Most dams were built before we understood the devastating effects they could have on river systems. And most were built before laws such as the Endangered Species Act existed. The majority of California’s dams were built with no opportunity for fish passage and for too long hatcheries were placed below dams as ‘mitigation’ for blocking upstream spawning and rearing habitat. Over time the science has made clear that, in most cases, hatcheries do more harm than good primarily due to diluting the gene pool of wild fish and reducing population resilience in the process.
Severely altered flows also impact rivers below dams. Too often, outdated flow regimes significantly degrade river and riparian ecosystems and fail to maintain healthy downstream habitat. Many dams operate under a cycle of capturing high winter flows and then releasing a steady minimum base flow from the dam throughout the spring, summer and fall. CalTrout advocates for dam management to better mimic a natural flow regime with winter peaks that clean spawning gravel and dynamic spring flows that gradually decrease to a healthy base flow.
Turning the Tide: Adding Nature Back Into the Mix
After more than half a century of dams blocking fish passage and altering stream flows, it became clear that dams were playing a key role in ecosystem and fish population collapse in watersheds throughout the United States. New laws passed in the 1970s, such as the Endangered Species Act and the Clean Water Act, helped to shift the discussion around managing natural resources to support native plants and wildlife while also maximizing beneficial uses for people.
Beginning in 1986, FERC mandated that dam management give equal consideration to fish and wildlife populations and habitat protection along with beneficial uses for people. Since that time, many old dams have been retrofitted to enable fish passage and flow management regimes have been updated to benefit wildlife with varying degrees of success. Even in dams with such retrofits in place, native fisheries often still struggle.
Improving, Not Removing, Some Dams
Fortunately, ecosystems do recover when dam management is done right. The Pit River in northern California is a success story of a hydropower project that has been updated using science-based recommendations, and is now successfully managed for a balance of human use (hydropower), healthy wild trout populations, and dynamic water flows.
The Lower Pit passes through a series of hydropower projects before reaching Shasta Reservoir. The various Pit River dams were built between 1925 and the mid-1960s. One big problem in this case was the flow regime, which at times would completely dewater sections of the river. Pit 3 dam is a great example. In the 1980’s CalTrout advocated for a FERC license amendment to provide flows below Pit 3. At the time the flow releases below the dam were a startling 0 cfs! The license amendment was successful in providing 150 cfs to the river and the trout fishery quickly responded. In 2003 a series of Pit River dams went through the full relicensing process and again CalTrout successfully advocated for a flow regime that mimicked the natural hydrograph. Today, the Pit River is one of the best wild trout fisheries in the California while maintaining power generation and other beneficial uses.