Faculty of Engineering

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1 Faculty of Engineering BACKWATER EFFECT AT SUNGAI MAONG KIRI Basil Anak Benjamin Bachelor of Engineering with Honours (Civil Engineering) 2008

2 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 TERHAD (Mengandungi maklumat yand berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972). (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan). TIDAK TERHAD Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat tetap: No Lorong Bayor, Bukit No. 8, Tabuan Jaya, Kuching, Sarawak. DR. ONNI SUHAIZA BINTI SELAMAN Nama Penyelia 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.

3 The Final Year Project Report as follow: Title: Author: Backwater Effect at Sungai Maong Kiri Basil Anak Benjamin Matric: is hereby read and approved by: 8 JUNE 2009 Dr. Onni Suhaiza Selaman Date Project Supervisor

4 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

5 Dedicated To my beloved family, friends and lecturers for your.tolerance.encouragement.help ii

6 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. iii

7 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 tetapi terdapat limpahan air dari CH ke CH 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 iv

8 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 but water overflow from CH to CH 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 v

9 TABLE OF CONTENTS PAGE Dedication Acknowledgement Abstrak Abstract Table of contents List of Tables List of Figures List of Abbreviations List of Abbreviations ii iii iv v vi x xi xiii xiv CHAPTER 1 INTRODUCTION 1.1 Research Background Problem Statements Objectives Scope of Study 6 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction 7 vi

10 2.2 Rainfall-runoff Estimation Methods Rational Formula Characteristics of Rational Method Limitations of Rational Method Open Channel Flow Unsteady Flow Governing Equations Dynamic Equation Continuity Equation Methods of Solution Gradually Varied Flow Flow Classification Backwater Profiles Computation Hydrologic Engineering Center River 33 Analysis System 2.7 Types of Tide Phenomena Chart Datum 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 vii

11 3.2 Acquiring and Analyzing the Digital Map Division of Area Determination of Runoff Coefficient Determination of Rainfall Intensity Determination of Rational Peak Discharge Hydraulic Analysis Data Collection Hydraulic Model HEC-RAS Geometry Data Flow Regime Steady Flow Analysis Boundary Conditions and Flow Data 51 CHAPTER 4 RESULT AND DATA ANALYSIS 4.1 Introduction Hydrology Analysis Hydraulic Analysis Geometrical Data Flow Data and Boundary Condition Flow Regime of Sungai Maong Kiri Results of Steady Flow Analysis Leeve Introduction 64 CHAPTER 5 DISCUSSION 5.1 Discussion 67 viii

12 CHAPTER 6 CONCLUSION AND RECOMMENDATIONS 6.1 Conclusion Recommendations 74 REFERENCES 75 APPENDIX A Calculation for Average Rational peak discharge, 78 (m 3 /s) for all ARI APPENDIX B Determination of Flow Regime at Sungai Maong Kiri 86 APPENDIX C Profile Output Table Steady Flow Analysis 88 ix

13 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 Table 4.3: Boundary Condition and Flow Data 59 Table 4.4: Normal Depth, y o and Critical Depth, y c 60 Table 4.5: Water Levels With Different ARI at CH Table 4.6: Comparisons between existing system and proposed system 65 x

14 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 3 Town in 1963 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 xi

15 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 Figure 4.4 (b): Cross Section at CH Figure 4.4 (c): Cross Section at CH 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 Figure 5.3: Water level at CH Figure 5.4: Water level at CH Figure 5.5: Water level at CH xii

16 LIST OF ABBREVIATIONS ARI - Average recurrence interval, year HAT - Highest Astronomical Tide HEC -RAS - Hydrologic Engineering Center River Analysis System xiii

17 LIST OF SYMBOLS IL - Invert level, m RL - Reduced level, m R - Storage coefficient, hr t c - Time of concentration, hr Q peak - Peak discharge, m 3 /s t - Duration, hr n - Manning s coefficient representing the roughness of channel bed u - Changing factor unit, 1.0 for Unit SI System S o - Slope of channel bed A, R - Function for y o g - Gravity acceleration, m 2 /s Ac, Tc - Function of y c y c - Critical depth, m y o - Normal depth, m E - Specific energy, m z - Elevation, m z o - Bed elevation αv 2 /2g - Specific velocity θ - Bottom elevation xiv

18 h - Specific energy H - Peizometric head xv

19 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 1

20 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 ( 2

21 Figure 1.2: Flood occur due to the creation of backwater from tide at Bau Town in 1963 ( 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. 3

22 Sungai Maong Kiri begins at near the center of the Kuching City. It then traverses the Central Park at the 3 rd 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 km 2. (KTA, 1997) 4

23 Sungai Maong Kanan Sungai Maong Kiri 40 km 2 Figure 1.3: Sungai Maong Catchment Area (Google Earth, 2008) 5

24 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. 6