During the spring and summer I have a habit of sneaking away on the weekends to guide whitewater rafting trips in the Sierra Nevada foothills. I’ve been doing this for 10 years, and have been lucky enough to explore the majestic canyons and exhilarating whitewater runs of rivers like the American, Tuolumne, Merced, North Stanislaus, and Kaweah. In the process of learning to navigate these rivers I gained a deep understanding of the linkages between winter snowpacks, weather conditions, dam releases, and the volume of water flowing through a given drainage; however, it was only when I began working with Save The Bay that I adopted a complete “watershed” view of how water travels from the Sierra to the Bay.
Back in December I wrote a blog entry titled Driving over the Drain, investigating the ecological and hydrological significance of the Golden Gate (not the bridge, but the strait of water beneath it). This piece explained how roughly 40% of California’s landmass is contained within the San Francisco Bay watershed. By definition this means that all water falling on this land as rain, snow, and sleet should ultimately flow into the Bay and out through the Golden Gate. I deliberately use the word “should” in the previous sentence rather than “will,” because the truth is that while some of this runoff will ultimately reach the Bay, it certainly won’t be following the natural course it did 200 years ago.
Humans began damming, diverting, and modifying the physical structures of California rivers as early as the Gold Rush. Today, the 1,400 named dams in California provide valuable services such as flood protection, hydroelectric power generation, and water storage for our state’s vast agricultural industry. However, damming and diverting rivers comes at a significant ecological cost. Not only do dams flood entire river canyons and destroy riparian habitat, they also change the quantity and characteristics of waters passing through them.
The dams and aqueducts of the Central Valley Project and State Water Project currently divert roughly 30% of the freshwater inflow to the San Francisco Bay delta. Less freshwater entering the Bay means that water in the estuary is now saltier, and saltwater is moving farther upstream into the Delta. This is a direct cause of fish mortality and ecological disturbance. Dams also obstruct the natural flow of suspended sediments (sand and soil in the water), ultimately causing less sediments to reach the Bay. While this may at first seem like a beneficial side effect in that it improves water clarity, the presence of suspended sediments is a key factor in determining the potential rate of accretion (accumulation) of tidal marshes. Tidal marsh vegetation, such as the native plants installed by Save The Bay volunteers, have the ability to trap sediments, thus allowing marshes to rise vertically over time to adjust to changes in sea level; however, this is partially dependent upon availability of these sediments.
Though the situation I’ve outlined above may seem concerning, the saving grace of manmade water projects is that they can be removed. The road is dam removal is a long and costly one, but venerable organizations like Friends of the River and Tuolumne River Trust are tackling these challenges head-on. As we plan for the future of water management in California, it’s important to maintain a “watershed” perspective, remembering the myriad ecological interdependencies existing within the complex network of natural and manmade waterways connecting the High Sierra to the Bay.