Consequences of training walls and jetties for aquatic habitats at two British Columbia estuaries

Abstract

The effects of training walls and river channelization on macroinvertebrates and their habitats were studied at the Squamish and Fraser River estuaries in southwestern B.C. A very similar but undisturbed estuary, the Homathko, was also examined. Training walls deflected fresh water from sectors of the Fraser and Squamish estuaries, whereas the Homathko salinity distributions were uniform across the delta front. At the Squamish estuary, the training wall has allowed penetration of a salt wedge into a former river channel; flow of water through culverts through the wall has only a local mitigative effect. Erosion is continuing in the trained portion of the Squamish River, but important intertidal habitats behind the wall have been unchanged for 6 to 7 years. Sedge ( Carex lyngbyei) rhizome mats are heavily used by a nestling gammarid amphipod ( Eogammarus confervicolus) in protected sectors of the Squamish estuary, but river currents wash amphipods from similar microhabitats at the Homathko estuary. Marine plankton was present in parts of the estuaries isolated from river flows by training structures. Sediments stabilized or re-distributed by river channelization at Squamish have been rapidly colonized by invertebrates. To assist in the design of programmes to monitor environmental effects, a table showing time scales of the various impacts is presented.