FLOOD ESTIMATION AT UNGAUGED RIVER BASINS IN SARAWAK

BY REGIONALISATION TECHNIQUE

ONNI SUHAIZA BT SELAMAN

A thesis submitted

In fulfilment of the requirements for the degree of Doctor of Philosophy

Faculty of Engineering

UNIVERSITI MALAYSIA SARAWAK

2007

ACKNOWLEDGEMENTS

In the name of Allah, the most Gracious, the Most Merciful. All praises and

thanks are due to Allah s. w. t,, the Lord of the Universe. It is through His grace,

mercy and help that the researcher is able to complete this research on Flood

Estimation at Ungauged Basins in Sarawak by Regionalisation Technique.

Heading the list of individuals whom the researcher would like to thank is her

respected supervisor, Prof. Salim Said. It would be impossible for the researcher to

get this study completed without the help, support, motivation and guidance given by

Prof. Salim Said. The researcher has learnt and benefited in many ways from the

professional advice and guidance given by him. The researcher is truly grateful for

the valuable time he has given all throughout his appointment as a supervisor.

The researcher would also like to express appreciation and gratitude to her

co-supervisor, Assoc. Prof. Dr. Nabil Bessaih for his valuable suggestions to improve

the quality of the study.

Special thanks from the researcher are also due to all staff members of

UNIMAS, particularly to those who are in the Engineering Faculty, Centre for Post-

Graduate Studies and Centre for Academic and Information Services (CAIS); and

also to all staff members of the Department of Irrigation and Drainage (DID),

particularly to Mrs Hidayati bt Ismail and Mrs Siti Khadijah bt Abdul Rashid. The

11

researcher highly appreciates their kindness, cooperation and friendliness in

rendering their assistance to her.

Further, gratitude and thanks to Dr Vishwas A. Sawant for his guidance and

sincere help in producing FORTRAN programming for the study; Mrs Zaiton bt

Hassan and Miss Nor Zameera bt Zainal for their guidance and help on using SPSS

software; Assoc Prof Dr Wang Yin Chai, his research officer (Mr Lee), and his post-

graduate student (Mr Victor) for their guidance and help in using ArcGIS; and also to

Cikgu Rashid, Cikgu Farah and Cikgu Norhayati Abg Zamhari for correcting and

editing the thesis manuscript.

The researcher would also like to express heartfelt thanks to her beloved

family: Mr Selaman b. Boyot, Mrs Halimah Hj Mat, Hamsiah Selaman, Salmiah

Selaman, Masturi Selaman and family, Sa'adiah Hj Mohd Ali, Zainab Hj Mat and

Habsah Hj Mat for their sincere and continuous support.

Furthermore, the researcher would also like to thank and express feelings of

indebtedness to her very helpful and supportive friends: Mah Yau Seng, Lai Sai Hin,

Rosmina Ahmad Bustami, Lisa Yong, Ngu Lock Hei, Bertha Dies and Kueh Kim

Meow for their genuine help and support.

Finally, to all individuals who have contributed any amount of help but their

names are not mentioned in person, the researcher would like to thank all of you

very much and pray that may your best reward come from the Almighty.

111

ABSTRACT

This study is about flood estimation at ungauged basin in Sarawak by

utilising the regionalisation technique. There are 21 major river basins in Sarawak.

Being the largest state in Malaysia and still not fully developed, Sarawak has only

about 60 gauging stations distributed throughout the state. However, due to limited

records and tidal influence, discharges records from only 19 stations could be used in

this study.

A study on the flood frequency regions for the Sarawak state was carried out

using the Gumbel Distribution with Weibull, Gringorten and the L-Moment formula.

The probability plot and flood-frequency curves by Gumbel distribution of each of the

19 individual stations were prepared using three different plotting position formulae

(i. e. Weibull, Gringorten and L-moments). Superimposed flood frequency curves from

Gumbel distribution with the Gringorten formula along with other factors

influencing the flood flows in a river basin such as the climate, topography and

hydrological characteristics were taken into consideration before finalising the

regional flood frequency boundaries and regional dimensionless flood frequency

curves. Further, a study on mean annual flood regions for Sarawak was carried out

using the Multiple Regression Analysis Method. For the derivation of the regional

mean annual flood equations and mean annual flood regions, the mean annual

discharge records from the 19 stations and their catchment's characteristics such as

catchment area and mean annual catchment rainfall that could affect the mean

annual discharge are considered. Once the flood frequency region and mean annual

iv

flood region for the site to be estimated have been identified, the designer could come

out with the flood estimation for the site by multiplying the regional dimensionless

flood frequency curve and the regional mean annual flood equation representing the

site.

