GIS APPLICATION ON GEOLOGICAL CHARACTERISTICS AS THE PREDICTINGFOR SOIL EROSION IN KHAEW NOI WATERSHED, PHITSANULOK PROVINCE

摘要

In the rainy season, soil erosion is a serious problem in Khaew Noi watershed where located on Phitsanulok province. The effect of soil erosion was a lot of soil sediments eroded into rivers, muddy water and flooding. In this events had derived from deforestation, misuse of agricultural land on sloping land, and lack of the knowledge on soil conservation. Although various strategies of soil conservation have been investigated, most of them emphasize land resources, whereas geological research in rates of soil formation and soil erosion in still rare. The present study applies an integrated scientific knowledge, i.e., the Geographic Information Systems (GIS), to improve the management of geo-spatial data and support the decision-making and planning of land use in watershed. The Objective of this research applied GIS technique to study the effects of geological characteristics on degrees of rock weathering and soil erosion in Khaew Noi watershed. Among 4 from 14 sub-watershed were randomly selected. The 15 geological index were collected in the field, including degree of rock weathering, particle size, degree of rock hardness, number of joint direction, 8 joint spacing in the direction, fault, fold, and slaking index. All data were analyzed, using correlation and stepwise multiple regression to examine effects of the geological characteristics on degree of rock weathering. Soil erosion rate was calculated by using Universal Soil Loss Equation (USLE) and GIS technique. The result revealed that some geological characteristics, such as degree of rock hardness, predict 66.8% of rock weathering. When adding slaking index to the regressing model, these two geological characteristics predict 69.2% of rock weathering. Other geological indices were, not significant. The average soil loss, as ranked from slight to severe, was classified at the severely level (≥20 t ha~(-1) yr~(-1)) in sub-watershed, which covered 49.34% of total area. Correlation between degree of rock weathering and soil erosion, as presented in overlay of maps, showed that the weathering of rock and soil erosion rate were severe in sub-watershed, Therefore, the intensive soil and water conservation measures should be practiced in these areas in order to decrease soil losses and sediments accumulation in the sub-watershed.