Filling wetlands to save them - Seawater encroachment on low-lying land forces unprecedented choices

HUMBOLDT – Sea level rise could change the way the state deals with coastal development, as expansion and construction of dikes will fill wetlands but also protect large agricultural areas that double as freshwater habitat.

A workshop on Humboldt County’s early stages of developing sea level rise defense continued at the December 13 Planning Commission meeting.

The county’s primary concern is the impacts of sea level rise in the Humboldt Bay planning area. Senior Planner Lisa Shikany told commissioners that in a scenario of 3.3 feet of sea level rise – which is projected by 2070 – 33 miles of protective structures like dikes and road grades would be overtopped.

That will put thousands of acres of land, a variety of public utility and transportation assets and 62 percent of the bay area’s ag lands underwater.

Shikany said that the bay’s diked shoreline is made up of 170 parcels and a breach on any one of them will affect multiple “assets and land uses.”

Humboldt Bay is in a subduction zone where land level is sinking but the lands behind dikes are also subsiding because of what Shikany described as a “soil issue” – the dikes have blocked introduction of new sediment so lands behind them have “gotten lower than they were when they were tidelands.”

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