Temef Watershed is located in the Benanain River Basin with a catchment area of 551.50 km2. River characteristics in the Temef Watershed are influenced by three main river streams from upstream to downstream. Conventional collection of data on watershed characteristics requires a relatively long process and time. However, when based on Geographic Information Systems (GIS), the cost and time will be more efficient. The floodwater level is affected by the amount of rainwater runoff that occurs in the Temef Watershed. The amount of runoff depends on the level of soil permeability and land cover. To determine the level of soil permeability, hydrogeological maps are used. Based on this, a study of the characteristics of flood waters from GIS-based hydrogeology is needed. The analysis method used ArcGIS overlay on hydrogeological maps, while data on watershed characteristics used the Archydro and HEC-GeoHMS features. The results of the analysis showed a level 3 permeability type with limestone lithology, solid volcanic breccia, sandy marlene, conglomerate, and alluvium consisting of sand and gravel having moderate to high permeability. The metamorphic and basalt rocks have low to moderate permeability and the scaly clay has low to very low permeability. This condition causes runoff that turn into flood streams.
Badai siklon Seroja yang terjadi dari tanggal 3 April 2021 di daratan Pulau Timor merupakan salah satu badai siklon dengan kekuatan besar yang terbentuk di selatan Nusa Tenggara Timur. Seroja ini mengakibatkan badai petir dan hujan dengan intensitas tinggi di bebarapa kawasan di Nusa Tenggara Timur yang mengakibatkan banjir besar. Luapan banjir akibat badai Seroja ini juga terjadi pada DAS Temef di Kabupaten Timor Tengah Selatan. Berdasarkan data dari Badan Meteorologi Klimatologi dan Geofisika bahwa siklon tropis Seroja merupakan siklon ketujuh dalam musim siklon wilayah Australia 2020-2021 dan satu-satunya badai yang menyebabkan korban jiwa. Penelitian ini dilakukan untuk mengetahui seberapa besar intensitas hujan terhadap debit sungai di DAS Temef saat badai Seroja terjadi di awal April 2021. Metode yang digunakan dalam analisis ini dengan cara kuantitatif berdasarkan data citra satelit Global Precipitation Measurement (GPM) dan dari ground station. Hasil yang didapatkan dari analisis ini diperoleh bahwa tinggi hujan saat badai Seroja adalah 146.38 mm/hari - 149.81mm/hari secara merata pada luasan DAS. Kondisi ini diperburuk dengan hujan yang terjadi secara terus menerus selama 5 hari sebelumnya yang sudah diatas 80-90 mm. Badai Seroja ini bisa menjadi tolok ukur dalam mitigasi bencana untuk kondisi anomali cuaca di Nusa Tenggara Timur.
Temef Dam is located in Oenino Village Oenino District and Konbaki Village Polen District, Timor Tengah Selatan Regency which has a capacity of 45.79 millions m3. This research aimed to determine the amount of potential evapotranspiration using Penman Modification Method, the amount of dependable discharge with three methods that are NRECA, F.J. Mock, and Tank Methods, from those three methods will be selected a method that have closest characteristic of Temef Watershed, and filling timein Temef Reservoir. The maximum half monthly potential evapotranspiration in Temef Watershed using Penman Modification Method is 142.72 mm and the minimum is 71,25 mm. The average of annual discharge using NRECA Method is 249.89 m3/sec, F.J. Mock Method is 258.66 m3/sec, and Tank Method is 92.15 m3/sec. Based from three methods that have been used, Tank Method is the closest method to the characteristics of Temef Watershed, which RMSE value from Tank Method is 2.99. Filling time of Temef Reservoir to reach the planned reservoir volume in normal water year condition is three months and fifteen days and in low water year condition is six months.
Rainfall data collection based on the TRMM (Tropical Rainfall Measuring Mission) satellite provides a good alternative in estimating rainfall. TRMM technology can minimize manual rainfall recording errors and increase rainfall accuracy for hydrological analysis. From the results of the statistical relationship analysis, the most accurate results obtained are 9 years of calibration and 1 year of validation, the selected equation is a polynomial with the following equation y = 0.0112 x2 - 0.2564x + 4,1293, so that validation analysis is carried out with the selected equation so that the validation results are obtained against 1 year rainfall data for the RMSE value of 7.022. The NSE value is 0.923, the Correlation Coefficient is 0.94 and the relative error value is 5.48 and the results of the equation for discharge are modeling return periods of discharge 2, 5, 10, 20 and 25 years for discharge observations of 2 years return period; Q = 84.44, m3/s at 5 years return period; Q = 105.95 m3/s, 10 year return period; Q = 120.86 m3/s, 20 years return period; Q = 135.16 m3/s, 25 years return period; Q = 139.69 m3/s. Meanwhile, for the simulation discharge, the return period is 2 years; Q =51,84 m3/s at 5 year return period; Q = 65,35 m3/s, 10 year return period; Q = 74,15 m3/s, 20 years return period; Q = 84,89 m3/s, return period of 25 years; Q = 94,65 m3/s.
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