Science Center Objects

The formerly free-flowing Elwha River was famous for the diversity and size of its salmon runs. After the construction of the Elwha Dam (1912) and the Glines Canyon Dam (1927), fish lost access to more than 70 miles of mainstem river and tributary habitat. As a result, all 10 runs of native Elwha salmon and sea-going trout declined sharply. Restoration of the Elwha River ecosystem will be accomplished primarily through the removal of the two dams.

To help resource managers understand the effects of dam removal on sediment transport, watershed ecology, and aquatic habitat, the USGS is developing a suspended-sediment monitoring system, studying how sediment may be redistributed, and assessing how dam removal will affect the ecosystem.

9722-BHS - Development of a continuous, real-time suspended sediment monitoring system and its evaluation in the Elwha River, Washington - Completed FY2005

Problem - Restoration of the Elwha River ecosystem will be accomplished primarily through the removal of two high dams, Glines Canyon and Elwha, which block the migration of anadromous salmonids. Erosion of deltas in Lake Mills and Lake Aldwell, the reservoirs formed by the dams, will produce elevated levels of suspended sediment in the river, which is the primary source of water for the City of Port Angeles. Operation of a new water treatment plant, to be constructed to mitigate the effects of dam removal, will depend on continuous, real-time suspended-sediment monitoring. Suspended sediment traditionally is monitored by manual collection of water samples and subsequent laboratory analysis. Results are not known for days after sampling. Continuous, real-time suspended-sediment monitoring remains an elusive goal that will be achieved only with new technologies.

Objective(s) - The project objective is to develop a system that transmits the concentration and mean particle size of suspended sediment in a river continuously and in real time.

Relevance and Benefits - This project supports the actions of other Department of Interior agencies (U.S. Bureau of Reclamation and National Park Service) related to the restoration of the Elwha River ecosystem. The applications for continuous, real-time suspended sediment monitoring also extend well beyond the Elwha River, especially since sediment is a leading cause of water quality impairment in the United States. The proposed system represents a step forward in developing less-expensive, more accurate, and safer sediment data-collection techniques. It will develop a new technical capability with national applications that previously has been unavailable. We expect that a continuous, real-time suspended sediment monitoring system will be broadly useful in many regions for river restoration, water management decisions related to dam operations, water treatment, and water quality such as administering Total Maximum Daily Loads (TMDLs) of sediment in rivers and streams. This project in combination with other efforts in the Grand Canyon and Midwest will provide a comprehensive set of test conditions representing much of the range of fluvial environments in the U.S.

Approach - The system will integrate a peristaltic pump for drawing water samples, a laser diffraction instrument (LISST 25X), and a chamber for single-stage, automated dilution. The LISST 25X provides concentration and mean particle size of all suspended material and of the fraction of material greater than 60 microns. The system will be deployed at the USGS streamflow gaging station at McDonald Bridge (station number 12045500), which has a data collection platform (DCP) for satellite telemetry. A summary of the project and its results will be prepared and presented at a national meeting such as the 8th Federal Interagency Sedimentation Conference, April 2006.

9722-9VL26 - Transport of suspended sediment and its effect on aquatic habitat in the Elwha River, Olympic National Park - Completed FY2005

Problem - In 1992, Congress enacted the Elwha River Ecosystem and Fisheries Restoration Act (PL 102-495), which directed the Secretary of the Interior to restore the Elwha River ecosystem. This will be achieved by the removal of the Glines Canyon Dam in the Olympic National Park (ONP) and the Elwha Dam, located downstream from the park. Dam removal will expose fine-grained sediments forming deltas in Lake Mills and Lake Aldwell to fluvial and hillslope erosion, increasing the load and concentration of suspended sediment in the river. The transport of sediment and its effects on aquatic habitat during and after dam removal are among the most important issues in restoring the Elwha River ecosystem. The increase in fine sediment as a percentage of a streambed has been associated with a reduction in riverbed permeability; spawning and rearing habitat for salmonids; and, more directly, reduced survival, diversity and abundance of a variety of aquatic organisms (Platts and others, 1989; Scrivner and Brownlee, 1989; Allan, 1995). Understanding how increased sediment loads will affect stream habitat is vital for assessing the short-term ecological effects of dam removal in the Elwha River.

Objective(s) - A 3-year intensive study of sediment transport in the Elwha River is proposed to assess the increase in suspended-sediment concentrations during dam removal and resulting changes in the particle-size distribution of bed material. The overarching hypothesis regarding channel response is that there will be repeated episodes of elevated suspended-sediment concentrations and deposition of fine sediment on the riverbed, but that these changes will be transient because of the river's high capacity to transport sediment. The primary objectives, then, are to assess: 1) the duration that suspended- sediment concentrations are elevated during storms, both during dam removal and over the multiple-year recovery period; 2) the response of the particle-size distribution of the riverbed to the increased sediment load; and 3) the time required for the riverbed to re-armor after a deposition event.

