Year Established: 2011 Start Date: 2011-03-01 End Date: 2012-02-28
Total Federal Funds: $11,745 Total Non-Federal Funds: $25,299
Principal Investigators: Elowyn Yager
Abstract: Steep, rough streams comprise the majority of mountainous drainage networks. The sediment supplied from these channels can significantly impact aquatic habitat and channel stability in lower-gradient rivers. Sediment transport equations typically over-predict the bedload flux in steep streams by several orders of magnitude. Without accurate predictions of the sediment flux from steep streams, we cannot determine the impacts of human practices (logging, grazing, mining etc.) on aquatic habitat throughout channel networks. Thus, we cannot evaluate the potential success of the several billion dollars per year that are spent on river restoration. Additionally climate change will affect sediment transport rates as hydrograph characteristics shift from snow to rain dominant. We propose that sediment transport equations do not perform well in steep streams because they use empirical measurements that are averaged over a reach scale. A mechanistic understanding of the interaction between flow turbulence and bedload transport is lacking in most transport equations. We will elucidate the physics involved in bedload transport using novel bedload transport and flow turbulence measurements in a steep Idaho stream. This knowledge could be used to modify reach-scale bedload transport equations to accurately predict sediment fluxes. One reason for inaccurate predictions of sediment flux in steep streams is that very few measurements of bedload transport are made in these channels. The cost of permanent instrumentation and the danger of using handheld samplers make obtaining transport measurements difficult in these streams. Furthermore, commonly used handheld samplers (Helley-Smith) can have large errors in bedload transport rates depending on the sampler aperture, measurement duration, and location of the sample. The irregular bed surface and the large spatial and temporal variation in bedload transport in steep streams make sampling particularly difficult. No Idaho streams have permanent instrumentation to measure bedload transport and very few currently have transport measured with Helley-Smith samplers. We therefore propose to instrument and install six modified Birkbeck-type bedload sediment traps in the Reynolds Creek Experimental Watershed (RCEW). This type of sediment trap offers significant advantages over Helley-Smith samplers particularly because it continuously monitors bedload transport across the entire channel width, which reduces the uncertainty associated with the spatial and temporal variability inherent in bedload transport. Furthermore, the permanent traps will use automated measurements, which eliminate the need for constant human monitoring and presence during hazardous flow conditions. We will calibrate and test the traps, prior to their installation, using a series of flume experiments in the CER laboratory flume. Furthermore, we will make detailed measurements of the flow hydraulics at the trap opening to ensure that they do not significantly alter the local flow field and sediment transport rate. These experiments will determine the measurement error, appropriate sampling interval, and efficiency of the traps as they fill with sediment. Once the traps are installed, a schedule for emptying them will be established based on precipitation, temperature, and snowmelt monitored and telemetered from nearby sites in RCEW. The data from the traps and other field measurements (e.g. flow discharge, flow velocity, grain size) will be used to determine the frequencies and patterns of sediment transport and relate such patterns to the flow turbulence, flow hydrograph shape, and channel bed conditions. The traps will improve the already extensive network of research infrastructure present at RCEW, where water resources research data has been collected since 1960 using a network of weirs, meteorological measurement stations, precipitation stations, snow study sites, eddy covariance systems and soil profile testing and analysis.