Effects of Beaver Dams on Groundwater Elevation and Temperature in an Incised, Semiarid Stream

In hot summer months the base flow of small, semi-arid streams is typically low and instream habitat available to biota is limited.  This can limit water exchange between floodplains and channels, impairing instream habitat important for maintaining communities of stream and riparian biota. The presence of beaver dams or man-made beaver dam analogs (BDAs) can cause sediment deposition and overbank inundation can occur along accessible floodplains, raising the groundwater table.  Although anecdotal evidence supports this process, few studies provide quantitative evidence of water table rise associated with beaver dam analogs. From 2006 to 2014 we monitored hourly water table elevation and temperature in two groundwater well fields on Bridge Creek, an incised tributary to the John Day River in northeastern, OR, USA. In 2009, BDA structures were installed to increase the number and lifespan of beaver dams adjacent to one well field, while the second well field remained untreated. Post-restoration monitoring measured larger increases in surface water extent at the BDA-treated well field and increased both the absolute and rate of water table rise relative to the untreated well field. In addition, groundwater and surface water temperature patterns became more similar post-restoration, suggesting increased aquifer recharge relative to before conditions.  Results suggest BDAs can be successfully utilized to raise groundwater tables and increase surface-groundwater exchange.