How does the culvert system work?

The culvert system consists of two pipes: an 8-inch pipe and a 24-inch pipe. The 8-inch pipe draws water from bottom of the lagoon and is intended to remove the heavier salt water (high salinity) for the purpose of improving fish habitat in the lagoon. The 24-inch pipe is the overflow pipe which is designed to receive surface water and maintain water elevation at the design elevation of 5 ft for the purpose of preventing minor flooding.

The intakes of both pipes are fitted with fish-screens which are designed to protect fish from getting sucked into the system.

Once water enters through the intake screens it is conveyed through the pipes and discharged into the ocean at the outlet located near the end of San Lorenzo Point. Each pipe outlet has a check-valve which allows the water to flow out but prevents ocean water from flowing backwards through the system. The system works entirely on gravity and does not involve any electric pumps.

Why is the culvert project needed?

The project will have multiple benefits across environmental, public safety and infrastructure fronts, and has been in design, in partnership with regulatory agencies for many years including NOAA's National Marine Fisheries Service, the U.S. Fish and Wildlife Service, the California Coastal Commission, the U.S. Army Corps of Engineers, the California State Water Resources Control Board and the California Department of Fish and Wildlife. The project will

• Prevent flooding of the lower Ocean and Beach Flat neighborhoods caused by a closed lower San Lorenzo River (a condition that has been exasperated unnaturally by the construction of the harbor jetties in the 1960s).
• Reduce or eliminate “catastrophic” breaches of the closed lower San Lorenzo River which seriously damages habitat for, and can purge, protected species including steelhead trout and tidewater goby.
• Mitigate or eliminate the life-safety danger posed by closed lower San Lorenzo River breaches which can sweep beachgoers into life-threatening swift waters.

How will the project accomplish all of the above?

The project will provide a lower San Lorenzo River (also referred to as the “lagoon” when closed) water height control system to prevent the unnatural flooding, and reduce or eliminate the “catastrophic” breaches of the lagoon, and mitigate or eliminate the life-safety dangers.

What causes the high water?

High water levels often occur in the lagoon when the river mouth is shoaled (closed) in the summer and fall seasons.

What causes the shoaling?

In the decades since the construction of the Santa Cruz Harbor entrance jetty in 1964, sand has slowly aggraded along the beaches west of the jetty to the extent that sand on both Seabright and Main beaches now reaches the end of San Lorenzo Point. This increase in sand causes the San Lorenzo River mouth to more easily and persistently shoal in the summer and fall when river flows are low, and sand accretion is accelerated by summertime wave action from southerly swells. This sand accretion eventually causes shoaling of the river mouth, and as a result, the water level in the lower river begins to rise.

Will the proposed water height control system hurt environmental habitat?

No, to the contrary, this water control system will protect water level of environmental habitat. In fact without this project, when the lagoon reaches high water levels and then breaches, the rapid dewatering of the lagoon is extremely harmful to the habitat that the lagoon provides to many species, including protected species such as juvenile steelhead salmon, and northern tidewater goby and can terminally flush these species to the ocean. This project will stop such harm to habitat.

What are specifics of the problem when the flooding spreads out to the west over vast portions of Main Beach as well as under the San Lorenzo Point cave onto Seabright Beach?

This is highly problematic as it makes unusable large portions of Main Beach during the summer, and exacerbates area flooding. More importantly, it creates serious public safety concerns as the lagoon’s stagnant waters can create unhealthy water conditions, and the lagoon can easily be breached illegally, creating an extremely dangerous fast flowing river on Main Beach at times when there can be thousands of people of the beach.

How else is the high water problematic?

When the lagoon reaches extremely high levels, it causes flooding in the lower Ocean Street and Beach flats neighborhoods and even downtown basements.  It reduces Main Beach access and cuts off emergency vehicle access from the access road under the train trestle. When the water gets extremely high, the City has needed to undertake emergency mechanical openings of the lagoon to reduce the river’s water level. The City is obligated by regulatory agencies to then attempt close the river to ensure the river does not empty below 5 feet NGVD29 in water surface level height, an exceedingly difficult challenge with many requirements that make mechanical breaches unsustainable as a long term lagoon management solution.

What would be the cost of this project to the City and residents?

Construction is funded by a $2,215,000 grant from the California Wildlife Conservation Board’s Streamflow Enhancement Program and $658,000 from Storm Water, General and Liability Funds. This covers construction, construction management and installation.  This project is included in the approved FY 2020-2024 Capital Investment Program, San Lorenzo River Lagoon Culvert Project (c601403) and has been continuously present in the City’s Capital Investment Program since FY 2014.

Will this project provide any cost savings?

Yes. The opening and closing of the river are expensive, as they require the presence of biologists, Public Works and Water Department staff, lifeguards, a geomorphologist, construction contractors and several pieces of rented heavy equipment (two excavators and a bulldozer). Once the project is completed, the City will greatly reduce these costs.