Opportunities and Limitation of Hyporheic Restoration in a 4th Order Semi-Arid Floodplain: a Case Study of Meacham Creek, Oregon

Abstract:

Persistent societal interest in improving water quality and recovering imperiled, native, aquatic species has expanded the scope of stream restoration to include the hyporheic zone as a focus. Despite the lack of detailed studies, hyporheic restoration is often invoked as a means to achieve multiple objectives including moderation of water temperature, delay of seasonal flows and increasing the localized volume of floodplain water. We present interim results from an ongoing case study that monitors the changes as a result of stream restoration of the hyporheic zone of a 4^th order, alluvial floodplain in northeast Oregon, USA, Meacham Creek. Active and passive restoration of 2.5 km of Meacham Creek has altered the creek from a single-threaded, incised and bedrock-dominated channel to a perched, alluvial channel that seasonally exchanges overbank flows with the surrounding floodplain. Our results suggest that the stream restoration effort on Meacham Creek has increased the volume of annual hyporheic storage and created a more diverse distribution of flowpath lengths within the restoration site. Furthermore, our monitoring indicates that hyporheic process response to stream restoration, analogous to other geomorphic processes, conforms to a systematic hierarchy where nested flow paths range in length and residence time from meters and hours at the habitat scale to tens of meters and months at the floodplain scale. We assert that scale-explicit and measurement-focused restoration planning has a greater likelihood of meeting the stated objectives and result in improved water quality and encourage recovery of many native aquatic species.