Streambed restoration to remove fine sediment alters reach‐scale transient storage in a low‐gradient fifth‐order river, Indiana, USA

• Published in: Hydrological processes 2018-06, Vol.32 (12), p.1786-1800
• Main Authors: Ward, Adam S., Morgan, Joseph A., White, Jeffrey R., Royer, Todd V.
• Format: Article
• Language: English
• Subjects: Accidental release; Aquatic plants; Computer simulation; Descaling; Ecosystem services; Fluvial sediments; Gravel; hyporheic; Hyporheic zones; Interstices; Mathematical models; Monte Carlo simulation; Morphology; Parameter identification; Parameter sensitivity; Removal; Restoration; Rivers; Sediment; Sediment pollution; Sediments; Sensitivity analysis; solute; Solutes; Statistical analysis; Statistical methods; Stream pollution; Streambeds; Streams; Time series; tracer; Tracer experiments; Tracers; transient storage; Waterways
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.11518

Hyporheic restoration is of increasing interest given the role of hyporheic zones in supporting ecosystem services and functions. Given the prevalence of sediment pollution to waterways, an emerging restoration technique involves the removal of sediment from the interstices of gravel‐bed streams. Here, we document streambed sediment removal following a large, accidental release of fine sediment into a gravel‐bed river. We use this as a natural experiment to assess the impact of fine sediment removal on reach‐scale measures of transient storage and to document the responses of reaches with contrasting morphology (restored vs. unrestored) to changing discharge one‐field season. We conducted a series of conservative solute tracer experiments in each reach, interpreting both summary statistics for the recovered in‐stream solute tracer time series. Additionally, we applied the transient storage model to interpret the results via model parameters, including a Monte Carlo analysis to measure parameter identifiability and sensitivity in each experiment. Despite the restoration effort resulting in an open matrix gravel bed in the restored reach, we did not find the significant differences in most time series metrics describing reach‐scale transport and transient storage. We hypothesize that this is due to enhanced vertical exchange with the gravel bed in the restored reach replacing lateral exchange with macrophyte beds in the unrestored reach, developing a conceptual model to explain our findings. Consequently, we found that the impact of reach‐scale removal of fine sediment is not measureable using reach‐scale solute tracer studies. We offer recommendations for future studies seeking to measure the impacts of stream restoration at the reach scale.