Two decades of fish habitat restoration and bioengineering on the Fraser River estuary, British Columbia, Canada

The Fraser River estuary is the most important estuary on Canada´s Pacific coast. To achieve a net gain of fish habitat, a goal of Canada´s fisheries management policy, a large number of habitat restoration projects have been conducted in the estuary since 1980. In this paper the author focuses on bioengineering aspects of some of the older projects and an ecological assessment of more recent projects conducted on the outer estuary. Most of the projects have involved transplanting single species of vegetation, including sedges (Carex iyngbyei; Scirpus americanus), pickleweed (Salicornia virginica), eelgrass (Zostera marina), and riparian shrubs such as red osier dogwood (Cornus sericea (stolonifera). Several of the larger projects to restore brackish marsh have used placement of dredged sand as a medium to increase the substrate elevation. This was done so the vegetation could be planted at the intertidal zone level that matched its adaptation to specific durations of emergence and submergence. Development of marshes on dredge spoil islands can occur without human intervention since several islands in the lower river are well vegetated without being subject to transplantation. The stability of the sand used to develop the areas for planting was a key factor in the evaluations of coastal habitat restoration. Sand eroded quickly on Outer Sand Island because of wave energy. The sand was moved shoreward by wave action, with waves up to 1.0 m in height observed, and the peak of the island eroded by -1 m. In later years surplus concrete pipe was placed on the seaward site of Outer Sand Island to reduce erosion. The island´s shape and size had been modified significantly and a lagoon had formed on the landward side. Currently, the island is -2 ha in size and is mostly submerged at high tide. Similar problems were encountered with small projects in the lower Fraser River, where wave action from passing vessels caused erosion. Floating logs were successful in dampening the waves, but long term maintenance was required to secure them.