HYDROSYSTEM FOR INTEGRATED CONTROL OF FLOOD AND LOW FLOW FORA RIVER BASIN IN SARAWAK

04-01-09-SF0004

Charles Bong Hin Joo Rosmina Ahmad Bustami

Salim Said Frederik Josep Putuhena

Un i TC

A ScienceFund Project 2009

530 H9 95 2009

Puatnidmat Matl.....tAJtlldelm UN RIm MALAVSrA SARAWAK

9000 k ota SLlm....h.n ·

P.KHIDMAT MAKLUMAT AKADEMIK UNIMAS

111111111111111111 ,111111 1000200154

HYDROSYSTEM FOR INTEGRATED CONTROL OF FLOOD AND LOW FLOW FOR A RIVER BASIN IN SARAWAK

04-01-09-SF0004

Leader Charles Bong Hin Joo

Fellows Rosmina Ahmad Bustami Prof Dr Salim Said Prof Dr Frederik Josep Putuhena

Faculty of Engineering UNIVERSITI MALAYSIA SARA WAK

2009

Acknowledgements

This work was made possible by the generous support of the State Planning Unit (SPU),

Department of Irrigation and Drainage Sarawak (DID), Sarawak Rivers Board (SRB), Kuching

Water Board (KWB), State Geomatic Centre of Information and Communication Technology

Unit (lCTU), Sarawak Land and Survey Department (L&S), Sarawak Natural Resources and

Environmental Board (NREB) and Kuching Barrage Management (KBM). We would like to

thank Ministry of Science, Technology and Innovation (MOSTI) for the financial support

through Science Fund (04-01-09-SF0004) to conduct this applied research.

Special thanks to the contributions of the following:

• Onni Suhaiza Selaman. Flood Estimation at Ungauged River Basins in Sarawak by

Regionalization Technique. Ph.D. Thesis. Faculty of Engineering, Universiti Malaysia

Sarawak. Supervised by Prof Dr Salim b Said.

• Hii Ching Poon. GIS-based Floodplain and Hydraulic Infrastructure System Modelling

for Integrated Water Resources Management. Ph.D. Thesis. Faculty of Engineering,

Universiti Malaysia Sarawak. Supervised by Prof Dr Frederik Josep Putuhena.

• Zait Aima Yuinzy bt Yacub. Extreme Rainfall Frequency Analysis for Sarawak.' M.Eng.

Thesis. Faculty of Engineering, Universiti Malaysia Sarawak. Supervised by Prof Dr

Salim b Said.

• Ting Sie Yew. Securing Instream Flow for Sarawak River Basin Development. M.Eng.

Thesis. Faculty of Engineering, Universiti Malaysia Sarawak. Supervised by Mr.

Charles Bong Hin Joo.

• Nur Afnie Faryisha bt Mohamad Hamsah. Design of Long Storage for Excess Water

and Development of Hydrological Framework in Sungai Sarawak Kanan Sub-basin.

M.Eng. Thesis. Faculty of Engineering, Universiti Malaysia Sarawak. Supervised by

Ms. Rosmina Ahmad Bustami.

• Zickry Azizan Yusuf. Hydraulic Modelling in Levee System Design for Integrated

Drainage System in an Urban Area Adjacent to Sarawak River. B.Eng. Final Year

Project. Faculty of Engineering, Universiti Malaysia Sarawak. Supervised by Prof Dr

Frederik Josep Putuhena.

• Chong Mui Jing. Hydraulic Modelling to determine Pump Sizes for Internal Drainage

System in an Urban Area Adjacent to Sarawak River. B.Eng. Final Year Project.

Faculty of Engineering, Universiti Malaysia Sarawak. Supervised by Prof Dr Frederik

Josep Putuhena.

11

• Marina Patrick. Flood Mitigation Structures for Sungai Sarawak Kiri Basin. B.Eng.

Final Year Project. Faculty of Engineering, Universiti Malaysia Sarawak. Supervised

by Ms. Rosmina Ahmad Bustami.

• Dayang Haroni Awang Sani. Study on Backwater Impact of Kuching Barrage. B.Eng.

Final Year Project. Faculty of Engineering, Universiti Mal'aysia Sarawak. Supervised

by Prof Dr Frederik Josep Putuhena.

