PENGEMBANGAN MODEL ANSWERS UNTUK PERHITUNGAN EROSI DAN SEDIMENTASI PADA SUB-DAS SECANG DAN SUB-DAS KEDUANG

model ANSWERS (Areal Nonpoint Source Watershed Environment Response Simulation) is a ofdistributed hydrological which have the ability to predict the spatial erosion and sedimentation in certain or specific watershed. The objective of this study were: 1) To evaluate the performance of the ANSWERS model to predict erosion and sedimentation 2) To deploy and evaluate the ANSWERS model to predict erosion and sediment.tion done Development of a model made by rewriting the source code in FORTRAN 90 ANSWERS. The model has been developed further in trials using secondary data at Sub-Watershed Secang and Sub-watershed keduang. The analysis usedin this research are the sensitivity analysis, the spatial analysis and temporal analysis. Validation and verification by calculating the actual erosion based on outcrop plant roots. The study results the demonstration of the ANSWERS v.1.01 in Subwatershed Secang provide information of erosion value generated by 8 tonnes / ha and the sedimentation of 1.3 ton / ha, while for Sub-watershed Keduang, erosion value obtained by 5 tons / ha and sedimentation of 3.3 tons / ha. The developed ANSWERS curently has ability to process more than 100,000 pixels compared to the previous version which only 1000 pixels. The results could also simulate the development of 12 rain stations while the previous version only capable to stimulate 3 stations. Simulation in two areas of research using the developed ANSWERS indicate the total erosion obtained in Sub-watershed Secang is 9.1 tons / ha while in Sub-watershed Keduang is 62.9 tons / ha. Results validation showed the difference between average and actual erosion model using the developed ANSWERS is about 163.87 t / ha / yr, while using the ANSWERS v.1.01 difference obtained by an average of 311.6 tonnes / ha / yr

PENGELOLAAN SUMBERDAYA AIR DAERAH IRIGASI WADUK BATUJAI KABUPATEN LOMBOK TENGAH UNTUK PENINGKATAN PRODUKSI PADI

Dam Batujai in Central Lombok Regency is the locus of study. The dam provides service to eight irrigation zones, encompassing ±8000ha farm area that extends over three districts� administrative area, being the District of West Praya, the District of Southwest Praya, and the District of Jonggat. This research aims at: 1) identifying the amount of water available in Dam Batuja

DETERMINING THE IMPACT OF VOLCANIC ERUPTION ON THE DISCHARGE USING HYDROLOGICAL MODEL Case in Code Watershed, Yogyakarta Special Province, Indonesia

After Merapi eruption (October � December 2010), several conditions change as consequence of the eruption. This research analyzed the hydrologic change of the Code watershed (30 km2) in north Yogyakarta. Therefore this research developed a hydrologic model for the watershed by means of available data and hydrological equations to predict the discharge and further simulate the extreme rainfall event to predict flood in Code river. The research concluded that the changes related to hydrological process in Code watershed due to the eruption is mainly affected the soil. The change includes: sand fraction increased on soil texture composition, additional ash deposition of 32-41 mm on soil depth, and decreased of infiltration rates. Related with the model, statistically it has high error and low correlation of 0.46 and 0.22 for pre and post eruption model respectively. The model simulated that soil depth has the most sensitive to the discharge. It performs positive response while the other parameters tested, Ksat, porosity and maximum storage gives negative response to the discharge. In addition, the amount of discharge in the model is lower than the amount in measured discharge for the pre eruption model. Meanwhile, the post eruption model performs higher than the measured discharge. Predicted discharge based on extreme rainfall event on 5, 20, 50 and 100 year periods gives the amount of discharge in a day reaching 2,171,967 m3/day, 2,969,264 m3/day, and 3,515,760 m3/day respectively. About 19, 29, 35 and 37 of 50 sections of Code river were prone to flood when 5, 20, 50 and 100 year extreme rainfall event occurs respectively. Sub disctrics that prone to flood are Jetis, Gondokusuman, Gedong tengah and Mergangsan