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CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
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).
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
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).

Flood – stage at which the stream channel becomes filled and above which is
overflows its banks (Wisler et al., 1957).
2.2
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. 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 of
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).
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Figure 2.1: Causes of Floods and Flood-Intensifying Factors (Smith et al. 1988)
2.3
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. The Government has embarked on a
comprehensive flood mitigation program involving expenditure of RM 500 million,
construction of large 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
channelization 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 developments are required to utilize runoff minimization measures such as
retarding basins, rainwater tanks and infiltration trenches to ensure that post development
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discharges do not exceed pre-development discharges (DID, 2000). The implementation
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 – MASMA).
2.4
Sources of project data
Real-time data is collected in the field via the existing hydro-meteorological
networks in Selangor and the 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 have
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 station 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 2.1.
Table 2.1: Klang River Basin Telemetry Network
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Station
No.
Telemetr
Station Name
Water Level
Rainfall
y
Network
1
-
3116190
DID,Wilayah Persekutuan
KL
2
3117480
3117180
Gombak River Simpang Tiga
KL
3
-
3216190
Sek. Men. Keb. Kepong
KL
4
-
3317191
Genting Sempah
KL
5
-
3117190
JPS Ampang
KL
6
-
3317190
Batu River Waterfall
KL
7
-
3219190
Kg. Kuala Seleh
KL
8
3216490
3216180
Klang River at Leboh Pasar
KL
9
3217480
3217190
Klang Gates Dam
KL
10
3015491
3015190
Klang River at Puchong Drop
KL
11
3016480
3016180
Klang River at Petaling Bridge
KL
12
3116492
-
Batu River at Sentul
KL
13
3116490
-
Klang River at Sulaiman Bridge
KL
14
3117482
-
Klang River at Lrg.Yap Kwan Seng
KL
15
3217481
-
Klang River at Jalan Tun Perak
KL
16
3117481
-
Bunus River at Jalan Tun Razak
KL
17
3116491
-
Gombak River at Jalan Tun Razak
KL
18
3115480
3115180
Paya Jaras, Sungai Buloh
19
3015490
3015180
TTDI Jaya, Shah Alam
Selangor
20
3015480
3015181
Taman Sri Muda
Selangor
Selangor
21
3014480
3014180
Bandar Klang
Selangor
22
3118490
3118180
Kg Sungai Lui
Selangor
23
2917490
2917190
Kajang, Hulu Langat
Selangor
24
2816490
2816180
Dengkil, Hulu Langat
Selangor