• Norliza bt Asian Joe @ Joshua. Hydrodynamic Analysis of Proposed Flood Bypass

Channel Upstream of Kuching City. B.Eng. Final Year Project. Faculty of Engineering,

Universiti Malaysia Sarawak. Supervised by Prof Dr Frederik Josep Putuhena.

• Norazliza bt Mohamad. The Use of Pumping Station in Conjunction with Kuching

Barrage for Flood Mitigation. B.Eng. Final Year Project. Faculty of Engineering,

Universiti Mal1aysia Sarawak. Supervised by Prof Dr Frederik Josep Putuhena.

• Stephen anak Nyambar. Long Storage as Water Source for Sarawak River Basin.

B.Eng. Final Year Project. Faculty of Engineering, Universiti Malaysia Sarawak.

Supervised by Mr. Charles Bong Hin Joo.

iii

,....

Executive Summary

Sungai Sarawak River basin is generally quoted as 1430 km2 in size and only 6% of the area

is developed. Nevertheless, the catchment size is enormous (nearly the size of one Melaka

State of 1650 km 2) and the river networks covers huge areas including some hard to reach

topography. Due to this, Sungai Sarawak basin was chosen as research area. The following

are achievements from the drawn studies:

1. By using regionalization technique, Sarawak was sub-divided into five flood frequency

regions (FFR) and two mean annual flood regions (MAFR). Sungai Sarawak basin is

located in FFR-1 and MAFR-2. With that, engineers could come out with flood

estimation for a certain site within the Sungai Sarawak catchments, by multiplying the

regional dimensionless flood frequency curve and the regional mean annual flood

equation representing the site.

2. The existing 23 rainfall stations within Sungai Sarawak basin were subjected to

pattern and frequency analyses to better understand the rainfall occurrence and

characteristics in the basin. Monthly rainfal l pattern analysis was carried out to

determine the factors influencing the rainfall distribution in Sungai Sarawak basin.

Meanwhile, rainfall frequency analysis was performed in reduced variate curves

based on Gumbel distribution.

3. InfoWorks RS modeling software was applied to model the Sungai Sarawak systems.

To this end, 7 models were developed to provide a platform for understanding of the

river behaviors, its processes during high flow events and possible engineering

solutions. Such computer models were proven a powerful tool to show "what would be

happening" and then assisted decision making.

4. For low flow analysis, there is no critical time of dry season found. The volume of

available water from the selected locations of Git and Buan Bidi are enough to provide

water for the water demand of Kuching City.

5. Finally, Logical Framework Approach was demonstrated as the designing tool for

outlining a proposed framework for achieving the Integrated Flood Management

IV

settings and objectives of a collaborative network among the responsible agencies.

This framework was intended to serve as an interface for shaping a currently lacking

basin based flood management in the capital city.

v

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94300 Kota Sam

Table of Content

Acknowledgements

Executive Summary

Table of Content

List of Figures

List of Tables

List of Appendices

List of Abbreviations and Notations

CHAPTER 1 INTRODUCTION

1.1 Background

1.2 Objectives

1.3 Organization of Report

CHAPTER 2 REGIONAL ANALYSIS BASED ON FLOW

2.1 Overview

2.2 Flow Data

2.3 Results and Analysis

2.4 Conclusions

CHAPTER 3 REGIONAL ANALYSIS BASED ON RAINFALL

3.1 Overview

3.2 Rainfall Data

3.3 Rainfall Pattern Analysis

3.4 Frequency Analysis

3.5 Results and Analysis

3.6 Conclusions

CHAPTER 4 FLOOD I HIGH FLOW

4.1 General

4.2 InfoWorks RS

4.3 Model #1 - Sungai Sarawak Kanan Modelling

vi

Page

ii

iv

vi

viii

xi

xii

xiii

1

1

3

4

5

5

6

8

16

18

18

19

20

21

22

30

31

31

31

32

[,

4.4

4.5

4.6

4.7

4.8

4.9

4.10

CHAPTER 5

5.1

5.2

5.3

5.4

5.5

5.6

5.7

CHAPTER 6

6.1

6.2

6.3

6.4

6.5

CHAPTER 7

Model #2 - Sungai Sarawak Kiri Modelling

Model #3 - Batu Kitang Submersible Weir Modelling

Model #4 - Sungai Sarawak Modelling on Backwater Effects

Model #5 - Sungai Maong Modelling

Model #6 - Combined Sungai Maong - Sarawak Modelling

Model #7 - Flood Bypass Channel Modelling

Conclusions

LOW FLOW

General

Analysis of Water Supply

Analysis of Water Demand

Comparison of Discharges

Mass Curve Analysis for Git

Location Selection for Long Storage

Conclusions

INTERFACE DEVELOPMENT

Initial Remarks

Integrated Flood Management

Logical Framework Development

Sub-Logical Framework

Conclusions

CONCLUSIONS

REFERENCES

APPENDICES

34

36

39

41

42

46

49

50

50

50 .

