Hydraulic Modeling On Steep Slope Watersheds (At Kali Putih Watershed, Magelang, Central Java, And Nasiri Watershed, West Seram, Maluku)

ADI PUTRI ANISA W, Ir. Adam Pamudji Rahardjo, M.Sc., Ph.D.; Prof. Ir. Djoko Legono, Ph.D.

2017 | Tesis | S2 TEKNIK PENGELOLAAN BENCANA ALAM

Pemodelan hidrologi dan hidraulika perlu dilakukan untuk meneliti respon suatu DAS terhadap suatu data masukan hujan, khususnya pada DAS yang rawan terhadap bencana seperti DAS Kali Putih di Magelang, Jawa Tengah, dan DAS Nasiri, di Seram Bagian Barat, Maluku. Model hujan-aliran grid terdistribusi berbasis GIS digunakan untuk mensimulasikan transofrmasi hujan-aliran. Pemodelan aliran hidrodinamika dua dimensi kemudian dilakukan untuk mensimulasikan proses kejadian banjir di sungai dan di bantaran banjir. Analisis sensitivitas dilakukan pada laju infiltrasi, nilai n Manning, dan intensitas hujan. Studi kasus terhadap pemodelan hujan-aliran di Nasiri berdasarkan kejadian hujan pada 19 April, 3 Mei, dan 12 November 2016 juga dilaksanakan. Hasil pemodelan menunjukkan bahwa hasil pemodelan hidrologi-hidraulika memiliki kecocokan yang baik dengan data terukur. Laju infiltrasi, nilai n Manning, dan intensitas hujan memberikan efek yang perlu dipertimbangkan terhadap hidrograf aliran yang dihasilkan. Aktivitas manusia pada permukaan lahan juga terbukti menimbulkan dampak pada perubahan laju infiltrasi dan nilai n Manning.

Hydrologic and hydraulic modeling is important to be conducted to examine the watershed response based on a rainfall input, especially over disaster-prone watersheds such as Kali Putih watershed in Magelang, Central Java, and Nasiri watershed in West Seram District, Maluku Province. A GIS-based grid-based distributed rainfall-runoff model was utilized to simulate the rainfall-runoff transformation. A two-dimensional hydrodynamic flow modeling was then carried out to simulate the flood processes on the stream and floodplain area. A sensitivity analysis was conducted on infiltration rate, Manning's n value, and rainfall intensity. A case study of rainfall-runoff modeling in Nasiri based on real rainfall events on April 19th, May 3rd, and November 12th 2016 was conducted. The modeling results show that the results of hydrologic-hydraulic modeling has a good agreement with the observed results. Infiltration rate, Manning's n value, and rainfall intensity give considerable effects to the resulted flow hydrographs. Human activities on the ground surface give effects on the change of soil infiltration rate and Manning's n value.

Kata Kunci : hydrologic-hydraulic model, rainfall-runoff model, two-dimensional hydrodynamic model