Rational hydrograph method for small urban catchment (Sungai Kayu Ara, Damansara, Selangor)
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Date
2011-04-01
Authors
Wei Sim, Lee
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Abstract
This study presents a rational hydrograph method as an alternative approach to compute
the runoff of an outlet for a small urban catchment, which is Sungai Kayu Ara
catchment in Damansara, Selangor. Instead of using computer model which consume
more time to compute runoff hydrograph, the Rational Hydrograph method developed
in this study provides a simple hand calculation formula for the runoff hydrograph. The
rational hydrograph method is expanded from rational method based on system memory
concept. Moving average rainfall intensity is used to reduce the cycle of data. As for
the time of concentration, Kirpich Formula is applied by considering the length and
slope of the catchment. On the other hand, runoff coefficient is estimated based on the
land use map of the catchment. This approach was tested on five events recorded from
small catchment in Damansara, Selangor. Moreover, the predicted runoff using this
method was compared with simulated runoff by HEC-HMS. The modeling of HECHMS
is also discussed in this study to ensure the model compute a relatively accurate
result compared to observed data. The Rational Hydrograph method tends to
overestimate the rising limb of the hydrograph because the initial abstraction is ignored.
However, the Rational Hydrograph is able to compute relatively accurate peak flow as
well as the trend of the observed hydrograph. Overall, the rational hydrograph method
gives satisfactory results when compared to both observed data and HEC-HMS model.