BACKWATER EFFECT AT SUNGAI MAONG KIRI

Basil Anak Benjamin

Bachelor of Engineering with Honours

(Civil Engineering)

2008

Faculty of Engineering

UNIVERSITI MALAYSIA SARAWAK

BORANG PENGESAHAN STATUS TESIS

Judul: BACKWATER EFFECT AT SUNGAI MAONG KIRI

SESI PENGAJIAN: 2008/2009

Saya, BASIL ANAK BENJAMIN_____________________

(HURUF BESAR)

mengaku membenarkan tesis * ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti

Malaysia Sarawak dengan syarat-syarat kegunaan seperti berikut:

1. Tesis adalah hakmilik Universiti Malaysia Sarawak.

2. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat

salinan untuk tujuan pengajian sahaja.

3. Membuat pendigitan untuk membanguankan Pangkalan Data Kandungan Tempatan.

4. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat

salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi.

5. ** Sila tandakan (√) di kotak yang berkenaan.

SULIT (Mengandungi maklumat yand berdarjah keselamatan atau kepentingan Malaysia

seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972).

TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di

mana penyelidikan dijalankan).

TIDAK TERHAD

Disahkan oleh

_________________________ ___________________________ (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA)

Alamat tetap: No. 1345 Lorong Bayor, DR. ONNI SUHAIZA BINTI SELAMAN

Bukit No. 8, Nama Penyelia

Tabuan Jaya, 93350 Kuching,

Sarawak.

Tarikh: 8 JUN 2009 Tarikh: 8 JUN 2009

CATATAN * Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah, Sarjana dan Sarjana Muda

** Jika tesis ini SULIT dan TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi

berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai

SULIT dan TERHAD.

The Final Year Project Report as follow:

Title: Backwater Effect at Sungai Maong Kiri

Author: Basil Anak Benjamin

Matric: 13800

is hereby read and approved by:

_________________________________ 8 JUNE 2009

Dr. Onni Suhaiza Selaman Date

Project Supervisor

BACKWATER EFFECT AT SUNGAI MAONG KIRI

BASIL ANAK BENJAMIN

A dissertation submitted to

Faculty of Engineering, University Malaysia Sarawak

in partial fulfillment of the requirement for the

Degree of Bachelor of Engineering

With Honours (Civil Engineering)

2009

ii

Dedicated To

my beloved family, friends and lecturers

for your

….Tolerance

….encouragement

….help

iii

ACKNOWLEDGEMENT

In preparing this thesis, I was in contact with many government departments which

are Department of Irrigation and Drainage of Kota Samarahan and Marine Department

Sarawak. They have contributed towards all my data collection for this project.

In particular, I wish to express my deep and sincere appreciation to my main

research supervisor, Dr. Onni Suhaiza Selaman, for encouragement, guidance, critics

and friendship. I am also indebted to Universiti Malaysia Sarawak (UNIMAS) for

providing an accessible academic websites and journals.

I am also very thankful to my friends for their helping hands, guidance, advices and

motivation. Without their continued support and interest, the thesis would not have been

the same as presented here.

My sincere appreciation also extends to all my colleagues and others who have

indirectly provided assistance at various occasions. Their views and tips are useful

indeed. Unfortunately, it is not possible to list all of them in this limited space. I am

grateful to all my family members for their continuous support morally and financially.

iv

ABSTRAK

Sungai Maong Kiri adalah salah satu sungai di tadahan Sungai Sarawak yang

berkecenderungan mengalami masalah banjir disebabkan Sungai Maong Kiri adalah

kawasan yang dipengaruhi aliran pasang surut. Analisa air balik dijalankan untuk

mengkaji kapasiti Sungai Maong Kiri yang sedia ada sama ada masih mampu untuk

menampung kadaralir air yang merangkumi air larian dari kawasan tadahan di hulu

sungai dan kesan pasang surut di hilir sungai. Kesan air balik boleh menyebabkan

limpahan di saliran Sungai Maong Kiri yang sedia ada. Analisa hidrologik menggunakan

kaedah Rational dijalankan untuk mendapatkan purata kadaralir puncak dengan kala

kembali yang berbeza digunakan sebagai syarat sempadan hulu semasa analisa aliran

mantap. Aras tertinggi air pasang surut 6.4m dipilih sebagai syarat sempadan hilir. Data

aras air pasang surut tertinggi didapati daripada Jabatan Laut Sarawak. Analisa air balik

dijalankan menggunakan HEC-RAS 4.0 berkeadaan aliran mantap. Keputusan analisa

hidraulik telah menunjukkan bahawa Sungai Maong Kiri yang sedia ada mampu

menampung kadaralir daripada CH 0 ke CH 20000 tetapi terdapat limpahan air dari CH

