FLOODPLAIN AND HYDRAULIC INFRASTRUCTURE SYSTEM MODELING FOR

INTERGRATED FLOOD MANAGEMENT

Hii Ching Poon

Doctor of Philosophy 2010

I Pusa, 'dmat ~ akJumat . k UNlVERSm MALAy 'J ,.

FLOODPLAIN AND HYDRAULIC INFRASTRUCTURE SYSTEM MODELING FOR INTEGRATED FLOOD MANAGEMENT

P.KHIDMAT MAKLUMAT AKADEMIK

1llIllllIlli'rn 111111111 1000246294

HII CHING POON

A dissertation submitted in fulfilment of the requirements for the degree of

Doctor of Philosophy

Faculty of Engineering . UNIVERSITI MALAYSIA SARA W AK

2010

I ,

Acknowledgements

I wish to acknowledge with deepest gratitude the guidance and

encouragement provided throughout the course of this research project by my

supervisors, Professor Ir. Dr. Frederik Josep Putuhena and Professor Dr. Salim

Said. I am very grateful of their ideas, feedbacks, comments and mentorship

throughout the journey of the study. I would like to thank UNlMAS, the Faculty of

Engineering and the Center of Graduate Studies for the opportunity, assistance and

arena to conduct this applied research.

I am also indebted to the academic, secretarial and technical staffs of

the Department of Civil Engineering for their kind help, in particular Dr. Darrien

Mah Yau Seng for his assistance and invaluable advice for the hydrological and

hydraulic modeling works.

The research was only made possible due to generous support from the Director of

State Planning Unit, State Secretary Sarawak and other government departments

and agencies for their assistance provision of research materials for which the

author is grateful. I have benefited from the suggestions and comments provided by

the Natural Resources and Environmental Board Sarawak (NREB), Jabatan Kerja

Raya Sarawak (JKR) , Jabatan Pengairan dan Saliran Sarawak (JPS) , Sarawak

Rivers Board (SRB) and Captain Goh Chin Guan from Kuching Barrage

Management Sdn Bhd.

Finally, I wish to express my earnest thanks to Rolin and Madelyn,

wonderful parents, brothers and sisters for their love, encouragement, patience,

and unwavering support throughout the journey to completion of my PhD study.

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Abstract

en recent years, river floods in Sarawak River seemed to occur more frequently and

had been causing more and more economic and social damages. One of the greatest

deficiencies of the current flood management system for Sg. Sarawak basin is its

inadequate optimization of the existing structural measures. This optimization may

be achieved by application of some of the models and the framework developed

recently for enhancement of participation of various local stakeholders in flood

management.)

Hydrological simulations had been conducted and carried out using HEC-HMS for

Sg. Sarawak catchment. The model was calibrated and validated using years 1976

and 2000 flood events. The rainfall - runoff hydrographs generated from calibration

and validation processes showed Nash-Sutcliffe values of 0.78 and 0.71,

respectively. Sensitivity analysis was perfonned to examine the impacts of the three

parameters, namely, initial loss, constant loss and lag time parameters on the HEC­

HMS hydrological model. The analysis revealed that the initial loss parameter acted

as the most sensitive parameter with respect to peak flow and total runoff volume.

It was also found that an increase in constant loss could result in a lower peak,

while the lag time was the most sensitive parameter with respect to peak time. ~ .

However, lag time parameter was found to be the least sensitive among the three

parameters tested.

The calibrated hydrological model was then used as inflow hydrographs in

InfoWorks RS model. Two hydraulic models, namely, Pre-barrage Sg. Sarawak

Model and Post-barrage Sg. Sarawak Model were developed, calibrated and

validated by modifying Manning's n values corresponding to field observations.

. " . 111

Years 1976 and 2000 flood events were used for calibration and validation purposes,

and showed to have an accuracy of approximately 90% for both processes.

Sensitivity analysis was carried out to investigate the impact of Manning's n on the

water levels. Manning's n sensitivity was tested using values ranging from 0.025 to

0.055. The results revealed that the peak water level was not sensitive to Manning's

n values. The hydraulic model was intended to integrate the existing flood

mitigation structures available in Sg. Sarawak Basin.

Two Scenarios: 1) Sarawak River basin-wide modeling and 2) Flood Bypass Channel

modeling were carried out using the models developed for this research to

investigate the performance of the existing flood mitigation measures in Sg.