Results and analysis of the probability plot and flood-frequency curves by

Gumbel Distribution of each of the 19 individual stations plots, have consistently

shown that Gumbel Distribution plotted with the Gringorten formula always lie in

between the Gumbel Distribution plotted with Weibull formula which always give

the highest discharge, and the Gumbel Distribution plotted with L-Moment formula

which gives the lowest discharge. Some literatures have stated that regionalisation

techniques work best with L-Moments, but if used with Gumbel Distribution, the

results may not be consistent. Thus, the Gringorten formula is recommended for use

in determining flood frequency and magnitude in Sarawak. The derivation of the

regional dimensionless flood frequency curves and regional flood frequency

boundaries shows that the state of Sarawak could be represented by five regional

flood frequency curves and five flood frequency regions. As for the derivation of

regional mean annual flood equations and mean annual flood region, two regional

mean annual flood equations and two mean annual flood regions are the outcomes.

By using the combination of index flood method (in regional flood frequency

analysis) and multiple regression method presented in this study, the predicted Qio

(from regional analysis) of the 19 sample stations are within 0.75 to 1.50 times the

observed Qio (from individual analysis).

V

ABSTRAK

Anggaran Banjir bagi Lembangan Tadahan Tanpa Tolok di Sarawak dengan

menggunakan Kaedah Serantau

Kajian ini adalah berkenaan anggaran banjir bagi lembangan tadahan tanpa

tolok di Sarawak dengan menggunakan kaedah serantau. Terdapat 21 lembangan

tadah utama di Sarawak. Sebagai negeri terbesar di Malaysia yang masih belum

membangun sepenuhnya, Sarawak cuma memiliki kira-kira 60 stesen tadahan yang

berserakan di seluruh negeri. Oleh kerana rekod yang terhad dan pengaruh air

pasang surut cuma rekod-rekod kadar alir dari 19 stesen sahaja yang dapat

digunakan dalam kajian ini.

Kajian berkenaan frekuensi kadar alir serantau bagi negeri Sarawak ini

dijalankan menggunakan Agihan Gumbel dengan formula Weibull, Gringorten dan

L-Moments. Plot kebarangkalian dan lengkung frekuensi kadar alir menggunakan

Agihan Gumbel bagi setiap satu stesen tersebut dihasilkan dengan menggunakan

tiga formula plot kebarangkalian yang berbeza (iaitu Weibull, Gringorten dan L-

Moments). Lengkung-lengkung frekuensi kadar alir yang dibiarkan saling bertindih

yang bersumber dari Agihan Gumbel dengan formula Gringorten bersama-sama

dengan faktor-faktor lain yang mempengaruhi aliran kadar alir sesebuah kawasan

tadahan seperti cuaca, topografi dan kriteria-kriteria bersifat hidrologi adalah

diambilkira semasa memutuskan garis-garis sempadan bagi kawasan frekuensi

kadar alir serantau dan lengkungan frekuensi kadar alir serantau tanpa dimensi.

VI

Seterusnya, kajian terhadap min kadar alir tahunan serantau bagi Negeri Sarawak

pula dijalankan menggunakan kaedah Analisa Regresi Berganda. Untuk

menerbitkan persamaan min kadar alir tahunan serantau dan menentukan batasan

kawasan min kadar alir serantau, rekod kadar alir min tahunan serantau dari 19

stesen bersama-sama dengan beberapa kriteria kawasan tadahan seperti keluasan

kawasan tadahan dan min air larian tahunan yang boleh mempengaruhi min kadar

alir tahunan adalah diambilkira. Setelah dikenalpasti kawasan serantau bagi

frekuensi kadar alir dan kawasan serantau bagi min kadar alir tahunan bagi

sesuatu tapak yang ingin dicari anggaran kadar alirnya, perekabentuk bolehlah

mendarabkan nilai tanpa dimensi dari lengkung frekuensi kadar alir tanpa dimensi

serantau bagi kala kembali tertentu yang mewakili tapak yang ingin dianggarkan

kadar alirnya dengan nilai dari persamaan min kadar alir purata tahunan serantau

bagi tapak tersebut bagi mendapatkan nilai anggaran kadar alir yang mewakili

kala kembali yang sedang dicarinya.

