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40 BIOLOGICAL REPORT 90(5) Use of Multiple Methods for Instream Flow Recommendations-A State Agency Approach by Steven E. Reed and James S. Mead Division of Water Resources Aquatic Ecology Branch P.O. Box 27687 Raleigh, North Carolina 27611 North Carolina's waters range from the coldwater trout streams of the Appalachian Mountains to the meandering blackwater streams of the Coastal Plain. In between lie the coolwater streams and rivers of the Foothills and the Piedmont's broad, tur- bid rivers. The State's instream flow issues are also diverse. Many of these issues involve hydropower projects-either the existing facilities or the plan- ning and design of new ones-and include peak power production, diversions of various lengths, and run-of-river projects that illegally peak. There are also concerns with existing reservoirs constructed for purposes such as municipal and industrial water supply, recreation, or irrigation. Many of these projects are old, and most do not have a required minimum flow. Direct withdrawals of water from streams also affect instream flow and aquatic habitat, including withdrawals for municipal and in- dustrial water supply, irrigation, aquaculture, and thermal power plant cooling water. The Division of Water Resources has been in- volved in instream flow studies since 1977. The divi- sion has conducted over 50 wetted perimeter studies and 24 Instream Flow Incremental Methodology (IFIM) studies, and it has made numerous flow recommendations using desktop methods. Every available opportunity is taken in project evaluation to address instream flow concerns. The State Dam Safety Law is applicable to all non- Federal dams higher than 15 feet that impound at least 10 acre- feet of water. This law is used to stipulate minimum flows from new dams unless they are located on intermittent streams. Hydropower projects must obtain a Certificate of Public Convenience and Necessity (CPCN) from the North Carolina Utilities Commission before construction. If the hydropower project will not be receiving a license or exemption from the Federal Energy Regulatory Commission, then the Division of Water Resources will attach its instream flow recommendation to the Utilities Com- mission certificate. Instream flow recommendations may also ~e added as conditions to State 401 water quality certification and Federal 404 permits for projects that affect stream flow regimes. Many factors are considered in selecting an in- stream flow assessment method. First, the value of the resource to be protected is considered. For ex- ample, a prime redbreast sunfish stream is handled differently than a severely degraded stream. The magnitude and duration of the project's impact are also evaluated by such factors as distance to the next major tributary, length of the diversion, or number of acres of potentially affected habitat. An attempt is made to determine whether the project will become controversial and what type of negotiations might take place. Other concerns include the man- power available for a study and how much time re- mains before a decision must be made. The instream flow methods used can be separated into desktop and field methods. Desktop methods are used for projects with small impact or when a recommendation must be made quickly. A recon- naissance visit is usually made, and a recommenda- tion is developed using one of several desktop methods. A previous recommendation may be ratioed by drainage area to a new location if there is an existing instream flow study site nearby and if the initial field visit indicates that the projects are similar. Review of hydrologic data may be used to develop a recommendation. Stream flow data from an appropriate U.S. Geological Survey gage are analyzed for mean annual flow and 7Q10 (lowest flow for 7 consecutive days, with a 10-year recur- rence interval), as well as monthly means, medians, and lowest daily flows of record. These data are used to compare natural and proposed flow regimes. In areas where aquatic habitat is deemed minimal or nonexistent, the 7Q10 flow becomes the instream