7934

• 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

certain measures of water depth and wai
sidered minimum, maximum, and optimum
measurement of water surface area which
depth and velocity is a viable method of
for instream recreation uses.
;er velocity which may be con-
for an activity; and (3) the
meets certain requirements of
describing recreation potential
This method is comprised of four components: (1) computer simula-
tion of a stream reach, (2) determination of the combinations of stream
depth and velocity, (3) determination of a composite probability-of-use
for each combination of depth and velocity, and (4) calculation of a
weighted usable surface area.
1. Simulation of the Stream. The stream reach simulation model
utilized in this approach uses several cross sectional tran-
sects, each of which is subdivided into subsections. For any
stage (water surface elevation) the mean depth and velocity of
each subsection is calculated. Typically, a transact would be
established across a pool, a riffle, and an intermediate area.
Together these cross sectional measurements would represent a
stream reach which may extend several miles. In Table 2 a 100
foot length of stream is represented.
Table Z. Depth velocity matrix showing total
surface area of stream in square feet.
Depth ft Velocity ~n feet per second
<0.5 0.5-1.0 ~ 1.0-1.5 >1.5 Total
<1 500 4 0 1 0 0 1,0 0
1-2 600 700 800 300 2,400
2-3 100 300 500 100 1,000
>3 0 0 100 0 1.00
Total 1,200 1,400 1500 400 4,500
2. Distribution of Combinations of Depth and Velocity. The
output of the stream reach simulation model is in the form of
a matrix showing the surface area of a stream having different
' combinations of depth and velocity. Table 2 illustrates a
depth velocity matrix. The outlined number in the upper left
matrix cell refers to 500 square feet per I00 feet of stream
having a combination of depth less than 1.0 foot and velocity
. less than 0.5 foot per second. This figure is the sum of the
areas within the stream reach with this combination of depth
and velocity.