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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
t KIliOl t M.tlamat AI1l0e1!1l1& UNtVEUrrr LAYS[ AltA
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
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
• ~AUSTAnDIII , IMR twJGE STATION
...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