PERUBAHAN MORFOLOGI KALI GARANG-BANJIR KANAL BARAT TANPA BENDUNG SIMONGAN ( PENDEKATAN MODEL SIMULASI BRI-STARS )

EDHISONO, SUTARTO (2004) PERUBAHAN MORFOLOGI KALI GARANG-BANJIR KANAL BARAT TANPA BENDUNG SIMONGAN ( PENDEKATAN MODEL SIMULASI BRI-STARS ). Masters thesis, Program Pascasarjana Universitas Diponegoro.

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Abstract

The Simongan Weir is a weir which was built by the Government of the Netherlands Indic in the beginning of the 20th century. The weir is layed at the end of the Garang River, which functioned to regulate the river flow to the Semarang River and to the West Flood Way. In accordance to the changing of the land use on the upper part of the Garang River, changing of the flood flow and sedimentation are occured on this river which tends increase the flood discharge and the water level that may cause disasters. In order to reduce the flood water level, it is planned to change the Simongan Weir which formely a 'fixed weir' to a 'movable weir' which called barrage, by cutting the crest of the fixed weir in 3.7 meters height. Because of the cutting of the weir body, it will influence to the morphology of the river, the Garang River in the upper part and the West Flood Way in the lower part of the Simongan Weir. This research contains simulations of the changing of the river morphology of the Garang River and the West Flood Way without the Simongan Weir. Simulation used the BRI-STARS soft ware ( BRIdge Stream Tube Model for Alluvial River Simulation), which this simulation model generalitationed a semi two dimensionals flow of water and its sediment that capable to compute erosion and sedimentation in sub-critical, super critical flows and combination of both flow conditions. Input of the simulation model in this research used main data, which consisted of sediment fraction, twelve years reliable discharge hydrograph, Manning's coefficient, and river cross sections data. Simulation was started from 20 time steps for trial in 2 (two) conditions, i.e. : existing ( sediment data 1992) and prediction (sediment data 1997). Stage 2 was simulation to predict a stable slope. Condition of the stable slope prediction used river profile 1997 and sediment data of the year 2003. Hydrograph of the stable slope prediction simulation used reliable discharges from 1990 - 2001. Manning's coefficient which used was 0.028 (SMEC, 2000). Simulation result indicated, that the river bed slope found its stability process which indicated a horizontal slope ( I = 0.000 ) and Fr <1 at the time step 9000th. The stability was occured in an average slope 0.00055. The morphology of the Garang River was changed because of the deletation of the Weir from its river system. The dominant changing in upper part was erosion, in the middle was transition beetween erosion and sedimentation, and in lower part, sedimentation process was tended, occured although was not as big as in the middle part of the longitudinal profile of the river. Bendung Simongan merupakan bendung tetap yang dibangun Pemerintah Hindia Belanda diawal abad ke 20 yang terletak ujung Kali Garang yang berfungsi untuk mengatur aliran sungai tersebut ke Kali Semarang dan Banjir Kanal Barat. Seiring dengan perkembangan perubahan tata guna lahan dihulu Kali Garang, terjadi perubahan aliran banjir Kali Garang dan sedimentasi pada sungai tersebut yang cenderung meningkatkan debit banjir dan muka aimya yang dapat menimbulkan bencana.Dalam usaha untuk menurunkan muka air banjir, direncanakan Bendung Simongan ini akan diganti dari yang semula bendung tetap (weir) menjadi bendung gerak (barrage), dengan memotong mercu bendung tetap setinggi 3,7 meter. Akibat pemotongan mercu ini akan berpengaruh pada morfologi sungai, pada Kali Garang yang terletak dihulu dan Bendung Simongan dan Banjir Kanal Barat (BKB) di bagian hilimya. Penelitian ini berisi tentang simulasi perubahan morfologi Kali Garang- Banjir Kanal Barat tanpa Bendung Simongan. Simulasi menggunakan perangkat lunak SRI-STARS (BRIdge Stream Tube model for Alluvial River Simulation), dimana simulasi model ini menggeneralisasi aliran semi-dua dimensi untuk air dan sedimennya yang mampu untuk menghitung penggerusan dan pengendapan dalam aliran sub-kritis, super kritis dan kombinasi dari kedua kondisi aliran tersebut. Input model simulasi pada penelitian ini menggunakan data-data utama berupa data fraksi sedimen, hidrograf Debit andalan dua betas tahun, koefisien manning, dan data penampang melintang sungai. Simulasi dimulai pada 20 time step untuk uji coba dalam dua kondisi yaitu eksisting (data sedimen tahun 1992) dan kondisi prediksi (data sedimen tahun 1997). Tahap kedua merupakan simulasi untuk prediksi slope stabil. Kondisi prediksi slope stabil menggunakan data penampang sungai 1997 dan data sedimen tahun 2003. Hidrograf simulasi prediksi slope stabil yang digunakan adalah debit andalan tahun 1990-2001. Koefisien manning yang digunakan besamya 0,028 (SMEC, 2000). Hasil simulasi menunjukkan pada time step ke 9000 slope dasar sungai mengalami proses kestabilan dengan indikator slope datar ( I = 0,000) dan Fr < 1. Kestabilan terjadi pada kemiringan rata-rata 0,00055. Morfologi Kali Garang mengalami perubahan akibat dihilangkannya Bendung pada sistem sungainya. Perubahan dominan di hulu adalah erosi, ditengah adalah transisi antara erosi dan sedimentasi dan di hilir cenderung terjadi sedimentasi meskipun tidak sebesar di bagian tengah penampang memanjang sungai.

Item Type:Thesis (Masters)
Subjects:T Technology > TA Engineering (General). Civil engineering (General)
Divisions:Postgraduate Program > Master Program in Civil Engineering
ID Code:12029
Deposited By:Mr UPT Perpus 2
Deposited On:27 May 2010 13:20
Last Modified:27 May 2010 13:20

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