RILL EROSION ALONG THE THALWEG OF A HILLSLOPE HOLLOW - A CASE-STUDY FROM THE COTSWOLD HILLS, CENTRAL ENGLAND

Rill erosion is an important erosional form on agricultural soils in E ngland, causing large losses of soil, particularly on cultivated slope s. This paper describes a rill system that developed in a small agricu ltural catchment in north Oxfordshire during the winter of 1992-93. Th e rill system comprised two components: a system of 'feeder rills' alo ng the valley-side slopes, which were the result of flow concentration and erosion along wheelings, and a thalweg rill, which formed along a dry valley bottom as a result of surface runoff concentration from th e feeder rills. Total volumetric soil loss from the rill system was 32 .28 m3, equivalent to 3.01 m3 ha-1 for the rill catchment area, or 3.9 1 t ha-1. Mean discharge for the thalweg rill and feeder rills, calcul ated during a storm event, was 31.101 s-1 and 1.171 s-1, respectively. All flows were fully turbulent and supercritical. We emphasize the ne ed for a spatially distributed approach to the study of runoff and ero sion at the catchment scale.