Sarawak basin. The results revealed that the existing structure, Sg. Sarawak

barrage was able to trim down the backwater due to King Tide or the flood flow from

the upstream. However, the barrage had insignificant on water level during king

tide and flood event. The modeled results were used in Logical Framework Analysis

to look into the possible alternatives that may help reduce the damage. The

outcomes of this study showed that the existing condition could be significantly

improved once the Flood Bypass Channel and Early Flood Warning System are

constructed.

Flood Bypass Channel modeling was carried out to determine the impact of the

proposed alternatives on the existing conditions of Sg. Sarawak Basin. In this

scenario, a flood bypass channel and an additional barrage are proposed to divert

the excess flood water from Kuching City in the event of severe flood. It was shown

that flooding problems in Kuching can be significantly reduced. However, the areas

located upstream of Kuala Maong could still be subjected to flooding. Early Flood

Warning system could be provided to evacuate the floodplain dwellers before severe

floods strike. An analytical logical framework for Early Flood Warning System IS

presented in this dissertation.

The models and methods developed in this study are flexible and easy for Sg.

Sarawak Basin. In this research, both the feasibility of and effectiveness in

incorporating the premise of the combined technical information and institutional

setup in flood management are addressed.

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Abstrak

Sejak kebelakangan ini, bencana banjir di lembangan Sungai Sarawak semakin

kerap dan membawa kerugian ekonomi and sosial kepada penduduk dan kerajaan

tempatan. Salah satu kekurangan besar sistem pengurusan banjir yang wujud di

lembangan Sg. Sarawak adalah kekurangan sistem yang dapat mewujudkan

prestasi optimum bagi struktur-struktur yang terbina. Keadaan optimum ini dapat

dicapai melalui model yang dibangunkan dan rangka pengurusan yang

menggalakkan penyertaan berbagai pihak berkepentingan.

Simulasi hidrologi telah dijalankan dengan menggunakan HEC-HMS. Model yang

digunakan telah ditentukur dan disahihkan dengan menggunakan data berasal

daripada banjir tahun 1976 dan 2000. Hidrograf yang dihasilkan melalui proses

penentukuran dan pengesahan menunjukkan nilai Nash-Sutcliffe 0.78 dan 0.71

masing-masing. Analisis kepekaan parameter telah diadakan untuk menguji kesan

dan tindakbalas parameter seperti "initial loss", "constant loss" dan "lag time" ke

atas model yang dibangunkan. Keputusan analisis menunjukkan "initial loss"

merupakan parameter yang amat sensitive kepada air larian puncak dan jumlah

isipadu air larian. Peningkatan "constant loss" boleh menurunkan puncak air larian.

IrLag time" memberi kesan sensitif kepada parameter tempoh ke puncak hidrograJ

Manakala, "lag time" merupakan parameter yang kurang sensitif berbanding dengan

parameter yang lain.

Model hidrologi yang ditentukur telah digunakan untuk menghasilkan hidrograf

sebagai input kepada model hidraulik, Info Work RS. Dua model hidraulik telah

dibangunkan, iaitu, sebelum baraj Sg. Sarawak dan selepas baraj Sg. Sarawak.

Model-model ini telah ditentukur dan disahihkan dengan mengubahsuaikan nilai

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Manning's n yang dikaitkan kepada tinjauan lapangan. Data danpada banjir tahun

1976 dan tahun 2000 telah digunakan untuk tujuan pentukuran dan pengesahan

bagi model hidraulik. Keputusan menunjukkan 90% ketepatan bagi kedua-dua ujian.

Analisis kepekaan parameter juga telah diadakan ke atas parameter Manning's n

untuk mengkaji kesannya ke atas aras air. Manning's n dalam julat 0.025 - 0.055

telah diuji. Keputusan menunjukkan nilai puncak paras air kurang sensitif kepada

parameter Manning's n. Model hidraulik yang telah ditentukurkan mengintegrasikan

struktur tebatan banjir yang sediada di lembangan Sungai Sarawak.

