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

r, model output. Thus, a model may be employed for sensitivity analysis,
which is very useful in establishing research and data collection
priorities.
Hydraulic simulation for instream flow investigations is defined,
for the purposes of this paper, as the description of the physical
characteristics of a stream reach in mathematical terms. In the simplest
of examples, a series of measurements of depth, velocity, and width across
a cross section describes the spatial distribution of depths and
velocities within the cross section at the discharge (flow) which was
measured. Repetition of the process at many discharges would result in a
different description of these- distributions at each discharge measured..
Extensiort of the process to several cross sections, related to one another
by measurement, allows the description of such distributions for a stream
reach.
Approaches utilized in the determination of the distribution of
hydraulic parameters at different discharges vary considerably in the
level of field effort and reliability of the output (i.e. predicted values
of hydraulic parameters as compared to measured values for the same flow).
The selection of a particular approach may be constrained by limitations
of cost and manpower, limitations imposed by on-site considerations, and
the required level of accuracy of the predictions.
In order for- the mathematical simulation model to be useful for
planning purposes, it not only has to reflect existing conditions (employ
a rational logic process); but the model must also be capable of extension
over space and into time (have predictive abilities). In reference to
hydraulic simulation models, a researcher should select a study area which
is representative of a much larger segment of stream, and be cognizant of
the base line equilibrium condition of the watershed.
Extension of the model over-space can be quite satisfactorily handled
by proper study site selection. If, in fact, the study reach modelled is
representative of a larger system, then the logic follows that the
response of the study reach is indicative of the response of the system.
Study site selection and the representative reach concept are presented in
detail in pages qI to S7.
Extensions of the model over, time is-irrevocably tied to the water-
shed hydrology and geomorphology.. Whether a hydraulic simulation model or
art empirical assessment of stream flow characteristics is used, the
general procedure is to examine historic stream flow records, measure the
physical characteristics of the stream under present day conditions, and
then predict relationships which will occur at some future date.
Axiomatically it has been assumed that neither the physical character-
istics of the stream nor the hydrologic characteristics of the watershed
will change, or have changed, significantly with time. It is further
assumed that the period of hydrologic record is sufficiently long to have
incorporated most of the random variability in stream flow which will ever
?. occur in the watershed.
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