Sediment delivery from interfluve slopes into river valley

Abstract

A complex approach for estimating sediment delivery from drainage basin slopes into river valley is proposed. The method includes morphometric analysis of drainage basin, mathematical modelling and radioactive isotope tracers application. The approach effectiveness is demonstrated by analysis of the River Lokna drainage basin slopes (Central Part of the European Russia). Total area of the drainage basin is 174.8 km 2 . Morphometric characteristics of 1293 elementary slopes (facets) were collected from the 1:100 000 scale topographic map and analysed. Average soil erosion rate from facet under conditions of bare fallow is 46.2±31.9 t/ha/year. For a range of locally typical crop rotations this value varies from 17.2±13.0 to 33.3±19.1 t/ha/year. Mapping of drainage basin slopes allowed distinguishing areas with highest potential erosion rates. About 33% of elementary slopes of the studied drainage basin are characterized by the LS -factor value exceeding 1.5. In hypothetical case of cultivation of all basin slopes under bare fallow, 77% of elementary slopes will be characterized by very high and catastrophic potential erosion rates (>20 t/ha/year). For a range of locally typical crop rotations this percentage is reduced to 44%. Application of radioactive isotopic tracer allowed us to obtain an independent evaluation of the model validity. Comparison of soil loss rates obtained independently by the model and the 137 Cs radioactive tracer for the morphologically simple short runoff-dissipating slope has shown high degree of coincidence. However for the more complex long convex slope the model produced higher values of soil loss rates (sometimes more than twice) than the 137 Cs-based estimates. It can be explained by the fact that the model takes no account of within-slope sediment redeposition which cannot be estimated by its current version.