WSP04581

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1996
• Author: USGS
• Title: Relations of Discharge and Specific-Conductance Trends to Reservoir Operations in the Lower Arkansas River - Southeastern Colorado
• Water Supply Pro - Doc Type: Report/Study

1951

:.~;;~2LdlijjNARY RcPCH:
.~,LJ8JECT TO REVlsr(""

Arkansas River below John Martin Reservoir

.

Station 07130500 (Arkansas River below John Martin Reservoir) is located 0.2 mi downstream from John

Martin Reservoir (fig. I). A substantial change in reservoir operations occurred with adoption of the 1980 Operating

Plan. as previously discussed in the description of John Martin Reservoir; therefore discharge and specific conduc-

tance step trends were evaluated for changes that might have occurred after 1979. Water quality at station 07130500

is important from an irrigated-agriculture perspective, but it is also important from a domestic water-supply perspec-

tive, because the city of Lamar diverts water from the river to provide artificial recharge to the alluvial aquifer in the

vicinity of their municipal well field. Discharge and specific-conductance data were available at station 07130500

for 1955-94.

The median annual discharge at station 07130500 increased significantly (p<O.O 1) from about 142.000 acre-

ftlyr during 1955-79 to about 231 ,400 acre-ftlyr during 1980-94. The median annual discharge that entered the lower

basin from the upper basin, as indicated by the record at station 07096000, increased from 481,000 acre-ft in 1955-

.79 to about 574,400 acre-ft in 1980-94. The increased median annual discharge at station 07130500 is anributable

to the increased inflow from the upper basin and Fountain Creek, the decreased diversion and consumptiye use of

winter discharge upstream from the reservoir, and finally to the storage of winter water in John Martin Reservoir by

three canal companies. As previously discussed in the description of John Martin Reservoir. 35 percent of the winter

water stored in the reservoir by the three canal companies is shifted to Arkansas River Compact use and is subject

to downstream release.

The daily discharge at station 07130500 tended to increase after 1979, during the months of April-October,

while the daily discharge in the winter months tended to decrease slightly or remain constant (fig. 20). All increases

in the daily discharge. except for in April, were statistically significant (table 11). The increase in the daily discharge

during the growing season is a function of the increased availability of water in the reseryoir and in the cbanges in

reservoir-operating principles. Reservoir storage that was previously released in the spring is now released through-

out the summer months. Although discharge tended to decrease significantly during the winter months, the winter

eischarge is typically so small that the decreases are relatively inconsequential (table II).

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