Managed Flow Regimes and Resource Values: Traditional versus Alternative Strategies

Home Browse Search

A- �} h tain beaches, remove sediment in the channel, and shape channel features such as sloughs, riffles, or pools (Hill et al. 1991; Jackson and Beschta 1992). Recreation researchers have also documented important relations between flows and recreational quality (Shelby et al. 1992b; Whittaker et al. 1993). A study of boat- ing quality in the Grand Canyon, for example, showed that very low and very high flows were perceived as less safe, harder on equip- ment, and less satisfactory than medium flows (Shelby et al. 1992a). Taken together, this work suggests that dif- ferent flows create different combinations of resource values and that incremental changes in flows have measurable effects on those val- ues (Schmidt et al. 1998). In theory, the step is to use this kind of information to devel- op water management guidelines, usually in the form of requests for water through legal or administrative mechanisms. "Managed flow request" is an umbrella label that we use to describe these guidelines. Such requests can occur in many different venues, including the operation of dams, management of diversion canals and ditches, or administra- tion of water rights in a basin. Similarly, man- aged flow requests can occur in different man- agement contexts, ranging from informal agreements to formal legal rights (Goldfarb 1988). In this paper, we consider the conse- quences of different types of flow requests, independent of the venue or context. The term "managed flow request" is chosen to reflect this focus on the generic; in particular settings, this term might be replaced by "dam operation requirements" or "water rights claims." In any venue or setting, it can be challeng- ing to develop managed flow requests that serve a variety of resource values. Natural regimes generally include a range of flows through time, providing for a diversity of aquatic species and life stages, creating and maintaining a diversity of channel features, and providing a diversity of "niches' fo recreational activities. In contrast, manage regimes typically specify distinct flows to b provided at distinct times, usually adopting the model employed for out -of- stream uses Resulting "request structures," often with single flow identified per resource value impose a relatively coarse and static flo regime that removes potentially benefici variation. There are other ways to institute flo ider a tradition al managed flow request and two alternatives, exploring their ability to produce the range and quality of resource values provided by natural flow regimes. By applying a simplified case study focused on recreation to illustrate how alternative request structures work, our specific objectives of the paper are to (1) briefly review the information that is typically developed in studies of flow and recreation, (2) identify and review alternative request structures, and (3) discuss the advantages and disadvantages of these structures. Although the example focuses on recreational values, the ideas related to requests are relevant for other instream flow values as well. The case study is taken from Colorado's Dolores River. For simplicity, the paper focus- es on two recreational opportunities (scenic and whitewater boating) for two different craft (rafts and canoes), although in real situa- tions there are often more (Shelby et al. 1998). Flow- recreation data for the Dolores were pre- sented in a previous paper (Shelby and Whit- taker 1995), based on a Bureau of Land Man- agement (BLM) study that explored the effects — of flows on a wide range of resource lues (Vandas et al. 1990). The recreational compo- nent of the study included a survey of boaters and explored the relations between flows and recreational quality for different craft. Hydrology for the present paper is based on 1995 flow information as well as analysis conducted by the BLM in the 1990 study. The year 1995 was slightly wetter than average based on data for the period of record and was chosen for its ability to illustrate concepts in the paper. The hydrograph used also refers to flows at the USGS gauge at Dolores, which is upstream of McPhee Reservoir but includes most of the reservoir in -flow. Increasing diver- sions from the reservoir in recent years, as well as dam operating procedures, make downstream gauge information less useful for illustrating alternative request structures. r Additional analysis could be completed for d other years, or to address complexities of the e Dolores River's hydrology and diversions (which involves multi -year storage as well as both downstream and senior water rights a obligations). However, our purpose is to illus- trate the concepts involved in developing a w recreation flow request, and the single year is al adequate for that use. Similarly, we are not proposing allocation regimes for the Dolores w with these examples, which have been simpli- regimes. In this paper, we cons - fied for illustrative purposes. 234 Rivers Volume 7, Number 3 2000 x.