Analisis Hidrologi Menggunakan Model SWAT di Sub DAS Samin DAS Solo

Abstract

Samin sub watershed (26 950.4 ha) is a part of Solo watershed that is listed as highest priority to manage. The relationship between rainfall, land cover and soil type is very complex, so hydrology based model is needed to look at characteristics watershed. Soil and Water Assessment Tool (SWAT) is a model that could be used to understand hydrology condition of watershed. The aim of this research is to analyze the hydrology condition and water balance in Samin Sub Watershed using SWAT model in sub watershed Samin. The input that are used in this SWAT model consist of 1:25 000 scale land cover map, 1:50 000 scale soil map, 1:25 000 scale river network map and daily climate data from year 2008-2013. Land cover consist of dry secondary forest (638.5 ha), forest plantations (1550.9 ha), bush (309.9 ha), plantations (902.8 ha), bare land (3.0 ha), 3 dryland agriculture (8628.0 ha), dryland agriculture with bushes (9451.9 ha), and paddy field (3550.4 ha). Soil consist of association of grey alluvial and greyed brown alluvial (4339.0), association of dark grey grumosol and brown mediteran (4743.3 ha), reddish brown latosol (14 714.9 ha), and brown mediteran (3153.2 ha). The validation of the SWAT model results in a NSE value of 0.6 and R² 0.7. This means SWAT model could be used to predict hydrology condition. Water balance of SWAT model shows that with rainfall of 3543 mm/year. Samin Sub Watershed could produce ground water flow of 311.0 mm/year (8.8%), percollation 452.0 mm/year (12.8%), lateral flow 4.3 mm/year (0.1%), surface runoff 2078.4 mm/year (58.7%), and evapotranspiration 697.3 mm/year (19.7%). River in sub watershed Samin will experience drought if there is no rain during the day and time of occurrence 50.75 more rain into the peak flow during the 19.825 days.