Instream Flows Policy

Volume Depletion Approach Study

The Policy for Maintaining Instream Flows in Northern California Coastal Streams (Policy) section 10.4.1 requires the State Water Board to perform a study of the Volume Depletion Approach (VDA) applicable to permitting of onstream reservoirs on Class II and III streams. This study was completed on March 31st, 2014. The study purpose was to determine whether the VDA described in Policy Appendix A section A.1.8.3 effectively protects fishery resources and can be used to support use of the alternative regional criteria. The evaluation includes assessing the effects on fisheries and aquatic habitat resulting from diversions located upstream of anadromy. The effects were assessed for cases where the cumulative diversion (including the proposed project) is greater than 5 percent but no more than 10 percent by volume of the unimpaired seasonal flow volume between November 1 and March 31 as measured at the upper limit of anadromy.

This VDA study concluded that the alternative regional criteria are protective for Class III streams, but only protective with additional requirements for Class II streams. Water right applicants may review the information below to evaluate whether the VDA is applicable to their project and whether it is a preferable alternative to the criteria contained in Policy Sections A.1.8.1 or A.1.8.2. Division staff is reviewing the results of the VDA study and will determine at future date if revisions to the Instream Flows Policy will be proposed.

Useful Information

• Policy Excerpt: Section A.1.8.3 (Volume Depletion Approach)
• Flow Chart for Implementation of Policy Section A.1.8.3
• Example Calculation of VDA for a Proposed Project

Final Study Report

The Volume Depletion Approach Study was funded by the State Water Board under contract # No. 11-130-300. The study was conducted by Stetson Engineers Inc. in cooperation with R2 Resource Consultants, Inc.

• Final Study Report - March 31, 2014
  • Appendix A. Final Field Study Report
  • Appendix B. Final Hydrologic Modeling Report
  • Appendix C. Habitat Flow Curves
  • Appendix D. Flood Frequency
  • Appendix E. Passage and Spawning Results
  • Appendix F. Implementation and Policy Review
• Request for Peer Review of Draft Study Report
  • Jeffrey J. McDonnell, PhD, DSc, PH
  • Julian Olden
  • Matthew Reidenbach

NOTE: Some appendix material contains large data files not posted above. This information may be viewed upon request.

More Information

For questions regarding using the Volume Depletion Approach for a specific water rights permitting project, refer to the Water Right Permitting and Licensing Contacts by Geographical Area listing.