Stream order, hierarchy, and energy convergence of land use

The streams in a watershed are organized as a network. From an ecological energetic point of view, this hierarchical organization is a result of the convergence of energy. This paper investigates the convergence of river energy and its relation to the energetic hierarchy of land use in the Tansui River Basin. Stream order is used to rank and measure stream position in the hierarchy of tributaries. Stream transformity is used to measure the energetic hierarchy of streams and the relative position of any particular stream in a scale of increasing energy quality. The spatial analysis capability of GIS is used to calculate the spatial distribution of accumulated rainfall emergy, the geopotential energy of runoff, and transformities of surface runoff and streams. The results indicate that stream order corresponds to transformity. The series of transformities increase with successive convergence of streams and this explains the hierarchical organization of the Tansui River. The spatial pattern of land-use transformity is also compared with runoff and stream transformities in the Tansui River Basin. As a result, the hierarchy of land use in Tansui River Basin is correlated to the hierarchy of streams and runoff and supports the hypothetical influence of stream energetic convergence on the spatial pattern of land use.