1 rnnnrr 11 0000092384

STUDY OF RAINFALL-KUNU!'.t< KhLAllUNSHlP us1NG HYDROLOGICAL

MODELLING SYSTEM (HEC-HMS) FOR JOHOR RIVER, MALAYSIA

NURUL SYAFIQAH BT MOHD AZMI

Thesis submitted in fulfilment of the requirements

for the award of the degree of

Bachelor of Civil Engineering (Hons.)

Faculty of Civil Engineering and Earth Resources

UNIVERSITI MALAYSIA PAHANG

JULY 2014

VI

ABSTRACT

This study focused more in flood estimation model for Johor River in Kota Tinggi watershed, Malaysia using HEC-HMS (Hydrological Modeling System). HEC-HMS is necessary tool for analyzing and simulating rainfall and runoff process. In this study, HEC-HMS version 3.5 is used to simulate stream flow for Johor River basin. Calibration and validation process were carried out using different sets of data. Data of precipitation and stream flow used in this study is from the period of January 2012 until December 2012. The precision of data used during calibration and validation process depend on parameter used in HEC-HMS. Results of simulation can be generated in summary table, hydfograph and time series table. Correlation coefficient R 2 and root mean square (RMSE) are used to measure the performance of the modeling. A model with the R2 value is nearly to 1.0 and RMSE value is close to 0 is considered as good and satisfactory. During calibration process, value of RMSE for 1836402 station is 1.9 m3/s while value of RMSE for 1737451 station 1.89 m3/s. During validation process, value of RMSE for 1836402 station is 1.2 m3/s while value of RMSE for 1737451 station is 1.69 m3 Is. The simulated model were fit with the observed data and show that the HEC-HMS are suitable model to predict the hydrologic changes in Johor River.

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ABSTRAK

Kajian ini memberi tumpuan lebih kepada pemodelan anggaran banjir di Sungai Johor dalam kawasan tadahan air di Kota Tinggi, Malaysia dengan menggunakan HEC-HMS (Hydrological Modeling System). HEC-HMS adalah alatan penting yang digunakan untuk menganalisa dan membuat simulasi hujan dan proses larian air. Di dalam kajian ini, HEC-HMS versi 3.5 telah digunakan untuk membuat simulasi pergerakan air untuk kawasan tadahan Sungai Johor. Proses kalibrasi dan pengesahan telah dijalankan dengan mengguna set data yang berbeza. Data hujan dan pergerakkan air yang digunakan di dalam kajian ini diambil dari tempoh Januari 2012 sehingga Disember 2012. Ketepatan data yang digunakan semasa kalibrasi dan pengesahan proses bergantung kepada parameter yang digunakan dalam HEC-HMS. Keputusan simulasi ini boleh dilihat di dalam jadual ringkasan, hidrograf dan jadual siri masa. Pekali korelasi, R2 dan punca kuasa dua (RMSE) adalah digunakan untuk mengukur prestasi pemodelan ini. Pemodelan dengan pekali korelasi yang menghampiri 1.0 dan punca kuasa dua yang menghampiri 0 adalah dianggap tepat dan memuaskan.Semasa proses kalibrasi dalam kajian ini, nilai punca kuasa dua adalah 1.9 m3 Is untuk stesen 1836402 manakala untuk stesen 1737451 adalah 1.89 m31s. Semasa proses pengesahan, nilai punca kuasa dua untuk stesen 1836402 adalah 1.2 m31s manakala untuk stesen 1737451 adalah 1.69 m3 Is. Simulasi pemodelan adalah tepat dengan data yang diperhatikan dan ianya menunjukkan bahawa HEC-HMS adalah pemodelan yang sesuai digunakan untuk meramal perubahan hidrologi di Sungai Johor.

