10
CHAPTER 2
LITERATURE REVIEW
2.1
Definitions of Flood
A flood is a natural event that can have far reaching effects on people and the
environment. Flood can be defined as relatively high stream flow, which overtops the
natural or artificial banks in any part of a stream, river, estuary, lake or dam, and/or
overland runoff before entering a watercourse and/or coastal inundation resulting from
super elevated sea levels and/or waves overtopping coastline defenses. Given the
concepts of flooding that are being addressed, it is essential that the terminology used is
consistent and understood. The following definitions of floods from different hydrologist
and researcher are referred:

Flood is a relatively high flow, which overtaxes the natural channel provided for the
runoff (Chow et al., 1988).

Flood is any high stream flow, which overtops natural or artificial banks of a stream
(Rostvedt, 1968).

Flood is a body of water, which rises to overflow land that is not normally submerged
(Ward, 1978).

Flood – a relatively high flow as measured by either gage height or discharge rate
whenever the stream channel in an average section is overtaxed, causing overflow to
the usual channel boundaries (Jarvis, 1949).
11

Flood – stage at which the stream channel becomes filled and above which is
overflows its banks (Wisler et al., 1957).

Flood – the result of runoff from rainfall and/or melting snow in quantities too great
to be confined in the low water channels of stream (Linsley, 1964).

Flood - relatively high stream flow that overtops the natural or artificial banks in any
part of a stream or river (DID, 2000).

Flash Flood – flood events where the rising water occurs during or a matter of a few
hours after associated rainfall. It is often caused by sudden and unexpected local
heavy rainfall or rainfall in another area (DID, 2000).

Major Flood – appreciable urban areas are flooded and/or extensive rural areas are
flooded. Properties, villages and towns can be isolated (DID, 2000).

Minor Flood – causes inconvenience such as closing of minor roads and the
submergence of low level bridges. The lower limit of this class of flooding on the
reference gauge is the initial flood level at which landholders and townspeople begin
to be flooded (DID, 2000).
2.2
Types of Flood
Types of flood in Malaysia are: monsoon flood, urban flash flood, debris flow and
mud flow, landslide, tidal flood, dam release, and bund breach (DID, 2000). Generally,
Smith et al. (1998) classified floods into two types, which are river floods and coastal
floods with different characteristics as follow:
12
River Floods

Floods in river valleys occur mostly on floodplains or wash lands as a result of flow
exceeding the capacity of the stream channels and over spilling the natural banks or
artificial embankments. Mainstream Flood, inundation of normally dry land occurring
when water overflows the natural or artificial banks of a stream, river, estuary, lake or
dam (DID, 2000).

Sometimes inundation of the floodplain, or of other flat areas, occurs in wet
conditions when an already shallow water table rises above the level of the ground
surface. This type of water table flooding is often an immediate precursor of overspill
flooding from the stream channels (Smith et al., 1998).

In very dry conditions, when the ground surface is baked hard or becomes crusted,
extensive flat areas may be flooded by heavy rainfall ponding on the surface. This
rainwater flooding is typical of arid and semi-arid environments but is also
experienced much more widely (Smith et al., 1998).

Also typical of arid and semi-arid areas is the situation where there are no clearly
defined channels and where sheet wash flooding occurs by the unimpeded lateral
spread of water moving down a previously dry or near-dry valley bottom or alluvial
fan.

In urban areas flooding often results from over spilling or surface ponding, as
described above, but may also occur when urban storm-water drains become
surcharged and overflow. Storm water is resulting from runoff from a storm event.
During rainfall event some water remains on the surface or is held in the soil or
underground aquifer as ground water, a portion of the water is used directly by plants
and the remainder flows over the surface. This overland flow is called storm water
(DID, 2000).
13

Local Overland Flood where inundation by local runoff rather than over bank
discharge from a stream, river, estuary, lake or dam (DID, 2000).
Coastal Floods

Floods in low-lying coastal areas, including estuaries and deltas, involve the
inundation of land by brackish or saline water. Brackish-water floods result when
river water overspills embankments in coastal reaches as flow into the sea is impeded
by high-tide conditions. Overspill is exacerbated when high-tide levels are increased
above normal by storm-surge conditions or when large freshwater flood flows are
moving down an estuary (Smith et al., 1998).

