7910

• UCREFRP Catalog Number: 7910
• Author: Bovee, K. D. and R. T. Milhous.
• Title: Hydraulic Simulation In Instream Flow Studies
• USFW Year: 1978.
• USFW - Doc Type: Theory And Techniques, Instream Flow Information Paper No. 5.
• Copyright Material: NO

The number of samples taken is a function of the variance within the
population to be sampled. If explicit zonation is used to generate the
population, then only one sample from each population is needed, although
more might be taken to satisfy any uncertainties concerning the zonation.
If implicit zonation is used, at least three samples should be taken. The
purpose of this exercise is to determine areas which are to be inspected
on-site, without having to inspect the entire river. Therefore, the
number of samples taken is not critical, but it should not be more than
about half the total population of candidate reaches.
Now that a small number of candidate reaches have been selected, the
investigator should arrange for an on-site inspection of each selected
"representative reach." If, on inspection, all of the representative
reaches are fairly similar, only one is required as a location for a study
site. In this case, such considerations as access, logistics, and
landowner permission may guide the selection of the study site. However,
if on-site inspection reveals that all of the "representative reaches" are
significantly different, it may be necessary to either set up study sites
in each reach or revert to an explicit zonation and resample the
population of candidate reaches.
At this time, it is necessary to determine the length of river within
the stratified segment represented by each selected candidate reach. If
explicit zonation is used, the represented reach length equals the river
length in each explicitly defined zone. If implicit zonation is used, the.
length represented is proportional to the number of samples taken. If
four samples are taken, and each is to be studied separately, then each
selected representative reach represents 25% of the total stream length
within the stratified segment. However, if after inspecting the four
sites, three seem to be very similar and one different, then only two
selected representative reaches are used, one representing 75% of the
segment length and one representing 25%.
The study site itself is then set up within the representative reach.
The study site may encompass the entire representative reach, or a portion
of it. The guiding principle is that the study site should be a sample of
most of the variance in habitat types, in the proportion that they occur,
within the representative reach. If this variance can be described in
only half of the representative reach, then the study area may encompass
this area only-
ESTABLISHMENT OF STUDY AREAS
As previously mentioned, a study area may encompass the entirety of
the selected representative reach, or only a portion of it, depending on
the variation in habitat encountered within the representative reach. The
purpose of the study area is to provide a sample of the variation in
hydraulic conditions and habitat types, as well as the proportion occupied
by each habitat type within the representative reach. The variation and
proportionality of habitat types are determined through the use of
strategically placed transects, delineating discrete areas of the stream.
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