Conceptual Model Deterministic Empirical Model
Department of Irrigation and Drainage, Malaysia Direct Runoff
Fraction Impervious
FC Penman Open Pan Evaporation
GAWSER Guelph Agricultural Watershed Storm-Event Runoff GDEL Groundwater Store Delay
GSP Groundwater Store Index
RC RDEL RK ID I.H.U.K.
IL IUH MSMAM
GSU Groundwater Store Factor
HEC-HMS Hydrologic Engineering Center - Hydrologic Engineering System
HM Huggins and Monke
HYMO Hydrologic Model
HYRROM Hydrological Rainfall-Runoff Model Identity
Institute of Hydrology United Kingdom Initial Loss
Instantaneous Unit Hydrograph Manual Saliran Mesra Alam Malaysia Surface Runoff Partitioning Factor Routing Store Delay
Routing Store Factor
RORB RX
SCM SCS
Rainfall-Runoff Routing Model Routing Store Index
Stochastic Conceptual Model Soil Conservation Service
SCS TR-20 Soil Conservation Service Technical Report-20 SEM
s g SKC SMI SS SSARR UH WAHS
Stochastic Empirical Model Sungai
South Kinta Consolidated Soil Moisture Index
Size of Vegetation and Interception and Surface Detention Store Strearnflow Synthesis and Reservoir Regulation
Unit Hydrograph
Watershed Hydrology Simulation
xxi
CHAPTER 1
INTRODUCTION
1.1 General Background
Water is classified as one of the five essential and fundamental elements found on earth. In fact it is the basis of life to all living things. This being so, it was almost inevitable that the development of water resources preceded any real understanding of their origin and formation. The distribution and availability of water has influenced the development of human society through the course of history.
Examples of the earliest influences were the emergence of civilization along rivers like the Nile, Thames, Ganges and etc. In short, throughout centuries, water has remained an important element of the physical environment up to this day. With the ever-continuing growth of global development and population, demand for water has increased greatly in all regions.
In the tropical region, where rainfall occurs all year round with an average annual precipitation of above 2500 mm, an abundance of water is available for many uses, like in the field of industrial, domestic water supply, agriculture and power generation. Furthermore, countries in this region still have a relatively high percentage of undeveloped tropical rain forests and mountains, which is an important source of water and water retention basins which can be utilized to meet the growing demand.
On the other hand, such high precipitation when brought about during intense thunderstorms or prolonged rainfall which is common in the tropical region, if uncontrolled usually results in flooding occurrences. This leads to other disasters such as erosion problems, landslides, structural collapse and etc. Consequently, flooding is one of the more frequent natural disasters in this region and not to be looked lightly upon.
As a result, availability of accurate and reliable methods for estimating and predicting water budget and flood discharge of any particular area is crucial for the purpose of water resources and flood evaluation, planning and management. The efforts will prevent flooding and to ensure efficient and optimum utilization of potential water resources. It is therefore no doubt that research and analysis into the field of hydrology and hydraulics should and has become one of the focuses of community and national development. To date, many technical approaches have been developed to quantify it with watershed modelling being the forefront approach
at present.
With the advancement of technology and continual development that changes the catchment characteristics significantly, watershed modelling plays a major role in estimating and predicting runoff flows. With a versatile approach and wide application, modelling enables the rainfall runoff process in a catchment to be analysed and assessed under varying scenarios. The results of the model will allow optimisation of designs for water management measures.
According to Moore (1969), models are used in hydrology for three main purposes namely:
(0 (ii)
(iii) To plan the future use of water resources To simplify and generalise a complex reality To predict forthcoming hydrological events
And specifically, models are used in hydrology to do the followings:
(ii)
Increase our understanding of drainage basin processes and the interrelationships between processes and forms.
Predict drainage basin response to variations in input or catchment characteristics, especially those caused by human activities.
(iii) Explain the interrelationships of the various hydrological phenomena.
(iv) Solve various hydrological and water resource problems.
The hydrologic system synthesis involves selecting an appropriate hydrologic model and testing the operation of the model by analysis (Dooge, 1973). In watershed modeling, models are created for better understanding and to define the responses of hydrologic system for the areas under study, which may then be used to makc predictions in a deterministic or probabilistic sense. For natural water resources, many efforts concentrating on the analysis of the physical hydrological system via representing its components and their linkages by conceptual and mathematical relations have already been made. To date, there are a few models of these processes that do not require fitted parameters, for example, a mathematical model,
