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

• Description: Instream Flows for Recreation: A Handbook on Concepts and Research Methods
• Date: 1/1/1993
• Author: Whittaker, Doug; Shelby, Bo; Jackson, William; Beschta, Robert - National Park Service
• Title: Instream Flows for Recreation: A Handbook on Concepts and Research Methods
• Water Supply Pro - Doc Type: Report/Study

How River Environments Respond to Changes in Flow
Indirect effects of flow play important roles in creating and sustaining high quality recreation experiences
although it is often difficult to predict how changes in flows will change the river environment. Two examples of
how changes in flow regimes may affect important features are given below.
1. Sustained Decreases In Flow
A sustained decrease in flow throughout a year or season is a common situation with rivers across the country
as water is diverted for municipal water supply, industry, or agriculture. But what are the likely or possible effects of
decreased flows? Table 3 provides a list of possible effects for Beaver Creek, an alluvial river in Alaska, where
researchers explored these effects. If there were to be a sustained decrease in flows on that river, a number of
important physical features would change and thus affect the recreational opportunities on the river. A few of the
more important changes include decreases in size of gravel bars or beaches (detracting from camping opportunities
which depend on open bars for good views, fewer insects, and ease of access to the river), loss of sloughs and the
filling of pools (both of which provide important habitat and good fishability for arctic grayling, the principal sport fish
on the river), and the increase in riffles, thus creating more critical reaches for navigation during low flow periods.
Readers should note that non - alluvial rivers, and even some alluvial rivers, may react somewhat differently than
is shown below. In fact, the Beaver Creek conclusions are hypothesized rather than observed changes (there has
been no decrease in flows on the river). The point is that there are a myriad of factors involved in how rivers adjust
to new flow regimes. These are simply descriptions of the common changes one might expect; the goal of an
instream flow assessment is to determine whether these will hold true as well as estimate the magnitude of them
for given decreases in flows.
many of the river's important natural features would be altered by sustained decreases in
flow.
25