TRANSPORT OF DETRITAL SEDIMENTS IN LOW-GRADIENT STREAM SECTIONS IN THE TETON MOUNTAIN RANGE AND THE GUADALUPE AND SACRAMENTO MOUNTAINS

The Teton Mountain Range of Wyoming and the Guadalupe and Sacramento Mountains of New Mexico offer differing mountain stream environments, though all three lie along the eastern margin of the Basin and Range Province. Due to the arid setting of the Guadalupes and Sacramentos, stream beds remain dry until activated by storm events, while streams actively flow year-round in the Tetons, thus transporting detrital sediment through varied processes. However, in mountain streams, obstacles such as talus accumulation, glacial incision, and vegetation may reduce local slope so that sand transport is limited. Such sediments may be useful in determining erosion rates and patterns, but results may not be faithful if the sediments are trapped in certain portions of the stream. In this study, we examine low-gradient sections of mountain streams in the Tetons, Guadalupes, and Sacramentos in order to determine whether sand sized sediments are accumulated or transported in these channels. Cross-sections were measured and sediment samples were collected during 2011 and 2012 in the Tetons and during 2013 in the Guadalupes and Sacramentos in canyons with catchment areas ranging from 0.974 - 94.8 km and 0.13 - 120.78 km respectfully. Sediment samples were then sieved using sieve classifications from <0.063 – 45 mm and sorted to determine d₅₀ and d₉₅ values. We calculated total stream power based on cross-sectional information and determined its relation to catchment area, elevation, and annual precipitation. Despite a large decrease in total stream power in the Tetons from 2011-2012, we found that d₅₀ particles would be transported through everyday flow based on measured average stream velocities. However, nearly all of the largest observed clast sizes require higher velocity storm flow in order to be transported. In the Guadalupes and Sacramentos, there was a negative correlation between catchment area, total stream power, and d₅₀ grain size, with increasing areas resulting in decreasing stream powers and d₅₀ values. Based on calculated velocities, sand sized sediment will be transported, but only when precipitation events occur. Despite the differences in climate and main mode of sediment transportation, detrital sediments are successfully transported in these streams and should offer accurate erosion information.