WSP00380

• File Number: 8149.100
• Description: Miscellaneous Small Projects-Project Studies - NRCS-Ft Lyon Canal Co-Limestone-Graveyard Creeks
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 9/1/1992
• Author: US Dept of Agricultu
• Title: Lower Arkansas River Basin - Water Quality Study - Colorado
• Water Supply Pro - Doc Type: Report/Study

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002553

20

C. USGS Arkansas River Model

1. USGS Mainframe Computer Model

The u.s. Geological Survey developed an interactive-
accounting model to simulate dissolved solids,
streamflow, and water-supply operations in the Arkansas
River Basin, Colorado. This model was prepared in
cooperation with the Southeastern Colorado Water
Conservancy District.

The model calculates streamflow for incremental drainage
areas by use of regression equations and a time series
of independent variables such as snowpack,
precipitation, or streamflow gauges. Dissolved-solids
concentrations can be calculated at each model node
location for the corresponding streamflow. streamflow
and dissolved-solids loads then can be routed downstream
by the model. Use of the model incorporating relations
of specific conductance to streamflow enabled the
computation of dissolved-solids loads throughout the
basin.

To simulate streamflow only, all of the water-supply
operations were incorporated in the incremental
streamflow regression relations and the model was
calibrated for 1940-1985 water years. Coefficients of
determination for streamflow-only simulation for 20
nodes ranged from 0.89 to 0.58. The model input was
then revised to incorporate 74 water users and 11
reservoirs to simulate water-supply operations.

Two periods were used for calibration: 1943-74, which
included John Martin Reservoir; and 1975-85, which also
included the Fryingpan-Arkansas project with Pueblo
Reservoir. Calibration of the water-supply operations
resulted in coefficients of determination that ranged
from 0.87 to negative for 37 selected water users. Even
for those users whose simulated irrigation diversions
did not relate well statistically to the observed
diversions, plots of data generally indicated reasonable
model results. Plots of simulated reservoir contents
also indicated reasonable similarity to observed values.
Coefficients of determination for 13 selected streamflow
nodes ranged from 0.87 to 0.02.

When all of the model options are used, the water-use
and ground-water systems in the basin are included.
Types of water users that can be simulated include:
agricultural, municipal, and industrial users, and