Gully Migration on a Southwest Rangeland Watershed

Abstract

Most rainfall and almost all runoff from Southwestern rangelands are the result of intense summer thunderstorm rainfall. Gully growth and headcutting are evident throughout the region. A large, active headcut on a Walnut Gulch subwatershed has been surveyed at irregular intervals from 1966 to present. Runoff at the headcut was estimated using a kinematic cascade rainfall-runoff model (KINEROS). The headcut sediment contribution was about 25% of the total sediment load measured downstream from the headcut; and the sediment contribution from the swale drainage above the headcut, as estimated from a depth-integrated pumping sampler, was about the same. Although more data are needed to quantify sediment contributions from other tributary watersheds, the total contribution from gully banks and headcuts on Walnut Gulch must be an important portion of the total sediment load.