Form‐based river restoration decreases wetland hyporheic exchange: Lessons learned from the Upper Colorado River

• Published in: Earth surface processes and landforms Vol. 44; no. 1; pp. 191 - 203
• Main Authors: Sparacino, Matthew S., Rathburn, Sara L., Covino, Timothy P., Singha, Kamini, Ronayne, Michael J.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.01.2019
• Subjects: Aquatic ecosystems; Berms; Case studies; Channel storage; Complexity; Consolidation; Ecosystem services; Electrical resistivity; Environmental changes; Environmental restoration; Exchanging; Flow; Hydrology; hyporheic exchange; Imaging techniques; Realignment; River channels; River restoration; Rivers; Service restoration; Sodium; Sodium chloride; Storage; Storage capacity; Storage conditions; Thalweg; tracer test; Tracers; Water storage; Water yield; wetland restoration; Wetlands; Colorado River
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.4525

Restoration of river–wetland systems to recover lost ecosystem services and restore consistent flood regimes is commonly directed at modifying in‐channel storage and hyporheic exchange. Here, we monitored the hydrologic response to channel realignment in a montane river–wetland system by comparing pre‐ and post‐restoration measurements. In 2015, an earthen berm and 190 m segment of the Upper Colorado River were constructed to consolidate flow from multiple channels into the historic thalweg. We injected a sodium chloride tracer during baseflow and used mass‐balance calculations and electrical resistivity imaging to assess changes in near‐channel hyporheic exchange. Results indicate a decrease in hyporheic exchange within the wetland due to lost complexity along the consolidated flow path. Subsurface complexity appears to control hyporheic exchange more than surface complexity. Flow consolidation increased the area‐adjusted wetland water yield by 231 mm, indicating a loss of wetland water storage capacity. One year of post‐restoration monitoring suggests that the form‐based channel restoration directed at consolidating flow into a single thread adversely affected the hyporheic exchange functioning in the pre‐restoration system. Results from this case study are applicable to restoration planners as they consider the effects of form‐based projects on water storage capacity in similar systems. © 2018 John Wiley & Sons, Ltd. One year of post‐restoration monitoring suggests that form‐based channel restoration, directed at consolidating flow into a historic thalweg, adversely affected natural hyporheic processes functioning in the pre‐restoration system.