ERDC TN-EMRRP-SR-46 "Alternative Environmental Flow Management Schemes"

OVERVIEW: As demand on fresh water increases, water and environmental managers must trade off potentially conflicting uses of this resource, one of which is the maintenance of aquatic ecosystem integrity (Baron et al. 2002, Postel and Richter 2003, Arthington et al. 2006). In some cases, the process of analyzing trade-offs can identify solutions where numerous outcomes benefit (i.e., win-win scenarios, King and Brown 2010). Although the importance of “environmental” or “instream” flows is widely acknowledged, challenges arise in specifically identifying the flow regime needed to obtain a desired ecological state (Richter et al. 1997). Historically, environmental objectives were treated as a constraint whereby a minimum flow level for a given river is identified and used to maintain low flow conditions for critical needs. Although this provides some benefit, a minimum flow approach only addresses a single portion of a river’s flow regime (low flows). This approach omits the magnitude, frequency, duration, timing, and rate of change of a river’s entire hydrograph and the ecological significance of those parameters both individually and in combination (Poff et al. 1997). This technical note reviews multiple techniques aimed at managing water for environmental and ecological objectives. Review of these techniques is followed by a brief discussion of key considerations in selecting an environmental flow management scheme.