Mostly Trapping

Impacts of Beaver Dams on Mountain Stream Discharge and Water Temperature
Aug 11, 2020 07:19 ET

(Reprinted from above link)

Abstract
Beaver dam complexes have been shown to affect the hydrologic processes controlling river systems. These processes include surface and groundwater exchanges, water chemistry and temperature variations, and river discharge magnitudes. Majerova et al. (2015) explored the effects of beaver dams on surface and groundwater exchanges and water temperature by evaluating three years of water discharge and temperature data recorded at multiple locations within a small stream in northern Utah. They found that beaver dams increase the water surface elevation and force water into the floodplain resulting in increased inundation and groundwater recharge. They additionally found that beaver dams increase residence time of the water and together with increased surface area, generally result in increased water temperature at reach scales. Majerova et al. (2015) noted the importance of long-term data sets to more fully understand the impact of beaver dams on river systems. Towards this end, this report builds on the original study by extending the daily average water temperature and discharge time series at three locations along a 1.3 km section of Curtis Creek in Northern Utah to provide insight into the long-term effects of the beaver dam complexes. The entire data set spans 2008-2018 and represents periods before the beaver dams were built, during dam construction and various levels of dam maintenance, and after the dams breached or washed out after beaver were trapped in the area. The original 3 years of data presented in Majerova et al. (2015) showed that an increase in beaver dams generally increased the baseflow discharge and water temperature variations during the summer. However, longer term data that represent a larger range of annual flows and different states of dam building and maintenance show that beaver dams only increase baseflow discharge when the dams are relatively young and consistently inundate the floodplain. This suggests that beaver dam complex age and pond sedimentation is important for understanding groundwater exchanges. When comparing the streamflow data, weather data, and daily average water temperatures together, it is clear that beaver dams do consistently increase water temperatures, but local weather and longer term hydrologic conditions are also important factors affecting (or contributing to) water temperature variations. A review of the sub-daily water temperature data for a single week in September, revealed a daily variation of approximately 0.7°C without beaver dams and approximately 5°C with beaver dams. This represents a significant change in daily water temperatures and highlights the need to investigate shorter temporal scale influences on long term temperature responses.