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Water agency outlines flood mitigation

Wednesday evening, the Sonoma County Water Agency and its partners presented to a full room of concerned citizens a multi-benefit project to mitigate flooding in two area creeks and to revitalize groundwater in the Valley.

The Jan. 29 meeting, hosted in the Community Meeting Room, outlined the City Watersheds of Sonoma Valley project, which was awarded a highly competitive $1.89 million grant by the California Department of Water Resources through Proposition 1E funding. To receive the grant, the group had to demonstrate a strong partnership of agencies working on a multiple-use project with an education component.

The project, which is still in preliminary and test phases, will be located on the Montini Preserve and along Fryer Creek.

Sonoma County 1st District Supervisor Susan Gorin, who serves on the water agency and Agricultural Preservation and Open Space District boards, as well as on the county’s Water Advisory Committee, said, “It’s strange to talk about flooding during a dry period, but the reality is what’s part of climate change is unpredictable weather, so we have to look at the long term.”

After numerous scoping studies to identify an area ideal for a multi-benefit project, the water agency’s Principal Engineer, Kent Gylfe, explained that the Fryer Creek and Nathanson Creek areas, along with the Schell Creek area in Kenwood, were prime locations to both mitigate flooding in high-risk urban areas and increase groundwater supplies that are on the decline throughout the county. While the first part of the project, Gylfe explained, will look specifically at Fryer and Nathanson creeks, eventually the group plans to implement similar projects throughout the Valley.

The multi-benefit wetland enhancement project includes a detention basin in the existing pasture, off Fifth Street West, at Montini Open Space Preserve, to reduce flood risks during large storms and to recharge the groundwater supply.

It also includes an education component for public awareness and a restoration and re-vegetation of the basin to make it compatible with the surrounding landscape. The raised culvert on Fryer Creek at MacArthur Street that bisects the creek and creates a water and fish blockage will also be replaced or modified.

The collaborative effort includes the water agency, the City of Sonoma, Sonoma County Agricultural Preservation and Open Space District and the Sonoma Ecology Center. It also includes private contractors who specialize in hydrogeology and water projects.

Betty Andrews, a contractor on the project and a principal engineer focusing on environmental hydrology at Environmental Science Associates, Phillip Williams and Associates (ESA PWA), explained how humans modify watersheds by building homes and businesses, and adding things like storm drains.

“Undisturbed water moves more slowly, but humans come in and create these slick, flat surfaces that don’t absorb water,” she said. “So, when we have more water in a storm, water moves more quickly and can up the chance of flooding.” The project, she added, will “chip away” at this flooding path and the changes humans have created in the watershed.

Within the Sonoma Valley watershed, Gylfe said, the Nathanson and Fryer creeks sub-watershed covers 80 percent of the City of Sonoma and has the potential to cause serious damage to the highly developed area.

Within the area, the water agency, with help from the United States Geological Survey, also identified declining groundwater supplies, particularly west of Verano Avenue and toward the southern end of the Valley. “Some of these groundwater basins are declining at a rate of two to three feet per year,” Gylfe said, adding some areas are reaching or dipping below sea level and becoming non-potable with increased salinity.

The goal, Gylfe explained, is for the detention basin, which will be achieved by creating a subtle grade to a central area of the preserve, to hold back water and slow it down to minimize run off into the storm drain and into the creek. Then, the water will be allowed to sink back into the ground and spread out in such a way as to be able to hold 12-acre feet of water within a large basin. “This would be a benefit from flood hazard to people downstream,” he said.

City Engineer and Director of Public Works Dan Takasugi recalled the January 2006 storm and the massive flooding it created, explaining the city’s role would be to use the Storm Drain Master Plan, which outlines the 46 miles of storm drain pipeline and management in city limits, to assist in project implementation.

In December 2013, researchers tested soil using a drill rig at several locations on the Montini property and near the Fryer Creek culvert. Results from the initial soil samples should be available next month.

Andrews explained the Montini project is still in design phase, while no decisions for the culvert at Fryer Creek have been made. The project will be designed by 2015, with construction slated for summer 2016, followed by re-vegetation and monitoring.

The cost, as outlined by SWCA engineer and project manager Greg Guensch, will total $4.5 million. The initial phases of the project already completed – including a culvert on First Street West and trails at Montini, were funded through the city’s general fund and the water agency’s Zone 3A Flood Control funding. The remainder of the project, including Montini wetland recharge and re-vegetation, and the MacArthur culvert, will cost $3.7 million, with half funded by the grant. The remaining $1.8 million will be funded through the water agency’s Zone 3A Flood Control funding and is budgeted over the next few years.

Residents in attendance at the meeting also had a chance to ask questions and share concerns.

Many residents who live near the Montini property, and along Fryer and Nathanson creeks, voiced concerns about the water agency’s creek and drain maintenance, with some residents noting accumulations of trash and debris in the lower part of Fryer Creek. At one point, Bill Montini, whose family sold the preserve land to the county, said, “There is one main problem and that is that we have a storm drain system that hasn’t been maintained for 15 years … We need to be spending more money getting the creek cleaned out,” he said, noting several logjams in Sonoma Creek and recalling that 40 years ago, the creek was nearly three times as wide.

Gylfe said while maintenance is absolutely important, simply maintaining the creeks to regulation standard as outlined in the agency’s permits would not solve the flooding issues in the risk area. Maintaining the creeks, he added, will also not add any groundwater recharge benefit.

Patricia Talbot, who lives next to the Montini Preserve, said she is worried about increasing flooding in the neighborhood surrounding Montini. “If we fix flooding downstream, will we just be moving the flooding upstream in our neighborhood,” she asked.

Talbot also voiced concerns about increasing the mosquito population by keeping stagnant water in the area. According to Andrews, the project will be designed to “evacuate” the water in a few days, so as to avoid creating a mosquito-breeding habitat. “From my understanding,” Gylfe said, “mosquito breeding takes places in the 4- to 14-day period. We are holding water for 72 hours then draining it into the ground so we don’t have standing water.”

“This project is really about furthering stewardship of water here in the Valley,” Gylfe said during the meeting. Afterward, he noted, “It was a very successful meeting with a number of legitimate concerns and many have been given consideration, but some not as much as others. So we have a good basis of things to make sure we are thinking about and address at the next meeting.”

The water agency and its partners will host a follow-up meeting with details to come. For more information on the water agency, visit sonomacountywater.org, and for more information on the City Watersheds Project, go to scwa.ca.gov/svflood.