Environmentally Friendly Levee Could Protect Against Sea Level Rise

MARCH 19, 2015

What are now seedlings will play a key role in an experiment that could be an environmental triple win -- improving water quality and protecting against sea level rise while providing wildlife habitat. An army of volunteers will plant more than 70,000 native plants next fall on a first-of-its-kind ecotone levee and wetland basin. The levee and basin will be built on a vacant field near the Oro Loma Sanitary District wastewater treatment plant.

Treated wastewater will flow into the basin and then be piped under the ecotone, percolating out and sustaining the plants. The plants also will improve water quality by removing nutrients that can contribute to algae growth.

Source: Environmental Science Associates

Climate change will cause a 55 inch rise in the water level along the shoreline by the end of the century, scientists predict. If nothing is done, the rising water will cause flooding that will directly affect 80,000 East Bay residents, according to one study. Industrial areas and wastewater treatment plants also are found along the shoreline. That danger has prompted several agencies to collaborate to figure out how to prepare for the rising water level.

On one extreme, civil engineers propose building a sea wall; on the other, environmentalist would allow the flooding to take place, Warner said. The ecotone should meet the concerns of both groups, he said. "People can't agree on most things, but on this one we do," he said.

Oro Loma is contributing $4.55 million of the project cost, and Castro Valley Sanitary District $2.45 million. The two sanitary districts jointly own the treatment plant at the end of Grant Avenue. A $2.1 million state grant also will help pay for the $9 million project, with work expected to start this spring.

Oro Loma has been the main catalyst for the project, along with Castro Valley Sanitary and the East Bay Dischargers Authority. Also involved are the San Francisco Estuary Partnership, Save the Bay and The Bay Institute.

UC Berkeley professor David Sedlak and other scientists will monitor the site and collect samples from four combinations of soil types, plant species and water flow to see which works best to purify the water. "I'm very interested in the potential that the ecotone could improve water quality," Sedlak said.

The gently sloped levee, designed to mimic the natural slope from wetlands to uplands, will be 800 feet wide and 160 feet long. It will be blocked off behind a dike along the flood control Bockman Channel, which flows into the bay.

For now, the remaining water will be returned to the plant for a second treatment, but it is hoped that it will be clean enough so that one day it could be discharged directly into the bay, Warner said. "The ecotone should be sitting on the bay's edge. But it's an experiment; we're not sure if it's going to work," he said.

The ecotone proposal came out of one of the first reports on how rising sea level will affect the area's shorelines and possible solutions. The 2010 report was commissioned by the Hayward Area Shoreline Planning Agency.

Save the Bay is raising the native plants that will be transplanted to the ecotone and basin. The area will be overplanted to give the native varieties a better chance of getting established before weeds appear, said Jessie Olson, Save the Bay nursery manager. The plants also will get a boost from the continuous supply of treated wastewater being fed through the ecotone.

The ecotone is not the first sloped levee built, but with only seasonal rainwater available, invasive weeds have been a problem, said Jeremy Lowe of Environmental Science Associates, one of the project consultants. Dikes along the shoreline block water from naturally flowing inland. "Combining slopes with discharge from the wastewater plant means we can create some of the habitats we used to have," he said. The levee could provide refuge for wildlife during storms, Lowe said. The wetland basin also can store 8 million gallons of primary-treated wastewater during heavy rains.

Source: Daily Review, March 19, 2015, Rebecca Parr