Hydrologic soil group based curve number matrix modeling for Enset-Based land use system in Meki River Watershed, Western Lake Ziway Sub-Basin, Central Rift Valley of Ethiopia

Background Enset-Based land use system (EBLUS) exhibits good carbon stock and infiltration rate equivalent to forest covered areas, which enhances infiltration and water holding capacity and it can reduce the curve number (CN) of the watersheds but it was not considered in former studies. Therefore, this study is planned to model the hydrologic soil group (HSG) based CN matrix of EBLUS relative to other LUSs with established hydrological characteristics in the Meki river watershed. The soil data is used to determine the HSG of the watershed collected from Ministry of Water, Irrigation and Energy (MOWIE) and verified by Harmonized World Soil Database (HWSD). A Model is developed for CN of EBLUS relative to other LUSs (Alemu’s formula). The model considers both infiltration rate measured using Amozi-meter and carbon stoke of soil weighed as 85% and 15% respectively. HEC-GEO-HMS model is used to consider the CN of EBLUS as a separate LUS to verify the developed CN matrix model to generate CN of the sub-watersheds. Result The field measurement results show that an infiltration rate of 12.9675,11.1875,10.375,7.065 and 12.8125mm hr -1 for Natural Forest, Grassland and plantation, cultivated, built-up and EBLUS respectively. The model is: and the resulting CN matrix of EBLUS is 39,51.5,58.3 and 61.6 for HSG of A,B,C and D respectively. Conclusion Significant reduction in mean CN of the watershed that shows the role of EBLUS in managing the water resources and flood is high. Therefore, escalating EBLUS will reduce the CN of the watershed which reduces runoff volume in the watershed and it ensures the sustainability of Lake Ziway by reducing sedimentation.

Penentuan hydrologic soil group untuk perhitungan debit banjir Di Daerah Aliran Sungai Brantas Hulu

Bendungan direncanakan dibangun untuk dimanfaatkan dalam memenuhi kebutuhan di bidang sumber daya air. Disamping manfaat yang terkandung di dalamnya, akan terdapat bahaya besar bila ada ketidakmampuan struktur bendungan dalam menahan banjir yang masuk ke dalam waduk. Pemilihan metode yang tepat untuk memperkirakan besaran banjir rencana merupakan bagian dari keamanan bendungan. Permasalahan yang terjadi di Indonesia adalah pencatatan data pada pos duga air tidak tersedia. Salah satu metode perhitungan kehilangan air (losses) pada pemodelan banjir adalah NRCS-CN. Kelebihan metode ini dapat digunakan untuk wilayah yang tidak memiliki data hidrograf banjir maupun tinggi muka air waduk, tetapi tersedia data pencatatan hujan. Dalam penentuan nilai CN, Indonesia belum memiliki peta HSG (Hydrologic Soil Group) sehingga perlu dibuat peta tanah seperti HWSD. Penelitian dilakukan dengan penentuan CN menggunakan peta tanah (HWSD), tataguna lahan (BAPPEDA). Kehilangan air dilakukan dengan model HEC-HMS. Penelitian dilakukan di DAS Brantas Hulu dengan titik outlet Bendungan Sutami. Simulasi dilakukan dengan kalibrasi tinggi muka air. Kelompok HSG yang didapat dari peta HWSD pada DAS Brantas Hulu adalah D (lempung), B (tanah liat berlanau), dan A (pasir bertanah liat). Penentuan HSG dari peta tanah HWSD dengan metode kehilangan air NRCS-CN dan hidrograf satuan NRCS menghasilkan kalibrasi terbaik didapatkan dari RMSE dan beda tinggi pada AMC II dan λ=0,2 untuk bulan Maret 2007 (RMSE=0.55) serta AMC II dan λ=0,05 bulan Desember 2007 (RMSE=0.65).

Penentuan hydrologic soil group untuk perhitungan debit banjir Di Daerah Aliran Sungai Brantas Hulu

Dams are planned and built to be used for water resources activities. Besides the benefits, there were a great danger if the inability of the dam structure to holding the flood is available. The choice of the right method for the magnitude of the plan flood is part of the dam security. Problems that occurred in Indonesia former record data from AWLR is not available. One method of losses flood modeling is NRCS-CN. Moreover, this method can be used for areas without flood hydrograph or reservoir water leveldata, however rainfall record data is available. In CN's determination, Indonesia does not have a HSG (Hydrologic Soil Group) map that needs to be made from another soil map like HWSD. The research was conducted using CN method using land map (HWSD), land use (BAPPEDA). Losses were carried out with HEC-HMS model. The study was conducted in the Upper Brantas basin withSutai Dam outlet. The simulation was done by calibrating the water level. HSG groups obtained from HWSD maps in Upper Brantas basin are A (loamy sand), B (loam), and D (clay). Determination of HSG from HWSD soil map with NRCS-CN loss method and NRCS UH resulted the best calibration of AMC II and ? = 0.2 in March 2007 (RMSE = 0,55) and AMC II and ? = 0.05 December 2007 (RMSE = 0.65).