Keputusan dan analisa plot kebarangkalian dan lengkung frekuensi kadar

alir menggunakan Agihan Gumbel bagi setiap satu stesen tersebut dihasilkan dengan

menggunakan tiga formula plot kebarangkalian yang berbeza (iaitu Weibull,

Gringorten dan L-Moments) telah menunjukkan secara konsisten bahawa plot

Agihan Gumbel dengan formula Gringorten selalu terletak di antara plot

kebarangkalian Agihan Gumbel dengan formula Weibull yang selalu memberikan

nilai kadar alir tertinggi dan plot Agihan Gumbel dengan menggunakan formula L-

Moment yang selalu memberikan nilai kadar alir terendah. Beberapa kajian telah

menunjukkan bahawa teknik serantau memberikan hasil yang sangat bagus jika

menggunakan L-Moments, tetapi sekiranya L-Moments digunakan bersama dengan

vii

Agihan Gumbel, hasilnya mungkin tidak begitu konsisten. Oleh itu, formula

Gringorten disarankan untuk digunakan dalam menentukan frekuensi dan

magnitud kadar alir di Sarawak. Perolehan dari analisa lengkung frekuensi kadar

alir serantau dan kawasan kadar alir serantau menunjukkan, Negeri Sarawak dapat

diwakili oleh lima lengkung frekuensi kadar alir serantau dan lima kawasan kadar

alir serantau. Manakala perolehan dari analisa min kadar alir tahunan serantau

dan kawasan mean kadar alir tahunan serantau menunjukkan, dua persamaan min

kadar alir tahunan serantau dan dua kawasan min kadar alir tahunan serantau

dapat dihasilkan bagi Negeri Sarawak.

Dengan menggunakan kombinasi Kaedah Indeks (dalam analisa frekuensi

kadar alir serantau) dan Kaedah Analisa Regresi Berganda yang dipaparkan dalam

kajian ini, didapati Qlo diramal (dari analisa secara serantau) adalah dalam julat

antara 0.75 - 1.50 berbanding Qlo dicerap (dari analisa secara individu).

