The Elwha submarine delta, today and in the past: sediment dispersal and seabed habitats
Presentation Abstract
The marine impacts of the Elwha dam removal and restoration project extend beyond the visible shoreline to encompass broader-scale seabed and associated habitat changes on the submarine delta. Our goals are to evaluate and predict transport-process and seabed evolution during and after dam removal based on studies of both modern sediment dynamics and historical geologic formation of the delta. We link time-series sediment-transport data, seabed sampling and imagery, and seismic data to understand both the past and present sediment dispersal and deposition in the marine ecosystem. In the past, Elwha River sediment load has fluctuated between two extremes, due to both human (dam placement) and natural (e.g., 100 yr flood) events. Even with this large range in sediment delivery, strong tidal currents induced by interactions with coastal morphology created a situation where fine-grained sediment likely did not accumulate except under the most infrequent floods. Thus, the coarse, gravelly lag layer found across much of the delta surface immediately prior to dam removal likely was similar to the seabed prior to dam installation. The present dam-removal conditions of highly concentrated sediment loading replicate those during episodic floods, and deliver both sand and mud to the Strait via a surface plume. Sediment disperses and settles from the thin plume, reducing light at the seabed. Understanding the dispersal mechanisms of sediment under extreme loading conditions is critical for reconstructing delta evolution and evaluating restoration programs throughout the Salish Sea. This research has been used as the foundation for a series of intensive, applied research experiences for Washington college students interested in coastal sediment dynamics and Salish Sea management issues. Through these educational activities, we train future resource managers to consider long-term system evolution as well as short-term impacts of natural processes and restoration activities in the region.
Session Title
Session S-07F: Elwah River Restoration: Evolution of Habitats and Ecosystems During a Dam Removal Project
Conference Track
Restoration
Conference Name
Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)
Document Type
Event
Start Date
1-5-2014 3:30 PM
End Date
1-5-2014 5:00 PM
Location
Room 602-603
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Sediment transport--Washington (State)--Elwha River; Reservoir sedimentation--Washington (State)--Elwha River; Dam retirement--Environmental aspects--Washington (State)--Elwha Dam
Geographic Coverage
Salish Sea (B.C. and Wash.); Elwha River (Wash.); Elwha Dam (Wash.)
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
The Elwha submarine delta, today and in the past: sediment dispersal and seabed habitats
Room 602-603
The marine impacts of the Elwha dam removal and restoration project extend beyond the visible shoreline to encompass broader-scale seabed and associated habitat changes on the submarine delta. Our goals are to evaluate and predict transport-process and seabed evolution during and after dam removal based on studies of both modern sediment dynamics and historical geologic formation of the delta. We link time-series sediment-transport data, seabed sampling and imagery, and seismic data to understand both the past and present sediment dispersal and deposition in the marine ecosystem. In the past, Elwha River sediment load has fluctuated between two extremes, due to both human (dam placement) and natural (e.g., 100 yr flood) events. Even with this large range in sediment delivery, strong tidal currents induced by interactions with coastal morphology created a situation where fine-grained sediment likely did not accumulate except under the most infrequent floods. Thus, the coarse, gravelly lag layer found across much of the delta surface immediately prior to dam removal likely was similar to the seabed prior to dam installation. The present dam-removal conditions of highly concentrated sediment loading replicate those during episodic floods, and deliver both sand and mud to the Strait via a surface plume. Sediment disperses and settles from the thin plume, reducing light at the seabed. Understanding the dispersal mechanisms of sediment under extreme loading conditions is critical for reconstructing delta evolution and evaluating restoration programs throughout the Salish Sea. This research has been used as the foundation for a series of intensive, applied research experiences for Washington college students interested in coastal sediment dynamics and Salish Sea management issues. Through these educational activities, we train future resource managers to consider long-term system evolution as well as short-term impacts of natural processes and restoration activities in the region.