Direct inundation by saline water floods may occur when exceptionally large windgenerated waves are driven into semi-enclosed bays during severe storm or stormsurge conditions, or when so-called 'tidal waves', generated by tectonic activity, move
into shallow coastal waters.
2.3
Mechanisms of Flood
Flood flow deriving directly from rain falling on a river basin originates mainly
from hydrological responsive source areas, which vary in size (variable source areas)
depending on the interaction of rainfall and catchment’s conditions. The source areas
have saturated ground surfaces, which effectively shed, as saturation overland flow,
virtually all the rain falling on them (Smith et al., 1998).
Smith et al. (1998) documented the flooding mechanisms as follow: from early
stages of a storm (Figure 2.3.1), all rainfall (P) infiltrates into the soil surface. Then, as a
result of infiltration (I) and through flow (Qt) in the soil profile, the riparian areas and the
lower valley slopes become saturated as the shallow water table rises to the ground
14
surface (Figure 2.3.2). In these surface-saturated areas infiltration capacity is zero so that
all precipitation falling on them, at whatever intensity (i), becomes saturation overland
flow (Qo(s)). The groundwater flow (Qg) within the saturated zone will also contribute to
the flow in the channel.
Figure 2.3.1: The Generation of Flood Flow – Early Stage of Rainfall (Smith et al.,
1998).
Figure 2.3.2: The Generation of Flood Flow – Rainfall Event (Smith et al., 1998).
15
Where rainfall is particularly intense, or where natural infiltration capacities have
been reduced by anthropogenic effects such as soil compaction or overgrazing, overland
flow may result from the process described by Horton (1933) and illustrated in Figure
2.3.3. During those parts of a storm when rain falls at a rate that is greater than the rate at
which it can be absorbed by the ground surface there will occur an excess of
precipitation, which will flow over the ground surface as overland flow:
(i – f) t = Pe = Qo
Figure 2.3.3: The Generation of Flood Flow – The Formation of Overland Flow in
Areas of Low Infiltration Capacity (Smith et al., 1998).
Overall, it is useful to consider formation of floods based on two categories based
on the type of causative event:

Formation of natural floods
These are the floods, which result from heavy rainfalls or/and snow-ice melts
water on natural (or substantially modified by man) catchments.

