QUANTIFYING HYPORHEIC FLOW IN BEAVER PONDS OF VARYING SIZE AND STREAM MORPHOLOGY

Mountain desert ecosystems tend to have intermittent surface water flows. Driven by snowpack melt, these low-order streams lose the majority of their water by the late summer months. Since the reintroduction of beavers (Castor canadensis), surface water is able to remain year round due to a beaver dams ability to slow water velocity and impound water. This results in an increase of water retention time which allows for a greater hyporheic zone and surface to ground water interaction. In theory, beaver ponds of larger sizes should have an increased surface to ground water interaction relative to ponds of smaller size. To test this hypothesis and quantify seepage flux in beaver ponds, 18 seepage meters were placed along 6 beaver ponds of differing area and stream morphology. Meters were run for 4 weeks during the summer months and 1 week in the fall. Surface to ground water interactions had a positive relationship with pond size. This supports the hypothesis that beaver dams noticeably affect the interaction of surface and ground water in low-order desert streams. To better understand the seepage meter results, particle size analyses via pipette method were conducted on sediment samples taken at each meter. Additional sediment samples were taken along transects within each pond to aid in an overall estimation of a ponds surface to groundwater interaction.