635-400-0015 Determination of Instream Flow Measurement Methodologies (1) Instream flow requirements requested in Department instream water right applications shall be based on the methodologies and standards in this section. (2) Discussion of and guidelines for implementing the rules in this section are provided in the Oregon Department of Fish and Wildlife Guidelines for Instream Flow Methodologies (1989). (3) Habitat requirements for conservation, maintenance or enhancement of fish and wildlife migration, spawning, nesting brooding, egg incubation, larval or juvenile development, juvenile and adult rearing and aquatic life shall all be considered when developing an instream flow requirement. (4) Fish and wildlife species plans, basin and subbasin plans, management objectives, statutes, administrative rules and commission polices shall be used to assist in determining the required instream flows for conserving, maintaining or enhancing fish or wildlife habitat or populations. (5) Instream flow requirements shall be defined by either month or half-month intervals, depending on the temporal duration of particular fish and wildlife life stages. (6) The instream flow requirement shall be based on habitat criteria recommended by one of the following technical sources: (a) IFIM habitat suitability curves published in a series of technical reports by the U.S. Fish and Wildlife Service; (b) The Oregon Method; (c) The Forest Service Method. (7) An instream flow requirement shall be specified as a quantity of water or water surface elevation as determined by the methodologies in this section and dependent upon other habitat factors, fish or wildlife species plans, basin or subbasin plans, management objectives or other commission policies for the waterway. (8)(a) The instream flow requirement for any specified period shall be no less than the highest instream flow or water surface elevation required by any of the fish or wildlife species of management interest during that period; (b) Fish and wildlife species of management interest shall be determined by fish and wildlife species plans, basin and subbasin plans, management objectives, statutes, administrative rules and commission policies. (9) Site-specific studies may be needed to determine flows necessary for flushing of sediment deposits, gravel recruitment, stimulating upstream migration of fish species, maintaining passage for fish migration or other specific requirements. (10)(a) If hydrological estimates or gaging data can be obtained, the instream flow requirements shall be compared against the range of naturally occurring stream flows or water surface elevations; (b) Instream flow requirements greater than 70 percent or less than 30 percent of the naturally occurring stream flows or water surface elevations for any given time period shall be evaluated for appropriateness of the requirement in relation to naturally occurring stream flows or water surface elevations. (11) An instream flow requirement shall be specific to a stream reach or a particular standing body of water: (a) The length of stream reach shall be determined according to biological and hydrological factors; (b) A stream reach shall extend from the upstream end to a downstream point where either: (A) Species use of the stream changes; (B) Streamflow diminishes by at least 30%; or (C) Stream order changes. (12) Whenever possible, actual measurements of stream flow or water surface elevation shall be made at or near the required instream flows or water surface elevations. Preferably these measurements shall be made at times when the waterway is occupied by the fish or wildlife life stages to be protected. (13)(a) Instream flow requirements in the OSGC Environmental Basin Investigation Reports shall be used to apply for instream water rights for waterways listed in the reports; (b) If the physical conditions of the waterway have changed since the instream flow requirements were established, such as construction of a dam, reservoir or major channel changes, one of the methods in section (14) of this rule shall be used to determine the instream flow requirements. (14) The acceptable methodologies for determining new instream flow requirements for aquatic and fish life, wildlife and their habitats shall be the following: (a) On large lower reaches of main stem rivers, instream flow requirements shall be determined through an IFIM study by an interagency interdisciplinary team drawn from specialists in hydrology, water quality, water resources planning, fish and wildlife biology, limnology, recreational planning and any other related filed. Besides fish and wildlife biology, three or more of the above specialties may be represented on a team; (b) On principal tributaries to main stem rivers, either the IFIM or the Oregon Method shall be used; (c) On secondary tributaries to main stem rivers, either the IFIM, Oregon Method or the Oneflow Method may be used: (A) The IFIM shall be used before the Oregon Method if Department resources are available; (B) The Oneflow Method may be used only when there is not enough time to conduct the IFIM or Oregon Method. Optimum spawning discharge shall be estimated using this technique. Corresponding incubation, rearing and migration instream flows shall be based on OSGC or Department streamflow requirement conversion factors; (C) Instream flow requirements estimated through use of the Oneflow Method and conversion factors shall be verified through measurement of actual streamflows during the next spawning season and next low flow rearing conditions. (d) Minor tributaries are second or third order streams and may include headwater streams, minor direct tributaries to the ocean, estuaries or main stem rivers: (A) Instream flow requirements may be determined by either direct measurement of flow or surface water elevation during each critical fish or wildlife life history stage or by IFIM, Oregon Method or Oneflow Method; (B) Direct measurement may be used to determine lake, pond or wetland water surface elevations or volumes needed to maintain fish, wildlife or their habitats. Statutory/Other Authority: ORS 496 & 537 Statutes/Other Implemented: ORS 496 & 537 History: FWC 110-1989, f. 10-24-89, cert. ef. 10-28-89