 |
|
 |
| ||
|
Screening the Screens
Men on the moon, nuclear fission and fish screens. Whether fish screens can move from the realm of scientific utopia to practical use by small farmers is being tested this summer at four quiet spots along the Sacramento River by BurRec in cooperation with farmers, engineers and seven other agencies.
Three types of experimental screens are new this summer. The fourth, musical screens employing underwater speakers to frighten fish away from pumps, are already in the second year of testing near Grimes. Though the sonar has worked to scare off adult fish, it hasn't worked to protect tiny fry or eggs. Officials say the baby fish, even if they wanted to, are too weak to avoid the pumps.
The new idea is to take screens out into the middle of the river and away from the slack water along the bank many believe fry prefer. At the Pelger Mutual Water Company and the nearby farm of Fred Cannell, two different types of experimental self-cleaning mid-river screens are being tested. Further upstream at the Deseret Ranch, the experiments feature more conventional bank screens.
This May, scientists in dive gear examined the Pelger screens - which consist of two tanks the size of Volkswagons on the end of 20 feet of pipe (see diagram) - and found no tears or problems. The tanks are wrapped in screen wire and kept clean by a whirring propeller inside. Water is pumped by conventional slant pumps.
At the Cannell farm, half a dozen 20-inch pipes with smaller tanks on the ends are now being installed. "It's like six straws with a bubble on the end," says engineer Gilbert Cosio, whose company Murray, Burns and Kienlen is overseeing all three field installations. The straw-and-bubble combo is accompanied by an experimental centrifugal pump to suck water from the river and by an air burst pump to clean the screens.
Cosio says BurRec is looking for a lot more than one type of screen. "One screen might work well in deep water but something totally different might be needed in shallow water," says Cosio. He says bank-type screens may be ideal in a place like Deseret Farms, where flow is slow and space to work plentiful.
The 26-foot-deep water in which the Pelger screens are sunk is described as a good test of whether the screens can survive debris and currents. "I've seen whole orchards come down that river," says Scott Tucker, an owner of some of the 3,000 acres of tomatoes and corn served by Pelger.
Tucker and other farmers put up matching funds for the program. "I think one of the most important things that may come out of this is to show that farmers like Mr. Tucker are willing to put their necks on the line and work with us," says BurRec's Ron Brockman.
Contact: Ron Brockman (916)978-5313
[ ABAG HOME | SFEP HOME ]
Copyright © 2002, San Francisco Estuary Project