Vlll

TABLE OF CONTENTS

Acknowledgements

Abstract

Abstrak

Table of Contents

List of Tables

List of Figures

List of Abbreviations

List of Appendices

CHAPTER 1 INTRODUCTION

1.1 Research Background and Statement of Problems

1.2 Objectives or Purpose Statement

1.3 Delimitation of the Study

1.4 Organisation of the Study

Page

11

iv

V1

ix

xiv

xv

xvii

xix

1

1

4

5

5

CHAPTER 2 LITERATURE REVIEW 6

2.1 Introduction 6

2.2 General Review of Design Flood Estimation Techniques 7

2.3 General Review of Regionalisation Techniques 19

2.3.1 Identification of Homogeneous Regions 20

ix

2.3.2 Estimating Flood According to the Identified 28

Region

2.4 A General Review on Hydrological Procedure No. 4 37

(HP4) and its Related Concept

2.5 Flood Frequency Analysis (FFA) 39

2.5.1 The Data to be Utilised in FFA 40

2.5.2 The Probability Distribution to be adopted in 42

FFA

2.5.3 Fitting the Distribution 51

2.5.3.1 Graphical Method 52

2.5.3.2 Regression (Least-Square Method) 53

2.5.3.3 Method of Moments 53

2.5.3.4 Method of Maximum Likelihood 58

2.5.3.5 Probability Weighted Moments Method 59

2.5.4 Goodness-of-fit Test and Confidence Limits in 60

HP4

2.5.4.1 Smirnov-Kolmogorov Goodness-of-fit 60

Test

2.5.4.2 Confidence Interval Limits 61

2.5.5 The Plotting Position Formula to be used with

Gumbel Distribution 62

2.5.6 Modifications to Gumbel Distribution 64

2.5.7 Derivation of Regional Flood Frequency Curves

in HP4

65

X

2.5.8 L-Moments Approach in Regional Flood

Frequency Analysis

2.6 Multiple Regression Analysis

2.7 Summary of the Chapter

CHAPTER 3 RESEARCH METHODOLOGY

3.1 Introduction

3.2 Research Design

3.3 Data Collection Procedures

3.4 Data Analysis

66

66

70

73

73

74

75

81

3.4.1 Frequency Analysis of Flood Data from 81

Individual Stations

3.4.2 Derivation of Regional Dimensionless flood

Frequency Curve along with the Regional flood

Frequency Map (RFFM) 87

3.4.3 Derivation of Regional MAF Equations along

with the Regional Mean Annual Flood Map

(RMAF) 91

3.5 Peak Flood Estimation 94

3.6 Comparison between Observed Flood Estimates and

Predicted Flood Estimates for the 19 Sample Stations 95

3.7 Limitations 97

CHAPTER 4 RESULTS AND ANALYSIS 100

4.1 Introduction 100

X1

4.2 Flood Frequency Analysis of Individual Station 100

4.3 Regional Dimensionless Flood Frequency Curves and

Flood Frequency Regions Map 105

4.4 Regional Mean Annual Flood Equations and Regional

Mean Annual Flood Map 111

4.5 Peak Flood Design Estimates based on a Combination

of Index Flood Method and Multiple Regression

Analysis Method 115

4.6 Comparison between Observed Flood Estimates and

Predicted Flood Estimates for the 19 Sample Stations 117

4.7 Summary 120

CHAPTER 5 DISCUSSIONS 121

5.1 Introduction 121

5.2 Frequency Analysis of Individual Station Flood Data 121

5.3 Regional Dimensionless Flood Frequency Curves and

Flood Frequency Regions Map 123

5.4 Regional Mean Annual Flood Equations and Regional

Mean Annual Flood Map 125

5.5 Accuracy of the Peak Flood Design 127

5.6 Summary 128

CHAPTER 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 130

6.1 Introduction 130

6.2 Brief Overview of the Problem 130

xii

6.3 The Purpose Statement

6.4 Review of the Methodology

6.5 Summary of Major Findings

6.6 Limitations of the Study and Recommendations for

Future Research

6.7 Conclusion

131

132

134

136

137

REFERENCES 139

APPENDICES 152

X111

LIST OF TABLES

Page

Table 2.1 Hydrological Procedure for Flood Estimation in Malaysia 14

Table 2.2 Summary of the Recommended Frequency Types 45

Table 2.3 Mean y,, and Standard Deviation 6, of Gumbel Variate (y) Vs

Record Length (n) 57

Table 2.4 Critical Values of the Kolmogorov-Smirnov Test Statistic for a

Significance Level of 0.20,0.10,0.05 and 0.01 61

Table 2.5 Plotting Position Formula 62

Table 3.1 Annual Maximum Water Level Data Records 77

Table 3.2 The Selected River Stations Inventory List 79

Table 3.3 Annual Evaporation Record (Year 1997) 90

Table 3.4 Summary of Area and Mean Annual Rainfall for the Study 92

Table 4.1 Results of Gumbel Distribution for Station Boring by Weibull,

Gringorten and L-Moments Formula 102

Table 4.2 Summary of Regression Analysis Results for the Study 112

Table 4.3 Regional Mean Annual Flood (MAF) Equations of Sarawak 114

Table 4.4 Summaries of Worked Examples 117

Table 4.5 Comparison between Observed Flood Estimates and Predicted

Flood Estimates for the 19 Sample Stations 118

xiv

LIST OF FIGURES

Page

Figure 1.1 Maps of Malaysia 1

Figure 1.2 Gauged River Basins in Sarawak and Delineated

Homogeneous Regions Based on a Study by Lim and Lye