51

54

56

57

59

60

60

60

61

77

79

80

82

85

Vll

,...

I' I'

List of Figures

Figure Page

1.1 A Hydrosystem 1

1.2 Proposed Research Area (Sungai Sarawak Basin) 2

2.1 Location of the River Flow Gauges Selected in the Study 7

2.2 Gumbel Distribution Using Weibull Formula for Station Boring 11

2.3 Gumbel Distribution Using Gringorten Formula for Station Boring 11

2.4 Gumbel Distribution Using L-Moments for Station Boring 12

2.5 Gumbel Distribution Using Weibull, Gringorten and L-Moments Methods 12

2.6 Flood Frequency Regions (FFR) for Sarawak Based on Gumbel 13

Distribution Using Gringorten Formula

2.7 Mean Annual Flood Region (MAFR) of Sarawak 14

2.8 Frequency Diagram showing the Percentage Breakdown of the Ratio of 16

0 10 Values from Regional Analysis to 0 10 Values from Observed

Records

3.1 Rainfall Pattern Based on DMR for Station Padawan 23

3.2 Rainfall Pattern Based on MMR for Station Padawan 25

3.3 Rainfall Pattern Based on MMR for Station China, Sg. 26

3.4 Trendlines of DMRlADMR versus Reduced Variate by Gringorten and 28

Weibull Formulas for Station Padawan

3.5 Trendlines of DMR/ADMR versus Reduced Variate for All Rainfall 29

Stations

4.1 Topographical Map of Sungai Sarawak Kanan Catchment between 33

Buan Bidi - Siniawan

4.2 Simulated Maximum Inundation of Sungai Sarawak Kanan Catchment 33

for February 2003 Fllood IEvent

4.3 Sungai Sarawak Kiri Model 34

4.4 Flood Map for 1 DO-year Flood (With Retention Ponds) 35

4.5 Flood Map for 1 DO-year Flood (With Retention Ponds and Levees) 35

4.6 Batu Kitang Submersible Weir 36

4.7 Flood Map of February 2003 Flood in Batu Kitang 38

viii

4.8 Long Section Profile of February 2003 Flood along Sungai Sarawak Kiri 38

4.9 Long Section Profile of 10-year Design Flood along Sungai Sarawak Kiri 38

4.10 Sungai Sarawak Basin-Wide Simulation Results for Backwater Effects 40

4.11 Simulated Maximum Inundation of Sungai Maong Catchment for 41

January 2000 Flood

4.12 Graphical Results of With and Without Levee (on 1 DO-year Flood), (a) 43

4.13 Scenario without any measures, (b) Scenario with Levee System

4.14 Long Section Results of With and Without Levee (on 1 ~O-year Flood), 44

(a) Long Sectional View without Levee, (b) Long Sectional View with

Levee

4.15 Graphical Results of Sungai Sarawak - Sungai Maong Systems, (a) 45

Flooding Simulation without any measures, (b) Flooding Simulation with

Levee and Internal Pumping, (c) River Cross Sectional Profiles at 50 m

Chainage, (d) Pump at the Confluence

4.16 Model Simulating Flood Bypass Channel on January 2004 Flood Event 47

5.1 Cumulative Total Monthly Discharge at Buan Bidi Station in Year 2001 50

5.2 Cumulative Total Monthly Discharge at Git Station in Year 2001 51

5.3 Cumulative Maximum Monthly Discharge of Batu Kitang Treatment Plant 52

in Year 2001

5.4 Cumulative Average Monthly Discharge of Batu Kitang Treatment Plant 52

in Year 2001

5.5 Cumulative Minimum Monthly Discharge of Batu Kitang Treatment Plant 53

in Year 2001

5.6 Cumulative Monthly Discharge of Kuching Barrage in Year 2001 54

5.7 Cumulative Maximum Discharge of Water Demand and Available Water 54

Supply Discharge

5.8 Cumulative Average Discharge of Water Deman<;J and Available Water 55

Supply Discharge

5.9 Cumulative Minimum Discharge of Water Demand and Available Water 55

Supply Discharge

5.10 Mass Curve Analysis for Git to Determine the Required Storage 56

5.11 Location of Proposed Long Storage at Sungai Sarawak Kanan 57

5.12 Cross Section of Proposed Checkgates Structures for Long Storage 58

