Instream flow studies typically focus on the effect of project-related alterations in instream flows on the availability of habitat for aquatic organisms. After these studies are conducted, relicensing participants are often tasked with developing flow prescriptions for the project area. Although the methods discussed above are primarily focused on establishing base flows, or the minimum required flows for a particular species and life stage, natural variability in flow regimes is also important to ecological integrity, as discussed in Poff et al. (1997). Other ecological functions of flows, such as lateral connectivity to riparian zones and floodplains, are crucial, as discussed in Annear et al. (2004). This report focuses on assessing project effects on instream flows, and does not attempt to compare approaches to developing flow prescriptions. However, four methods to determine flow prescriptions are briefly discussed below to provide a general overview, including a geomorphic approach, a population dynamics modeling approach, an environmental approach, and an approach using a combination of predictive models. In some cases, data collected during other relicensing studies are adequate to employ these approaches, but in other cases, flow prescriptions become a key element to a new license, and specific studies are necessary. Although the Tennant (1976) method (also known as the Montana method) is not discussed here, it is a hydraulic approach based on percentages of averages of annual flow.
Selected references
Anderson, K. E., A. J. Paul, E. McCauley, L. J. Jackson, J. R. Post, and R. M. Nisbet. 2006. Instream flow needs in streams and rivers: the importance of understanding ecological dynamics. Frontiers in Ecology and the Environment 4: 309-318.
Annear, T., I. Chisholm, H. Beecher, A. Locke, P. Aarrestad, N. Burkhart, C. Coomer, C. Estes, J. Hunt, R. Jacobson, G. Jobsis, J. Kauffman, J. Marshall, K. Mayes, C. Stalnaker, and R. Wentworth. 2004. Instream Flows for Riverine Resource Stewardship, revised edition. Instream Flow Council, Cheyenne, WY.
Poff, N. L., J. D. Allan, M. B. Bain, J. R. Karr, K. I. Prestergaard, B. D. Richter, R. E. Sparks, and J. C. Stromberg. 1997. The natural flow regime: a paradigm for river conservation and restoration. BioScience 47: 769-784.
Tennant, D. L. 1976. Instream flow regimens for fish, wildlife, recreation and related environmental resources. Pages 359-375 in J. F. Orsborn and C. H. Allman, editors. Instream flow needs. American Fisheries Society, Bethesda, Maryland.
 | 4.1.9 Floodplain assessments | Page 52 of 134 | 4.1.10.1 Geomorphic approach |  |