(2003) 3

Figure 3.1 Locality Map of the 19 Selected River Stations 80

Figure 3.2 Sarawak Topographical Map 88

Figure 3.3 Mean Annual Rainfall Map of Sarawak Up to Year 1998 89

Figure 3.4 Mean Annual Rainfall Map of Sarawak Up to Year 2002 89

Figure 4.1 Gumbel Distribution Using Weibull Formula for Station 103

Boring

Figure 4.2 Gumbel Distribution Using Gringorten Formula for Station 103

Boring

Figure 4.3 Gumbel Distribution Using L-Moments Method for Station 104

Boring

Figure 4.4 Comparison of Gumbel Distribution Using Weibull, Gringorten

and L-Moments Formula for Station Boring 104

Figure 4.5 Dimensionless Flood Frequency Curves for Sarawak Based on

Gumbel Distribution Using Weibull Formula 106

Figure 4.6 Dimensionless Flood Frequency Curves for Sarawak Based on

Gumbel Distribution Using Gringorten Formula 106

xv

Figure 4.7 Dimensionless Flood Frequency Curves for Sarawak Based on

Gumbel Distribution Using L-Moments Formula 107

Figure 4.8 Regional Flood Frequency Map for Sarawak Based on Gumbel

Distribution Using Gringorten Formula 109

Figure 4.9 Dimensionless Regional Flood Frequency Curve for Sarawak

Based on Gumbel Distribution Using Gringorten Formula 110

Figure 4.10 Schematic Diagram of the Residual Refinement. Process 111

Figure 4.11 The Residual Signs Up to the 2nd Level of Refinement Process 113

Figure 4.12 Mean Annual Flood Regions (MAF Regions) of Sarawak 114

Figure 4.13 Scatter Diagram Comparing Predicted Qio (from Regional

FFA) and Observed Qio (from Individual FFA) 119

Figure 4.14 Frequency Diagram Showing the Percentage Breakdown of the

Ratios of Qio Values from Regional Analysis to Qio Values from

Observed Records 120

xvi

LIST OF ABBREVIATIONS

ARI Annual Recurrence Interval

CCA Canonical Correlation Analysis

cdf Cumulative distribution function

DID Department of Irrigation and Drainage

DRC Discharge Rating Curve

EV1 Extreme Value Type I or Gumbel Distribution

EVII Extreme Value Type II or Frechet Distribution

EVIII Extreme Value Type III or Weibull Distribution

FF Flood Frequency

FFA Flood Frequency Analysis

FFR Flood Frequency Region

GEV Generalized Extreme Value

GL Generalized Lamda Distribution

GLO Generalized Logistic Distribution

GLS Generalized Least Squares

GNO Generalized Normal

GPA Generalized Pareto

HP4 Hydrological Procedure No. 4

IdF Intensity-duration-Frequency

IFM Index Flood Method

XVll

LP 3 Log Pearson Type III

MAF Mean Annual Flood

MAFR Mean Annual Flood Region

NAHRIM National Hydraulic Research Institute of Malaysia

NERC Natural Environmental Research Council

pdf Probability distribution function

PE 3 Pearson Type III

POT Peak over Threshold

PWM Probability Weighted Moments

QdF Flood-duration-Frequency

Q-T Flood Magnitude - Return Period

RFFA Regional Flood Frequency Analysis

RFFM Regional Flood Frequency Map

ROI Region of Influence

SCS Soil Conservative Service

SHYB Sarawak Hydrological Year Book

SMA Soil Moisture Accounting

T Return Period

USMMM Urban Stormwater Management Manual for Malaysia

y Reduced Variate

xviii

LIST OF APPENDICES

Appendix A Sarawak River Basins and River Gauged Stations According to

Their River Basins

Appendix B Conversion of Annual Maximum Water Level to Annual

Maximum Discharge

Appendix C FORTRAN Programming to Calculate Gumbel Distribution

Using L-Moments Method

Appendix D Procedure to Perform Multiple Regression Analysis Using

Microsoft Excel Spreadsheet

Appendix E Calculation of Flood Frequency Distribution by Gumbel

Distribution Using Weibull Formula

Appendix F Calculation of Flood Frequency Distribution by Gumbel

Distribution Using Gringorten Formula

Appendix G Calculation of Flood Frequency Distribution by Gumbel

Distribution Using L-Moments Formula

Appendix H Graphs Showing the Comparison of Flood Frequency Curves

from Flood Frequency Analysis by Gumbel Distribution Using

Weibull, Gringorten and L-Moments Formula

Page

152

176

196

199

201

221

241

271

xix

Appendix I Flood Frequency Curve by Gumbel Distribution Using

Gringorten Formula with Dual x-axis [i. e. y and T] 291

Appendix J Results of Multiple Regression Analysis to Obtain Mean

Annual Flood Regions and Regional Mean Annual Flood

Equations 311

Appendix K Flood Frequency Analysis for the Worked Examples together

with their Location in the FFR and MAFR Map for Sarawak 320

xx

CHAPTER 1

INTRODUCTION

1.1 Research Background and Statement of Problems

The state of Sarawak, with an area of 124 450 km2, is the largest state of Malaysia

(329 750 km2), almost equal in size to Peninsular Malaysia (see Figure 1.1).