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TABLE OF CONTENTS

Page

SUPERVISOR'S DECLARATION 11

STUDENT'S DECLARATION 111

DEDICATION lV

ACKNOWLEDGEMENT v

ABSTRACT Vl

ABSTRAK Vll

TABLE OF CONTENTS Vlll

LIST OF TABLES Xl

LIST OF FIGURES Xll

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS XVl

CHAPTER 1 INTRODUCTION

1.1 Backgroundof Study 1

1.2 Problem Statement 2

1.3 Objective 3

1.4 Scope of Study 3

1.5 Significance of Study 4

CHAPTER 2 LITERATURE REVIEW

2.1 Hydrology 5

2.1.1 Hydrologic Cycle 5 2.1.2 Hydrological Characteristic 7

2.2 Rainfall 9

2.2.1 Rainfall Characteristic 9

2.3 Runoff 11

2.3.l Source of Runoff 11 2.3.2 Factor Affecting Runoff 13

lX

2.3.3 Runoff Process 14

2.4 Physical Characteristic of Basin 14

2.4.1 Land Use 14 2.4.2 Elevation of the Basin 15 2.4.3 Slope 15

2.5 Rainfall and Runoff Relationship 15

2.5.1 Hydro graph 15

2.6 Method of Analysis Rainfall and Runoff Data 17

2.6.1 Peak Discharge Method 17 2.6.2 Rational Method 17 2.6.3 Unit Hydrograph Method 18

2.7 Software for Analyze Rainfall and Runoff Relationship 22

2.7.1 HEC-HMS 22

CHAPTER 3 METHODOLOGY

3.1 Introduction 24

3.2 Flowchart of Methodology 25

3.3 Study Area 26

3.4 Data Collection 26

3.4.1 Rainfall Data 27 3.4.2 Stream Flow Data 27

3.5 Method of Simulation Rainfall-Runoff Data in HEC-HMS 27

3.5.l SCS Method 28

CHAPTER 4 RESULT AND DISCUSSION

4.1 Introduction 29

4.2 HEC-HMS 29

4.3 Rainfall and Runoff Relationship Analysis 30

4.4 Analysis and Simulation 56

4.4.1 Model Parameter 56 4.4.2 Calibration 59 4.4.3 Validation 62

4.5 Evaluation of the Model through Correlation Coefficient, R2

Result

4.6 Evaluation of the Model through Root Mean Square Error

(RMSE)

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS

5.1 Conclusions

5 .2 Recommendations

REFERENCES

APPENDICES

A

B

Sample Data of Rainfall

Sample Data of Steam Flow

64

67

68

68

70

74

74

75

x

xi

LIST OF TABLES

Table No. Title Page

4.2 Summary data for analysis in year 2012 for Sg. Sayong 31 di Jam. Johor Tenggara 1836402 discharge station

4.3 Summary data for analysis in year 2012 for Sg. Johor Rantau Panjang 1737451 discharge station 32

4.17 Example of loss rate parameter used for SCS method 58

4.18 Transform parameter for SCS method 58

4.20 Example of parameters used in calibration process 60

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LIST OF FIGURES

Figure No. Title Page

2.1 Hydrological cycle 6

2.2 Example of a hydrograph for Athabasca River 8

2.3 Characteristic ofhydrograph 9

2.4 A diagram showing flash flood and rainfall intensity 10 intensity in Spain

2.5 Runoff comes from natural processes 12

2.6 Runoff comes from human activity 13

2.7 Flood hydro graph shows /base low and direct runoff 16 element

2.8 Snyder' s Unit Hydrograph where Up= peak 19 standard of UH

3.1 Flowchart of the study 25

3.2 Johor river basin 26

4.1 HEC-HMS layout model 30

4.4 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 33 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in January 2012

4.5 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 35 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in February 2012

4.6 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 37 1836402 discharge station b) Sg. Johor Rantau Panjang 1737451 discharge station in March 2012

4.7 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 39 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in April 2012

4.8 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 41 1836402 discharge station (b) Sg. Johor Rantau Panjang

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1737451 discharge station in May 2012

4.9 Runoff hydrograph (a) Sg. Sayong di Jam. Johor Tenggara 43 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in June 2012

4.10 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 45 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in July 2012

4.11 Runoff hydrograph (a) Sg. Sayong di Jam. Johor Tenggara 47 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in August 2012

4.12 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 49 1836402 discharge station (b) Sg. Johor Rantau Panjang 173 7 451 discharge station in September 2012

4.13 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 51 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in October 2012

4.14 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 53 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in November 2012

4.15 Runoffhydrograph (a) Sg. Sayong di Jam. Johor Tenggara 55 1836402 discharge station (b) Sg. Johor Rantau Panjang 1737451 discharge station in December 2012

