At first we hypothesized that natural cyclical fluctuations were to blame for the late emergence of aquatic macrophytes (large plants). This in turn would explain why water levels have been low because aquatic plants, when present, restrict flow. As flows slow, the river backs up and water levels rise.
It turns out, however, that this is likely only part of the story. Thanks to info provided by PG&E, we now know that actual outflows of Fall River’s large spring systems appear to fluctuate dramatically over time. Considering that almost 90% of Fall River water originates from large spring systems, it makes sense that water levels will rise and fall as outflows change.
Fall River Spring Flows at only 69% of 2000 Outflow Levels
Here’s the interesting part. According to hydrologist Gary Freeman at PGE (Power Generation and Water Management):
“The Fall River’s aquifer outflow of its large porous volcanic springs, which have historically contributed 88% of its total water year surface runoff below the springs, has been on a declining trend since its peak in the year 2000. It is currently only 69% of that high or down about 300 TAF this year from the 2000 water year peak, a decline in flow rate from the springs for this time of year of approx. 413 cubic feet per second (CFS) (equiv. to almost 3 ‘Burney Falls’ in total flow rate change…Burney Falls is about 150 cfs long term ave flow rate). In other words the current flow from Fall River’s contributing springs is only about 69% of its daily flow 13 years ago. Historically, since the early 1900’s the Fall River has experienced multidecadal ‘underground droughts’, most recently starting about 1908 and returning to somewhat more ‘normal’ flow rates in the early 1970’s. I believe that 40-60 year multidecadal groundwater “droughts” are fairly common for this river.”
Where will it go from Here?
Where will it go from here? Nobody can say for sure, but it’s interesting that over the last decade we’ve observed near historic highs and now near historic lows in total spring outflows. Other key questions to consider? How do these flow changes influence Eurasian watermilfoil density, sediment supply issues, and food web cycles in the Fall River? Why are some spring systems like Thousand Springs and Lava Springs apparently producing normal flows?
What should we expect to see from aquatic vegetation if flows remain low for the remainder of the summer and into next season? According to Carson Jeffres at the UC Davis Center for Watershed Science, “A wide range of variables could be responsible for the late emergence of aquatic macrophytes on the Fall River this year. At this point, it’s too early to say. Water year type, natural cycles, geomorphic events, reductions in nutrient loads, and other factors, can all have an effect on aquatic vegetation.” So although it may appear that a correlation exists between low flows and slower plant growth, numerous factors may be at work here.
The Fall River Conservancy (FRC), in partnership with California Trout, PG&E, USDA, the CA Dept. of Fish and Game, and the UCD Center for Watershed Sciences, will continue to work on answering these questions.
Bill Bunker: New Fall River Hydropower Manager
FRC would like to thank Bill Bunker (Fall River Hydropower Manager) and staff at PG&E for sharing the information above. For those for those of you who have not met Bill yet, he is new to the valley and now responsible for the operations and maintenance of 19 powerhouses along the Pit and McCloud river systems, Battle Creek, and Cow Creek. This network of generating facilities and associated reservoirs and waterways can produce over 800 megawatts of clean electricity for northern California. Prior to Bill’s current role, he was Vice President of Hydropower Operations for Alcoa Power Generating in Tennessee and North Carolina. He has 20 years of leadership experience in manufacturing and hydropower generation and currently serves on the Board of Directors for the National Hydropower Association and is Chair of Emerging Issues for the Electric Utility Cost Group.
Bill is a retired U.S. Navy Commander, having devoted much of his 20 year career to Middle East logistics. Having raised three sons, he and his wife Arla love their new home in northern California and enjoy hiking, kayaking and flying.