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In Sarawak alone, there are altogether 22 major river basins. Many of these

river systems remain ungauged mainly due to poor accessibility, difficult terrain and

large drainage basins. Some gauged stations in operation also face problems such as

1

shortness of records, incomplete records and unavailability of flow rating curve. For

engineers and planners who are involved in project design, the limited numbers of

hydrological data and information remains as one of the major obstacles towards an

accurate estimation of the design floods.

It is well accepted that regionalisation technique is a very essential method in

estimating parameters in hydrology compensating for the lack of long hydrological

time series and the lack of information. But in the absence of any relevant

authoritative guidelines with regard to regionalisation technique, Lim and Lye (2003)

revealed that many practicing engineers in Sarawak rely on rainfall intensities to

generate flood peaks using a simple classical method called the rational method for

flood estimations. They said, despite the fact that the rational method is intended for

very small basins, its application in some large basins without any modification is a

common practice. They also mentioned that there are many circumstances where

flood estimation procedure applicable to Peninsular Malaysia, adopted for use in

Sarawak with the assumption that the basin characteristics are similar. They also

highlighted that some rainfall-runoff simulation programs have been used to obtain

flood peaks but there are attempts to simulate programs using default values of

internal parameters without actual comprehensive calibration of regional basins and

there are also circumstances where calibrations are done on common flood events

and then extrapolated to make estimations for extreme floods.

With regard to the abovementioned flood estimation design problems and its

present solution, Lim and Lye (2003) had conducted a prior research on regional

flood estimation for ungauged basins in Sarawak. They employed cluster analysis

2

and index-flood estimation procedure based on L-moments method for their study.

Based on their research, they had identified two homogeneous regions for Sarawak,

Region A and Region B. See Figure 1.2. They found that Generalised Logistic

distributions and Generalised Extreme Value are suitable to describe the

distribution of extreme flood events appropriately within Region A and B

respectively. Subsequently, they had developed a regional growth curve for each of

the basins in Sarawak within the limitations identified for the method.

Region A

Figure 1.2 : Gauged River Basins in Sarawak and Delineated Homogeneous Regions Based on a Study by Lim and Lye (2003)

As for Peninsular Malaysia, peak flood at ungauged basins are designed based

on the authoritative guidelines known as Hydrological Procedure No. 4 (HP4)

entitled "Magnitude and Frequency of Flood in Peninsular Malaysia", which put into

practice regionalisation technique. The guidelines had existed since 1974 and in 1984

the procedure was revised and updated. The regional analysis carried out in the

revised and updated version of the procedure consists of two major parts : (i) the

3

development of a set of regional dimensionless flood frequency curves (using Gumbel

distribution) and accompanied by its flood frequency regions map (FFR); and (ii) the

development of a set of regional regression equations relating mean annual flood to

the catchments characteristics (catchments area and mean annual catchments

rainfall) plus its mean annual flood regions (MAFR). By multiplying the two major

parts, design flood for the site in interest could be obtained. Wardah and Zaidah

(2002) made further revisions on the Regional Flood Frequency Analysis for

Peninsular Malaysia.

Lim and Lye (2003) had classified Sarawak into only two homogeneous

regions. That classification is too broad to accurately estimate the design floods for

ungauged basins in Sarawak. This study is, therefore, an attempt to refine the

classification that had been done by Lim and Lye (2003). The refinement is done

based on a different regionalisation technique. Methodology wise, this study is

similar to the existing regionalisation technique being used in hydrological procedure

for Peninsular Malaysia. It gives emphasis on Gumbel distribution for the

construction of its regional dimensionless flood frequency curves. L-moments

approach is also considered but only in the context of its application with Gumbel

distribution.

1.2 Objectives or Purpose Statement

The main intention of this study is to determine the regional dimensionless flood

frequency curves and the mean annual flood regional equations for Sarawak along

with its accompanying map so as to enable their utilisation in peak flood design.

4