Curvature distribution within hillslopes and catchments and its effect on the hydrological response

摘要

Topographic convergence and divergence are first order controls onthe hillslope and catchment hydrological response, as evidenced bysimilarity parameter analyses. Hydrological models often do nottake convergence as measured by contour curvature directly intoaccount; instead they use comparable measures like the topographicindex, or the hillslope width function. This paper focuses on thequestion how hillslope width functions and contour curvature arerelated within the Plynlimon catchments, Wales. It is shown thatthe total width function of all hillslopes combined suggest thatthe catchments are divergent in overall shape, which is incontrast to the perception that catchments should be overallconvergent. This so-called convergence paradox is explained by theeffect of skewed curvature distributions and extreme curvaturesnear the channel network. The hillslope-storage Bossiness (hsB)model is used to asses the effect of within-hillslope convergencevariability on the hydrological response. It is concluded thatthis effect is small, even when the soil saturation threshold isexceeded. Also described in this paper is a novel algorithm tocompute flow path lengths on hillslopes towards the drainagenetwork, using the multidirectional flow redistribution method.