About the Talk

STABILIZING PORT ANGELES’ COASTAL LANDFILL

In 1947, the City of Port Angeles created a 25-acre dump at its shoreline, between Ediz Hook and the Elwha River. Over the ensuing 60 years, the site evolved into a 70-acre sanitary landfill with numerous waste containment cells.

Since closure in 2007, and for about 5000 years before that, wave action at the beach site has been continuously eroding the 135-foot tall feeder bluffs. In June 2011, a small exposure of garbage from one of the seaside landfill cells was observed hanging over the edge of the bluff. Further erosion could easily have resulted in a large release of garbage onto the beach since there were only eleven to fifteen feet of native bluff between the eroded face and a 60-foot deep pit of municipal solid waste.

Kathryn Neal will review the geologic setting, bluff retreat rates and the sediment contribution of the bluffs to Ediz Hook, the history of public works construction at the site, wave energy and beach morphology studies that the City conducted, and summarize the design alternatives that the City considered before deciding to relocate the landfill.

In her time with Port Angeles, this has been one of the largest and most significant projects she has been involved in, and arguably the most unique. The project, which was completed this year at a cost of about $21.3M, protects the environment, will last for many decades and was successfully accomplished within the financial constraints of a small city.

 

About the Speaker

Kathryn Neal, P.E. is Civil Engineering Manager with the City of Port Angeles. Kathryn has a Bachelor of Architecture and Civil Engineering from the University of Washington and has been a practicing Professional Engineer since 1994. She grew up in Port Angeles and was thrilled to be able to move back to the Olympic Peninsula about 15 years ago. When she has time off, she enjoys hiking, kayaking, reading, and imagining alternate realities.

About the Talk

Bridge of the Gods & the Bonneville Landslide

In the heart of the Columbia River Gorge, where the Columbia River breaks through the Cascade Range, an 1800-feet-long steel truss bridge spans the Columbia River at a particularly narrow spot near the town of Cascade Locks. This bridge is known as the Bridge of the Gods. But this modern name derives from a much larger Bridge of the Gods that crossed the Columbia River in about 1450 AD. This earlier “bridge” was not really a bridge, but a blockage, the result of a huge landslide, known as the Bonneville Landslide, which headed on Table Mountain on the Washington side of the river and cascaded downward, filling and damming the Columbia River valley with 5 square miles of debris up to 400 feet thick. Recent investigations using radiocarbon dating and dendrochronology show the landslide occurred around 1450 AD, whereas earlier dating permitted a possible link to the 1700 AD Cascadia earthquake.

The Bonneville Landslide almost certainly gave rise to the Native American legend of the Bridge of the Gods. Oral histories of the region indicate that the Native Americans “could cross the river without getting their feet wet.” After blockage by the Bonneville landslide, the Columbia River formed a great lake behind the debris dam, also noted by Native American accounts of the Columbia River rising to great heights upstream. Sometime after overtopping, the Columbia River cut cataclysmically through and around the southern edge of the landslide mass. But the downcutting was not complete, and large rocky debris too big to be carried away by the river remained, creating the set of foaming rapids, first mapped by Lewis and Clark as “The Great Shoot.” Cascade Rapids were drowned by the 1938 completion of Bonneville Dam.

About the Speaker

Jim O’Connor is a Research Geologist at the U.S. Geological Survey in Portland, Oregon, where he has been stationed since 1996. His primary research focus is landscape evolution in the Pacific Northwest. He majored in Geological Science at the University of Washington and earned M.S. and Ph.D. degrees at the University of Arizona.