Instream Flows for Recreation: A Handbook on Concepts and Research Methods

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Chapter 5 EVALUATING FLOWS OR RESOURCE CONDITIONS There are several ways of collecting evaluative information about flows or conditions. Choosing among these methods depends on a number of factors, including the type of river, the recreation opportunities in question, the type and availability of users, and the amount of time, staff, and money one can spend on the study. This chapter categorizes and reviews the variety of evaluation methods and /or criteria currently used in research. Recognizing the impossibility of fully explaining each method, the goal is to identify basic concepts, assess relative advantages and disadvantages, and suggest the keys to applying each method successfully. At the end of the chapter, a summary section reviews the key issues in choosing among the various methods. Much of the material in this chapter has also been discussed in a technical paper on streamflow and recreation (Shelby et al., 1991). Readers with greater interest in these methods and the places where they have been applied should consult that paper. Readers should also note that most studies utilize a combination of methods; no single method offers all the answers. In addition, some methods are more narrowly focused — a way of answering a specific question — while others are more comprehensive and provide an approach to answering several questions. When combinations of methods are particularly useful, this is noted. As discussed in Chapter 3, it is often easier and more direct to evaluate flows than resource conditions (e.g., when whitewater boaters are asked about flows rather than the size of hydraulic reversals (holes) or standing waves). In other cases, however, evaluations will center on resource conditions such as the type of vegetation or size of camping beaches, and researchers also need to be able to trace those conditions back to the flows that generate them. The techniques involved in developing relationships between flows and conditions were presented in Chapter 4. In this chapter, the focus is on evaluating flows or the effects of flows. Readers should also note that while many methods presented below tend to focus on the direct or short -term effects of flows (such as hydraulics or the shape, depth, or velocity of water in the river), it is possible and important to apply them to long -term or indirect effects as well. Scientists may be able to discover how flow changes will affect a river's environment, but it is also critical to evaluate whether those changes are acceptable or not before deciding on appropriate flows. HISTORICAL USE METHOD With this method, information about the intensity of recreation use on a river is correlated with flow levels at the times when use occurred. If use has historically occurred at a particular flow, that flow is considered adequate. Output from this method is typically expressed as a range of acceptable flows, with the low and high ends defined by the lowest and highest flows for which use occurs. In some cases, the logic of this method is extended to define an optimum flow as the flow when use is at its highest levels. Advantages and Disadvantages This is a potentially quick and easy method which shortcuts many of the steps presented in this handbook. If good use data is available for 33 a resource, it can provide some insight. However, like most easy techniques, it has significant limitations. Most importantly, this method rests upon a pair of suspect assumptions. First, it assumes that users will only take trips when flows are adequate. In fact, people have multiple motivations for taking a recreation trip, and the absence of good flows does not necessarily mean that users won't go. Second, the method assumes that if good flows are available, users will take trips. But any number of other reasons may prevent users from taking trips. In the Pacific Northwest, for example, there is no shortage of good flows throughout the rainy winters, but use is often higher during the spring and summer when flows are less advantageous but the weather is better. There simply may not be a good correlation between flows and use.