Sea level rise response requires radical rethinks

PAST AND FUTURE Flooding around 1975 illustrates future coastal indundation scenarios thanks to sea level rise.
Photo courtesy City of Arcata

Patrick Evans
Mad River Union

ARCATA – Arcata is almost an island in a photo taken after heavy winter rain in 1975. Water laps at the edges of U.S. Highway 101 and Samoa Boulevard and connects the Mad River to Humboldt Bay via the Arcata Bottom.

The photo is a preview of the city’s future, as global warming raises sea levels, Arcata Community Development Director David Loya told the Arcata City Council at a study session with the Planning Commission Thursday, Aug. 24.

The city is drafting a set of policies to protect areas threatened by sea level rise and retreat infrastructure and development to higher ground. Loya has been shopping the new policies around to relevant citizen advisory committees, eliciting comment before presenting them to the council.

Much of the Arcata Bottom and the city south of Samoa Boulevard and west of U.S. Highway 101 will be inundated by the end of the century due to sea level rise, according to Federal Emergency Management Agency (FEMA) flood risk studies.

Water could cover farmland on either side of U.S. Highway 101 south of Arcata and spread north as far as the Samoa Boulevard overpass, threatening to swamp Arcata’s wastewater treatment plant. Tides would push into streams like Jacoby Creek and flood inland neighborhoods.

The plan would establish a line of flood protections based on a moderate FEMA estimate of an increase in average monthly high water of 13 feet by the year 2100. Extreme estimates of a high water rise of 17 feet would be beyond the city’s ability to prepare for, Loya said.

“We’re projecting for a feasible range of what we can build to, and being hopeful the world will get its act together and turn the climate scenario around,” Loya said.

The neighborhoods and industrial zones built on former tide land south of Samoa Boulevard would be the first line of defense, designated in the plan as the Urban Protection Area. Threatened businesses and city infrastructure in the proposed protection area is estimated to be worth $140 million, and will generate a revenue of $2.5 million for Arcata over the next 10 years, according to Loya. The city needs to find funding sources for the cost of building the protection area, estimated at $15 million.

The city would improve existing barriers and build seawalls around the protection area to create a buffer between the rising bay waters and the coastline. City owned land adjacent to U.S. Highway 101 south of Samoa Boulevard would be converted to salt marsh, creating flood protection and new habit in areas formerly drained for agriculture.

The city wastewater treatment plant sits on the edge of the Humboldt Bay and is the southern portion of the protection area. The treatment plant would be bordered with a barrier of salt marsh to slow incoming water and reduce erosion. A city pilot project is currently underway to determine the feasibility of expanding tidal marsh land.

Loya said the city will try to avoid a sudden drop in property value in the area by allowing development and business to continue.

“We are trying to prevent a fire sale, telling people today that their property is worthless because of something that is going to happen in a hundred years,” Loya said.

New development would be allowed inside the protection area, but owners would waive their right to sue the city for property damage due to flooding. New development outside the protection area on the seaward side of Old Arcata Road and Samoa Boulevard would be permitted but owners would waive their right to build shoreline protections.

The protections will not hold back the bay indefinitely. As water rises land in the flood zone that is too expensive to protect will be abandoned, and property owners will have to demolish structures which they can’t afford to protect on their own. Arcata would secure easements for bayshore agriculture and industrial land, removing threatened structures and converting the coastline to tide flats and marshes.

Arcata’s sea level rise project must be reviewed by the California Coastal Commission for compliance with Coastal Plan requirements to protect public access and natural resources on the coast. The city will have to update other projects such as storm water control and water quality management to cope with flooding and ground water rise.

Arcata is coordinating its emergent standards with the Coastal Commission to expedite approval. One problem is that the state commission is looking at sea level rise scenarios 70 to 100 years into the future – well beyond the 20-year planning horizon Arcata can manage.  As for retreating to higher ground, Loya said during a recent briefing to the Economic Development Committee that there is perhaps 20 to 30 years of infill development on underutilized lots inland.

But, voicing some explosive news, he warned that some may want to “grab their torches and pitchforks” at the possible, far-future eventuality of pushing municipal development up into the Arcata Community Forest and Sunny Brae Tract.   

The City Council’s next step is reaching out to Arcata residents. The city will be holding a month of activities in October to educate the public about sea level rise, table during the Farmers’ Market and host a sea level rise event at the Marsh Interpretive Center in September.

Editor Kevin L. Hoover contributed to this story.


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