6.1 Basic Logical Framework Layout 62

6.2 Cause and Effect of Framework Link 62

ix

6.3 Problem Tree 63

6.4 Objective Tree 67

6.5 Option Tree 68

x

List of Tables

Table Page

2.1 Selected River Flow Stations 6

2.2 Example of Frequency Analysis of Individual Station Boring 9

2.3 Results of Gumbel Distribution for Station Boring by Weibull Formula, 10

Gringorten Formula and L-Moments Method

2.4 Regional Mean Annual Flood (MAF) Equations of Sarawak 14

3.1 Rainfall Stations and Locations in Sungai Sarawak Basin 19

3.2 Tabulated DMR Data for Ech Year for Station Padawan 22

3.3 Year with Highest DMR Value for Each Rainfall Station 23

3.4 Number of Rainfall Station by Year of Highest DMR 24

3.5 Tabulated MMR Data for Stations Padawan and China, Sg. 25

3.6 Tabulated Calculation Sheet of Gumbel Distribution for Station Padawan 27

by Gringorten and Weibull Formulas

4.1 Comparison of Simulated Flood Depths at Stage Level for Flood 35

Scenario With Retention Ponds

4.2 Comparison of Simulated Flood Depths at Stage Level for Flood 35

Scenario With Combination of Retention Ponds and Levees

4.3 Simulation Results for 1 a-year Design Flood 39

4.4 Estimation of Rise and Spread of Floodwaters from Sungai Sarawak 48

5.1 Characteristics of Proposed Long Storage at Sungai Sarawak Kanan 58

6.1 List of Stakeholders 64

6.2 Alternative Analysis 70

6.3 Indicators and Mean of Verification 73

6.4 Logical Framework Matrix for Sungai Sarawak Illtegrated Flood 75

Management

6.5 Sub-Logical Framework of Sungai Sarawak Integrated Flood 78

Management

xi

List of Appendices

Appendix Page

A Regional Flood Estimation Method Based on Flow 85

B Frequency Analysis for Rainfall Stations 88

C Analysis of Water Supply and Demand 99

XlI

List of Abbreviations and Notations

ADMR

DID

DMR

FFR

HP1

HP4

HP26

IFM

InfoWorks RS

IWRM

JKC

LFA

Logframe

MAF

MAFR

MMR

NERC

SHYB

Q

QT

Average Daily Maximum Rainfall

Department of Irrigation and Drainage

Daily Maximum Rainfall

Flood Frequency Region

Hydrological Procedure No 1

Hydrological Procedure No 4

Hydrological Procedure No 26

Integrated Flood Management

InfoWorks River Simulation

Integrated Water Resources Management

Jabatan Kaji Cuaca

Logical Framework Approach

Logical Framework

Mean Annual Flood

Mean Annual Flood Region

Monthly maximum Rainfall

Natural Environmental Research Council

Sarawak Hydrological Year Book

Discharge or River Flow

Peak Discharge at T-year Return Period

Xlll

CHAPTER 1

INTRODUCTION

1.1 Background

Hydrosystem is a term originally coined by the late Professor Chow Ven Tee to describe

collectively the technical areas of hydrology, hydraulics and water resources (Mays and Tung,

1992). Hydrosystem includes advance understanding of the functioning of a water system, its

processes, drivers of change and patterns of response. A study on hydrosystem is important

in addressing disparate environments spanning a wide range of time and space scales that

working from the local controls to the influence of climate, land-use on shaping rivers and

their catchments over time. Therefore an effort of developing such an integrated system

would optimize the regulation of flood and low flow in a river basin.

The research group had decided to choose

Sungai Sarawak basin as the research area.

The scope of the study was to conduct a

hydrologic analysis of this basin and to come

out with a logical frame or management

strategies for watrr resource management

and decision-making purposes in the basin.

