A research team coordinated by the State of Washington Water Research Center and led by WSU Associate Professor Stephen Katz provides technical guidance for implementing streamflow restoration requirements under RCW 90.94 to mitigate against the effects of future groundwater pumping in Washington State watersheds.


In 2018, the State of Washington passed a new streamflow restoration law entitled Engrossed Substitute Senate Bill (ESSB) 6091 (codified as RCW 90.94).  This law was issued in response to the 2016 Whatcom County vs. Hirst, Futurewise, et al. decision (i.e. the Hirst Decision”), which had ruled that water would not legally be available for any new permit-exempt wells that impacted a protected surface water source or existing senior water right, and placed the burden of proving “no impact” on the counties or well applicants.  With the codification of RCW 90.94, proving “no impact” for each well application is no longer required.  Instead, counties and water resource inventory areas (WRIAs; Figure 1) must develop plans that can offset the potential consumptive impacts of new permit-exempt domestic water uses to instream flows.

Figure 1. Planning Watersheds under RCW 90.94. The WRIAs submitting plans under section 202 are in red and pink based on timing. WRIAs submitting plans under section 203 are in green. Downloaded from and available in pdf format from here.

Before plans are adopted, the Department of Ecology must determine that actions identified in a plan, after accounting for new projected domestic uses of water within a WRIA over the next twenty years, will result in a Net Ecological Benefit (NEB) to instream resources within that WRIA.  The Department of Ecology’s webpage for these efforts can be found on their Streamflow Restoration webpage.  The Final Guidance for developing project and program plans can be found here.  The final NEB guidance will be used to evaluate plans submitted to Ecology through 2021.

Under RCW 90.94 “A Net Ecological Benefit determination means anticipated benefits to instream resources from actions designed to restore streamflow will offset and exceed the projected impacts to instream resources from new water use.”  As stated, NEB determination is essentially a transaction amounting to a comparison in the quantity and quality of anticipated instream resources prior to water withdrawals and following the deployment and maturation of proposed offset projects over 20 years.  To evaluate this transaction a clear understanding of what instream resources are relevant, and how to structure the assessment of the transaction, is needed. Under RCW 90.94, the state of Washington has interpreted instream resources to primarily reflect populations and habitat for anadromous and resident salmonid fish.

WRC’s Technical Guidance

To assist the agency in formalizing how they determine whether a plan has achieved NEB, Ecology developed a consultation with an academic research team through the State of Washington Water Research Center (WRC) at Washington State University to support the technical aspects of the Final Guidance. The research team included researchers from Washington State University, the National Oceanic and Atmospheric Administration, and the Washington Department of Fish and Wildlife.  The team coordinated their efforts closely with the Washington State Department of Ecology’s Water Resources Program staff. The Technical Guidance is published as a Technical Supplement after page 33 of the Final Guidance document, and is also available as a stand-alone document here.

Figure 2. Decision Tree for approaches to NEB determination. Users should keep in mind these are sufficient, but not necessary criteria deciding an NEB determination approach.

In this technical guidance, steps for determining NEB were developed in four parts (See Box 1), and include a discussion of anticipated issues associated with monitoring and measuring at different spatial scales as well as the rationale for making out-of-kind NEB comparisons.

In addition, this technical document outlines five existing, relevant approaches for establishing NEB including the equivalency metrics commonly used and the merits and limitations of each approach.  These five approaches include: 1) In-kind/In-place Habitat Replacement, 2) Habitat Function Replacement, 3) Habitat Capacity for Single Species Replacement, 4) Fish Abundance Replacement and 5) Fish Production Replacement (Figure 2).

Additional Resources

  • For more information, contact the Lead investigator Stephen Katz at steve.katz@wsu.edu, or the Director of the WRC, Jonathan Yoder at yoder@wsu.edu.
  • Read a copy of the technical report (stand-alone document) here.
  • See a copy of Ecology’s Final Guidance (including the Technical Supplement) here.