4.16 Parameter used in HEC-HMS at Johor river basin 57

4.19 Constant baseflow for subbasin 1 59

4.21 Calibration result (a) Sg. Sayong di Jam. Johor Tenggara 61 1836402 in December 2012, (b) Sg. Johor Rantau Panjang 1737451 in December 2012

4.22 Validation result (a) Sg. Sayong di Jam. Johor Tenggara 63 1836402 in October 2012, (b) Sg. Johor Rantau Panjang 1737451 in0ctober2012

4.23 Graphs of simulated versus observed flows for the following 65 events. (a) Sg. Sayong di Jam. Johor Tenggara 1836402 in December 2012, (b)Sg. Johor Rantau Panjang 1737451 in December 2012 (Calibration stage)

4.24 Graphs of simulated versus observed flows for the following 66 events. (a) Sg. Sayong di Jam. Johor Tenggara 1836402 in

October 2012, (b) Sg. Johor Rantau Panjang 1737451 in October 2012 (Validation stage)

XIV

xv

LIST OF SYMBOLS

Q Design discharge

Cu Unit conversion coefficient

A Watershed drainage area

1 Design rainfall intensity

c Runoff coefficient (dimensionless)

t1 Basin lag time

tr Effective rainfall duration

CP UH peaking coefficient

c Conversion constant (2.75 for SI)

A Basin area

CN Curve Number

A Total watershed area

At Cumulative watershed area

Tc Time of concentration of watershed

RMSE Root Mean Square Error

'Xobs,i Observed value

Xmodel,i Simulated values at time/place

Rz Correlation coefficient

CFS

HEC-HMS

IDF

JPS

scs

SG

UH

UNESCO

LIST OF ABBREVIATIONS

Cubic feet per second

Hydrologic Engineering Center Hydrologic Modeling System

Intensity Duration Frequency

Jabatan Pengairan dan Saliran

Soil Conservation Service

Sungai

Unit Hydrograph

XVl

United Nations Educational, Scientific and Cultural Organization

CHAPTERl

INTRODUCTION

1.1 BACKGROUND OF STUDY

Basically, water can be defined as a chemical substance that is essential

for the survival of all forms of living creatures. Without it, there would be no life

on earth. Th~re is about 70 to 75 percent of the earth is covered with water or

about 1400 x 1015 m3 quantity of water in the world. So, not impossible for

human use large amount of water everyday and every time. According to

analysis of Australian water usage, water commonly used for various purposes.

For instance, human used them as direct consumption by households, food

production such as cook for lunch and dinner, as a dish and drinks and other

domestic purpose. (National Water Policy of Australia, 2006). Besides of

domestic purpose, water also important to use in agriculture and industries. For

example, human used them as an ingredient of product during production

processes in industries.

Hydrology deals with the waters of the earth, their circulation,

occurrence and distribution on the planet, their chemical and physical properties

and their interactions with the physical and biological environment including

their responses to human activity. Hydrology also discusses about a process that

controls the fertility of the water and their disappearances from the surface of

earth.

2

Hydrological cycle begins with passage of water from the atmosphere

and stored in one of the following major reservoirs such as rivers, lakes, oceans,

soils and glaciers. Hydrological cycle also describes the constant movement and

endless recycling of water between the atmosphere, land surface and under the

ground. Water moves from one storage to another by the ten physical processes

like condensation, evaporation, runoff, precipitation, deposition, infiltration,

transpiration, sublimation, melting and groundwater flow.

Basically, river flooding occurs because of the incidence of the heavy

rainfall and the resultant large concentration of runoff, which can exceed the

capacity of the river. Commonly, the major problem in Malaysia due to

hydrological problem is flooding. Due to the flooding problem, there are many

software have been created to analyze and stimulate rainfall and runoff process.

In this research, I have gone through a new program which is Hydrologic

Engineering Center Hydrologic Modeling System (HEC-HMS) to predict

rainfall data and determined runoff process. By using this software, we can

obtain the relationship between rainfall and runoff by producing a hydrograph.

Structure of the model, analysis of sensitivity, results obtained from the

data and calibration and verification procedures are some of the parameter

estimation in HEC-HMS hydrologic model. All of this parameter is selected to

analyze the surface runoff from the watershed. Finally, the result of a simulation

can be generated in summary table, time series table and hydrograph.