25000 ke CH 30780. Untuk mengelakkan limpahan pada saliran sungai sedia ada dan

memenuhi piawai freeboard saliran terbuka, penghadang limpahan air yang setinggi

0.4m dan 0.6m telah dicadangkan untuk dibina pada kedua-dua belah tebing sungai

sepanjang CH 0 ke CH 30780.

v

ABSTRACT

Sungai Maong Kiri is one of the rivers in Sungai Sarawak River Basin that may face

flood tendency because Sungai Maong Kiri is under tidal influence. Backwater analysis

is carried out to investigate whether existing channel of Sungai Maong Kiri is still able

to accommodate the volume of water comprises the discharge from upstream and high

tide from downstream. Backwater effect will cause overflow at Sungai Maong Kiri

existing channel. Hydrologic analysis by using Rational Formula has been carried out to

achieve average peak discharge. Different Average Recurrence Interval (ARI) has been

used as the upstream boundary condition during the steady flow analysis. Highest

Astronomical Tide (HAT) 6.4m has been chosen as a downstream boundary condition.

Highest Astronomical Tide data was collected from Sarawak Marine Department.

Backwater analysis is carried out by using HEC-RAS 4.0 on steady flow analysis. From

the result, the channel is still capable to accommodate the water from CH 0 to CH 20000

but water overflow from CH 25000 to CH 30780. To prevent overflow at existing

channel and satisfy the standard freeboard size for open channel, a 0.4m and 0.6m height

leeve has been proposed to build at both side of the channel along CH 0 to CH 30780.

