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Instream Flow

Peshastin River

Steward and Associates are recognized experts in the field of instream flow science. Our work spans a variety of challenging applications, including flow negotiations for hydroelectric projects, instream flow assessment for watershed planning, field studies and computer modeling of fish/flow relationships, assessments of hydrologic alteration, and many others. We are well versed in the emerging topics of the instream flow field, as well as in the uses and limitations of traditional tools and methodologies.

  • Instream Flow Modeling
  • Field studies
  • Indicators of Hydrologic Alteration (IHA) Analysis
  • IFIM/PHABSIM
  • Flow Analysis and Negotiation for Hydroelectric Projects
  • Instream Flow Analysis in Watershed Planning

Sample Projects:
Walla Walla and Tucannon Instream Flow Analysis: As part of the Watershed Planning efforts in the Walla Walla and Tucannon basins, Steward and Associates provided instream flow modeling and analysis expertise to the respective watershed planning units. As a sub-contractor to Economic and Engineering Services, our firm assumed a lead role in the development of IFIM/PHABSIM-based instream flow recommendations through technical analysis and workshop facilitation in the Walla Walla basin. In the Tucannon basin, we are providing in-depth technical review of completed IFIM studies that were completed in support of the planning effort.
Baker River – Assessment of the Environmental Impacts of Increased Flood Protection: In the context of the Baker River hydroelectric facility relicensing proceedings and under contract with Skagit County, Steward and Associates is evaluating the biological, ecological and hydrological impacts of increased flood protection in the Baker River basin and the mainstem Skagit River. This ongoing project involves the assessment of both reservoir-related and instream flow-related impacts expected from proposed amendments to operations.
WRIA 5 - Stillaguamish Instream Flow and Hydrology: Under contract with the Washington State Department of Ecology, Steward and Associates (working with a sub-contractor) performed a hydraulic and hydrologic study of the Stillaguamish Basin. The work included hydraulic and fish habitat modeling using the PHABSIM approach, synthesis of existing information regarding the relationships between fish habitat and instream flow, as well as hydrologic modeling for several tributary and mainstem locations. The information is utilized by the Department of Ecology, Stillaguamish and Tulalip Tribes, and basin planning groups to develop administrative instream flows.
Central Puget Sound Low Flow Survey, Washington Department of Fish & Wildlife: Steward and Associates served as lead author of a report identifying streams with low flow problems from the Stillaguamish River to the Chambers-Clover Creek basin. The investigation also addressed suspected causes and recommendations for a strategic approach to improve conditions for salmon.
Big Creek Hydroelectric Relicensing: Working with Entrix Environmental Consultants, Steward and Associates conducted in-field assessments of flow conditions in relation to fish behavior and habitat availability. The data collection activities included snorkel surveys for salmonid and non-game fish species, as well as measurements of instream water velocities in the San Joaquin River and its tributaries. The data will be used to recommend appropriate instream flows as part of the Big Creek hydroelectric relicensing agreement with Southern California Edison.
Instream Flow – Physical Habitat Modeling: Steward and Associates has directed several instream flow data collection and modeling studies relating flow to fish habitat availability in Alaska, Idaho, and Washington rivers. These efforts involved the collection of voluminous field data and the use of same to calibrate hydraulic and physical habitat models subsumed under the Instream Flow Incremental Method. Steward and Associates, subcontracted under Entrix environmental consultants, has also been involved in the collection of data relating flow to fish habitat availability for Southern California Edison in the San Joaquin River, California.