Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-28
Total Federal Funds: $1,000 Total Non-Federal Funds: $440
Principal Investigators: Michael Jahnke, Michael Jahnke
Abstract: Understanding sediment routing from hillslopes to channels and downstream through the channel is crucial in conserving steep mountain streams. Fluvial systems carry large fluxes of sediment along with water from their headwaters to the oceans. From this only a small percentage of eroded sediment makes it from its origin to the ocean (Fryirs, 2013). Identifying what processes take place as sediment travels to the outlet can help to explain the disparity between erosion and sediment yield. Streams constantly rework landforms in the channel, the rate at which this happens and the amount of sediment stored there has a major impact on sediment flux (Fryirs, 2013). To better understand sediment routing in mountain streams, the rate at which sediment is processed must be understood. In mountain streams sediment is supplied in large pulses, which can often take a long time to process and can leave a legacy on stream morphology (Hoffman and Gabet, 2007). This reality of sediment delivery in mountain channels has consistently made predictive modeling of sediment routing difficult. Erosion and deposition of sediment are variable with the majority of sediment movement occurring during short-term events (Smith and Wilcock, 2011). Predictive models generally allow for consideration of fine-scale or coarse-scale processes. A model that allows for channel evolution and exchange between in-channel sediment and sediment delivered by a pulse (i.e. debris flows) would allow predictive modelling of these steep mountain channels. Morphodynamic and Sediment Tracers in 1-D is a numerical model that allows channel evolution and grain size-specific transport of a river channel and floodplain over decadal scales (Lauer et al., 2014). Utilizing MAST-1D in steep mountain channels will be a novel application of this numerical model and will consider lateral sediment inputs from debris flows rather than floodplain interaction. I will investigate these processes by studying Rye Creek in the Sapphire Range of southwestern Montana. The study area is typical of semiarid mountain landscapes of the northern Rockies with snowmelt-dominated hydrology and fire-influenced erosion regimes (Forum, 2014). My research aims to simulate and quantify hillslope-channel connectivity through sediment routing from hillslope to channel and downstream. By creating a predictive model of sediment routing, I will also investigate how the pulses of material from debris flows are processed by the stream.