vi

TABLE OF CONTENTS

PAGE

Dedication ii

Acknowledgement iii

Abstrak iv

Abstract v

Table of contents vi

List of Tables x

List of Figures xi

List of Abbreviations xiii

List of Abbreviations xiv

CHAPTER 1 INTRODUCTION

1.1 Research Background 1

1.2 Problem Statements 3

1.3 Objectives 6

1.4 Scope of Study 6

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 7

vii

2.2 Rainfall-runoff Estimation Methods 7

2.2.1 Rational Formula 8

2.2.2 Characteristics of Rational Method 13

2.2.3 Limitations of Rational Method 15

2.3 Open Channel Flow 17

2.4 Unsteady Flow 19

2.4.1 Governing Equations 21

2.4.2 Dynamic Equation 21

2.4.3 Continuity Equation 24

2.4.4 Methods of Solution 25

2.5 Gradually Varied Flow 26

2.5.1 Flow Classification 27

2.5.2 Backwater Profiles Computation 31

2.6 Hydrologic Engineering Center – River 33

Analysis System

2.7 Types of Tide Phenomena 35

2.8 Chart Datum 37

2.9 Case Study: Backwater Effect in the 39

Amazon River Basin of Brazil

2.10 Summary of Literature Review 39

CHAPTER 3 METHODOLOGY

3.1 Introduction 40

viii

3.2 Acquiring and Analyzing the Digital Map 41

3.3 Division of Area 42

3.4 Determination of Runoff Coefficient 43

3.5 Determination of Rainfall Intensity 44

3.6 Determination of Rational Peak Discharge 44

3.7 Hydraulic Analysis Data Collection 45

3.8 Hydraulic Model – HEC-RAS 46

3.8.1 Geometry Data 46

3.9 Flow Regime 48

3.10 Steady Flow Analysis 49

3.10.1 Boundary Conditions and Flow Data 51

CHAPTER 4 RESULT AND DATA ANALYSIS

4.1 Introduction 53

4.2 Hydrology Analysis 54

4.3 Hydraulic Analysis 55

4.3.1 Geometrical Data 56

4.3.2 Flow Data and Boundary Condition 57

4.3.3 Flow Regime of Sungai Maong Kiri 59

4.3.4 Results of Steady Flow Analysis 60

4.4 Leeve Introduction 64

CHAPTER 5 DISCUSSION

5.1 Discussion 67

ix

CHAPTER 6 CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion 73

6.2 Recommendations 74

REFERENCES 75

APPENDIX A Calculation for Average Rational peak discharge, 78

(m3/s) for all ARI

APPENDIX B Determination of Flow Regime at Sungai Maong Kiri 86

APPENDIX C Profile Output Table –Steady Flow Analysis 88

x

LIST OF TABLES

Page

Table 2.1: Runoff Coefficient Values for the Rational Method 12

Table 2.2: Mild Slope Profile (Backwater Curve) 30

Table 4.1: Average Rational Peak Discharge 55

Table 4.2: Highest Astronomical Tide Table for Pending Station from year

1997-2007

58

Table 4.3: Boundary Condition and Flow Data 59

Table 4.4: Normal Depth, yo and Critical Depth, yc 60

Table 4.5: Water Levels With Different ARI at CH 30780 62

Table 4.6: Comparisons between existing system and proposed system 65

xi

LIST OF FIGURES

Page

Figure 1.1: Flooded area at Bau Police Station due to high tide 2

Figure 1.2: Flood occur due to the creation of backwater from tide at Bau

Town in 1963

3

Figure 1.3: Sungai Maong Catchment Area 5

Figure 2.1: Prismatic channels 18

Figure 2.2: Derivation of the dynamic equation for gradually varied

unsteady flow

21

Figure 2.3: Flow Transitions 26

Figure 2.4: Profile types for a mild slope 29

Figure 2.5: Water surface profile definition 32

Figure 2.6 (a): Semi-Diurnal Tide 35

Figure 2.6 (b): Diurnal Tide 36

Figure 2.6 (c): Mixed Tide 37

Figure 2.7: Datum for tide level measurement 38

Figure 3.1: Backwater analysis of Sungai Maong Kiri 41

Figure 3.2: River Schematic Diagram 46

Figure 3.3: Cross section data, Manning’s n values and other data of CH 0 47

Figure 3.4: Analyzing steady flow 49

Figure 3.5: Input of steady flow data 50

xii

Figure 3.6: Boundary Conditions for Sungai Maong Kiri Hydraulic

Analysis

51

Figure 4.1: Schematic Cross Section 56

Figure 4.2: Geometric input data from one of river station 57

Figure 4.3: Water surface profile plot 61

Figure 4.4 (a): Cross Section at CH 25000 62

Figure 4.4 (b): Cross Section at CH 30000 63

Figure 4.4 (c): Cross Section at CH 30780 63

Figure 4.5: Water levels along channel cross section with different ARI 66

Figure 5.1: Water surface profile with propose of leeve at both side of

channel

70

Figure 5.2: Water level at CH 5000 71

Figure 5.3: Water level at CH 15000 71

Figure 5.4: Water level at CH 25000 72

Figure 5.5: Water level at CH 30780 72

xiii

LIST OF ABBREVIATIONS

ARI - Average recurrence interval, year

HAT - Highest Astronomical Tide

HEC -RAS - Hydrologic Engineering Center – River Analysis System

xiv

LIST OF SYMBOLS

IL - Invert level, m

RL - Reduced level, m

R - Storage coefficient, hr

tc - Time of concentration, hr

Qpeak - Peak discharge, m3/s

t - Duration, hr

n - Manning’s coefficient representing the roughness of

channel bed

u - Changing factor unit, 1.0 for Unit SI System

So - Slope of channel bed

A, R - Function for yo

g - Gravity acceleration, m2/s

Ac, Tc - Function of yc

yc - Critical depth, m

yo - Normal depth, m

E - Specific energy, m

z - Elevation, m

zo - Bed elevation

αv2/2g - Specific velocity

θ - Bottom elevation

xv

h - Specific energy

H - Peizometric head

1

CHAPTER 1

INTRODUCTION

1.1 Research Background

Flood frequently occurred in our country since few years ago. Besides the

significant changes of global climate, the impact from urbanization process is the main

reason that causes flood occurs at many places in our country. With the increase of

impervious area, the volume of surface runoff from catchment area will also be

increased. Flood will occur if the existing drainage system or channel not capable to

accommodate the big volume of flow from catchment area.