Figure 1.2 shows the proposed research area.

Flooding is a common occurrence in Sarawak,

particularly during the monsoon season

between November to March every year. On Figure 1.1: A Hydrosystem. average, the annual rainfall in Sarawak ranges

from 3500 mm to 4000 mm (Memon and Murtedza, 1999). Sungai Sarawak is one important

river due to the establishment of Kuching city, the capital of Sarawak State within the

catchment. It runs 125 km long and drains a catchment of 1430 km2. The river consists of two

principal tributaries, which are Sungai Sarawak Kiri and Sungai Sarawak Kanan. The two

tributaries meet near Batu Kitang, some 34 km upstream of Kuching. Kuching city is very flat

and low lying. Parts of the city are susceptible to flooding from fluvial and tidal events.

1

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...1MIt 80UCWtY - CATOEfT 8CIUI)MY -~

KAYAN BASIN

INDONESIA

11C1"OO' E

5 o 5 10 ilia

"". E

Figure 1.2: Proposed Research Area (Sungai Sarawak Basin).

On the eastern of the city, Sungai Sarawak divides and prior to 1998, there were two exits to

the sea on Sungai Sarawak and Sungai Santubong. In order to protect the city, the Sarawak

State Government blocked the two rivers and allowed only one river outlet which is now the

Kuching Barrage, aimed at controlling the river and tidal flows (KTA, 1994). The river flow

was modified from the naturally tidal regime to a regulated gates system cons~ructed along a

2

land isthmus just downstream of Kuching city (Sharp and Howe, 2000). However, the

opening and closing operations of barrage gates for flushing, desiltation and navigation were

operated in way that allowing a certain degree of tidal influx into the Sungai Sarawak system.

Tidal effects were significant till the river confluence.

After the completion of the barrage with the downstream flow regime altered, the February

2003, January 2004 and January 2009 floods were major floods. Further to mitigate the

flooding problems, the State Government had announced the construction of a 8 km flood

bypass channel from Tanjung Paroh to Batang Salak (Jurutera Jasa, 2006). Sungai Sarawak

would be cut off by a second barrage. The facilities were expected to be in full operation by

2011. Then, Sungai Sarawak would be separated into lower and upper rivers. In near future,

Sungai Sarawak would have these two hydraulic structures - Barrages and Flood Bypass

Channel to mitigate flood.

Since the hazard of flooding in Sarawak is quite high, the growing momentum of economic

development and urban expansion had exposed urban area to flood risk. The Department of

Irrigation and Drainage (DID) Malaysia had published regional flood frequency regions for the

Peninsular Malaysia only (HP4) (010,1974 and 010,1987). There are as yet no such

publication for Sabah and Sarawak, which can be used as a source of reference. The results

from a study on water resources at national level which was conducted more than 20 years

ago by DID/JICA (Abdullah, 1982), had shown that Malaysia as a whole has abundant water

resources and only 3% of the runoff is suffice to meet present water demand. Yet, there are

consistent problems of water shortage due to insufficient approach in sustainable

development of water resources. Low flow and high/flood flow analyses had been well­

documented in several water resources projects locally. However, what is lacking currently is

an integrated-form of those data that can be "plug-and-play" by stakeholders. The significant

of this project is therefore to develop an interface-b~sed framework to support decision

making.

1.2 Objectives

a) To develop a mechanism (by regionalization) that can estimate flooding frequency

from a river basin with the available hydrological data;

b) To develop a mechanism for storing excess storm water which could be utilized

during dry season; and

3

,c) To develop an interface for integrated framework for Sungai Sarawak basin.

1.3 Organization of Report

The flow of this report is divided into seven chapters. The first chapter deals with the

background of study. Chapters 2 and 3 discuss the hydrological analysis of flow and rainfall

that would lead to regionalization methods. Chapter 4 reports on high fl'ow while chapter 5 on

low flow. Chapter 6 includes the interface development of a logical framework strategy.

Chapter 7 conclUdes the findings.

4

Punt Kbidmlt Makin tAt emik UNlVD.SITJ WALAYSrA SAltAWn

9 .. 300 Kot. Saawaban

CHAPTER 2

REGIONAL ANALYSIS BASED ON FLOW

2.1 Overview

The State of Sarawak, with an area of 124 450 km2 is the largest state of Malaysia. There are

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 problem such as 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 remain as one of the major problem to

accurately estimate the design floods.