1.2 PROBLEM STATEMENT

Generally, in urban area, rainfall-runoff directly changes due to

environment, season and also human behaviors. Flooding is one of the regular

natural disasters due to this factor and flooding is becoming a common

phenomenon nowadays in Malaysia especially Johor. Basically, river flooding

occurs because of the incidence of the heavy rainfall and the resultant large

concentration of runoff, which can exceed the capacity of the river. One of the

rivers that contributes flood problem in the big city like Johor is Johor River.

3

Johor River has a watershed system that's not enough to cattle runoff capacity

especially in Kota Tinggi due to urbanization. An increase in rainfall intensity

will increase the peak discharge and volume of runoff for a given infiltration

rate. So, modeling system (HEC-HMS) is designed to stimulate hydrological

data and precipitation-runoff processes of watershed systems because it's

commonly used in a wide range of areas. For example, small urban area, large

river basin water supply or natural watershed runoff.

1.3 OBJECTIVES

This research is carried out to accomplish several objectives:

i) To analyze the rainfall-runoff relationship in Johor River using

HEC-HMS.

ii) To determine the best method in HEC-HMS for analyzing the

rainfall - runoff relationship in Johor River after calibration,

validation and verification process.

iii) To predict discharge based on appropriate model using rainfall

data.

1.4 SCOPE OF STUDY

Johor River is the case study in this research which is located in Kota

Tinggi, Johor. Johor River is the main river of Johor and 122.7 km long with a

catchment of 1126 km2• It comes from Mount Gemuruh and flows in a north to

south direction part of Johor and lastly into the Johor Strait. The shape of the

catchment is irregular. The hydrology data are analyzed by using hydrological

modeling like HEC-HMS that obtained from rainfall data and flow rate from the

runoff. By analyzed this data using HEC-HMS, we can predict the discharge and

determine the rainfall-runoff relationship for Johor River in certain period of

time. The method used to analyze rainfall and runoff relationship in this case of

study is Soil Conservation Service (SCS) Method.

4

1.5 SIGNIFICANCE OF STUDY

From this research, the rainfall-runoff relationship can be obtained using

Hydrologic Modelling System (HEC-HMS). Besides that, SCS Method used

during simulation in HEC-HMS can analyze the relationship between rainfall

and runoff quickly. It is important to do this research because the data from this

research is effective to use in order to solve and prevent flash flood and

insufficient capacity of drainage problem.

CHAPTER2

LITERATURE REVIEW

2.1 HYDROLOGY

According to UNESCO, 1964 hydrology deals with the waters of the

earth, their circulation, occurrence and distribution on the planet, their chemical

and physical properties and their interactions with the physical and biological

environment including their responses to human activity. There are two parts of

hydrology which are regional hydrology and global hydrology. The regional

hydrology studies flow of water from precipitation such as rain and snowing to

run off to sea in regional scale while global hydrology cover hydro logic cycle in

global scale such as global evapotranspiration between sea and land.

2.1.1 Hydrologic Cycle

The hydrologic cycle is a conceptual model that describes the movement

and storage of water between the atmosphere, lithosphere, biosphere and the

hydrosphere (Hubbart, J., 2011). Hydrological cycle begins with passage of

water from the atmosphere and stored in one of the following major reservoirs

such as rivers, lakes, oceans, soils and glaciers. It slowly passes through the soil

and rock layers underground. Hydrological cycle describes the constant

movement and endless recycling of water between the atmosphere, land surface

and under the ground (Danne, T. and L.B. Leopard, 1977).

Water moves from one storage to another by the ten physical processes

like condensation, evaporation, runoff, precipitation, deposition, infiltration,

CHAPTER2

LITERATURE REVIEW

2.1 HYDROLOGY

According to UNESCO, 1964 hydrology deals with the waters of the

earth, their circulation, occurrence and distribution on the planet, their chemical

and physical properties and their interactions with the physical and biological

environment including their responses to human activity. There are two parts of

hydrology which are regional hydrology and global hydrology. The regional

hydrology studies flow of water from precipitation such as rain and snowing to

run off to sea in regional scale while global hydrology cover hydro logic cycle in

global scale such as global evapotranspiration between sea and land.

