Kajian ini mempersembahkan kaedah Hidrograf Rasional sebagai satu alternatif untuk mendapatkan air larian dari kawasan tadahan kecil, iaitu Sungai Kayu Ara di Damansara, Selangor. Kaedah ini adalah lebih senang untuk menganggar air lairan daripada menggunakan model komputer kerana hanya perlu mengira dengan menggunakan formula yang mudah. Kaedah Hidrograf Rasional ini mengaplikasikan konsep sistem memori. Kaedah “moving average” juga digunakan untuk mengurangkan pengulangan data. Kajian ini mengaplikasikan formula Kirpich untuk mendapatkan masa tumpuan manakala pekali air larian pula diperoleh melalui anggaran daripada peta penggunaan tanah untuk kawasan tadahan tersebut. Lima kejadian hujan telah diuji dengan menggunakan kaedah tersebut. Selain itu, hasil air larian daripada kaedah tersebut juga dibandingkan dengan keputusan daripada model HEC-HMS. Process permodelan dalam HEC-HMS telah dibincangkan dengan lebih teliti dalam kajian ini untuk memastikan dapatan daripada model adalah tepat. Keseluruhannya, kaedah Hidrograf Rasional ini memberi keputusan yang memuaskan walaupun bahagian menaik dalam hidrograf adalah lebih tinggi berbanding dengan data cerapan. Keadaan ini beraku kerana kaedah ini tidak mengambil kira kehilangan atau takungan air awalan.
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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.
Rational hydrograph method for small urban catchment (Sungai Kayu Ara, Damansara, Selangor)_Lee Wei Sim_A9_2011_NI