Pengembangan Model Hidrograf Satuan Sintetis (HSS) DPMA-IOH dan Penerapannya pada Daerah Aliran Sungai - Segel Ginting; Widya Utaminingsih (Institut Teknologi Bandung, 2020)
AbstrakDesain hidrograf banjir diperlukan untuk merencanakan infrastruktur sumber daya air seperti waduk atau bendungan. Umumnya lokasi rencana infrastruktur sumber daya air belum tersedia data hidrologi untuk mendapatkan hidrograf banjir. Model hidrograf satuan sintetis (HSS) digunakan untuk memperoleh hidrograf banjir pada lokasi yang belum tersedia data hidrologi (ungauged). Model hidrograf satuan sintetis sangat populer digunakan di Indonesia karena keterbatasan data yang tersedia dan penggunaannya yang sederhana yaitu berdasarkan karakteristik DAS. Namun untuk mendapatkan hasil hidrograf banjir yang sesuai dengan data pengamatan memerlukan kalibrasi paramater model hidrograf satuan sintetis. Model HSS DPMA-IOH merupakan salah satu model yang dikembangkan berdasarkan modifikasi metode DPMA-IOH (menghitung rata rata debit puncak banjir) yang dikembangkan oleh DPMA (Direktorat Penyelidikan Masalah Air) dan IOH (Institute of Hydrology). Metode DPMA-IOH merupakan metode empiris yang dikembangkan di Indonesia khususnya di Pulau Jawa dan Sumatera. Model HSS DPMA-IOH mengembangkan persamaan untuk menghitung debit puncak hidrograf satuan, waktu ke puncak dan waktu dasar berdasarkan karaktersitik DAS serta bentuk hidrografnya. Prediksi debit puncak hidrograf satuan ditentukan berdasarkan nilai rata-rata debit banjir tahunan yang dihitung dengan metode DPMA-IOH. Parameter waktu ke puncak dan waktu dasar ditentukan berdasarkan karakteristik DAS. Bentuk kurva hidrograf satuan menggunakan dua pendekatan yaitu pendekatan model distribusi probabilitas gamma dan berdasarkan fungsi persamaan kurva naik dan kurva turun. Model HSS DPMA-IOH yang telah dihasilkan, diterapkan pada beberapa DAS di Indonesia yaitu DAS Ciliwung-Katulampa (Pulau Jawa), DAS Palung-Surodadi (Pulau Lombok), DAS Tukad Bandung-Denpasar (Pulau Bali), DAS Tukad Nyuling-Tiyingtali (Pulau Bali), DAS Kendilo (Pulau Kalimantan) dan DAS Singkoyo (Pulau Sulawesi). Hasil ujicoba pada beberapa DAS tersebut menunjukkan bahwa model HSS DPMA-IOH memiliki koefisien Nash-Sutcliffe di atas 83 % untuk menghasilkan hidrograf banjir, sehingga dapat membantu para perencana sumber daya air dalam menjalankan tugasnya. AbstractWater resources infrastructure planning such as reservoirs or dams require the design of a flood hydrograph. Hydrological data are generally not available at the location of the water resources infrastructure plan. Flood hydrograph design uses hydrological data. Design of flood hydrographs at locations without hydrological data (ungauged catchment) can use synthetic unit hydrographs. The synthetic unit hydrograph model is a popular application in Indonesia because of the limited data, and its simple use which is based on the characteristics of the watershed. However, to get flood hydrograph results that are in accordance with observational data requires calibration of parameters of synthetic unit hydrograph models. The DPMA-IOH's synthetic unit hydrographs model is one of the models developed based on the modification of the DPMA-IOH method (calculating the mean annual flood discharge) developed by the DPMA (Direktorat Penyelidikan Masalah Air) and the IOH (Institute of Hydrology). This empirical method was developed in Indonesia, especially in Java and Sumatera to calculate the mean annual flood discharge. DPMA-IOH's synthetic unit hydrographs was developed based on mean annual flood discharge and watershed characteristics to predict the unit hydrograph peak flow, time to peak and base time of ungauged catchment. Prediction of unit hydrograph peak flow is determined based on mean annual flood discharge calculated by the DPMA-IOH method. The time to peak and base time parameters are determined based on the characteristics of the watershed. The unit hydrograph shape using two approaches. There are using the gamma probability distribution and a rising and limb recession curve function. The DPMA-IOH's synthetic unit hydrograph model is applied to several watersheds in Indonesia, namely the Ciliwung-Katulampa watershed (Java Island), Palung-Surodadi watershed (Lombok Island), Tukad Badung-Denpasar watershed (Bali Island), Tukad Nyuling-Tiyingtali watershed (Bali Island), Kendilo Watershed (Kalimantan Island) and Singkoyo Watershed (Sulawesi Island). The results of application in several watersheds have shown that the DPMA-IOH's synthetic unit hydrographs model has above 83 percent Nash-Sutcliffe coefficient for obtaining flood hydrographs. The DPMA-IOH's synthetic unit hydrograph model can help planners to design flood hydrographs.