Abstract
Instream channel restoration is a common practice in river engineering that presents a challenge for research. One research gap is the development of monitoring techniques that allow for testable predictions of sediment transport and supply. Here we use Radio Frequency Identification (RFID) transponders to compare the short-term (1-year) sediment transport response to flood events in a restored and a control reach. The field site is Wilket Creek, an enlarged creek in a fully urbanized catchment without stormwater management control in Toronto, Ontario. The responses to three flooding periods, each of which are at or above the design bankfull discharge, are described. Key results are that (i) particle mobility is lower in the restored reach for all three periods; (ii) full mobility occurs in the control reach during the first two floods while partial mobility occurs in the restored reach; and (iii) the constructed morphology exerted a controlling influence on particle entrainment, with higher mobility in the pools. Log-transformed travel distances exhibit normal distributions when grouped by particle size class, which allows a statistical comparison with power law and other predictive travel-distance relations. Results show that three bedload transport conditions can occur, with partial mobility associated with a mild relation between particle size and travel distance and full mobility associated with either a flat or steep relation depending on the degree of integration of particles in the bed. Recommendations on seeding strategy and sample sizes are made to improve the precision of the results by minimizing confidence intervals for mobility and travel distances. Even in a short term study, the RFID sediment tracking technique allows a process-based assessment of stream restoration outcomes that can be used to justify the instream intervention and plan future attempts to stabilize and enhance the system.
Highlights
Stream restoration refers to a wide range of manipulations of streams and their riparian corridors that are intended to improve the condition of the river relative to some degraded state [1,2]
The aim of this study is to develop and test a strategy for assessing stream restoration outcomes through the use of sediment tracking data
The particular results of this field study demonstrate success in the sense that sediment dynamics are positively affected by the pool-riffle design
Summary
Stream restoration refers to a wide range of manipulations of streams and their riparian corridors that are intended to improve the condition of the river relative to some degraded state [1,2] Instream structures such as artificial pools and riffles are commonly used for stream restoration projects due to their perceived benefits for ecology and channel stability [3,4]. Project evaluation is needed for adaptive management and progress in engineering practice [7,8], but monitoring is typically ineffective due to relatively short term monitoring projects that miss potential adjustments to relatively rare flood events, a reluctance to include the additional cost, and a tendency to collect qualitative data rather than quantitative data [9,10,11,12]. Cost effective, and repeatable techniques are needed to assess stream restoration outcomes
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