Andawayanti, Ussy (2013) Pengembangan Koefisien Limpasan Permukaan Guna Memprediksi Pola Penyebaran Sedimen Ke Muara Sungai (Studi Kasus Sungai Bang Kabupaten Malang). Doktor thesis, Universitas Brawijaya.
Abstract
Semakin intensifnya kegiatan pemanfaatan wilayah pantai dan muara sungai menimbulkan peningkatan kebutuhan dan prasarana. Kebutuhan tersebut mendorong terjadinya perubahan penggunaan lahan, yang dapat mempengaruhi perubahan koefisien limpasan permukaan (CN) dan debit limpasan permukaan. Salah satu metode guna memprediksi limpasan permukaan adalah metode SCS Curve Number (SCS CN). Namun metode tersebut, belum tentu sesuai dengan kondisi DAS daerah kajian, sehingga diperlukan penyesuaian koefisien limpasan permukaan (CN). Hal ini akan berpengaruh pada prediksi debit limpasan permukaan, dan berdampak pula pada penentuan erosi dan sedimen di sungai dan muara. Dengan pengembangan koefisen limpasan permukaan (USS CN) digunakan untuk memprediksi pola penyebaran sedimen ke muara sehingga dapat diketahui stabilitas muara dan arah penumpukan sedimen di muara. Penelitian ini dilakukan di DAS Bang Kabupaten Malang dengan luas daerah aliran sungai (DAS) 2.393.375 Ha terdiri dari 43 sub DAS. Sungai Bang panjangnya 12.36 km, bermuara di pantai Tamban. Analisis koefisien limpasan permukaan, debit limpasan permukaan, erosi dan sedimen menggunakan bantuan perangkat lunak AVSWAT 2000, yang juga untuk mendapatkan nomogram USS CN dengan mensimulasikan tata guna lahan. Sedangkan untuk memprediksi pola penyebaran sedimen spasial digunakan bantuan perangkat lunak SMS (Surface Water Modelling System) yaitu sub program RMA2 dan SED2D. Dari hasil analisis pada kondisi eksisiting didapat harga CN = 67. Hasil simulasi dengan mengurangi 10-100% hutan memperoleh besarnya CN=53-65, yang kemudian digambarkan pada Nomogram USS CN. Model persamaan pendugaan koefisien limpasan CN untuk pemukiman Qlp = 0.008 CN– 0.262 (CN=65.4-73.80) , kebun : Qlp = 0.005 CN – 0.145 (CN= 63.70-71.60), ladang : Qlp = 0.027 CN – 1.009 (68.20-77.50), semak: Qlp = 0.018 CN + 0.728 (CN = 68.50-78.60) , hutan : Qlp = 0.020 CN + 0.756 (CN = 68.00-77.50) , sawah tadah hujan : Qlp = 0.003 CN – 0.127 (CN= 73.40-80.40) dan tambak: Qlp = 0.022 CN + 0.870 (CN= 70.20-80.40). Adapun model debit limpasan permukaan Lp = a CH2 + b CH – c dan model besarnya sedimen Sed = a Lp2 + b Lp – c dengan a,b dan c adalah konstanta yang merupakan fungsi CN. Pola penyebaran sedimen ditunjukkan dengan adanya perubahan konsentrasi sedimen dari hulu ke hilr semakin kecil dan perubahan bed change dari hilir ke hulu, yakni untuk kondisi eksisting (6.7% hutan) dan 10% hutan terjadi perubahan 0.10m, untuk 50% hutan menjadi 0.005 m, sedang untuk 100% hutan menjadi 0.000028 m. Hal tersebut menunjukkan bahwa perubahan sedimen melayangnya hanya terjadi di hulu DAS. Di daerah hilir belum terjadi terjadi perubahan karena adanya pengendapan sedimen. Hasil simulasi menunjukkan dengan perubahan luas % hutan, terjadi penambahan secara linier jumlah sedimen yang menuju muara sungai. Di samping itu terjadi penumpukan sedimen ke arah sisi kanan garis pantai normal.
English Abstract
The more intense on the activity utilization of coastal areas and estuaries can increase the demands and infrastructure. These needs led to the changes in land uses, which in turn can affect changes in surface runoff coefficient (CN) and surface runoff discharges. One of the methods for predicting the surface runoff is the method of SCS Curve Number (SCS CN). However such method is not automatically suitable with the condition of watershed in the study area, therefore the adjustments of runoff coefficient are called for. These aspects will affect on the prediction of surface runoff discharges, and also have impact on the determination of erosion and sedimentation in rivers and estuaries. This research was conducted in the Bang Watershed of Malang Regency with the river basin of 2,393,375 hectares which consists of 43 sub river basin. The River Bang has a length of 12.36, with its estuary located at the Tamban Beach. The analysis of surface runoff coefficients, surface runoff discharges, erosion and sedimentation have been using the AVSWAT 2000 software, which has also been used to obtain the USS CN nomogram by simulating the land uses. For predicting the spatial sediment distribution pattern, the applied software is SMS (Surface Water Modelling System) which in the sub programmes of RMA2 and SED2D. The results of analysis in the existing condition show that CN = 67. Simulation with decreasing forest of 10~100% has produced CN = 53~65, which are illustrated in the USS CN nomogram. Estimated equation model of CN for residence: Qlp = 0.008 CN – 0.262 (CN=65.4-73.80), garden: Qlp = 0.005 CN – 0.145 (CN= 63.70-71.60), dry field: Qlp = 0.027 CN – 1.009 (68.20-77.50), shrub: Qlp = 0.018 CN + 0.728 (CN = 68.50-78.60) , forest: QLP = 0.020 CN + 0.756 (CN = 68.00-77.50), rice irrigated rained area: Qlp = 0.003 CN – 0.127 (CN= 73.40-80.40) and dyke: Qlp = 0.022 CN + 0.870 (CN= 70.20-80.40). However, the surface runoff model : Lp = a CH2 + b CH – c and sediment yield model : Sed = a Lp2 + b Lp – c where a,b and c: constant which is a function of CN number. The pattern of sediment distribution is indicated by the shift of sediment concentration which is decreased from upstream to downstream, and the bed change from downstream to upstream, for the existing condition, 10% forest was 0.10 m, and 50% forest was 0.005 m, whereas 100% forest was 0.000028 m. It indicates that the change of suspended sediment is only occurred in the upstream of watershed. In the downstream area, the change is not yet occurred as the result of sedimentation. The results of simulation show that the change in the forest percentage will cause a linear increase of the amount of sediment moving toward the estuary. Besides that, there are sediment accumulate toward the right side of normal shoreline.
| Item Type: | Thesis (Doktor) |
|---|---|
| Identification Number: | DES/551.488/AND/p/061400027 |
| Subjects: | 500 Natural sciences and mathematics > 551 Geology, hydrology, meteorology > 551.4 Geomorphology and hydrosphere |
| Divisions: | S2/S3 > Doktor Teknik Sipil, Fakultas Teknik |
| Depositing User: | Budi Wahyono Wahyono |
| Date Deposited: | 29 Apr 2014 10:47 |
| Last Modified: | 16 Oct 2024 03:08 |
| URI: | http://repository.ub.ac.id/id/eprint/161018 |
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