EDITORIAL: Studies are key to removal of Searsville dam EDITORIAL: Studies are key to removal of Searsville dam (June 14, 2000)

The spectacular hills that rise to the west of Portola Valley, Woodside, Menlo Park and Atherton provide more than a backdrop to some of Silicon Valley's most livable communities. The hills also are the watershed that funnels runoff into San Francisquito Creek, which flows into San Francisco Bay.

In most years, the rainfall is easily accommodated by Los Trancos and Corte Madera creeks in Portola Valley and Bear Creek in Woodside. Water moves down the hillsides and on to the San Francisquito, one of the few remaining natural creeks on the Peninsula that continue to support a run of steelhead trout.

But when the area receives extraordinary winter rains, like the storms of 1998, the dam does little to halt floods on the San Francisquito, which overflowed its banks in Menlo Park and Palo Alto that year, causing millions of dollars in damages. The floods brought up the need to study ways to control the creek, a task that is now being taken up by the cities, counties and other groups that share interest in the creek.

Two of San Francisquito's three tributaries -- Los Trancos Creek and the Bear Creek system -- run freely through the watershed. But for more than 100 years, Corte Madera Creek has been boxed behind Searsville Dam, which has controlled stream-flow and, more troubling, collected some 1 million cubic yards of sediment silt that has washed off the highly erodible hillsides of Portola Valley.

Searsville Lake, once nearly 60 feet deep at the dam, is barely 17 feet now, due to this tremendous buildup of silt. The 90 percent reduction in capacity creates unusually swampy habitat around the lake and, during heavy rains, causes flooding of nearby neighborhoods. With the renewed local interest in controlling San Francisquito and a national interest to remove dams that no longer serve a purpose, Portola Valley resident and stream biologist Matt Stoecker is urging Stanford and the other parties to seriously consider taking down the dam. For Mr. Stoecker, the payoff would be seeing steelhead swim up Corte Madera Creek to spawn in the shadow of Windy Hill, the famous bluff that overlooks the valley.

But while giving steelhead a boost into Corte Madera Creek may seem like a good idea, there are huge problems to overcome before the dam can be demolished safely.

First and foremost, there is the major question of what to do with the estimated 1 million cubic yards of sediment backed up behind the dam, enough to cover 200 acres with 3 feet of sediment. Experts like Jim Johnson, who monitors the creek closely, say that even releasing the silt over a period of time might have a harmful effect on San Francisquito, which could lose the ability to hold water due to siltation of its bottom.

Would removal of the dam create a more likely chance of flooding downstream during El Nino-like storms? And there are other major questions, like what would happen to the creek's ecosystems with such a release of silt, and whether such a release could interrupt the migration of spawning steelhead to Los Trancos and Bear creeks.

All of this is not to say that returning Corte Madera Creek to a natural, undammed state, is a bad idea. Far from it. But the cost and consequences of such a drastic move will require a major study, one that can accurately forecast the impact of removing hundreds of thousands of cubic yards of sediment from Searsville Lake and, more importantly, locate a site where it can be used or stored.

Stanford officials say they are not opposed to looking at options for Searsville dam. Sooner or later, probably in about 15 years, the lake will fill completely with silt, forcing a decision on the dam's future. Before that deadline is reached, it makes sense now to begin a comprehensive study of Searsville dam and its impact on San Francisquito Creek.