SHOREZONE LITERATURE REVIEW - HISTORICAL CHANGES|
POTENTIAL IMPACTS OF SHORELINE DEVELOPMENT
The conditions currently experienced by chinook and coho salmon, and bull trout in the Lake Washington watershed result from considerable human alterations of the environment. The lowering of Lake Washington that resulted from the construction of the Ship Canal and Hiram Chittenden Locks (completed in 1916), and concurrent elimination of the Black River and diversion of the Cedar River into Lake Washington were the most monumental modifications. Lake Union was connected to Lake Washington via the Montlake Cut, and the former outlet to Lake Union was enlarged to form the Fremont Cut. Locating the locks near the western terminus of Salmon Bay converted the formerly saltwater inlet into a freshwater channel, eliminating over 7 km (4 mi.) of estuarine habitat (Chrzastowski 1983). Lowering the lake and diverting the Cedar River affected both the fish populations and the condition of the habitat. Cedar River fish stocks were locally adapted to a riverine migration and an extensive estuary, instead of the current lengthy lacustrine migration and an abrupt entry from warm, fresh water into significantly colder, more saline conditions below the locks. Lake Washington and Lake Sammamish fish stocks, while accustomed to the lengthy lacustrine migration, were also adapted to an extensive estuary. The approximately 9-foot reduction in lake level eliminated much of the available shallow-water and freshwater marsh habitat, and decreased the length of the shoreline. Chrzastowski (1983) reports a loss of 15.3 km (9.5 miles) of shoreline, and an estimated loss of 410 hectares (1,013 acres) of wetland resulting from the lowering of the lake.
The channelization and straightening of the Sammamish River, at a loss of approximately 12 miles of river, eliminated the majority of riverine and off-channel rearing-habitat for juvenile salmon, disconnected the river from its floodplain, and eliminated riparian vegetation. The outlet weir on Lake Sammamish controls summer lake level and restricts flow to the Sammamish River during adult salmon migration. The Sammamish River now represents a substantial thermal migration-barrier to adult spawners. An additional consequence of the Sammamish River channelization, subsequent river trail construction, and removal of the riparian vegetation, is that migrating salmon lack significant refuge habitat and holding areas, and are subjected to disturbance by passing trail users (Malcom, pers. comm., 22 November 1999).
The regulation of the water level in Lake Washington by the USACE has eliminated the annual flood-driven seasonal inundation of the shoreline that shaped the structure of the macrophyte community. Historically, the lake would fluctuate as much as 7 feet during flood events (Chrzastowski 1983). The previously hardstem bulrush- and willow-dominated shoreline community has been replaced by developed shorelines with landscaped yards. The loss of natural shoreline has reduced complex shoreline features such as overhanging and emergent vegetation, woody debris (especially fallen trees with branches and/or rootwads intact), and gravel/cobble beaches. Evermann and Meek (1897) noted in 1896 that "the shore of Lake Washington is not well adapted to collecting with a seine" due to the abundant submerged woody debris, and dense underbrush, small trees, and tule (hardstem bulrush) that fringed the shoreline. Development of the shoreline of Lake Sammamish has reduced the once abundant overhanging vegetation and woody debris. Evermann and Meek (1897) noted in 1896 that the trees along the shore of Lake Sammamish were so dense that when water levels were high "Šit is difficult to walk any distance along the shore without swinging from one bough of a tree to another." The loss of native shoreline vegetation and wetlands in the two lakes has likely reduced allocthonous input of detritus and terrestrial insects. USACE water-level regulation has not similarly affected the shoreline of Lake Union, as the historical water-level fluctuation was similar to the present. Losses of wetland and shoreline vegetation in Lake Union are attributable to filling and shoreline development.The woody debris, once abundant along the shoreline of Lakes Washington and Sammamish in their historical conditions, has been replaced with structurally simple piers. A survey of 1991 aerial photos estimated that 4 percent of the shallow-water habitat in Lake Washington and 2.5 percent in Lake Sammamish within 30.5 meters of the shore was covered by residential piers (ignoring coverage by commercial structures and vessels) (Malcom, pers. comm., 22 November 1999). Approximately 81 percent of the shoreline of Lake Washington is bulkheaded (Warner and Fresh 1999). The loss of complex habitat features (i.e., woody debris, overhanging vegetation, emergent vegetation), and shallow-water habitat in Lakes Washington and Sammamish has reduced the availability of refuge habitat and forage for juvenile salmonids. Restoring and preventing future losses of these habitat features should be priorities for agencies responsible for managing lakeshore development.