Dua senano, iaitu, 1) Permodelan lembangan Sungai Sarawak dan 2) Premodelan

labJ.an pintasan banjir telah dilaksanakan dengan menggunakan model-model yang

dibangunkan untuk menyiasat prestasi struktur-struktur tebatan banjir yang wujud

di lembangan Sungai Sarawak. Keputusan permodelan menunjukkan baraj Sungai

Sarawak dapat mengurangkan kesan air prasang atau air lanan dan hulu Sungai

Sarawak. Namun, baraj Sungai Sarawak memben kesan kecil semasa banjir dan

pasang-surut berlaku. Keputusan danpada permodelan telah digunakan dalam

an a lis is rangka logik untuk menyiasat altematif-alternatif yang dapat

mengurangkan kerosakan yang dibawa oleh banjir. Keputusan permodelan

mendedahkan bahawa keadaan yang ada dapat dipertingkatkan jikalau laluan

pintasan banjir dan sistem amaran awal banjir dapat dibekalkan.

Permodelan laluan pintasan banjir telah dijalankan untuk mengkaji keberkesanan

alternatif tersebut kepada lembangan Sungai Sarawak. Dalam senano ini, laluan

pintasan banjir dan sekatan sungai telah dibekalkan untuk memintaskan air banjir

berasal dan hulu Sungai Sarawak jauh dan bandar Kuching semasa banjir.

Keputusan menunjukkan masalah banjir di Kuching dapat dikurangkan. Kawasan

yang terletak di hulu Kuala Maong masih berada dalam nsiko banjir. Sistem amaran

1

banjir harus dibekalkan untuk mengeluarkan penduduk yang tinggal dalam

kawasan tersebut. Rangka logik analitikal bagi sistem amaran awal banjir telah

dibangunkan.

Model-model dan prosedur yang dibangunkan dalam penyelidikan ini adalah

fleksibel dan mudah digunakan di lembangan Sungai Sarawak. Melalui penyelidikan

yang dilaksanakan, kebolehlaksanaan dan keberkesanan dalam menyatukan

maklumat teknikal dan instituisi dalam pengurusan banjir telah dibuktikan.

P sat Khidmat 1 kJum Akadtmik UNlVE m 1 LAY f • A WAf(

Table of Contents

Acknowledgements Abstract Abstrak Table of Contents List of Figures List of Tables List of Appendices List of Abbreviations

CHAPTER 1 INTRODUCTION

1.1 Background 1.2 Integrated Flood Management 1.3 Flooding Problem in Sarawak 1.4 Challenge of Applying Flood Model in Practice 1.5 Research Objectives 1.6 Research Hypothesis 1. 7 Structure of Dissertation

CHAPTER 2 LITERATURE REVIEW

2.0 Sungai Sarawak Basin and Kuching City 2.1 Flood Modeling of Sungai Sarawak 2.2 Flood Management for Integrated Water Resources

Management 2.3 Logical Framework Analysis 2.4 Interactive Multiobjectives Modeling of Discrete Decisions

in Water Resources Planning 2.5 Adaptive Management

CHAPTER 3 METHODOLOGY

3.1 Introduction 3.2 Hydrological Model Development 3.3 Hydraulic Model Development 3.4 Logical Framework Development

CHAPTER 4 RESULTS AND DISCUSSION

4.1 Introduction 4.2 Hydrological Model Calibration and Validation 4.3 Hydraulic Model Calibration and Validation 4.4 Logical Framework Analysis 4.5 Sarawak River Basin - Wide Modeling 4.6 Flood Bypass Channel Modeling 4.7 Sub-logical Framework Development

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III

VI

IX

Xl

XlII

xiv xv

1

1 1 4 7 9 9 11

12

12 31 61

69

71 72

76

76 76 84 85

93 93 106 120 132 134 138

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4.8 Summary of Findings 142 I' I

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 143 I'

5.1 Concl usions 143I, 5.2 Recommendations 145

References 146

--List of Figures

Page Figure 1.1 Flood-prone Areas in the State of Sarawak 7 Figure 2.1 Sg. Sarawak Catchment 13 Figure 2.2 Satellite Imagery of Sg. Sarawak System and Kuching City 17 Figure 2 .3 Mangrove Forest Reserves - Bako Area 17 Figure 2.4 A Comparison of Sg. Sarawak Bed: 1986 versus 1993

(Upstream of Barrage to Confluence - approximately 32km) 19 Figure 2.5 Comparison of Sungai Sarawak Bed Levels for Years 1986

and 2000 ( From River Mouth to Buan Bidi of Sg. Sarawak Kanan) 20

Figure 2 .6 Comparison of Sungai Sarawak Bed Levels for Years 1986 and 2000 (From River Mouth to Kpg. Git of Sg. Sarawak Kiri) 21

