Managed Flow Regimes and Resource Values: Traditional versus Alternative Strategies

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ALTERNATIVE FLOW REQUEST STRUCTURES .:4 � .rte t -. � { :y a •.r s :Y3 xT >r We define "managed flow requests" as any legal or administrative mechanism for speci- fying or protecting the amount of water need- ed for a particular purpose. In the United States (particularly the western states), these requests were first applied by mining and agricultural interests for out -of- stream pur- poses and were commonly codified into "legally enforceable expectations" or water rights issued by one or more branches of gov- ernment, usually states (Goldfarb 1988). The statutes that provide for these requests or water rights have varied over time and from state to state, but follow from complex inter- pretations of either riparian or appropriative allocation philosophies (Goldfarb 1988). A dis- cussion of these systems is beyond the scope of this paper. Applied to out -of- stream purposes, howev- er, requests of this type typically specify the purpose, the amount of water needed, the time when it is needed, and the location where it should be delivered. For example, with an out -of- stream use such as irrigation, a request might specify 4 cfs from 15 July to 30 Septem- ber at a particular point of diversion (an irri- gation ditch), and result in a legal water right granted by the state. Managed flow requests for instream flows are generally less simple and were rarely made before the 1970s when several federal and state agencies began to develop adminis- trative or legal mechanisms to protect instream flows (Shupe 1989). These mecha- nisms have also varied from state to state (or within various types of federal or state conser- vation units) and have included prohibitions against new diversions, water use permitting systems, conditions on dam or hydroelectric project operations, and various forms of instream flow water rights (MacDonnell et al. 1989). In many cases, however, instream flow requests have followed from the out -of- stream model, requesting water of a certain an aunt at a certain time in a certain segment of river. For an instream use such as fish rear- ing, for example, a request might specify 100 cfs from 1 April to 30 June at a particular point of quantification, with the understand- ing that flows are provided throughout an identified stream reach adjacent to this loca- tion. Similarly, applied in the case of a hydro- electric project license, instream flow condi- ' P�; 236 tions might require 150 cfs releases from a dam for fish passage in an otherwise bypassed reach. Because water requests have traditionally been developed for out -of- stream uses, their structure is well suited for those uses. This same structure, however, may be less appropriate for instream uses where variation is impor- tant. By definition, managed flow regimes rep- resent some departure from natural flow regimes; they generally cause some reduction in the diversity of flows provided. In these cases, the question is how much diversity should be sacrificed to out -of- stream uses, and the challenge is to develop flow requests that substantially protect diversity while still making some out -of- stream water available. Because instream flow requests assume that any unclaimed water will be removed from the river at some point in the future, new kinds of instream flow request structures that minimize the adverse impacts of managed systems may need to be developed. The following discussion considers three different types of managed flow requests and their ability to provide a diversity of high quality recreational opportunities. For each, we discuss how they are developed, show their advantages and disadvantages, and summarize the situations where they may be appropriate. Later, we explore some of the issues in choosing "threshold flows" to apply in each of the alternative requests. These thresh- old "decision rules," in combination with the type of request structure, prescribe how flow - recreation data are transformed into tangible flow requests that can be legally or adminis- tratively defined and managed. Traditional Fixed -time Requests The most traditional instream flow man- agement request follows from the structure of out -of- stream water requests, as discussed above. Requests specify an amount of water at a location during a particular time period. In the out -of- stream case, the water is removed from the river; with the instream case, water is ieft in the river. Developing a fixed -time request for recre- ation requires choosing a single threshold flow for each recreational value as well as choosing the period of time when it should be provided. Using the Dolores data, for exam- Rivers • Volume 7, Number 3 2000