Hyporheic flow in a mountainous riverine system

Abstract

Investigation into the effects of beaver dams on hyporheic exchange in peat dominated mountainous streams is needed to better understand stream-floodplain connections and improve our overall conceptual model of water storage and flow through riverine valleys. The objective of this study was to determine the influence of instream beaver dams on vertical and lateral hyporheic exchanges. Hyporheic interactions were examined using hydrometric methods to determine both flow pathways and water fluxes for a second-order stream draining a Canadian Rocky Mountain peatland. Investigation was conducted on two instream beaver dams and an undammed reference section for the ice free periods of summers 2006 and 2007 at the Sibbald Reseach Basin located in Kananaskis Country, Alberta, Canada. Lateral hyporheic fluxes dominated over vertical hyporheic fluxes, due to a layer with low saturated hydraulic conductivity (K ~ 10ˉ⁷ – 10ˉ⁹ m/s) just below the streambed throughout most of the study reach. The lateral flow around the north dam (> 0.6 m high) resulted in fluxes that ranged from 0.002 to 0.015 L/s in the near bank environment. These results confirm that hydraulic properties of the substrata are an important factor in the development of hyporheic exchange in stream systems draining peatlands. Results also demonstrate the ability of beaver to connect valley floors to their streams, which maintains seasonally stable water tables and wetland conditions in the riparian zone.