Figure 2.7 Location of Batu Kawa Urban Centre 27 Figure 2.8 Topographical map of Batu Kawa Urban Centre 28 Figure 2.9 Existing drainage system of Batu Kawa Urban Centre 29 Figure 2.10 Cadastral Plan of Batu Kawa Urban Centre 30 Figure 2.11 Local Scale Watershed Runoff Process 40 Figure 2.12 HEC-HMS Representation of Catchment Runoff 41 Figure 2.13 Simulated Maximum Inundation of Sg. Maong Catchment

for Flood Event in January 2000 49 Figure 2.14 Inundation of Bau Police Station 50 Figure 2.15 Simulated Maximum Inundation of Sg. Sarawak Kanan

Catchment for Flood Event in February 2003 53 Figure 2.16 Batu Kitang Submersible Weir 54 Figure 2.17 Typical Logframe Matrix Structure 71 Figure 2.18 Flowchart of Planning Setup including Competing

Decision- Makers 73 Figure 2.19 Logical Framework Approach with Adaptive Management

cycle 75 Figure 3.1a Flowchart of Hydrological and Hydraulic modeling and

Planning Framework Setup 77 Figure 3.1b Flowchart of Hydrological and Hydraulic modeling and

Planning Framework Setup 78 Figure 3.2 Basin model of HEC-HMS model 81 Figure 3.3 Basic Logical Framework Layout 85 Figure 3.4 Cause and Effect of Framework Link 86 Figure 3 .5 Problem Tree 87 Figure 3.6 Objective Tree 90 Figure 3.7 Options Tree 91 Figure 4.1 1976 Flood Event's Storm Hyetograph 94 Figure 4.2 2000 Flood Event's Storm Hyetograph 95.' Figure 4.3a Measure vs Modeled storm events for Year 1976 101 Figure 4.3b Measure vs Modeled storm events for Year 2000 Flood 102 Figure 4.4 Sensitivity Analysis for Peak Flow, Peak Time and Total

Volume for Initial Loss Parameter 103 Figure 4.5 Sensitivity Analysis for Peak Flow, Peak Time and Total

Volume for Constant Loss Parameter 104 Figure 4 .6 Sensitivity Analysis for Peak Flow, Peak Time and Total

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Volume for Lag Time Parameter 104 Figure 4.7 Sg. Sarawak Network Developed in InfoWorks RS 107 Figure 4.8 Property Tool Showing Cross-Section of Sg Sarawak using

InfoWorks RS 108 Figure 4.9 Flow Time Boundary for Inflow Point 111 Figure 4.10 Stage Time Boundary for Downstream Point 111 Figure 4.11 Property Sheet Showing the Operating Rules of Sluice Gate 112 Figure 4.12 Property Sheet Showing the Geometry and Gate 112 Figure 4.13 InfoWorks Simulation Controller 114 Figure 4.14 Comparison of Measured and Modeled Water Levels at

Batu Kawa Bridge in January 1976 117 Figure 4.15 Comparison of Measured and Modeled Water Levels at

Batu Kitang Bridge in January 1976 117 Figure 4.16 Comparison of Measured and Modeled Water Levels at

Batu Kawa Bridge in January 2000 118 Figure 4.17 Comparison of Measured and Modeled Water Levels at

Batu Kitang Bridge in January 2000 118 Figure 4.18 Comparison of Measured and Modeled Water Levels at

Batu Kitang Bridge 119 Figure 4.19 Comparison of Measured and Modeled Water Levels at

Batu Kawa Bridge 120 Figure 4.20 Sarawak River Basin - Wide Flood Map 133 Figure 4 .21 Simulated Flood Map for Flood Bypass Channel Modeling

Scenario 136

I­List of Tables

Page Table 1.1 Summary of Flood-Prone Areas in Sarawak 5 Table 2.1 Flood Historical Flood Levels 25 Table 2.2 Limitations of Models used in HEC-HMS 44 Table 2.3 GIS Operations Supportive of Surface Water Modeling 55 Table 2.4 Surface Water Hydrology Model 59 Table 2.5 Floodplain Hydraulic Software with GIS 60 Table 2.6 Level of Coverage of Aspect of IFM 68 Table 3.1 List of Stakeholders 88 Table 3.2 Category of Interactive Multiobjectives Decision-Making 89 Table 4.1 Initial - Constant Loss Model Parameters 96 Table 4.2 Lag Times Parameters for HEC-HMS 96 Table 4.3 Exponential Recession Model 97 Table 4.4 Hydrologic Routing Model 97 Table 4.4a Summaries of Calibration and Validation Statistics for HEC-

HMSModel 99 Table 4.5 The Storm Events used Sensitivity Analysis 103 Table 4.6 Summaries of Calibration and Validation for Statistic Hydraulic

Model 116 Table 4.7 Alternative Analysis 123 Table 4.8 Indicators and Mean of Verification 127 Table 4.9 Logical Framework Matrix for Sungai Sarawak Integrated

Flood Management 129 Table 4.10 Predicted of Rising and Spreading Rate of Floodwaters from Sg.

