Abstract
Over the past half century, urbanization has caused drastic changes to the hydrology and geomorphology of streams and rivers. The Serpentine River is a low-elevation, rain-dominant river located in the City of Surrey, British Columbia. Over the years, urbanization of the watershed, particularly in the upper reaches, has degraded what once was high quality spawning habitat for five salmonid species. The current project is an evaluation of previous restoration efforts at seven study sites and a restoration plan to effectively increase spawning habitat in the Upper Serpentine River. Grain size analysis of the study sites found up to 57% fine sediment in the subsurface particles, attributing to siltation rates of 1.2-1.6 kg/m2/day. Erodible grain sizes at the study sites ranged from 29-164 mm, which mostly exceeded the median size of spawning gravel. These results were verified with a tracer rock study, which together concluded that instream structures were required to reduce tractive forces and increase gravel retention. Newbury weirs, or constructed riffles, were proposed as treatments because their hydraulic characteristics increase flow resistance, promote gravel retention, and create intergravel flows. Newbury weirs involve large diameter rocks spanning across the entire stream, causing accumulation of gravel on the upstream side and pool formation downstream side. Substrate scoured at the pool will be deposited at the tail end of the pool, creating spawning habitat in accelerating and downwelling waters. Bank stabilization using dense live staking with a protective rock toe key was prescribed to reduce further channel incision and siltation. In the longterm, watershed-level priorities including passage through the Serpentine sea dam, monitoring for urban contaminants, and installation of green infrastructure was recommended. The proposed treatments are relatively inexpensive, and if successful, will reduce repeat addition of spawning gravel and increase salmonid production in the Serpentine River. However, the value of the current project extends beyond fish productivity estimates. Monitoring data from restoration works can be used to inform future urban stream restoration projects and contribute to the continual improvement of restoration techniques. The effects of restoration on not only sediment form (i.e.. gravel depth and size) but also processes (i.e.. sediment scour and fill) should be investigated in the field to verify theoretical models.