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Coneheaded Fish Screens

All fish screens are not created equal and surprisingly few meet the flow standards set by federal agencies to protect endangered fish. Suisun Marsh's new screens are an exception.

This 116,000 acre marsh north of Suisun and Grizzly bays has some 700 intake pipes that suck water into 56,000 acres of managed, seasonal, leveed wetlands. For Delta smelt or winter-run salmon, this is not good news: being seasonal, the wetlands eventually dry out, stranding the fish. To keep them out, the Suisun Resource Conservation District hired Fran Borcalli to design and install screens at key intake areas. Five screens have been installed to date and Borcalli is building seven more. An additional 17 may be added if the district gets funding.

"We're concentrating on priority areas with high habitat value for fish like salmon, Delta smelt, splittails, and green sturgeon," says the District's Lee Lehman. Borcalli's screens are receiving rave reviews from resource managers. "Most screens are designed for fresh water," explains Lehman, "but we're in a unique place here and have problems other places don't. We need something that can withstand the conditions in sloughs and brackish water where you get a lot of debris and salt. When Fran started to design the screens he sat down with us and discussed the specifics of this marsh. Other people just didn't understand how this marsh works."

In addition to the screens' state-of-the-art technology (resource managers can monitor flows via radio transmissions from the screens), Borcalli's screens are made of the best materials, say Lehman, a decision influenced in part by experience: after a beaver or muskrat chewed through wiring on one of the first screens installed, Borcalli wrapped the wiring on all of the screens in stainless steel. Bolts are also made of stainless steel and sheet pilings of interlocking vinyl, which resists corrosion. Borcalli's screens are also among the very few that meet the U.S. Fish & Wildlife and National Marine Fisheries flow standard of 0.2 cfs for Delta smelt (which is significantly lower than the 0.33 cfs required for salmon). "The Delta smelt is a poor swimmer," says Lehman. "You can only bring in so many cubic feet per second or the fish get slammed against the gates or sucked into areas where they become stressed and die."

According to Lehman, how much water comes in all depends on a properly-designed screen. Everything from the type of mesh used to the gates in the screens can affect flows. Water must come in at an even rate through all areas of the screen, and sections where water is coming in too quickly have to be fixed. "Some engineers can't design these things well because they've never dealt with the problems most fish screens have," says Lehman. "Experience is a good teacher."

Borcalli agrees that the success of his screens can be largely attributed to their unique design. "The technology isn't really any different than what's been done before, it's the configuration that's different," he says. While most screens are flat plates, either placed vertically or inclined at about 30 degree angles, Borcalli's is conical, and the water goes around it. "The apex of the cone is at the top, and the brushes rotate around the cone," he explains. "The cone stays above the mud. We didn't want the bottom of the screen in the silty marsh bottom."

Lehman says the new screens are among the least expensive permanent screens available, although the one-time installation cost can reach up to $250,000. Maintenance and operation is paid for by the private landowners of Suisun Marsh. And because many of Borcalli's screens are partially solar-powered, they are not energy-intensive, which Lehman appreciates. But perhaps Borcalli's most satisfied customers are the fish. Even when they swim very close to the screens, they are not drawn up against them. Instead, says Lehman, "they swim right by."

Contact: Borcalli & Associates (916) 564-3300 or Lee Lehman (707) 425-9302

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