Sarawak 137 Table 4.11 Sub-Logical Framework of Sarawak River Integrated Flood

Management 140

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List of Appendices

Page

Appendix A Description of Data Used in Modeling 158 Appendix B Summary of Publications 181

List of Abbreviations

APFM

DID

DEM

GIS

GeoHMS

GWP

HEC

HMS

HYDSIS

IFM

InfoWorks RS

IWRM

IWRC

IRBM

KURS

LFA

Logframe

LUAS

MASMA

MAFR

MMS

NERC

NGO

NREB

RAMSAR

SRSS

SPU

SRB

USACE

WA

WMO

Associated Programme on Flood Management

Department of Irrigation and Drainage (JPS)

Digital Elevation Model

Geographical Information System

GIS Incorporated HMS

Global Water Partnership

Hydrologic Engineering Center

Hydrological Modeling System

Hydrological System

Integrated Flood Management

InfoWorks River Simulation

Integrated Water Resources Management

Integrated Water Resources Council

Integrated River Basin Management

Kuching Urban and Regional Study

Logical Framework Approach

Logical Framework

Lembaga Urus Air Selangor

Malaysian Stormwater Management Manual

Mean Annual Flood Region

Malaysian Meteorological Service

Natural Environmental Research Council

Non Government Organization

Natural Resources and Environmental Board

International treaty for the conservation and sustainable utilization of wetlands

Sungai Sarawak Regulation Scheme

State Planning Unit

Sarawak River Board

U.S. Army Corps of Engineers

Water and River Commission

World Meteorological Organization

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CHAPTER 1

INTRODUCTION

1.1 Background

River basins are the ultimate source of water and the receptor of most wastewater.

Moreover, river basins have important non-consumptive uses, such as recreation,

nature, shipping and hydropower production. River basins are being used ever

more intensively than before. In most of the river basins, human activities have

been reaching the maximum sustainable level or have already surpassed this level.

Conflicts between different water uses, and between upstream and downstream use

are increasing. Many basins are overexploited and the capacity to meet the different

social demands is decreasing. The situation has been worsened with the occurrence

of more frequent floods in recent years than before that had incurred substantial

losses to human life and properties. A new integrated approach that takes into

account the interest of and needs of various stakeholders and natural system is in

urgent need to alleviate these problems.

Basic elements of the approach shall include a basin-wide scope; attention to the

different forms (surface and groundwater) and aspects (quantity, quality) of water;

attention to the relations between land and water resources; and the integration of

natural limitations, social and economic demands, and legal, political and

administrative processes (Teclaff, 1985; Lundqvist et aI., 1985; Newson, 1992; Lee,

1999; Molle, 2003).

1.2 Integrated Flood Management

Integrated Water Resources Management (IWRM) is a United Nations-initiated

paradigm for managing water resources in an international context, particularly in

developing nations. The IWRM can be defined as "a process which promotes the

coordinated development and management of water, land and related resources, in

order to maximize the resultant economic and social welfare in an equitable manner

without compromising the sustainability of vital ecosystems" (Global Water

Partnership, 2000). The IWRM is often supposed to deal with the shortcomings

associated with a fragmented approach in policies affecting water resources and its

management, which has been a prevailing characteristic of water management.

Malaysian Federal Government has set up the National Water Resources Council

(NWRC) in 1999 under the chairmanship of Malaysian Prime Minister to ensure

coordination of various stakeholders between Federal and State Government in the

management of river basins. The Selangor Waters Management Authority was

formed and supported by the Selangor Waters Management Authority Act (1999).

This authority is commonly known as LUAS (Lembaga Urus Air Selangor) and

became operational on 1st August 2000.

