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ABSTRACT
Due to the rapid development, flooding occurred progressively. This
scenario is worsened if improper drainage systems were implemented.
The inattentiveness to all the problems occurred will generate the
possibility for more severe flooding risk and creates further
damages of property and loss of lives.
Since the implementation of Urban Stormwater Management Manual of
Malaysia (MSMA) in 2001 by Department of Irrigation and Drainage,
Malaysia, the Best Management Practices (BMPs) through construction
of detention ponds have been encouraged. After 8 years of
implementation, there is a need to reconsider the recommendation of
constructing detention pond for water quantity control by evaluating
performance of the constructed dry detention ponds using computer
modelling.
This research focused on the evaluation of the existing and future
performance under the stress of development of the existing drainage
system particularly the constructed dry detention pond by using
InfoWorks CS through United States Soil Conservation Services Method
(SCS).
The case study is dry detention pond at Section 6, Kota Damansara,
Selangor built in 1996 with the total catchment area of
approximately 428 hectares. The major landuses in Kota Damansara are
housing areas and shops which contribute more than 50% of impervious
areas apart from forest, schools, landscape and fields.
From the research, it is found that the existing pond is functioning
well and could perform well up to the design rainfall of 100-year
ARI without flood on Cecawi 6/19 Road nearby. The dry detention pond
could attenuate flow at the outlet of the dry detention pond at
39.94 m3/s and slower by 40 minutes for 50-year ARI and 42.36 m3/s
and slower by 45 minutes for 100-year ARI events.
Under the landuse changed scenario, the existing dry detention pond
could still cater the 100-year ARI design rainfall without flooding
at surrounding area. The scenario show an increase in flow ranging
from 8.88% to 52.95% and also increase in water depth ranging from
8.09% to 28.79% in all simulated cases for 2-, 10-, 50- and 100-year
ARI. However, the time to peak after landuse changed condition is 5
minutes slower for existing scenario due to conduits full flow
condition that slow down the flow to downstream.
The comparison between the existing drainage condition and drainage
resized condition after landuse changed at the outlet culvert of
detention pond show an increase runoff about 30% for both 50- and
100-year ARI and quicker time to peak at 10 minutes.
As overall, the dry detention pond is functioning to cater 50-year
ARI recommended in MSMA. The construction of detention pond needs to
be encouraged for any new housing development to control water
quantity. Future development need to consider landuse changed factor
which could induce in more flow generation and water volume from
upper catchment area and it should be studied using the numerical
approaches to solve the problem and ease the decision making
processes.
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