STREAM MORPHOLOGY AND SEDIMENT TRANSPORT IN GARNET CANYON, TETON RANGE, WYOMING

Mountain stream morphology changes from upstream to downstream as elevation and slope decrease and drainage area and discharge increase. In alpine systems, the streams are influenced by glacial landforms and stochastic mass wasting events. Glaciers flatten upstream reaches of a catchment, resulting in segments of low slopes within a stream network followed by very steep slopes downstream. Random rockfalls contribute sediments to the system and can also deposit large boulders that may act as barriers to flow and sediment transport. If detrital sediments are used to understand spatial patterns of erosion, it is important to understand the potential for sediments to accumulate in those flat upstream reaches or behind barriers. This study investigates two questions related to post glacial stream systems in alpine mountain landscapes. How do glaciers and rockfalls influence the downstream progression of channel morphology? Do the changes in morphology influence the potential for sediment transport throughout the catchment? To review these questions, stream cross sections were surveyed and sediment size distributions in surface bedload were measured within a glacially flattened segment of Garnet Canyon in the Teton Range. Garnet Canyon is a mid-sized catchment that was glaciated during the last glacial maximum and still contains small glaciers today. It was also previously studied with detrital apatite minerals. The results of the stream morphology and sediment sizes observed in this study indicate that despite changes in channel morphology from upstream to downstream, most bedload sediments can be transported by observed flows. Although stream morphology changed, the sediment size distributions were similar, reflecting sediments influenced by hillslope sources. Stream morphology transitioned from high slope cascades to lower slope plane beds within the flattened canyon segment and returned to a cascade channel downstream of the flattened segment. Although it appears that sediments accumulate within the flattened area of the canyon, it is possible that some bedrock incision occurs. In conclusion, glaciers and rockfalls influence the morphology and hydraulics in mountain streams, but they do not prevent transport of sands and gravels typically used in detrital studies.