The LUAS was formed with the aim of adopting and implementing IWRM at the river

basin level within the State of Selangor, besides conserving coastal resources and

the environment. The LUAS becomes a management and an enforcement agency at

state level. In 2003, LUAS initiated a study on integrated catchment management of

Sungai Damansara that involved four local authorities, namely Petaling Jaya and

Subang Jaya Municipal Councils, and Kuala LumpuT and Shah Alam City Councils.

The study aimed to improve catchment management of Sungai Damansara by

addressing water quality issues and flash floods within the catchment. The study

incorporated the Malaysian Stormwater Management Manual (MASMA) in order to

control at source and additional runoff as result of project development

(www.water.gov.my).

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Integrated River Basin Management (IRBM) projects are being undertaken in two

river basins, namely Sungai Selangor and Sungai Kedah. These river basins were

chosen due to their different management practices; Sungai Selangor basin is

managed by LUAS acting as a single agency whilst Sungai Kedah basin is managed

by an inter-agency committee. Sungai Sdangor primarily serves the domestic and

industrial water supply sectors whereas Sungai Kedah primarily serves irrigation

sector.

As in the State of Kedah, Sarawak water resources are managed by various

agencies. Being the largest state in Malaysia, the land of Sarawak has a wide

network of perennial rivers. Most of the human settlements are concentrated on

river floodplains, Sibu and Sarikei towns are established on the bank of Batang

Rajang; Limbang town built next to Sg. Limbang, Lawas town situated next to

Batang Lawas and Kuching City on the bank of Sungai Sarawak. Due to their

geographical factors and rapid development, flood risk has became one of the major

threats among those settlements.

The IWRM and IRBM implemented in Peninsular Malaysia clearly lack defined

objectives for flood management. Most emphasis have been given in water, land and

related resources development and coordination. The occurrences of flood problems

at different temporal and spatial scales could increase the complexity of IWRM and

IRBM. There is a need to provide a sound scientific approach for the development

and implementation of supporting tools that can optimize the effectiveness of the

existing and proposed flood mitigation measures on the ground. In addition, the

approach shall be embedded with capabilities to model and to analyze the changes

in physical conditions (e.g. urbanization and climate change), economic

developments, management policy and measurement, and modelling technologies.

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Integrated Flood Management (IFM) integrates land and water resources

developments in a river basin, within the context of Integrated Water Resources

Management (IWRM), with a view to maximizing the efficient use of flood plains and

minimizing loss to life. Tbe primary aim of IFM is to put in place well-functioning

integrated measures for flood management.

To accomplish this, collaborative network among various relevant sectors becomes

very important. Thus, the most important key is the cooperation and co-ordination

across institutional boundaries, noting that the mandates of many institutions are

either to cover part of the river basin or to extend well beyond the basin boundary.

At the core of integration is effective communication across institutional and

disciplinary boundaries, which can take place only if there is a perception of

common interest (APFMjWMOjGWP, 2004).

A participatory approach includes a representative range of stakeholders in the

decision-making process. The degree of public participation can differ from region to

region. However, it should not be assumed that such stakeholder involvement will

necessarily result in a consensus. Therefore, a methodology for managing conflicts,

possibly a formal system of conflict resolution and technical supporting tools need

to be developed.

1.3 FloocliDg Problem in Sarawak

In Sarawak, flooding has been common and has brought about excessive damage

since last decade. Department of Irrigation and Drainage (DID) reported that about

13,400 sq. km. or about 10% of Sarawak total land are flood-prone and 494,000

4

Pu at Khid at [\: a umat it emik UNTVERSTT1 MALAY lA SARAWAK

people are dwelling on those areas. With areas subject to tidal inundation being

included, the total flood prone areas increase to 18,300 sq. km or 14.7% of total

land area of Sarawak. The tide inundated areas are estimated to be 4900 sq. km.

The distributions of the flood-prone areas by river basin in Sarawak are

summarized in Table 1.1.

