Search

Large dam removals are emerging as an important ecosystem restoration tool, and they often have direct influence on the marine nearshore zone, but dam removal plans give little consideration to nearshore restoration. We provide an overview of the relationship between large-scale dam removals and nearshore restoration, using the Elwha dam removal project, in Washington State, United States, as a basis. The following steps are essential for incorporating nearshore restoration planning into future dam removals: 1) Conceptual and technical modeling of nearshore physical and ecological processes at the drift cell scale to define nearshore priorities and geographic areas to be conserved or restored; 2) Acquiring seasonal field data to inform models, including: water quality; sediment delivery volumes, timing, trajectory and composition; and basic fish community data such as abundance, size, species composition, and trophic components; 3) Mapping nearshore habitat areal extent and ecological function prior to, during, and after dam removal, including vegetation composition and invertebrate community composition; 4) Defining and addressing the implications of habitat barriers and fish management actions for nearshore ecosystem function prior to dam removal. Structures and hatchery practices that conflict with nearshore ecosystem function for wild species prior to, during, and after dam removal should be identified and eliminated; 5) Anticipating nearshore invasive species colonization as a result of dam removal; 6) Developing and implementing long-term adaptive management plans to ensure nearshore restoration goals are identified and met. These steps must begin as early as possible in the planning process. [ABSTRACT FROM AUTHOR]

The Elwha River estuary has been significantly influenced by anthropogenic changes to the river, including two large dams upriver and rock dikes installed in the estuary. Together these have disrupted hydrodynamic processes and subsequent sediment delivery throughout the watershed. This article defines the functional response of fish distribution within the estuary as a result of these changes. We assessed fish distribution of three main areas of the Elwha estuary using standard beach seining techniques from March to August 2007. Species composition, ecological indices, and relative proportion of all salmonids, and in particular Chinook salmon ( Oncorhynchus tshawytscha), were consistently significantly different across the estuary. Differences corresponded to a rock dike installed 30 years ago, and a sediment lens that was observed to form at the entrance to the east estuary. Sediment lenses are documented to be a common occurrence in the Elwha nearshore, and symptomatic of documented, severely disrupted sediment processes of the Elwha River. Combining the fish distribution documented in this study with the rock dike and observed sediment lens and the sediment processes documented by other researchers we, therefore, conclude: (1) Fish use within the Elwha River estuary is complex, and even fragments of connected estuary are critically important for migrating salmon; (2) Anthropogenic effects, including in river damming and diking of the estuary, can be an important ecological driver in nearshore habitat function that should be appropriately considered in estuary habitat research, management, and restoration; and (3) Juvenile salmonids appear to be able to respond to dynamic sediment environments if there are habitat options available. [ABSTRACT FROM AUTHOR]