Geo-Environment Science

A GIS-based integrated distributed-parameter model was applied to Chikugo River Basin for predicting pestiside runoff from the basin. The targeted ingredients were Mefenacet, Bromobutide, Cafenstrole and Pretilachlor. The model consisted of the water balance sub-model and the pestiside runoff sub-model that described rainfall-runoff process and pestisides transportation process respectively. The model parameters that would be strongly related to farming pattern of each farmer and therefore could not be treated as deterministic ones, such as the amout and timing of pestisides application and the water management in each paddy plot, were dealt in stochastic manner in the model by introducing Monte Carlo method. The water balance sub-model showed high performance to predict the river discharge at Chikugo Barrage where is located at the downstream end of the targeted basin. The pestisides runoff sub-model incorporated with the water balance sub-model had a good agreement between the observed and the simulated pesticide concentrations in river water. The scenario analyses using the integrated model suggested that the water management in each paddy plot by each farmer was key factor for reducing the pesticide runoff from paddy plots and lowering the pesticide concentration in river water.