2.1.1 Hydrologic Cycle

The hydrologic cycle is a conceptual model that describes the movement

and storage of water between the atmosphere, lithosphere, biosphere and the

hydrosphere (Hubbart, J., 2011). Hydrological cycle begins with passage of

water from the atmosphere and stored in one of the following major reservoirs

such as rivers, lakes, oceans, soils and glaciers. It slowly passes through the soil

and rock layers underground. Hydrological cycle describes the constant

movement and endless recycling of water between the atmosphere, land surface

and under the ground (Danne, T. and L.B. Leopard, 1977).

Water moves from one storage to another by the ten physical processes

like condensation, evaporation, runoff, precipitation, deposition, infiltration,

6

transpiration, sublimation, melting and groundwater flow (Hubbart, J., 2011).

The hydrological cycle is shown in Figure 2.1.

Figure 2.1 : Hydrological cycle

Source: Hubbart, J., 2011

The hydrological cycle begins with evaporation of water from the surface

of reservoirs such as oceans, lake and rivers. It occurs when the physical state of

water is changed from liquid state to a gaseous state. Evaporated moisture is

lifted from land surfaces, ocean and water bodies as water vapor into the

atmosphere. After moist air is lifted, it cools and water vapor condenses to form

ice-crystal clouds. This process changes physical states of water vapor from

vapor to liquid. Condensation in the hydrological cycle occurs when warm air

looses its capacity to hold water vapor in the atmosphere.

After that, the moisture will undergo a precipitation process where the

water drop or returns to the ground surface. Precipitation can be described as any

solid aqueous deposit or liquid falls from cloud to ground surface from the

atmosphere. (Chahine, M. T., 1992). In some case, if a rainfall drop in small

quantity, high percentage of precipitation will return back to the atmosphere by

evaporation process. Then when rates of precipitation increases, the runoff rates

also increased. Runoff process includes groundwater flow and streamflow over

7

the land surface and through reservoirs. Runoff made up from precipitation that

falls directly on the stream.

Streamflow occur when water flows into lakes and stream in the low

points of the landscape while groundwater flow above ground surface (Hubbart.

J., 2011). The process where groundwater that released back into the atmosphere

is called as transpiration. Generally, the transpiration process occurs by stems of

plants or leaves. Transpiration affects by plants that are deep in the soil and the

amount of light which plants are exposed.

Then, hydrological cycle has no beginning and also has no end start from

the water that falls as precipitation, sublimates, run off the ground surface and

soaks into the ground as infiltration where it refers to the movement of water

into the soil layer (Pidwimy, M., 2011).

2.1.2 Hydrological Characteristics

Hydrological characteristic refer to rainfall distribution, runoff

distribution and peak discharge at a particular location along the course of river

or stream (Sudmeyer, R.A., 2004). One of the important graph to determine

hydrological characteristic of the river or stream is hydrograph. Annual

hydrograph can predict the changes in the flow of water over the year at a

certain location (RAMP, 2007). It shows all variations of the flow and periods of

high and low flows while hydrometric data refer to data collection of that flow.

Athabasca River hydrograph

4600

4000

3500

1500

1000

500

llasitd on dJtl r~ by Wlt!r ~yof Qn3da for lblion 07D\OO I , ~abm:a Awrt..I"" MMl'r;ry. Hst~ dm is fcrf>e period ~7- 2005 .

:lOOG dJtl is pro.;,;~.

. . . . .. .... . .

.. .. : ~:

.. · .. ; .:·.:

.. . : ?· .. .

. ~ :-~ : .. ·. ·' .. . ; :

••. . • Ml>im<Jm

- Upper Ouattile M?dian

- loolerOuanile

• •· · Mnimum --2000

·· . Jan 1 F~ I Mar 1 ~r I Mly l Jun 1 Jul I Alg I Sep I Oct I Novi Ote 1

Figure 2.2 : Example of a hydrograph for Athabasca River

Source : RAMP, 2007

8

There are three important parts of hydrograph which are crest segment

(peak flow), rising limb and falling limb (recession curve). These parts are

measured at a specific point in certain river and typically time variation

(Strandhagen et al., 2006). Rising limb represents the increasing of stream flow

rate while peak flow shows the maximum flow rate that occur and falling limb is

where the stream flow rate is decreasing.

ll.

