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ENVIRONMENT

Santa Cruz changes how it manages San Lorenzo River

Temporary culvert, not bulldozers, will relieve flooding

By Robin Estrin

restrin@santacruzsentinel.com @robin_estrin on Twitter

SANTACRUZ>> The era of bulldozing sand to breach the lagoon at the base of the San Lorenzo River is nearing an end, as the city of Santa Cruz takes steps toward more sustainable methods of flood relief.

Wednesday, the city installed a temporary culvert — a two-foot wide plastic pipe that allows rising waters to move safely from the lagoon down to the ocean — as a precursor to what it hopes is a long-term solution, a permanent culvert designed with residents, businesses and the river’s threatened and endangered species in mind.

The proposed culvert would pull salinated water from the bottom of the lagoon, but only after the water rises to 5 feet above mean sea level, a “sweet spot” for fish and flood control, said Public Works analyst Scott Ruble.

For years the city has relied on the use of heavy equipment to breach, or open, the lagoon, causing water to pour into the ocean by the millions of gallons, temporarily alleviating flooding but taking fish habitat with it.

Breaching, which costs the city $11,500 each time, is only a quick fix. After opening the lagoon, the city is tasked to immediately close it. Regulatory agencies instruct the city to leave a healthy amount of water for the species in the lagoon, but stopping the river is not as easy as turning off a faucet.

Ruble said that of the four breaches the city has conducted during the last three years, only twice has it been able to cap the river before it’s drained to roughly 2 feet.

Catch-22

Coastal flooding in Santa Cruz is a symptom of a centurylong struggle between the city and nature.

Man-made structures such as the jetty at the Santa Cruz Harbor have prevented the natural drift of sand along the coast, causing a build-up at the San Lorenzo River mouth. In the summer the lower-flowing river has difficulty breaking through the sand, and water levels rise to dangerous heights.

At 5 feet above mean sea level, local businesses and residents start to see water seep into their basements and streets. Occasional flooding is already an issue in the lower Ocean and Beach Flats neighborhoods, but the problem is expected to compound as sea levels continue to rise.

“It’s a really tricky situation, the balancing act between flood management, for protecting homes and businesses, and protecting fish,” said Greg Pepping, executive director of the Coastal Watershed Council. Pepping

City of Santa Cruz work crews bulldoze sand in an attempt to close off the San Lorenzo River mouth a few hours after breaching it Monday.

DAN COYRO — SANTA CRUZ SENTINEL


understands the situation as a Catch-22: Opening the lagoon tips the scale in favor of residents, and against the preservation of the rich ecological habitat.

On-site biologists scan the lagoon for stranded species during a breach, but the force of the river can sweep juvenile fish into the ocean before they’re ready, and those that stay see their habitat shrink to a fraction of its previous size, said Joel Casagrande, a fisheries biologist with the National Oceanic and Atmospheric Administration.

“If you can imagine a body of water that swells up to be the size of a small lake and then drains down to a simple little stream, for the most part, in less than an hour, it could have a devastating effect on the population of fish in the lagoon,” Casagrande said.

Sustainable solution

After the river levels approached the levee last weekend, the city supervised its last permitted breach of the year on Monday, installing the temporary culvert shortly after. But Ruble hopes to have the permanent culvert installed next summer.

Regulatory agencies have signed off on the project and the Watsonville- based construction company Graniterock was awarded a bid. Pending is a majority of the grant money that will fund the $1.5 million project, said Ruble, who calls the culvert “experimental” and “cutting edge.”

The city has received $500,000 from the Wildlife Conservation Board to pursue the project, and is applying for more funding from the state agency this week. Ruble sees the construction of a permanent culvert as well-worth the cost.

“We look forward to the day that [the culvert] is working, the day that people are safe, fish are happy and no one’s got flooding in their backyard,” Ruble said.

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