WSP05120

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 1/1/1983
• Author: USGS
• Title: Reservoir Development Impacts on Surface-Water Quantity and Quality in the Yampa River Basin - Colorado and Wyoming - 1983
• Water Supply Pro - Doc Type: Report/Study

001902

Model Verification

Most digital-computer models, such as those used in this study, must be
cal ibrated. This calibration procedure, as discussed by Hines and others (1975a,
1975b), is required to adjust certain model parameters so that the model results
adequately represent actual conditions. As noted by Shearman (1976), the multi-
reservoir-flow model is an accounting model and contains no model parameters that
can be cal ibrated. However, the model can be verified if sufficient data are
available. The model was verified previously using data for 1970-73 from the
reservoir system in the Wi I lamette River basin in Oregon (Shearman, 1976; Jennings
and others, 1976). However, a similar verification of the model for conditions in
the Yampa River basin could not be made because most of the reservoir system is
not in existence.

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To provide Some means of testing the model as a predictive tool for theYampa
River basin, model simulations were made using historical streamflow data for
50 water years (1927-76). This period was chosen for two reasons: (1) The model
is constrained by array sizes to a 50-year period; and (2) by starting with water
year 1927. the model analysis included the droughts of the 1930's and the 1950's.
For this analysis, comparisons between simulated historical and measured mean
annual streamflow were made for streamflow-gaging stations at control poi'nt 39
(Yampa River at Steamboat Springs, Colo.) as shown in figure 7; control point 18
(Yampa River near Maybell, Colo.) as shown in figure 8; and control point 42
eLi ttle Snake River near Li ly, Colo.) as shown in figure 9. Approximate locations
of the streamflow gages are shown in figure 6.

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The comparison between simulated historical and measured annual-mean stream-
flow values indicates agreement within 5 percent,for control points 39 (Yampa
River at Steamboat Springs, Colo.) and for control point 42 (Little Snake River
near Lily, Colo.) and agreement within 20 percent for control point 18 (Yampa Riv-
er near Maybell. Colo.). The less accura~e comparisons at the downstream control
point of the Yampa River may be explained by the effects of numerous small irriga-
tion diversions and tributaries that were not measured and could only be approxi-
mated in the multi reservoir-flow model. In contrast, the Little Snake River has
less irrigation and fewer unmeasured tributaries than the downstream Yampa River
locations; the result is closer agreement between the simulated historical and
measured streamflow values.

The unmeasured inflows and outflows were approximated within the multi reser-
voir-simulation model by an additive "local-flow" computation procedure that in-
volves starting at an upstream point and adding intervening flows in a downstream
direction. These intervening flows, called local flows, were determined either
directly by using existing streamflow records or were estimated by multiplying a
nearby streamflow record by the ratio of the intervening drainage area and the
drainage area upstream from the streamflow-gaging station. This assumes a direct
correlation between the flows at the streamflow-gaging stations and the interven-
ing flows. In some instances, the streamflow-gaging stations were located in or
near the intervening area. Records for 22 of the 36 streamflow-gaging stations
indicated in figures 3 and 4 were used in the local-flow computation.

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