'"' ~ ... I

t l -Cl

I 7Jmt! of: t'Oncentl'aJion

Fam ng Limb /

Figure 2.3 : Characteristic of hydro graph

9

Some of the hydrological indicators used in hydrological characteristic

include discharge, maximum flow, minimum flow and median flow. Overall,

hydrological characteristic deals with quantitative aspect of the hydrological

cycle as well as particular space-time variation of hydrological elements (T.A

Mahon, 1982).

2.2 RAINFALL

2.2.1 Rainfall Characteristic

2.2.1.1 Type of Rainfall

There are three types of rainfall which is conventional rainfall, frontal

rainfall and relief rainfall. All of the type has the common process of

precipitating. Convention rainfall occurs in areas where the ground warms up, it

heats the air above it. (J. Sohn, 2013). The air will rise, start to condense and

finally rain will fall. This type of rainfall very commons in summer month of

tropical areas. Besides, frontal rainfall happens when warm and cold air masses

meet together and form a front. Warm air is forced to rise and cools in contact

10

with cold air along the fronts. So, the formation of clouds happens after

condensation and rain fall. Lastly, relief rainfall or known as orographic rainfall

very commons in mountain or hill area. It occurs when prevailing winds pick up

warm and moist air to rise in high area. (J. Sohn, 2013). So, the formation of

clouds occurs after condensation and rain is formed.

2.2.1.2 Intensity of Rainfall

Rainfall intensity is defined as the amount of rain that falls over time in

millimeters per hour (mm/h). (Gabaldo Sancho et al., 2008). Intensity of rain can

be determined by measuring height of water layer covering the land with them.

High and low of intensity depends on local circumstance. For example, flash

flood comes from the high intensity of rainfall on steep slopes as shown in the

diagram below.

0:00 3 :00 €:00 9.00 12:0 () 15:00 18:00 2 1:00 0:00 3.00 6:00 9:00 12:00 0 12 0

20 10 0

~ Hyetc·~...., gravrr; c•nll-: "E 40 :>o.*.10G1. 1e:oo 80 .E. ln~ur. of:!>• riH cf t"• h)"C>':>;raph:

~ :.o.c-~. 1g'' · 1~ : 16 "' ;::; .. Pull: f .:,w (1i.:i r.13/s): 30.i>;!.01. .§. <:: €0 eo !!! 18:2' s: E 0

= Ci: .:! E eo 40 "' a:

!GO 20

120 0

Figure 2.4 : A diagram showing flash flood and rainfall intensity in Spain

2.2.1.3 Duration of Rainfall

Duration of rainfall commonly related to rainfall intensity. According to

Glossary of Meteorology, 2009, the intensity ofrainfall usually predicted for any

return period and rainfall intensity. The relationship of intensity-duration-

11

frequency (IDF) also is one of the common tools used for planning, operating

and design in water resources projects. (H. Ibrahim, 2011).

2.2.1.4 Distribution of Rainfall

Rainfall distribution is a various pattern of falling rain in a country. (G.K

Voigt, 1960). There is great temporal and regional variation in the distribution of

rainfall. For example, monsoons can affect the amount of rainfall in a country.

Besides, there are some factors in controlling the distribution of rainfall such as

ocean currents, air temperature and mountain ranges. (The Columbia Electronic

Encyclopedia, 2012). Distribution of rainfall also expressed as distribution

coefficient.

2.3 RUNOFF

2.3.1 Source of Runoff

Generally, runoff comes from two sources which is human activity and

natural processes while surface runoff can be refer as water flow when soil is

absorbed to full capacity and excess water from snowmelt, rain or other sources

flows above the ground. After analyzing the data collected, it shows that storm

runoff originated from a small portion of the total drainage area. The extent and

location of the source area are dependent on antecedent moisture, rainfall

intensity and depth of soil. (P. Betson et al., 2010).

Source of runoff can be divided into two which is coming from human

activity or natural processes. Runoff that comes from natural processes occurs

naturally as soil. It acts as a soil and carried to various bodies of water. The

picture of natural process as shown in the diagram below.