The flood problem is more serious especially at the downstream part of channel

which having a low topographic profile. The condition becomes worse if the existing

channel is under tidal influence. Flood might occur at upstream part of the channel due

to the creation of backwater from tide as shown in Figure 1.1 and Figure 1.2. Therefore,

in this research, impacts of backwater to the river basin need to be studied in order to

avoid any flood problem. Not only this, more detail and thorough investigation to the

2

existing system of the channel should be carried out in order to reduce the number of

flood effectively.

In hydrologic terms, backwater effects are changes in the conditions downstream

such as the construction of a dam or flooding in the next waterway. In order to capture

such effects, it is necessary to use the dynamic wave model, diffusive wave model or

mathematical model for the river flow simulation, which allows incorporation of

downstream in the forecasting. Backwater study is trying to find out what the water

surface profile looks like for various discharges.

Figure 1.1: Flooded area at Bau Police Station due to high tide

(www.bau.com.my)

3

Figure 1.2: Flood occur due to the creation of backwater from tide

at Bau Town in 1963 (www.bau.com.my)

1.2 Problem Statement

Sungai Maong is one of the small tributaries of Sungai Sarawak which is located in

the Kuching City. Sungai Maong can be divided into two, which are Sungai Maong

Kanan and Sungai Maong Kiri. Length of main Sungai Maong before it separate into

Sungai Maong Kiri and Sungai Maong Kanan is about 1.5 km. This project will focused

on Sungai Maong Kiri area due to the development and urbanization process.

4

Sungai Maong Kiri begins at near the center of the Kuching City. It then traverses

the Central Park at the 3rd

Miles, Kuching. Sungai Maong Kiri area also includes the

Batu Lintang residential area and Taman Bergawut. All of these places are consist of

residential area, commercial area and some open area.

The discharges and runoff from the residential area and commercial area would

flow through the trunk drain which is in the rectangular shape and 6 meter wide. The

discharges and runoff would then flow into Sungai Maong Kiri. At the downstream part

of Sungai Maong Kiri, it traverses some residential areas; include Taman Wee and Wee,

Taman Sky and Stapok. Along Sungai Maong Kiri, there is no industrial area. It has

small jungle area at the downstream part.

This project analysis is to investigate the existing of backwater at the Sungai

Maong Kiri channel. When the flows of the channel come across the tide from

downstream and collide with peak discharge, backwater will be created. Most probably

effect of backwater such as flood will be occurring because the channel cannot

accommodate the volume of backwater due to the high tide.

Therefore, hydrologic and hydraulic analyses have been carried out in order to

determine effect and extent of backwater at Sungai Maong Kiri. The worst scenario if

there is a high capacity of runoff from the upstream catchments coincided with highest

astronomical tide continuously will occur backwater effect such as flooding. Figure 1.3

shows a Sungai Maong catchment area which is about 40 km2. (KTA, 1997)

5

Figure 1.3: Sungai Maong Catchment Area (Google Earth, 2008)

Sungai Maong Kanan

40 km2

Sungai Maong Kiri

6

1.3 Objectives

Main objectives of my research are to:

i) Determine whether existing Sungai Maong Kiri channel is able to accommodate

excessive water that affected by backwater.

ii) Find out the extent of which the Sungai Maong Kiri channels affected by

backwater effect by analyzing using HEC-RAS software.

iii) Proposed new system on how to prevent backwater effect such as flood for area

affected.

1.4 Scope of Study

Location of the study is located at Sungai Maong Kiri catchment. Scope of study

mention below, which is:

i) Estimate flow of surface runoff by using Rational Formula method.

ii) Undergo hydraulic analysis on the existing river channel by using HEC-RAS

software and supervise the overflow area.

iii) Data collection that includes rainfall intensity, stream flow, channels cross

section and tide level in order to evaluate the backwater profile.

iv) Evaluate the causes of backwater effect and proposed new irrigation system that

afford to cater overflowed water.