Formation of artificial floods
These are the flood due to release of impounded water by failure of a structures
likes dam or other natural man-made barriers.
16
2.4
Origins and Factors Affecting Floods
Generally, a flood is caused by a combination of heavy rainfall causing river or
coastal to over flow from their banks, and can happen at any time of the year. Most river
floods result directly or indirectly from climatologically events such as excessively heavy
and/or excessively prolonged rainfall. In cold-winter areas, where snowfall accumulates,
substantial flooding usually occurs during the period of snowmelt and ice melt in spring
and early summer, particularly when melt rates are high. River floods may also result
when landslides fall directly into upstream lakes or reservoirs causing a sudden rise in
water level, which overspills the outlet or dam. Coastal areas are also at risk from sea
flooding, where coastal floods are usually caused by a combination of high tides and the
elevated sea level and large waves associated with storm surges, which result from severe
cyclonic weather systems and low atmospheric pressure.
Incidences of floods in urban areas are on the rise. This is because in new
townships, the total impervious areas is very high since the housing developers only have
to comply to an open space of 10%; the developers normally go for maximum built up
areas to maximize land use. With respect to catchment runoff, an increase in area
imperviousness from zero to 40% would cut the time to peak discharge by about 50% and
increase the discharge magnitude by about 90% (DID, 2000). Before urbanization,
rainwater is intercepted by the vegetation, infiltrates into the ground and takes time to
travel to the river, but now it is quickly collected from the roofs and other paved grounds
and canalized efficiently to public drains, which in turn rapidly brings it to the nearest
river. Although floods are natural phenomena, the effects of rainfall resulting in excess
water running into streams and rivers, uncontrolled development activities in watersheds
and along river corridors and high sea level areas can increase the severity of floods. The
high rate of sedimentation in the rivers can also lead to serious flooding.
17
Figure 2.4.1: Causes of Floods and Flood-Intensifying Factors (Smith et al. 1988).
2.5
Strategies for Flood Mitigation
By virtue of its steep topography and intense convective storm rainfall, the Klang
River Basin has been subjected to frequent flooding. As a result the Government has
embarked on a comprehensive flood mitigation program involving expenditure of RM
500 million, construction of dams and extensive channel works. Flood mitigation works
have been rendered ineffective because flood discharges have increased threefold since
1986, due to the effect of urbanization, which has been greatly underestimated in the past.
There are many factors that have contributed to the increase in flood discharges including
canalization works, creation of large areas of impervious surface, filling of swamps and
filling of flood plains, but the most significant factor has been forest clearing.
New development are be required to take runoff minimization measures such as
retarding basins, rainwater tanks and infiltration trenches to ensure that post development
discharges do not exceed pre-development discharges (DID, 2000). The implementation
18
of runoff minimization techniques into urban development has been emphasized by DID
with the introduction of the Urban Stormwater Management Manual for Malaysia
(Manual Saliran Mesra Alam – MSMA).
The Proposal for the Stormwater Management and Road Tunnel (SMART) Project
was identified as the most suitable alternative and the Government has decided for it to
be implemented as soon as possible. The Government has issued a Letter of Intent
appointing the MMC Engineering Group Berhad - Gamuda Berhad JV Consortium to
implement this project.
The Smart Project involves the diversion of flood runoff from the catchments area
(near the confluence of the Klang river and the Ampang river) through a bypass tunnel
before it is being directed back to the Klang River downstream. The Tunnel also provides
an alternative traffic route to lessen traffic congestion at one Kuala Lumpur's southern
gateway near the Sungai Besi Airfield. The general layout for the SMART Project is as
shown in Figure 2.5.1.
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Figure 2.5.1 – Alignment Of Stormwater Bypass Tunnel
2.6
Flood Forecasting System
The function of flood forecasting procedures is to predict the shape of the flood
hydrograph generated within the catchments, when it is subjected to various hydrologic
phenomena (Pattison, 1975). Based on Chow et al. (1988), flood forecasting is an
expanding area of application of hydrological techniques to obtain real time precipitation
and stream flow data, insert data into rainfall-runoff and stream flow routing programs,
20
and forecast flood flow rates and water level for periods of from a few hours to a few
days ahead, depending on the size of the watershed.
Smith et al. (1998) stressed that flood forecast, is a scientific evaluation of an
event in real time leading to the issue of a general alert about hazardous condition. In an
International Glossary of Hydrology published by World Meteorological Organization
(1974), flood forecasting is defined as the prediction of stage, discharge, time of
occurrence, and duration of a flood – especially of peak discharge at a specified point on
a stream – resulting from precipitation or snowmelt.
Linsley et al. (1949) documented that there are three phases in flood forecasting
operation:

Collection of weather data;

Formulation of the forecast; and

Dissemination of the forecast.
But Body (1969) documented that Flood Forecasting System can be considered to
consist of four phases as follow:

Observation of the operational data;

The transmission of operational data;