It is well accepted that regionalization technique is a very helpful technique in estimating

parameters in hydrology compensating for the lack of long hydrological time series and the

lack of information. As a guidelines to determine the magnitude and frequency of floods in

Peninsular Malaysia, the Department of Drainage and Irrigation (DID) of Malaysia had

published a hydrological procedure called Hydrological Procedure No 4 (HP4) (Ong, 1987).

The procedure was based on the regional frequency analysis method used by the Natural

Environmental Research Council (NERC, 1975). In NERC method, the flood frequency

analysis of individual station flood data was determined using Gumbel distribution and the

theoretical fits was determined by the method of L-Moments. The plotting position of each

samples were calculated using the Weibull formula. However, Cunnane (1978) had studied

various plotting position methods using the criteria of unbiased ness and maximum variance.

He found that the Weibull plotting position formula was biased and plots the largest values of

a sample at too small a return period. He said, for data distributed according to the Extreme

Value Type I distribution (or Gumbel distribution), the Gringorten formula (b =0.44) was the

best.

No such procedure had been developed for Sabah and Sarawak but there was a prior

research on regional flood estimation for ungauged basins in Sarawak by Lim and Lye (2003).

They had examined the flood records in Sarawak using an index-flood estimation procedure

based on L-moments technique. They adopted four-parameter Kappa distribution to simulate

the flood data. From the simulation, they obtained two homogeneous flood frequency regions.

The two regions (Region A and Region B) were described by the Generalized Extreme Value

5

and the Generalized Logistic distributions. Subsequently, they had developed a regional

growth curve for each of regions in Sarawak. The classification is seemed too broad to

accurately estimate the design floods in Sarawak. This study was an attempt to refine the

classification that had been done by Lim and Lye (2003). The refinement was done based on

another regionalization technique on the recorded flow data in Sarawak. Methodology wise,

this study was the same with the existing literature for Peninsular Malaysia. It gave emphasis

on Gumbell distribution for the construction of its regional dimensionless flood frequency

curves.

2.2 Flow Data

Data for analysis were extracted from DID of Sarawak. A total of 19 sample flow-recording

stations had been selected for the analysis. The selection was based on the criteria stated in

HP4. Details of the selected data and the approximate location of the 19 selected stations

are as shown in Table 2.1 and Figure 2.1 (extracted from Sarawak Hydrological Year Book

Series (SHYB».

Table 2.1: Selected River Flow Stations

Index Station No. Station Name Latitude (D,M,S)

Longitude (D,M,S)

Elevation (m)

1 1301426 Boring 001 2321 1100639 0

2 1301427 Buan Bidi 001 2354 1100646 67

3 1302428 Kpg Git 001 21 20 110 1550 1

4 1204441 Kpg Ma'ang 001 1554 1102433

5 1304439 Batu Gong 001 2046 1102623 4

6 1004438 Krusen 001 04 11 1102952 3

7 1005447 Meringgu 001 0300 11033 10

8 1114422 Entulang 001 0900 111 2535

9 1210401 Tuba 001 1750 1100450

10 1018401 Lubuk Antu 001 0235 111 4935 21

11 1415401 Nanga Lubau 001 2950 111 3520

12 1813401 Sebatan 001 4815 111 2000 1

6

13

14

15

16

17

18

19

1932408

2130405

2421401

3152408

4448420

1108401

3946411

Telok Buing

Nanga Benin

Stapang

Lio Matu

Nanga Insungai

Sabal Kruin

Long Terawan

001 5950

0020955

0022400

003 10 10

0042400

001 0835

0035935

113 1320

1130410

1120805

115 1320

1145330

1105335

1143750

-

0

0

-

-

--

Figure 2.1: Location of the Riv~r Flow Gauges Selected in the Study

R8W data from DID was in water level form. These values were then converted into

cllcharg., Q by using the discharge rating curve established by DID. After the conversion,

the annual extreme series were arranged in descending order of magnitude. Then the

lrithmetic mean of the annual flood series was calculated. After that, the plotting position of

each sample was determined. In this study, three plotting position formula were applied onto

the samples. The three plotting position formula were Weibull formula, Gringorten formula

and L-Moments method. As to construct the Gumbel distribution by L-Moment method with

Q,lMAF as the y-axis and Gumbel reduced variate (y) as the x-axis, a calculation of L­

7

Moments parameters in a Fortran Programming form was needed. The parameters and

nsauIts from the programming were then used as the inputs for the calculations of Gumbel

reduced variate, y.

