Story by John Vonderlin
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While researching my next posting about “The Stage Hole,” I came across a forum that had old articles (1970) about the planned dams in Pescadero’s watershed. Somebody mentioned the effect of coastal dams on our beaches and somebody else wondered where they got such nonsense. Since I’ve commented on the connection of coastal watershed dams and other factors to our disappearing beaches, I thought you might want to see the following quote:
“Dams along coastal streams that effectively impound water also trap the sand destined for the coastal beaches. Thus, the benefits of flood control or increased water supply and recreation have been countered by the gradual reduction of sand input to the coastline. Dams reduce sediment supply to beaches in two ways: by trapping sediment behind the dams and by reducing the peak river flows or floods that, under natural conditions, would have transported sand downstream to the shoreline. More than 1,400 dams over 25 feet high or impounding more than 50 acre-feet of water have been constructed across California, with 539 of these dams located in the coastal watersheds that drain directly into the Pacific Ocean . . . The combined effect of these coastal dams has been to reduce the average annual sediment supply by more than 25 percent to California’s 20 major littoral cells.”
The quote comes from “Living with the Changing California Coast”
by Gary Griggs, Kiki Patsch, and Lauret Savoy, University of California Press. Enjoy, John.