GIS-based influence analysis of geomorphological properties on pollutant washoff in agricultural area

摘要

This study improves the estimation of the self-purification coefficient for runoff analysis of pollution load using geomorphological factors. Formerly, the assimilative capacity, K, was estimated using a single geomorphological factor, Horton's form ratio, S-f. Here, K was divided into two factors, namely, a watershed self-purification coefficient (k) and a watershed form ratio (S-f). The watershed form ratio, S-f, is the equivalent stream density and is considered an index of accessibility of the pollution load to the water body. Even though Sf had shown a clear reciprocal relationship with k, in agricultural areas, there is a limitation that the k, estimated by using an Sf only can't reflect the variability of land coverage characteristics and/or land use. In this study, a new geo-characteristic index (GCI), S-R, which is composed of S-f and weighted flow accumulation ratio (F-r), is suggested. GIS and remote. sensing technique were used to calculate S-f and F-f. Interestingly, a clear reciprocal relationship exists between k and S-R, and this relationship seems to be stronger for agricultural areas, as urbanized areas have easier wash off due to the sewer network or paved surfaces.