The values of annual peak discharge over the arithmetic mean of the annual flood series,

QlMAF or QT/AMAF were then plotted against the reduced variate, y. Finally, regional

dimensionless flood-frequency curve of each individual station was constructed. Then, a

comparison of Gumbel distribution by the three plotting positions was made.

203 Results and Analysis

This section presented the results and analysis of Gumbel distribution for one of the

individual station (Le. Station Boring) using Weibull formula, Gringorten formula and L­

Moments method. The calculation of flood frequency curve for Stations Boring using Gumbel

distribution (Weibull formula) is as tabulated in Table 2.2. Summary of Gumbel distribution

from the three methods for Station Boring is as shown in Table 2.3. The results were utilized

to produce the probability plot and flood-frequency curves for Stations Boring. Figure 2.2

illustrates the probability plot and flood frequency curve of Gumbel distribution using Wei bull

formula for Station Boring. Illustration of the probability plot and flood-frequency curve of

Gumbel distribution of the station using Gringorten formula is as shown in Figure 2.3. The

flood-frequency curve of the station by L-Moments method is shown in Figure 2.4. The

discharge and reduced variate (y) data shown in Table 2.3 when plotted together in one

graph enabled comparison of the three plotting pOSition methods (see Figure 2.5).

Results and analysis had consistently shown that Gumbel distribution plots with the

Gringorten formula lied in between the Gumbel distribution plot with Weibull formula which

gave the highest discharge and the Gumbel distributi0!1 plot with L-Moments method which

gave the lowest discharge. Some literatures had stated that regionalization techniques work

best with L-Moments, but if used with Gumbel distribution as demonstrated here, the results

were not consistent. Thus, Gringorten formula was recommended to be used to determine

flood frequency and magnitude in Sarawak.

8

Table 2.2: Example of Frequency Analysis of Individual Station Boring

Station No : 1301426

Station Name : Boring (Sg.Pedi)

River: Sg. Pedi

Basin: Sungai Sarawak

Zero of Gauge : 9.98 m M.S.L.

Type of Gauge: Stick gauge

B.M. Value : 19.92 m M.S.L. Rating Curve

Formula : 0 = 7.44 ( H - 0.92) A 1.81 Effective Range of

Rating Curve Formula: 1.29 - 3.69 m

Catchment's Area : 124.5 sq.km.

