WSP06131

• File Number: 8149.911
• Description: Miscellaneous Small Projects and Project Studies - SE Needs Assessment and PSOP
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 8/1/2001
• Author: US Army Corps of Eng
• Title: Arkansas River From John Martin Dam To The Colorado-Kansas State Line Channel Capacity and Riparian Habitat Planning Study
• Water Supply Pro - Doc Type: Report/Study

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the existing channel capacity and coordinate with the U.S. Geological Survey (USGS) on
adjacent ground water problems within three problem areas. Specific problems and needs in
these areas are as follows:

Problem Area 1:
. Insufficient channel capacity;
. Negative gradient return flow of groundwater from the north La Junta area downstream to
Bents' Old Fort on the north bank of the Arkansas River extending northward to the Fort
Lyon Canal; , ;
. Possible significant sedimentation contribution from irrigation canals in the area.

Problem Area 2:
. Insufficient channel capacity;
. Levee instability and erosion.

Problem Area 3:
. Insufficient channel capacity;
. Decreased stream gradient with excessive sedimentation.

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The study identified the probable causes of these problems and ronked them in order of
importance. Factors affecting the channel capacity of the Arkansas River and groundwater
inundation in the study reach and flood plain areas included the following:

> Changing sediment transport effects due to regulation of flow by Pueblo Dam and watershed
development proctices in the Fountain Creek basin.
> Tamarisk introduction and proliferotion, which has impacted the channel shape, arid
subsequently. the hydraulics and sediment transport.
> Agricultural encroachment on the historic flood plain of the Arkansas River.
}> Changes in the base flow due to discharges from :urban areas (surface runoff and sewage
treabnent plant discharge), agricultural irrigation practices which have encouraged the
growth of phreatophytes, and transmountain diversions.
> Detention practices regarding surface runoff from urban areas.
}> Groundwater extraction and irrigation practices. .
> Channel modifications over the past 30 years.

Two analytical tools were used for ranking: Log Pearson III, HEC-I1 and the sediment transport
program (SAM). The study determined the effects of average annual water volume, the effects
of peak discharges, and the effects of the sediment transport capaCity. The specific problem
areas are described in Table I-I and are depicted in Figure I and Figure 2.

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