Assessing the Effects of Beaver Dam Analogues on Valley Bottom and Watershed Storage at a Site in Central Wyoming

Abstract

Western U.S. land managers have been investigating the use of in-stream structures such as beaver dam analogues (BDAs) to help restore natural stream processes. There is a presumption that BDAs may modify groundwater hydrology, but there have been few studies that have documented such changes. In this study we combine well transect measurements, streamflow measurements and hydrologic modelling to evaluate changes in riparian water storage and groundwater flow paths brought about by the installation of 45 BDAs across a 1.5-km stretch of Red Canyon Creek in Lander, WY. Based on 3 years of observations, we found that when the majority of BDAs were retaining water, there was an increase in the riparian water table, even in wells 50 m from the stream. Much of the stream reach with BDAs was a losing stream prior to BDA installation. As measured using well transects, the installation of the BDAs led to enhanced hydraulic gradients away from the stream. Additionally, BDA installation induced a measurable but very small increase in the subsurface down valley flow. Watershed-scale modelling validated against weekly-averaged streamflow observations indicated that a disproportionate fraction of streamflow in summer is contributed from higher elevation areas with sufficient storage to detain late spring snowmelt. Increases in the valley bottom water table elevation due to the BDAs added less than 0.5% of the subsurface storage already present in the high elevation portion of the watershed.