PENGEMBANGAN HIDROGRAF LIMPASAN UNTUK WILAYAH PERKOTAAN DI KOTA BEKASI - JAWA BARAT
Abstract
Sistem drainase perkotaan untuk mengelola air limpasan membutuhkan perencanaan agar dapat berkinerja maksimal dan berkelanjutan. Perencanaan sistem drainase tidak hanya bagaimana menentukan kapasitas saluran agar mampu mengalirkan debit puncak limpasan, tetapi bagaimana menentukan kapasitas volume tampungan (pond). Pond digunakan untuk mengurangi debit puncak dan dimensi saluran. Desain volume tampungan memerlukan informasi hidrograf limpasan permukaan, sementara metode yang biasa digunakan untuk desain drainase adalah metode rasional. Metode rasional hanya menghasilkan debit puncak. Agar dapat menghasilkan debit puncak dan hidrograf limpasan permukaan, maka dikembangkan metode perhitungan hidrograf satuan untuk wilayah perkotaan dengan ordinat lebih pendek (5 menit atau 1 menit) dan waktu konsenterasi yang lebih singkat (kurang dari 3 jam). Pendekatan yang digunakan untuk perhitungan hidrograf limpasan permukaan adalah dengan mengintegrasikan metode hidrograf satuan time-area dan metode SCS untuk perhitungan kehilangan air serta pola hietograf hujan di Kota Bekasi. Pendekatan yang dikembangkan ini telah diujicoba menggunakan data lapangan untuk kejadian hujan pada tanggal 20 Januari 2021 dan 21 Januari 2021 dengan parameter utama nilai CN sekitar 88.98 untuk λ = 0.05. Hasil ujicoba menunjukan bahwa kinerja metode yang dikembangkan menunjukkan hasil yang baik, dimana hasil perhitungan limpasan dengan data pengamatan cukup sesuai. Metode yang dikembangkan ini dapat digunakan pada cathment area kecil dengan waktu kosenterasi kurang dari 1 jam.
Urban drainage systems to manage runoff is require planning in order to perform optimally and sustainably. Drainage system design is not only how to determine the capacity of the channel to be able to drain the peak runoff discharge, but how to determine the capacity of the reservoir volume (pond). Ponds are used to reduce peak discharge and channel dimensions. The pond storage design is requires surface runoff hydrograph information, while the method commonly used for drainage design is the rational method. The rational method only produces peak discharge. In order to produce peak discharge and runoff hydrographs, a unit hydrograph calculation method for urban areas with shorter ordinates (5 minutes or 1 minute) and time of concentration less than 3 hours has been developed. The approaches are using time-area hydrograph method to calculate runoff hydrograph and SCS method for calculating water losses as well as the rain hietograph pattern in Bekasi City. This developed approach has been tested using field data for rainfall extreem events on January 20, 2021 and January 21, 2021 with the main parameter CN value around 88.98 for λ = 0.05. The test results show that the performance of the developed method shows good results, where the results of runoff calculations with observational data are quite appropriate. The developed method can be used in small area catchments with a concentration time of less than 1 hour.
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