WSP10371

• File Number: 8111.805
• Description: Arkansas River Compact Administration - Keesee Ditch
• Basin: Arkansas
• Date: 1/1/1986
• Author: HRS Engineering
• Title: Keesee Ditch Change of Water Rights Vol 1 - Historical Operation of Kessee Ditch
• Water Supply Pro - Doc Type: Publication

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Return Flow Analysis

A simple estimate of the net impact to the Arkansas River resulting from
the historical operation of the Keesee Ditch would be the average annual
consumptive use for the study period. This volume estimate, however, does not
account for the timing differences between river depletions or diversions, which
have an immediate effect on the river, and river accretions or return flows,
which are delayed. On a monthly basis, the net depletion or reduction in flow
of the Arkansas River, is the sum of the monthly diversions minus the monthly
return flows. Since the timing effects of diversions can easily be represented
by the Keesee Ditch diversion records, the major components in the analysis
of net stream effects involves the determination of the timing of return flows.

Irrigation return flows are the result of seepage losses from the irrigation
delivery system and excess irrigation water. Most of this water percolates
downward throught the soil and recharges the alluvial aquifer, while only a small
percentage. enters the stream directly as surface runoff. For this analysis, it
was assumed that all irrigation return flows recharged the alluvial aquifer
underlying the irrigated area. '5 '

The alluvial aquifer underlying the land irrigated by the Keesee Ditch consists
of deposits of sand, gravel, and clay laid down by the Arkansas River. Ground
water in this alluvium is part of the same hydrologic system as the river, although
movement of water through these materials is much slower than flow in the
river. Because of this, irrigation returns which recharge the alluvial aquifer
do not affect the surface stream to any significant extent for some time after
the recharge occurs. The timing of this effect is a function of the distance from
the stream at which recharge occurs and the hydrologic characteristics of the
aquifer. Not only are these effects delayed, but they are also "stretched out"
so that the effect on the surface stream occurs over a longer period of time
and with less intensity than the recharge. Consequently, the effects on the surface
stream continue to occur for some period after recharge has ceased. The
determination of the amounts and timing of these effects is made using a method
called stream depletion analysis.

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