Implications of Enhancing Forage Fish Spawning Habitat in the Absence of Sediment Processes that Maintain Spit Systems

Ediz Hook is one of the most well studied spits anywhere in the Salish Sea. The loss of sediment supply to the spit and the construction of a riprapped road prism to the tip of the spit has caused rapid erosion, necessitating “nourishment” on the outside (north side) of the spit by the US Army Corps of Engineers. The erosion was exacerbated by the installation of dams on the Elwha River, which have been recently removed. As part of this extremely large restoration project, there is a large international monitoring effort examining the impacts to the outside of the spit, which should see significant new sediment from the river over time. Though the outside of the spit has been of intense interest, a much smaller habitat enhancement program has been active since 2003 in improving shoreline conditions of the inside of the spit (on the south side). Here, sediment reduction has been complete. Not only is the sediment supply to the spit at large reduced, but the road prism completely blocks the overwash that supplied the inside of the spit with sediment. This sediment loss has caused rapid erosion of former spit deposits, also endangering the roadway. Although the shoreline is somewhat unusual in that the sediment supply has been eliminated completely by the placement of a riprapped road, the observations made in response to placed sediment and wood provide indications as the effectiveness of various approaches. First, the observations suggest that even in situations where sediment supply has been completely eliminated, nourishment can recreate productive habitat features. Also, it appears that the placement of large amounts of untethered but buried wood does enhance the ability of the beach to retain sediment appropriate for forage fish spawning. Finally, the project also illustrates a project setting where protection of infrastructure (in this case the road) if designed properly can also improve habitat