Abstract

Many important stream ecosystem functions occur in the hyporheic zone, the saturated area beneath and adjacent to a stream where groundwater and surface water interact. Hyporheic processes include water temperature moderation, recycling of carbon, energy, and nutrients, natural attenuation of certain pollutants, and habitat for benthic and interstitial organisms. The role of the hyporheic zone is increasingly recognized for its significance in the context of river management, conservation, and restoration, but stream restoration designs still are not often driven by the effects on hyporheic exchange and hyporheic habitats. This study evaluated hyporheic flow in the shallow subsurface of a recently-restored rural stream. The restoration project included two experimental hyporheic treatment cells, where excavations beneath the stream bed 12-16 feet long by 3 feet deep were filled with a mixture of coarse sand and gravel to improve groundwater-surface water interactions. Permeameter tests of the streambed gravels were conducted to estimate hydraulic conductivity (10.9 – 14.7 m/day) and a transect of monitoring well nests were installed to determine the vertical gradient of flow at various points within the treatment cells. Results revealed a statistically significant upward flow pattern in the treatment cells as compared to the control region between the cells. This suggests that the treatment cells are enhancing groundwater recharge to the restored stream and that the future use of permeable hyporheic treatment cells could be expanded to improve hyporheic exchange.

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