Donald Leroy Tennant of the Ohio Division of Wildlife wrote “Instream Flow Regimens for Fish, Wildlife, Recreation and Related Environmental Resources” in which he concludes the following regarding average annual natural river flow:
- “Ten percent of the average flow: This is a minimum instantaneous flow recommended to sustain short-term survival habitat for most aquatic life forms. Channel widths, depths, and velocities will all be significantly reduced and the aquatic habitat degraded.”
- “Thirty percent of the average flow: This is a base flow recommended to sustain good survival habitat for most aquatic life forms. Widths, depths, and velocities will generally be satisfactory.”
- “Sixty percent of the average flow: This is a base flow recommended to provide excellent to outstanding habitat for most aquatic life forms during their primary periods of growth and for the majority of recreational uses.”
- 10% to 30% of average flow is “fair or degrading” regarding habitat.
Average flow as defined by Tennant is the natural or unregulated mean annual discharge (MAD). The Districts state on page 4 of the Draft Snake River Flow Studies – Summary Document (previously submitted to the FERC) that the MAD of the South Fork of the Snake River above Heise is approximately 7,500 cfs and the MAD of the Henry’s Fork of the Snake River at Rexburg is approximately 2,100 cfs. Districts records show the unregulated MAD above the Osgood Reach is approximately 9,600 cfs.
Thirty percent of the 9,600 cfs MAD is 2,880 cfs. According to Tennant, the current 2,800 cfs average winter flow through the Osgood Reach is already below that necessary to maintain river habitat from degrading.
The irrigation districts are proposing to lower Osgood Reach flow to 1,000 cfs (1o.4% of MAD) for six months during the coldest part of of the year (October through March). According to Tennant, the districts proposed flow at 10% MAD would be sufficient to only sustain short-term survival habitat for most aquatic life forms. Clearly per Tenant, the districts proposed flow at 10% MAD over six months during the winter will harm river habitat.