Master of Science degree with a major in Environmental Systems, option Environmental Resources Engineering
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Environmental Resources Engineering
Ecologically functioning meadows provide critical ecosystem services including improving a catchment’s water yield, flood dispersion and attenuation, fostering groundwater-dependent ecosystems, and creating natural fire breaks (Loheide and Booth 2011). Degradation from past and current land use has resulted in incised channels that change the magnitude and timing of watershed and meadow fluxes and cause water table decline. Process-based restoration (PBR) is an approach which leverages fluvial processes to increase restoration efficiency. Though PBR is a promising tool to restore degraded meadow ecosystems, more studies are needed to understand its hydrologic outcomes and whether hydrodynamic modeling can be used as a tool to evaluate the effectiveness of process-based restoration designs.
To answer these questions, the USDA Forest Service has identified three degraded meadows in Plumas County, California for comparative study (Middle Creek, Fall River, and McRae). Middle Creek and Fall River meadows have experienced wildfire disturbance and all three meadows have significant channel incision. Process-based restoration techniques including installation of beaver dam analogs (BDAs) were employed in Middle Creek and McRae Meadows in August & September of 2022 to promote sediment aggradation and channel restoration.
Two-dimensional hydrodynamic modeling is used to explore the effect of restoration structures on meadow hydrogeomorphic function in Middle Creek Meadow by comparing pre- and post-restoration changes to water depth, velocity, and wetted area. Model input data include LiDAR-derived topographic data gridded to 0.50-meter resolution and bathymetric data collected with a total station. BDAs are simulated by modifying the model mesh to define these structures as part of the site topography.
Modeled comparisons were made between the LiDAR DEM and the LiDAR DEM augmented with topographic survey data to understand the importance of model input topography on model output. Changes to the LiDAR DEM to more accurately simulate channel geometry as measured by total station surveys resulted in increased maximum observed water depth in the modified DEM simulations and local increases in predicted velocity. The importance of DEM modifications to better define small channel geometry in meadow systems and their influence on hydrodynamic model predictions is likely constrained by model mesh size with smaller mesh elements capable of providing more detailed model predictions. Augmenting LiDAR with survey data alters modeling results in ways that are relevant to evaluating potential restoration outcomes, but these improvements are limited by model mesh size.
Hydrodynamic model output between the base case and restoration scenarios suggests the effectiveness of process-based restoration structures to reverse and arrest the processes of channel incision by slowing water velocities and promoting overbank flooding at the geomorphic flowrates (50% of Q2-year and Q2-year) simulated for the meadow site. Effectiveness of process-based restoration structures may be strongly influenced by the degree of channel incision as overbank flooding was less frequent in the deeply incised portion of Middle Creek Meadow even with restoration structure intervention. This may indicate that in deeply incised regions of the meadow channel may rely on a multi-step approach and additional treatment in order to promote lateral floodplain connection.
Sevier, Emma, "Hydrologic outcomes for ecological meadow restoration in the northern Sierra Nevada" (2023). Cal Poly Humboldt theses and projects. 630.