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Last modified
7/14/2009 5:02:32 PM
Creation date
6/1/2009 12:40:58 PM
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UCREFRP
UCREFRP Catalog Number
7934
Author
Hyra, R.
Title
Methods of Assessing Instream Flows for Recreation.
USFW Year
1978.
USFW - Doc Type
Instream Flow Information Paper No. 6,
Copyright Material
NO
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a short time during a boating trip, and the remainder of the trip will <br />be over water of greater depths and widths. An important assumption is <br />that all water greater than the minimum is equally useful for the activ- <br />ity (i.e., more is better until bank-full stage). <br />A computer program (IFG-1) has been developed which predicts width <br />and depth across the transact of any stage (water surface elevation). <br />The output shows discharge and the width with depth equal to or greater <br />than a specific depth. Different water surface elevations may be put <br />into the computer model which are translated into flow in cubic feet per <br />second. When a flow provides the minimum width and depth. necessary for <br />an activity, discharge may be considered minimum. Such a minimum indi- <br />cates that significant losses, if not elimination of this activity, will <br />occur if minimum flow is not equaled or exceeded. <br />THE INCREMENTAL METHOD <br />This method, more sophisticated than the single cross section <br />method, describes a relationship between the amount of water in a reach <br />of stream and the associated recreation potential. The incremental <br />method can describe the potential for any recreation activity at any <br />streamflow. A major difference between the methods is that the single <br />cross section method can only be used to identify low flow and cannot be <br />used to assess the recreation potential at any other flow; the incre- <br />mental method can be used to assess the potential at other flows or to <br />calculate the change in receation potential caused by a change in stream <br />flow. <br />The incremental method involves a modeling procedure whereby the <br />surface area of a stretch of .stream is calculated. In addition to the <br />total surface area of the reach of stream, the area which has certain <br />depths and velocities is calculated. The usable surface area for each <br />activity is then calculated by use of depth and velocity requirements. <br />It is necessary to make three assumptions regarding the relation- <br />ship between the quantity of water and the recreation uses of the water: <br />(1) water depth and water velocity are the two streamflow components <br />which are most important in determining whether or not a certain recre- <br />ation activity may be safely and pleasurably engaged inl; {2) there are <br />Other -parameters such as water quality and temperature are also very <br />important in determining the amount of instream recreation use but in <br />many cases are not significantly influenced by flow. Width is also <br />important but is considered outside of the computer model (i. e., width <br />is not a part of the calculation of usable surface area). <br />4 <br />
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