CHANNEL GEOMETRY AND SEDIMENT TRANSPORT IN A STEEP, FAULT-BLOCK MOUNTAIN RANGE: PAROWAN CREEK, SOUTHWESTERN UTAH

The Parowan Creek watershed located in southwestern Utah is a primary source of water supply to the town of Parowan, UT and the aquifer system of the Parowan Valley. Parowan Creek is a gravel bed stream that flows through a high relief landscape at the edge of the Basin and Range province, and appears to have a very high level of sediment transport with past impacts on water and road infrastructure through erosion and sedimentation. This investigation aims to use basin-wide measurements of stream channel morphology and bed sediment lithology to characterize downstream hydraulic geometry and assess patterns of dimensionless shear stress (τ^*) and bed load transport (Q_s) that may relate to the hydrology, geology, and sediment sources of the watershed. Field sites range in drainage area from ~5-150 km², 2-year flood discharges of 0.5-2.5 m³/s, and channel widths of 1-5 meters. We evaluate whether an equilibrium model of channel form, which states that gravel-bed channels adjust to maintain a relatively constant , is applicable in this small, steep watershed, and we compare our results with other sites in the western United States. Preliminary results show that the watershed geology and topography are strongly influenced by horst and graben structures that alter the valley width, channel steepness, and bedrock lithology. Downstream hydraulic geometry is strongly dependent on these changes in channel slope, such that steeper reaches in more confined canyons tend to be wider and shallower. While hydraulic parameters vary considerably between reaches, τ^* values calculated for a 2-year flood are relatively constant or increasing slightly, suggesting the channels generally fit with the equilibrium model. The lithology of the stream bed sediment also illustrates that proximal sediment sources often dominate bed sediment, suggesting strong hillslope-channel sediment connectivity. This analysis provides geomorphic context to anticipate future changes in channel morphology due to floods or sediment perturbations within the Parowan Creek watershed.