USGS Science to Support the Elwha River Restoration Project
What We Do: Estuary
The estuary of the Elwha River includes approximately 0.35 km2 of wetlands, which combined represent only about 0.04% of the total river watershed area. Although this area is relatively small, the estuarine habitat of the Elwha River provides an important refuge for juvenile salmon and other wildlife. Studies of the estuary have been carried out with collaboration with the Lower Elwha Klallam Tribe, which owns and manages most of the estuarine complex. These studies include investigations of the hydrology, sedimentation, ecology, and vegetation within this estuary, as detailed below.
The Elwha River estuary is the primary location of water mixing between the river, local aquifers and the coastal waters of the Strait of Juan de Fuca. This mixing—which is strongly influenced by the tides of the Strait—creates brackish water conditions that vary throughout the estuary and over tidal and annual cycles. Monitoring of the flow of water through this system and water properties within this system has been conducted through collaboration between the Lower Elwha Klallam Tribe and the USGS. These measurements of flow, salinity, temperature and water levels will be important to track during and following the dam removal to see how the hydrology of the estuary changes following this event.
For more information about the hydrology of the estuary see Magirl and others (2011), which is chapter 4 of the USGS Scientific Investigations Report 2011-5120, available at http://pubs.usgs.gov/sir/2011/5120/.
With the renewal of sediment supplies to the Elwha River following dam removal, the estuary will receive increased sediment loads. These increased sediment loads may enhance the sedimentation within the estuary. To measure the rate of sedimentation, the Lower Elwha Klallam Tribe and the USGS have installed approximately one dozen Surface Elevation Tables (SET's), which is a device for measuring the relative elevation change in wetland sediments.
For more information regarding the SET, including descriptions, use and installation locations throughout the U.S., please see http://www.pwrc.usgs.gov/set/. For more information about the sedimentation studies at the Elwha River estuary, please contact Dr. Jonathan Warrick.
The ecology of the Elwha River estuary is rich and diverse. The estuary ecosystem supports juvenile salmon before they transition to the sea, and collaborative studies between the USGS and Lower Elwha Klallam Tribe have chronicles the rapid growth rates of juvenile salmon within the estuary and the food sources and water quality of this estuary. The abundance of salmon within the estuary during the dammed state of the river was related to the physical connection of surface water between the river and the estuary.
For more information about the estuary ecosystem and water quality, please see Duda and others (2011), which is chapter 7 of the USGS Scientific Investigations Report 2011-5120, found at http://pubs.usgs.gov/sir/2011/5120/.
The Elwha River estuary supports one of the most diverse coastal wetland complexes yet described in the Salish Sea region, in terms of vegetation types and plant species richness. Most of the estuary is dominated by woody vegetation, although there are also areas with emergent vegetation and coastal dunegrass. Combined, the vegetation of the estuary provides important habitat to fish and wildlife and also provides shade to the waters flowing within the estuary.
A thorough mapping and description of the Elwha River estuary was conducted by collaboration between the USGS and the Lower Elwha Klallam Tribe. Results and maps of these surveys can be found in Shafroth and others (2011), which is chapter 8 of the USGS Scientific Investigations Report 2011-5120, found at http://pubs.usgs.gov/sir/2011/5120/.