Kajian respon hidrologi DAS keduang menggunakan model MWSWAT

Abstract

The research was conducted in Keduang watershed (36.426,87 Ha) in Wonogiri district, Central Java Province. The purposes of this research were (1) to analyse hydrological characteristic and erosion of Keduang watershed, (2) to simulate land use scenario response on hydrological characteristic and erosion of Keduang watershed. MWSWAT model was applied to define Hydrologi Response Unit (HRU). Hidrologycal analysis was done with SCS Curve Number and erosion analysis used MUSLE method. This research simulated four land use scenarios consist of (1) existing land use of 2005, (2) increasing forest area based on Act of Forestry No.41/1999, (3) land use change based on spasial plan (RTRW) Wonogiri Regency, and 4) agrotechnology in dry land area. The model was calibrated by using daily flow discharge from January 1st to March 31st and November 1st to December 31st 2004 as well as January 1st to March 20th 2005. The model was calibrated by using monthly sediment discharge from January to December 2004 and January to March 2005.The calibrated MWSWAT model was statisfied by Nash Sutcliffe efficiency (NSE) e.i 0,56 (2004) and 0,45 (2005) for flow discharge, and 0,40 (2004) and 0,48 (2005) for sediment discharge respectly. Although the calibrated model had been statisfied, but the values were below 0,75. It was due to input parameters that calibrating model is less sensitive to obtain the output that highly corelated with data. Calibration process was done by adjusting few parameters that are alpha BF, GW Revap, RCHRG_DP, CHK2, CHN1, ESCO, CH-Cov, CH_EROD, LAT_SED, SPExp, SPCon and USLE_P. The simulation showed that river regim coefficient Keduang watershed is 467,9 (2004) and 58,30 (2005). The runoff coefficient was 0,35 (2004) and 0,30 (2005). The simulation based on four scenario had affected on overlandflow, interflow and base flow. The second scenario resulted lowest overlandflow of 711,14 mm, or decreased 7% from existing condition. The fourth scenario gave lowest sediment yield on 2004 and 2005. Erosion prediction by appliying sediment delivery ratio method showed that simulation on 2004 was 178.634,38 mm/ha/year or 0,04 mm/year, that is lower than observation (75.580.248,11 ton/ha/year or 17,98 mm/year). Tolerable soil loss in Keduang watershed was 1,34 mm/year, however soil erosion of Keduang watershed is higher than tolerable soil loss. Therefore, it needs mitigation to decrease soil erosion in Keduang watershed.