Monthly Archives: October 2014

Restoration Sediment Now Arriving on Sediment Starved Elwha Feeder Bluffs: Understanding Sediment Delivery to the Elwha Nearshore

Elwha Drift Cell w FB

The Elwha drift cell extends from Freshwater Bay to the end of Ediz Hook.  Beaches along the Elwha drift cell have been starved of sediment for over a century as a result of shoreline armoring of critical feeder bluffs and the Elwha River dams.  However, now that both Elwha River dams have been removed, approximately 3,000,000 cubic meters of previously retained river sediments have already arrived to the nearshore.  Although the dam removal project was recently completed, the nearshore transformation has just begun…

sediment plume

As a result of dam removal, over 16,000,000 million cubic meters of river sediments will reach the Strait of Juan de Fuca at the Elwha River mouth.  About half of those sediments are sand, gravel and cobble that could potentially re-establish natural beaches along the shoreline.

freshwaterbaysummer20072013comparisioncwi

Soon after dam removal began in September 2011 the beaches to the west of the Elwha River mouth along Freshwater Bay were the first to benefit from the return of Elwha River sediments to the nearshore.  In August 2014 Coastal Watershed Institute documented surf smelt spawning on the beaches of Freshwater Bay and the new river delta surfaces. Read about it here.

roorda w arrows

However, It is not well understood how river sediments will be transported and deposited to 7 miles of sediment starved beaches east from the river mouth to the end of Ediz Hook.

dave

Dave Parks, senior resource scientist and hydrogeologist at Washington Department of Natural Resources, has been  working with CWI and WWU and Peninsula College interns conducting a long-term shoreline change study to help understand when and where sediments formerly detained by the Elwha dams will be deposited on the beaches of the Elwha drift cell.

deach deposits

Recent sampling by Dave Parks has shown that over a meter of new sand has been deposited on the low tide beach terrace along unarmored feeder bluffs approximately 1.5 miles east of the Elwha River mouth. This is just the beginning of sediment delivery to the sediment starved beaches of the Elwha drift cell. What does this mean ecologically? Feeder bluffs that are fronted by broad, flat, and sandier beaches erode more slowly than those without. So if sufficient, sediment deposition from the Elwha restoration will help slow erosion along sediment starved steep course beaches of the Elwha nearshore.  And for fish? Similar beaches along Dungeness Spit drift cell support surf smelt spawning,  indicating that, if restored properly, beaches along the Elwha drift cell could support surf smelt spawning in the future.

Coastal Watershed Institute has been working with our partners along central Clallam County shorelines for over a decade to predict how these sediments recently made available by dam removal may be transported along beaches of the drift cell  and define restoration opportunities  of the upcoming delivery of Elwha River sediments  to sediment starved beaches between the Elwha River mouth and the end of Ediz Hook.  We have alot more to do.

Coastal Watershed Institute will hold the 9th annual Elwha Nearshore Consortium in February 2015 in Port Angeles.  The event will feature one day of technical presentations and one day of public workshops and site visits.  Stay tuned for more details and updates about exciting changes to the shoreline and opportunities to be involved in the evolution.