Table 1.1 Summary of the Flood-prone Areas in Sarawak River Basin Catchment

Area (km2)

Flood Areas

(km2)

(%)

1 Lawas 1,070 II 28.60 2.7 I 2 Trusan 2,742 186.50 6.8 I

3 Limbang 3,978 II 261.75 6.6 I 4 Baram 22,325 4480.00 20.1 I

5 Miri 788 II 673.80 85.5 6 Sibuti 935 214.10 22.9 7 Niah 1,345 479.70 35.7 8 Suai 1,440 I 185.65 12.9 9 Simila,jau 1,268 17.00 1.3 10 Kemena 5,834 884.85 15.2 11 Tatau 5,008 698.45 13.9 12 Balingian 2,457 107.80 4.4 13 Mukah 2,562 I 179.70 7.0 14 Oya 2,209 396.70 18.0 15 Rajang 51,315 3034.10 5.9 16 Sadong 3,688 405.00 11.0 17 Sarawak 3,398 I 446.10 13.1 18 Kayan 1,838 180.05 9.8 19 Sri Aman 10,250 I 515.00 5.0

Total 124,450 II 13403.55 10.7 (Source: Keizrul, 2002)

The flood-prone areas in the State of Sarawak are illustrated in Figure 1.1 . Most of

the flood-prone areas are the estuaries, and low-lying riverbanks that are subjected

to frequent inundations. The average annual rainfall of Sarawak is about 3,800

mm. The wetter months are recorded from November to March during Northeast

monsoon season for coastal areas including Sungai Sarawak, Batang Samarahan,

Batang Sadong, Batang Rajang and Batang Baram. For the interior regions of

Batang Rajang and Batang Baram, floods are generally recorded from June to

September during Southwest monsoon.

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The coincidence of heavy rainfall with King Tide is generally perceiYed as

responsible event for the Sarawak historical extreme floods . These floods caused

serious problem in Sarawak in the past and shall continue in the coming decades.

In year 1963, 1976, 2000 2003, 2004 and 2009, Kuching City experienced rare

flood events which coincides with the king-tide that reached about 5.70 m MSL at

Batu Kawa along the Sungai Sarawak.

In 1997, the construction of the Su_ngai Sarawak Regulation Scheme (SSRS) was

completed, whereby both the Sungai Sarawak and Sungai Santubong were closed

with rock-filled causeways and the Sungai Sarawak flows were diverted through a

regulatory barrage constructed along a land isthmus just downstream of Kuching

City. Construction of barrage has largely stabilized the river water level in Kuching

at a level approximately midway between the former high and low tide elevations.

Some tidal affected areas are now permanently dry and available for development

(Sharp and Lim, 2000}. However, in years 2000, 2003, 2004 and 2009, the

Kuching City experienced rare flood events in a row which coincided with the king

tides in spite of Kuching Barrage in place to regulate the water level in Sg. Sarawak.

6

FLOOD PRONE AREAS OF SARAWAK

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"-<;>-' , " .. "." "" ,,­

--­

North East Monsoon (November-February)

(Sourced: DID)

Figure 1.1 Flood-prone Areas in the State of Sarawak

1.4 Challenge of Applying Flood Models in Practice

To engage in a successful flood modeling study, the researcher must not only

possess the requisite mathematical and systems methodology skills, but also an

understanding of environmental engineering, economic, political, cultural and

social aspect of planning implications (Daniel and Eelco, 2005). For instance, the

study of a flood mitigation project for an urban centre, one should be able to predict

how the proposed development will affect the quantity and quality of the surface

and subsurface runoffs, and the impacts on the community and ecosystem. Those

impacts might affect the proposed development or landuse downstream.

The clients are typically the planners and managers who would benefit from a better

understanding of what options they have and what impacts may result. Generally,

7

the aim of flood modelling analysis is to provide planners and managers with

meaningful, understandable, useful, accurate, reliable and timely information.

Those information serve to help them better understand the systems, problems, and

alternative ways to address them.

There is a gap between what researchers in flood modeling can produce and

publish, and what practitioner finds useful (Daniel and Eelco, 2005). Researchers

are naturally interested in developing new and improved tools and methods to

study, identify and evaluate alternatives flood mitigation options. If there are no

gaps between what is being developed and advocated by researchers actually used

by practitioners, either the research community would be very ineffective ill

developing new technology or the practitioners would be incredibly skilled In

assimilating, evaluating and adapting this research to meet their needs (Daniel and

Eelco, 2005). Evaluation, testing and inevitable modifications take time. Not all

published researches are ready or suited for implementation. Some research

outcomes or data are useful and yet some are not. It is a work in progress.

The other challenges include 1) How researchers can reduce the time required for

new ideas and approaches to be used in practice?, and 2) Will some new models or

computer programs facilitate the practitioners to carry out their responsibilities?

Practitioners are likely to accept new idea and .modeling approaches if it will

improve the performance of their works as well as help them address problems they

are trying to solve. Successful use of the information derived from the models or

programs is the ultimate test of the value of those tools.

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