Formulation of the forecast; and

The issue of the forecast.
Flood forecasting can contribute significantly to the reduction of flood damages in
rural and urban situations where advance warning permits the evacuation of people and
livestock, the removal of equipment and the establishment of emergency services. But the
errors in the forecast of flood stage or the time of arrival of conditions may lead to under
preparation and avoidable damage, or to over-preparation, unnecessary expense and
21
anxiety, and a subsequent loss of credibility (Smith et al., 1998). So, the need for
reliability in flood forecasting should be stressed. Flood forecasting system must be
improved from time to time to ensure the accuracy of the system and provide reliable
forecast. The accurate forecasting of flood conditions in both fluvial and costal
environments is an essential prerequisite for the provision of reliable flood warning
system (Smith et al., 1998). Singh (1989) stressed that the usefulness of forecasting
system is based on three criteria, which are: accuracy, reliability, and timeliness.
The procedures adopted for the preparation of a flood forecast depend largely on
the size and complexity of the river system, the minimum time required for the forecast to
be of benefit, the hydrologic data available for analysis, and the type of forecast required.
The requirement of a flood forecast might be either an estimate of the flood crest height
and the time of its occurrence or an estimate of the complete flood hydrograph (Pattison,
1975). However, the procedures may be grouped broadly as correlation methods, routing
methods or rainfall-runoff methods.
Floods cannot be totally prevented through structural measures due to technical
and economic reasons. Consequently flood forecasting and warning service constitutes
an effective and economical means to reduce live loss and property damage. In Malaysia,
since 1971, DID have been given the task to provide flood forecasting and warning
services. As part of the national flood relief machinery since 1971 and reviewed in May
1997 under the Operating Procedure of the National Security Council's Directive Number
20, DID is entrusted with the following functions in flood operation:

