Author : Kukuh Murtilaksono

Summary : A land use planning study was conducted for Upper Solo, Gajahmungkur Reservoir subwatershed to determine the best land use alternative through simulation models to obtain least erosion rate, well distributed streamflow, increased crops productivity and improved incomes of farmers. A PC-based ARC/INFO version 3.4 D-Plus was used in the analysis and processing of the data to generate spatial simulation models of the subwatershed land use. The Universal Soil Loss Equation (USLE) was used as the basic method for all computations. The ratios of maximum and minimum discharge and runoff coefficients from 1982 and until 1993 were observed to have no trend. The stream discharge and sediment load before and after 1988 were somewhat erratic. The present erosion rates ranged from 1.01 to 3,343.40 mt/ha/year in the different land mapping units, the average being 159.47 mt/ha/year or about 15.95 mm/year, higher than the tolerable soil loss (TSL) of 30.03 mt/ha/year or about 3.0 mm/year. The critical erosion areas are settlements and home gardens, unpaved roads ditches and trails. Results of the simulation models indicate land use alternative 4 as the best option. Land use alternative 4 was found to give the lowest erosion rate of 29.61 mt/ha/year, well distributed Qmax/Qmin of 16, best choice of LVR and LMR, and highest farmers' income. Land use alternative 4 is characterized by high quality bench terraces, conserved settlements and home gardens. The cropping patterns consists of paddy-paddy-soybean on irrigated paddy rice fields, paddy-soybean on rainfed paddy rice fields, and peanut-peanut monoculture on terraced upland areas. Land use alternative 4 was found to be economically feasible and highly profitable, the BCR, NPV and IRR being 1.45, 3,384.0 million rupiah and 68.98 percent, respectively. This best land use option is not sensitive to increase in production cost or reduction in prices of commidities. Increasing the production cost by 15 percent and decreasing the prize by 15 percent of rice, peanut and soybean.