Runoff assessment of small catchment using spatial semi-physical hydrological model :: A case study of Goseng catchment Karanganyar Regency Central Java Provinsi Indonesia

TRIMURTI, Wahyu, Dr. M. Pramono Hadi, M.Sc

2010 | Tesis | S2 Geo Informasi untuk Manajemen Bencana

A study of runoff assessment for small catchment has been done for Goseng Catchment in Karanganyar Regency, Central Java Province. The study area is about 655 ha. The purposes of this study are to assess runoff; to assess the landuse change through landuse scenarios in order to identify the best landuse scenario for reducing runoff amount; and to analyze meteorological data, rainfall, for identifying its characteristic and its magnitude. The study was calculating runoff for time period 2007 in which flood occurred in Bengawan Solo River since the study area is one of catchment that flows to the river. The model used is spatial semi-physical hydrological model approach which is run using PC Raster model language collaborated with other GIS application. It was chosen because it can express the nature condition and the dynamic condition of nature can be modeled. The study also considered the meteorological condition as input for runoff, rainfall, using Gumbel extreme value distribution method. The result of this study shows that the model could calculate the runoff after the model was calibrated with the actual runoff recorded by AWLR placed in outlet of Goseng River. The study also analyzed the sensitivity of parameters in the model using sensitivity analysis. The result shows that the most sensitive parameter is soil parameters such as its porosity, depth and its value of saturated conductivity (Ksat) rather than the vegetation parameter. The model also conducted 3 landuse/cover scenarios: converting dryland farm into sugarcane plantation (scenario 1); converting sugarcane plantation into dryland farm (scenario 2); and converting dryland farm and sugarcane plantation into forest (scenario 3). The result shows that annual runoff decrease for scenario 3 and 1 as 7.64 % and 0.25 % respectively. And the runoff increase 0.55 % in scenario 2. The meteorological data analysis shows that, the highest rainfall in 2007occurred in December 2007 and it has 5 year time return period.

Kata Kunci : Runoff, Semi-physical htdrological model, PC raster