Saving Water and Insuring Delivery: Flow Prescription and the Discharge to Habitat Relationship for a Listed Anadromous Salmonid
* Can we save water by agreeing with regulatory agencies about how much water to deliver for fisheries?
* Can we base our flow prescription on precise science: the relationship between discharge (Q) and habitat for listed steelhead?
Reclamation is required by law to enhance fisheries using the best available science and to reduce dependency on New Melones Project water. As a response to this requirement Reclamation is working to develop a Flow Prescription (FP) in a river inhabited by two important anadromous salmonid species: listed steelhead and Fall Chinook. The FP could be guessed at now but would not be precise. So, more water would be delivered for instream flows than perhaps is necessary. Generating a more precise predictive function of habitat that is provided by various Qs will allow Reclamation to save water by releasing what is necessary and sufficient for fishes. The balance may be stored for delivery for power generation, irrigation, and other environmental needs.
Need and Benefit
Reclamation must develop a Revised Plan of Operations (RPO) for New Melones Dam. And New Melones releases determine lower Stanislaus River (LSR) discharge. Public Law 108-361 directs that actions to enhance fisheries in the Stanislaus River are based on the best available science. As part of this effort, Reclamation is developing the biological basis for the Flow Prescription (FP). The Stanislaus FP will prescribe a flow schedule (on a monthly or weekly time step) that varies with water year type. This effort will provide a Microhabitat-Explicit Geographic Information System (GIS) (MEG) that will help Reclamation determine, with stakeholders and regulatory agencies, what instream discharge is appropriate for fall run Chinook salmon and federally listed steelhead in the LSR.
As part of the New Melones RPO, the FP will provide benefits to Reclamation, water users, and regulatory agencies by specifying instream discharge requirements: Reclamation can plan the facilities and operations necessary to meet the FP and the multiple other demands in the system, water users will know early in the year (based on that year s hydrologic forecast) how much water they will receive in that year, and regulatory agencies will receive flows capable of producing a sustainable fishery. Thus, the benefits of this study include: improving Reclamation operations efficiency, insuring water delivery and reliability, and assuring instream flows that will contribute to the potential de-listing of steelhead while avoiding the possible listing of Chinook salmon.
The need to save water that otherwise might have been released unnecessarily provides our principal objective: determine the discharge-habitat relationship sufficiently to write a precise FP.
An important benefit of this research will be the water saved by a precise FP. How much water will this be? It is impossible to determine at this time. One example could be: If discharge in a Dry Year were reduced from 250 to 235 cfs during the irrigation season, this would result in 4, 522 acre-feet of water saved. The value of this water ($125/acre-foot) over a 4-year period is $2, 261, 157. Total requested funds from the Science and Technology (S&T) Program is $160, 000 over 4 years. S&T's return on its research investment would be more than $14 to every $1.
Reclamation needs to develop a way to predict the discharge necessary to provide habitat throughout an entire river. In several cases, Reclamation possesses subsampled habitat units in rivers. There has been minimal Reclamation effort to date using GIS, to devise a method to "scale up" these subsamples to an entire river. Reclamation efforts have used Instream Flow Incremental Methodology (IFIM) methods with significant assumptions about limiting factors, independence of independent driving variables, and the position where water velocity is normally measured (6/10th of the water column) is seldom where the fish are found.
This research effort will develop a new method (MEG) for scaling up subsampled habitats to a discharge-habitat relationship for an entire river. If S&T provides matching funds to do this, the benefits can be used Reclamation-wide to predict habitat available at different discharges. To be clear, in each river system new information will have to be collected, (e.g., photographic imagery at the discharges at which habitat will be predicted). But this new MEG we are proposing to develop can be used to scale up the subsampled habitats using imagery. Thus, a manager could direct biologists to use the MEG to develop discharge-habitat relationships in any river where sufficient subsampled habitat data exists.
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