Filling wetlands to save them

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

Seawater encroachment on low-lying land forces unprecedented choices

Daniel Mintz
Mad River Union

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.” 

The upshot is that with one meter of sea level rise, the dikes will be overtopped and the area behind them won’t become salt marsh – it will become open water. 

The economic loss will be huge. Shikany said livestock alone comprises a $200 million commodity. 

But protection of the valuable assets has an obstacle – the state’s Coastal Act, whose policies are geared toward avoiding wetland fill. Most of the bay area’s ag lands are considered freshwater wetlands and Shikany said wetland fill will be necessary to bolster existing dikes and construct new ones. 

The wetlands issue will have to be worked out with the state’s Coastal Commission, which has permitting authority in the entire Humboldt Bay planning area. Shikany said the argument the county is advancing posits that without the dike enhancements, far greater areas of freshwater wetland and ag lands would be lost than what would be filled. 

Commissioner Noah Levy noted the ideological turnaround, saying that current thought associates human activity with loss of wetlands “but here, it’s like, if we do nothing, we will sooner or later lose most or all of the freshwater wetland in the bay.” 

“The consequence of not doing it is the loss of all those other resources – and there is no in between,” said Commissioner Ben Shepherd. Referring to negotiations with the Coastal Commission, he added, “I think that will be an interesting discussion.” 

The Coastal Act does allow wetland fill in some instances but it’s conditioned on mitigating the impacts by creating or restoring wetlands in other areas. Shikany said that will be difficult to do given the scope of sea level rise.  

She told commissioners that the strategy at this point is to describe the dike work as “self-mitigating,” since doing it will prevent vast wetland loss. 

Planning Director John Ford said an approach being considered is to have the county gain a comprehensive Coastal Commission permit. 

“Can you not find some allies within the commission who see the utter sensible-ness of what we’re trying to do here?” Levy asked. 

“One of things you’re struggling with, and we’re struggling with and, in all honesty, the Coastal Commission staff and management are struggling with, is that we have this traditional paradigm of protecting coastal resources,” Ford responded. “But then we have the reality that nothing we’ve created in the past is equipped to deal with sea level rise.” 

He added, “I think you’re right, it is a matter of finding that sympathetic ear within their staff and hopefully on the commission itself, to see the logic of having to deal with something that’s absolutely unprecedented.” 

Senior Planner Michael Richardson noted that the Coastal Commission co-sponsored the funding of the county’s sea level rise impact assessment, which was developed by hydrologist Aldaron Laird. 

Richardson added that although the permitting issues have been detailed as one of the grant’s “deliverables,” the county’s “engagement with the Coastal Commission at this point on these issues is rather limited – we gave it our best shot and now we’re engaging with the public more.” 

The process will be to draw public involvement, have the Planning Commission refer recommendations to the Board of Supervisors and then advance the board’s recommendations to the Coastal Commission. 

The Planning Commission will continue its discussion on sea level rise as 2019 begins.


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