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

Home Browse Search

Chapter 2 A CONCEPTUAL FRAMEWORK Assessing instream flows for any resource (including recreation) requires a conceptual understanding of how different flows or flow regimes affect various, and potentially competing, river resources. This chapter presents such a conceptual framework (see Figure 3) and explains its main elements: flow, resource conditions, resource outputs, and trade -offs and flow negotiation. In subsequent chapters, these elements and the relationships between them are explored in greater detail as they relate to recreation. FLOW Flow is the variable driving the system in any instream flow study. The amount and timing of flows (which define the hydrology of the system) are the first variables which need to be understood. The simplest case is a natural flow regime on a river with no human intervention ( "unregulated systems "). In systems with human interventions such as dams, withdrawals, or diversions ( "regulated systems "), complexity is added with various operational variables. In both cases, instream flow studies start by describing the range of water regimes and operational variables that produce water in the stream. These factors are represented by the faucet in Figure 3, recognizing that the faucet is controlled by some combination of natural and human factors. RESOURCE CONDITIONS At the most fundamental level, flow has a major impact on resource conditions. The conditions responding directly to flows are river hydraulics: water depth, velocity, width, wetted perimeter, and turbulence. "Indirect" responses also occur becuase of the interactions between flows and sedimet process and riparian vegetation. Indirect impacts include changes in channel features such as sinuosity, sediment movement, channel movement, gravel bars, and beaches. Indirect impacts also include changes in characteristics of riparian vegetation such as the type, amount, and location of plants, as well as the physical and chemical make -up the river, its water quality. Hydraulics, channel morphology, and riparian vegetation respond to changes in flow, 5 forming a dynamic interactive system that defines biological and recreation habitats. For example, when rivers flood, they become erosive and carry considerable amounts of sediment. During these periods, bars are formed and meanders adjust and migrate. Floodplain vegetation may cause sediment to settle out, creating rich riparian soils. Many of these flood - dependent processes in turn create habitat and transport seed for early successional -stage vegetation. The resulting channel form may provide water to later -stage vegetation such as large cottonwood trees. Because recreation opportunities often depend upon the character of the river and associated floodplain, it is important to consider how stream flows affect river hydraulics, channels, and riparian zones. Conversely, when identifying optimum stream flows for activities such as rafting or canoeing, it is also important to consider the effects those flows might have on resource conditions. Understanding the relationship between flow regimes and resource conditions is the subject of Chapter 4, Exploring the Effects of Flow on Resource Conditions. RESOURCE OUTPUTS The unique array of resource conditions associated with a given river provide different instream resource outputs. These include fish habitat, wildlife habitat, and various types of recreation opportunities. Within each category, there may be several alternatives. For example, different flow regimes may produce habitat for different types of fish or wildlife, or different types of recreation. These are the "products" to be evaluated in an instream flow study, analogous to "goods and services" produced in an industrial setting.