New weather forecasting technologies are being explored as a way to allow flood control dams and reservoirs to also take on a water storage function in addition to their primary flood control mission. From a flood control perspective dam operators release water as quickly as they can to ensure there is room to hold future flood waters. These rapid releases are often much more water than downstream water providers can capture and move to storage for later use. This extra water flows downstream and eventually into the ocean.
The Scripps Institution of Oceanography is using improved weather monitoring and forecasting technologies in a new program called Forecast Informed Reservoir Operations, or FIRO. This program provides data to flood control facility operators to allow them to confidently hold and release storm runoff more slowly while still fulfilling their primary mission of providing protection against downstream flooding. FIRO was pioneered at Lake Mendocino on the Russian River in Northern California and has allowed a 19% increase in capture of stormwater over flood control only operations of the facility.
Implementing FIRO at any location is a time consuming process typically taking six to eight years to ensure that the flood control mission is not hampered and provide appropriate environmental protection. The process begins with development of a Work Plan to define the parameters of the possible operational changes. This involves the facility operator, which is often the US Army Corps of Engineers, participating water agencies, and other affected parties.
Once a Work Plan is in place a Preliminary Viability Assessment is conducted. This involves limited implementation of storm water release at a slower rate than that dictated by flood control operation, monitoring of actual storm water flow vs. what the model predicted, success in capturing the slower release, and any environmental impacts.
After the Preliminary Viability Assessment, a Final Viability Assessment is conducted. This involves regular delayed release of storm water at a rate downstream water providers can capture, more comparison of forecasted stormwater flow compared to actual, more examination of environmental impacts, and ultimately update of the Dam Control Manual to reflect the new mode of operation.
Locally, Prado Dam, operated by the US Army Corps of Engineers, completed its Final Viability Assessment in December of 2023. Control Manual changes to fully implement the program are pending. To date implementation of FIRO at Prado Dam is increasing beneficial storm water capture by about 10% a year. This water is percolated into the underground aquifer by Orange County Water District for use by their customers. Extra water is stored in wet years for use in dry years.
Seven Oaks Dam is located upstream of Prado Dam and is also exploring implementing FIRO. Seven Oaks Dam is operated by Orange County Public Works, San Bernardino County Flood Control, Riverside County Flood Control, and Orange County Flood Control, with day to day operations by San Bernardino County Flood Control. Seven Oaks Dam is in the Preliminary Viability Assessment Stage.
If Seven Oaks Dam moves into full FIRO operations as Prado Dam is about to, the Santa Ana River would be the first entire watershed in the country to be under FIRO operations. This offers the possibility of timing stormwater release from Seven Oaks so that San Bernardino and Riverside County water providers can capture as much as possible. Any extra water will flow to Prado Dam for release at a rate Orange County Water District can capture. This can happen while protecting the primary flood control function of both Seven Oaks and Prado Dams and while providing needed flow in the river for environmental protection.
In the event of major runoff or predicted multiple large storms, water will be released more rapidly to protect the flood control mission of the dams.
Colorado River Update: The Lower Basin States of Arizona, California and Nevada had previously offered a reduction of 700,000 acre feet in Colorado River diversion. They recently increased that by 1.2 million acre feet a year for two years with added participation from the country of Mexico. This represents more than half of the 4 million acre feet reduction the US Bureau of Reclamation has said is needed to sustain the river. In this most recent proposal the additional reductions in diversion would be:
Arizona — 760 acre feet per year
California — 440 acre feet per year
Mexico — 250 acre feet per year
Nevada — 50,000 acre feet per year
Significantly, this latest offer recognizes a previously unquantified Native American Tribal Nation water right of 250,000 to 280,000 acre feet per year. The 1922 Colorado River Compact which made the current allocations did not quantify any Tribal Nation rights.
As of this writing the upper basin States of Colorado, New Mexico, Utah and Wyoming seem to be holding to their position that they will not agree to any cuts from the original 1922 allocations.
The new offer by the Lower Basin States and Mexico appears to be a significant concession and effort to resolve the issue. This may put pressure on the Bureau of Reclamation to push the Upper Basin States for a proposal, or to simply impose reductions on the Upper Basin states to make up the difference.
Any federal mandate is likely to be challenged in court, which typically is a long, and expensive, process. We need resolution quickly or risk loss of electricity generation capability from Lake Powell and Lake Mead which will adversely affect millions of people in several western states.
