The Effect of Hydrologic Response Unit on Ci Rasea Watershed Streamflow Based on Landsat Tm

Abstract

Abstract. This paper discusses spatial pattern of Hydrologic Response Unit (HRU), which is a unit formed of hydrological analysis, including geology and soil type, elevation and slope, and also land cover in 2009. This paper also discusses the impact of HRU on streamflow of Ci Rasea watershed, West Java. Ci Rasea watershed is located at the upstream part of Ci Tarum watersheds in West Java Province, Indonesia. This research used SWAT (Soil and Water Assessment Tool) model to obtain spatial HRU and river flow. The method used Landsat TM data for land cover and daily rainfall for river flow modeling. The results have shown spatial pattern of HRU which was affected by land cover, soil type and slope. In 2009, accumulated surface runoff and streamflow changes were spatially affected by HRU changes. The large amount accumulation of river flow discharge happened in HRU with landcover paddy field, silty clay soil, and flat slope. While the low discharge of river flow happened in HRU with plantation, clay soil, and slightly steep slopes as HRU dominant. It was found that accumulation of surface runoff in Ci Rasea watershed can be reduced by changing the land cover type in some areas with clay and slightly steep slope to become plantation area and the areas with sandy loam soil and flat slope can be used for paddy fields. Beside affected by HRU, the river flow discharge was also affected by the distance of sub watershed to the outlet. By using NS model and statistical t-student for calibration and validation, it was obtained that the accuracy of river flow models with HRU was 70%. It meant that the model could better simulate water flows of the Ci Rasea watershed. Keywords: SWAT, HRU, landcover, watershed, Landsat, Ci Rasea INTRODUCTIONLand cover changes can increase flood risk (Chubey and Harhout, 2004). The risk is caused by decreasing both ability of land to absorb water and ability of the river to accommodate water flow. Decreasing river water flow could be caused by silting, land conversion in the catchment and excessive groundwater use. Land cover change in the upstream region such as forest change to settlements or open land, also can affect flooding. It will cause increasing runoff due to reducing area of water catchment. The increasing runoff is caused by reducing ability of catchment in holding or permeating the water. The infiltration, surface runoff and évapotranspiration are controlled by the distribution of precipitation, topography, soils, geology and land use within the watershed (Anderson and Burt, 1978;Beven and Kirkby, 1979;Devito et al., 2005).Issey (2011) stated that flood always happens in South Bandung, Indonesia around Ci Tarum watershed area. Ci Rasea watershed is the branch of Ci Tarum watersheds. According to Yusuf (2010), land cover at Ci Rasea watershed from 1997 to 2007 had changed. According to Balitklimat (2007) and Pawitan (2002;2006), land cover changes in the watershed could cause hydrology characteristics of watershed changed. Emiyati et al. 98International Journal of Remote Sensing an...