Relevance and Benefits - The USGS Washington Water Science Center Science Plan (USGS, 2000a) identified sediment transport related to dam removal as an area of program opportunity because of local need and interest for scientific information. This project will also contribute to the USGS program strategic goal to provide and improve systematic analyses and predictive tools for scenario building and decisionmaking about natural systems (USGS, 2000b). The analysis of sediment transport in the Elwha River will improve the assessment of the timing and duration of elevated suspended-sediment concentrations in response to dam removal. The investigation supports management activities of two other Department of the Interior agencies (the National Park Service and U.S. Bureau of Reclamation) as they schedule dam removal, consider mitigating the effects of sediment on aquatic habitat, and plan a water-treatment plant for the City of Port Angeles.

Approach - A one-dimensional, sediment-transport model (Bennett, 2001) will be applied to the Elwha River from Glines Canyon Dam to Lake Aldwell and to the lower 4 kilometers of the river, downstream of Elwha Dam. The model represents 1) unsteady streamflow, 2) transport of mixed particle sizes, and 3) changes in the elevation and the particle-size distribution of the riverbed. It will be used to assess changes in suspended-sediment transport and the particle-size distribution of the riverbed in response to dam removal and the subsequent recovery of these processes and conditions. An existing sediment-transport model (USBR, 1996a) will be used to simulate erosion of the deltas in Lake Mills and Lake Aldwell, providing the sediment-input time series. Multiple runs will be made using different streamflow time series to represent a range of possible flows. The sediment input to the model will be varied in some runs to represent different dam-removal schedules.

Sediment transport during dam removal was analyzed as part of the initial planning for dam removal (USBR, 1996a). The proposed project will build on that analysis by providing a more detailed examination of suspended-sediment transport and its relation to changes in the particle-size distribution of the riverbed. By investigating the dynamic relations between suspended sediment and the riverbed, the proposed project represents an important contribution to sediment management efforts related to dam removal (T. Randle, USBR, written comm., Jan. 31, 2003). This information will improve the current assessment of the water-quality effects of dam removal in terms of both municipal water supply and the lotic ecosystem.

WA411 - Evaluation of Current Ecological Conditions with Respect to Nutrient Dynamics in the Elwha River, Olympic National Park - Completed FY1999

Background - The formerly free-flowing Elwha River was famous for the diversity and size of its salmon runs; it produced an estimated 380,000 migrating salmon and trout and supported 10 runs of anadromous salmonids, including chinook that exceeded 100 pounds (National Park Service, 1996). After the construction of the Elwha Dam (1912) and the Glines Canyon Dam (1927), more than 70 miles of mainstem river and tributary habitat were lost to anadromous fish production. This loss resulted in a precipitous decline in the native populations of all 10 runs of Elwha salmon and sea-going trout.

In response to the loss of the salmon runs in the Elwha River Basin, President George Bush signed the Elwha River Restoration Act in 1992, which began the process of assessing the feasibility of restoring the Elwha River ecosystem. One option being considered is the removal of existing dams and restoration of the salmon runs. Returning salmon will provide a large source of nutrients to the Elwha River ecosystem, which may dramatically change the river from its present ecological state. In order to manage the Elwha River during the process of restoration and evaluate the eventual success of the restoration effort, it is important to evaluate its present ecological status. The initial step in this evaluation is to develop an ecological framework upon which existing conditions and future changes can be characterized.

The adjacent Dungeness River basin is a free-flowing system with remaining runs of salmon and serves as a reference basin for comparison with the Elwha River.

Objective - Evaluate the current ecological status and nutrient dynamics of the Elwha River to assist in developing salmon restoration management plans and develop an ecological framework for describing current and future ecological conditions in the Elwha River Basin.

Approach - While the Elwha River is the primary basin of interest in this study, the Dungeness River will serve as a reference basin; therefore, some of the proposed Elwha tasks will also be done on the Dungeness River at a less intensive level. While this present proposal will focus on the approach for one year, the overall plan is to conduct additional studies in FY98 and FY99. Year one (FY97) will include the following tasks: 1) review and summarize all relevant available biological, chemical, and physical data on Elwha and upper Dungeness Rivers; 2) review stream classification systems and evaluate for potential application to the Elwha River; 3) analyze existing data in relation to the nutrient status and the various stream classification systems, and identify data needs; 4) design a study for the summer/fall of 1997 to collect additional data based upon needs identified in step 3; and 5) write a report which reviews present knowledge of the ecological status of the Elwha River, the stream classification system selected, and findings from the 1997 field effort. This report will also identify the physical, chemical, and biological data which should be collected in the next phase of the study.