Monitoring and reporting of real-time river levels

Providing river level forecasts for important flood assessing points

Providing logistic supports

Carrying out flood damage assessment and rehabilitation works
The Flood Forecasting Center of DID Headquarters is responsible for the planning
and development of flood forecasting systems in the country. The flood forecasting
22
system basically consists of telemetric hydrological stations and forecasting models.
Currently, the eight river basins that are equipped with operational flood forecasting
modules are Sg. Kelantan, Sg. Pahang, Sg. Muda, Sg. Perak, Sg. Muar, Sg. Johor, Sg.
Sadong and Sg. Kinabatangan. The models used are shown in Table 2.6.1.
Presently, The Klang River Basin Flood Forecasting System is operational since
2002 based on MIKE 11 Modeling System with FLOOD WATCH as the decision
support system. The core of this system is the hydrology module (NAM) to model the
rainfall-runoff (RR) process, and the hydrodynamic (HD) module to calculate flow and
water level within rivers and channels.
Table 2.6.1: Flood Forecasting Models In Malaysia (DID, 2003).
River basin
Forecasting models
Period in use
Sg. Kelantan
Sacramento Model
Tank Model
1973 - 1981
1981 to date
Sg. Pahang
Stage Correlation Curve
Linear Transfer Function
Stage Regression Equation
Prior to 1986
1986 to date
2001
Sg. Muda
Stage Correlation Curve
Stage Regression Equation
1974 to date
2001
Sg. Perak
Stage Correlation
1960 to date
Sg. Muar
Linear Transfer Function
1986 to date
Sg. Johor
Black Box Model
1979 to date
Sg. Sadong
Linear Transfer Function
1986 to date
Sg. Kinabatangan
Linear Transfer Function
1986 to date
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2.7
Flood Warning and Dissemination System
A flood warning contains additional information, including recommendations or
order for action, such as evacuation or emergency flood proofing, specifically designed to
safeguard life or property (Smith et al., 1998). U.S.D.C. (1997) defined local flood
warning system as a community based or locally based system use to warn local areas of
flood danger and consists of many, if not all, of the following: rainfall, river and other
hydrologic gages; hydrologic models; communication system; a community flood
coordinator; and interested and capable volunteers.
Flood warning system in Malaysia could be dated back to 1925 when floods
occurred along the Sg. Kinta in Perak and Sg. Kelang, Sg. Selangor and Sg. Bernam in
Selangor. It is also known that the flood warning system based on river levels of the Sg.
Kelantan at Bradley Steps, Kuala Krai to warn the people of Kota Bharu downstream, has
been in use since early1900’s. The police were reading and transmitting the rainfall and
water level information via VHF sets to the Flood Warning and Relief Committee in Kota
Bharu. Stage correlation method was generally used for forecasting floods in major
rivers such as Sg. Muar, Sg. Perak, Sg. Pahang and Sg. Kelantan.
After the floods of 1971 the flood warning systems of major rivers subjected to
severe flooding were reviewed. The major deficiencies identified were inadequacy of
rainfall and water level station networks to provide timely and reliable real-time data.
Based on this review and its recommendations, telemetric stations, both rainfall and water
level, were established at strategic locations to enable the transmission of real-time data
to flood operation centers.
In accordance with the Operating Procedure under the flood relief mechanism
(Figure 2.7.1), when the river stage of any flood warning station reaches the Alert level,
DID begins to monitor closely the flood situation. When it reaches Warning level, DID
will inform the relevant flood control center so that flood relief mechanism shall be
activated.
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Danger level
Warning level
Alert level
Flood
Gaug
e
Normal level
RIVER
Alert level:
river level significaritly above normal level,
DID Flood Operation Room activated
Warning level:
river level near flooding level,
District Flood Operation Room activated
Danger level:
river level caused considerable flooding,
evacuation may be initiated
Figure 2.7.1: Designated critical levels of Flood Warning Station in Malaysia (DID,
2003).
Dissemination of flood warnings is the way in which the warning message is
composed and issued risk communication with both the emergency services and those at
risk and also influences the performance of flood warning systems (Smith et al., 1998).
Warnings are disseminated through a daily flood bulletin, email, WebPages, newspaper,
radio, television, and others communication media.
Flood awareness is very important, where an appreciation of the likely effects of
flooding and knowledge of relevant flood warning, response and evacuation procedures.
In communities with a high degree of flood awareness, the response to flood warnings is
prompt and efficient. In communities with a low degree of flood awareness, flood
warnings are liable to be ignored or misunderstood, and residents are often confused
about what they should do, when to evacuate, what to take and where it should be taken.
25
2.8
Sources of Project Data
Real-time data is collected in the field via the existing hydro-meteorological
networks of Selangor States and Federal Territory of Kuala Lumpur and transmitted to
the Federal Territory of Kuala Lumpur DID Office. Currently, the Federal Territory of
Kuala Lumpur telemetry network being monitored includes 18 stations of which 6
stations are combined water level and rainfall gauges, 6 stations report only water levels
and the remaining 6 only rainfall.
The telemetry network of DID Selangor comprises 21 stations, of which 7
combined water level and rainfall gauging stations are included in the Klang River Basin
Flood Forecasting Model. All telemetry stations transmit via radio communication in a
real-time mode to the master station at DID Federal Territory of Kuala Lumpur. Real
time telemetry data are stored in an MS Access database. Station Name and Number,
Type and Operational status are as shown in Table 2.8.1.
26
Table 2.8.1: Klang River Basin Telemetry Network
Station
No. Water Level
Telemetry
Rainfall
Station Name
Network
1
-
3116190
JPS Wilayah Persekutuan
KL
2
3117480
3117180
Sg. Gombak Simpang Tiga
KL
3
-
3216190
Sek. Men. Keb. Kepong
KL
4
-
3317191
Genting Sempah
KL
5
-
3117190
JPS Ampang
KL
6
-
3317190
Air Terjun Sg. Batu
KL
7
-
3219190
Kg. Kuala Seleh
KL
8
3216490
3216180
Sg. Klang at Leboh Pasar
KL
9
3217480
3217190
Klang Gates Dam
KL
10
3217490
3217191
Sg. Klang at Leboh Pasar
KL
11
3015491
3015190
Sg. Klang at Puchong Drop
KL
12
3016480
3016180
Sg. Klang at Jambatan Petaling
KL
13
3116492
-
Sg. Batu at Sentul
KL
14
3116490
-
Sg. Klang at Jambatan Sulaiman
KL
15
3117482
-
Sg. Klang at Lrg.Yap Kwan Seng
KL
16
3217481
-
Sg. Klang at Jalan Tun Perak
KL
17
3117481
-
Sg. Bunus at Jalan Tun Razak
KL
18
3116491
-
Sg. Gombak at Jalan Tun Razak
KL
19
3115480
3115180
Paya Jaras, Sg. Buloh
Selangor
20
3015490
3015180
TTDI Jaya, Shah Alam
Selangor
21
3015480
3015181
Taman Sri Muda
Selangor
22
3014480
3014180
Bandar Klang
Selangor
23
3118490
3118180
Kg Sungai Lui
Selangor
24
2917490
2917190
Kajang, Hulu Langat
Selangor
25
2816490
2816180
Dengkil, Hulu Langat
Selangor