Weibull

V_ 1870

1871

1872

1973

1974

1975

1976

1977

1178

I: l;1I81

tI82-I 1884 1_,. 1887 -tl881. ,. 1891t_ 1183 t. t. tlll6

1887

Date

5-Nov

9-Jan

23-Jan

2~

1-Mar

24-Oec

12.Jan

&-Feb

24-Jan

27-Dec

22.feb

7·Feb

2-Mar

25-Jan

6-Mar

4-Mar

7.Jan

24-Dec

6-Oec

14-Oec

11·Feb

29.Jan

19-Jan

16-Mar

24-Jan

25-Dec

7·Feb

2O-Feb

Max. WL (Reading above zero of Records from incomplete

gauge In metre), H years is indicated with #

7.31

9.75

9.45

9.20

8.93

10.36

10.06

0

213.56

383.50

360.24

341.36

321.48

432.79

408.21

,i!Sorted ,\ i Oi IMAF= 291.86 1 T OT

1 487.34 29.00 487.34

2 432.79 I 14.50 432.79

3 408.21 9.67 408.21

4 383.50 7.25 383.50

5 373.34 5.80 373..34 I

6 371 .79 4.83 371 .79

7 369.46 4.14 369.46 I

9.60 371 .79 8 360.24 3.63 360.24 II

8.96 323.66 9 353.39 3.22 353.39

8.05 260.41 10 341.36 2.90 341 .36

7.92 251 .88 11 327.31 2.64 327.31

9.57 369.46 12 326.58 I 2.42 326.58 ,

9.01 327.31 13 323.66 2.23 323.66

11 .00 487.34 14 321.48 2 .07 321 .48

9.00 326.58 15 271.76 1.93 271 .76

8.02 258.43 16 260.41 1.81 260.41

9.62 373.34 17 258.43 1.71 258.43

7.67 235.84 18 255.81 1.61 255.81

8.22 271 .76 19 1 251 .88 1.53 251 .88

9.36 353.39 20 235.84 1.45 235.84 'I

6.67 176.43 21 225.82 1.38 225.82

6.32 157.47 22 213.56 1.32 213.56

7.98 255.81 23 203.39 1.26 203.39

6.47 165.48 24 183.72 1.21 183.72

7.14 203.39 25 176.43 1.16 176.43

5.81 131.59 26 165.48 1.12 165.48

7.51 225.82 27 157.47 1.07 157.47

6.80 # 183.72 28 131 .59 1.04 131.59

Station closed on May 1997 8172.04

Qr/MAF 1\1 'J

1.670 II 3.350

1.483 2.639

1.399 2.215

1.314 1.908

1.279 1.665

1.274 1.462

1.266 1.286 ,

1.234 1.131

1.211 0.990

1.170 0.861

1.121 0.740

1.119 0.627

1.109 0.520

1.101 0.417

0.931 0.317

0.892 0.220

0.885 0.125

0.876 0.031

0.863 -0.063,

0.808 ·0.157

0.774 ·0.253

0.732 -0.352

0.697 -0.455

0.629 ·0.564

0.605 1-0 .684

0.567 -0.819

0.540 -0.984

0.451 -1.214

9

Table 2.3: Results of Gumbel Distribution for Station Boring by WeibuU Formula, Gringorten Formula and L-Moments Method

Euler I 0.577

Ln 2 0.693

Weibull (1939) Gringorten (1963) Lamda 1 291.859 I

Lamda 2 -33.345

Alpha 48.106

Epsilon 264.091

QT/MAF Discharge YLM F(x) TLM

1.670 50.21 3.906 1.670 487.340 4.641 0.990 104.124

1.483 18.03 2.863 1.483 432.790 3.507 0.970 33.844

2.215 1.399 10.98 2.349 1.399 408.210 2.996 0.951 20.507

1.908 1.314 7.90 2.000 1.314 383.500 2.482 0.920 12.475

1.665 1.279 6.17 1.732 1.279 373.340 2.271 0.902 10.198

1.462 1.274 5.06 I 1.513 1.274 371.790 2.239 0.899 9.891

1.286 1.266 4.29 1.326 1.266 369.460 2.190 0.894 9.448

1.131 1.234 3.72 1.161 1.234 360.240 1.999 0.873 7.891

0.990 1.211 3.29 1.013 1.211 353.390 1.856 0.855 6.91

0.861 1.170 2.94 0.878 1.170 341 .360 1.606 0.818 5.501

0.740 1.121 2.66 0.753 1.121 327.310 1.314 0.764 4.244

0.627 1.119 2.43 0.636 1.119 326.580 1.299 0.761 4.188

0.520 1.109 2.24 0.525 I 1.109 323.660 1.238 0.748 3.974

1.101 2.07 0.418 II 1.101 321.480 1.193 0.738 3.822

0.931 1.93 0.316 0.931 271.760 0.159 0.426 1.743

0.892 1.81 0.216 0.892 260.410 -0.077 0.340 1.515

0.885 1.70 0.118 0.885 258.430 -0.118 0.325 1.481

0.876 1.60 0.021 0.876 255.810 -0.172 0.305 1.439

0.863 1.52 -0.076 0.863 251.880 -0.254 0.276 1.380

0.808 1.44 -0.173 0.808 235.840 -0.587 0.165 1.198

0.774 1.37 -0.273 0.774 225.820 -0.796 0.109 1.122

-0.352 0.732 1.30 -0.375 0.732 213.560 -1.050 0.057 1.061

-0.455 0.697 1.25 -0.483 0.697 203.390 -1 .262 0.029 1.030

-0.564 0.629 .19 -0.598 0.629 183.720 -1 .671 0.005 1.005

-0.684 0.605 1.14 -0.726 0.605 176.430 -1.822 0.002 1.002

-0.819 0.567 1.10 -0.874 I 0.567 165.480 -2.050 0.000 1.000

-0.984 0.540 1.06 -1.062 0.540 157.470 -2.216 0.000 1.000

-1.214 0.451 1.02 -1.365 0.451 131 .590 -2 .754 0.000 1.000

10