Modeling the Impact of Engineered Ponding on Floodplain Hydrologic Flow Paths and Solute Transport
Authors
Lijing Wang1,2*, Tristan Babey4, Zach Perzan5, Sam Pierce3, Kristin Boye1* (kboye@slac.stanford.edu), Kate Maher3, Eoin Brodie2 (elbrodie@lbl.gov)
Institutions
1SLAC National Accelerator Laboratory, Menlo Park, CA; 2Lawrence Berkeley National Laboratory, Berkeley, CA; 3Stanford University, Stanford, CA; 4University of Rennes, Rennes, France; 5University of Nevada–Las Vegas, NV
URLs
Abstract
In mountainous watersheds, warmer temperatures and less snow reduce river and groundwater flow. Meanwhile, growing beaver populations help mitigate these effects by enhancing seasonal floodplain storage and possibly groundwater baseflow. Understanding how hydrologic flows change as a function of beaver dams, together with floodplain structures and weather forcings, becomes important for future hydrologic predictions and understanding biogeochemical cycles in various floodplains. Specifically, the transient variations of beaver ponds might induce rapid shifts in redox conditions and subsequently influence the transport of solutes to river and aquifers. However, these impacts of biogeochemical variations from beaver ponds remain poorly understood, particularly in the context of uncertain floodplain structures and weather forcings.
To address this knowledge gap, the team assessed the impact of beaver ponds on hydrological connectivity and thereby the biogeochemical processes in mountainous floodplains, to date focusing on a floodplain along the Slate River, CO. Researchers integrated in situ water level and water quality data, geophysical surveys, and hydrologic modeling, to first reconstruct the hillslope- floodplain structure, and then simulate vertical flow from the topsoil layer to the underlying gravel layer, as well as horizontal groundwater flow. Sensitivity analysis indicated that beaver ponds enhance the cumulative vertical flow, particularly from fine sediment layers to the gravel bed, resulting in an increased export of reduced solutes to the gravel bed. However, beaver ponds have minimal influence on the deeper underflow within the gravel bed aquifer, suggesting that beaver ponds are hydrologically disconnected from deep groundwater flow.
Researchers now plan to employ the same approach to transfer the learned knowledge from the Slate River floodplain to other floodplain structures with varying numbers of beaver dams. For this purpose, researchers will leverage Beaver Dam Analogs constructed by humans to quantify hydro-biogeochemical impacts associated with new beaver dam constructions and compare to floodplains without beaver activity.