FLOOD06271

• County: Otero
• County: Pueblo
• Community: Otero, Pueblo Counties
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Arkansas River Channel Capacity and Riparian Habitat Planning Study
• Date: 7/1/1999
• Prepared For: CWCB
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

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loss of flow capacity. Since the interior channel was designed to be stable at 1,000 cfs,
degradation would be minimal, as well.

Probtem Area 4. The improved channel for this sub-reach uses a 400 ft bottom-width
channel along the existing channel alignment with a slope of 0.00096 and 1:3 sideslopes, and a
slightly more sinuous interior channel with a 140 ft bottom width on a slope of 0.000925. The
sideslopes of this interior channel were modeled at t:2.5 for the outside of the bend and 1:10
for the inside. The "n" value for the large channel was estimated at 0.060 and the interior
channel was modeled using 0.038. This configuration would pass 3,000 cfs; A profile plot of
this area with the improved channel is shown in Plate 7 and a typical improved cross-section is
shown in Plate 12.

The sediment yield calculated for this configtrration was 19,300 tOllSl'yr with a mean
daily transport of 53 tons/day. This represents almost a four-fold increase in sediment transport
capacity for this subreach, which would greatly decrease required maintenance and loss of flow
capacity. Since the interior channel was designed to be stable at 1,000 cfs, degradation would
be minimal, as well.

Probtem Area 5. The improved channel for this sub-reach has two configurations; one
downstream of the Buffalo diversion structure, and one upstream. The downstream portion
uses a 400 ft bottom-width channel along the existing channel alignment with a slope of
0.0011 0 and 1:3 sideslopes, and a slightly more sinuflus interior channel with a 130 ft bottom
width on a slope of 0.000723. The sideslopes of this interior channel were modeled at I :2.5 for
the outside ofthe bend and 1: 10 for the inside. The upstream portion uses a 500 ft bottom-
width channel along the existing channel alignment With a slope of O.OOIIa and 1:3 sideslopes,
and a slightly more sinuous interior channel with a 140 ft bottom width on a slope of 0.000723.
The sideslopes of this interior channel were modeled at I :2.5 for the outside of the bend and
I: 1 0 for the inside. The "n" value for the large chan)1el was estimated at 0.060 and the interior
channel was modeled using 0.038. This configuratioh would pass 3,000 cfs. A profile plot of
this area with the improved channel is shown in Plate 8 and a typical improved cross-section is
shown in Plate 13.

The sediment yield calculated for this configuration was 33,300 tonslyr with a mean
daily transport of91 tons/day for the downstream portion, and 25,800 tons/yr and a mean daily
transport of 71 tons/day for the upstream portion. This is a mismatch, but not necessarily bad
considering the diversion impacts. More analysis would be required to account for water
diversions and their effect on sedimentation. These values compare closely to the existing
condition values of29,600 tons/yr and 30,700 tons/ir for downstream and upstream,
respectively. This indicates a slight increase in sediment transport capacity for this subreach.
Since the interior channel was designed to be stable at 1,000 cfs, degradation would be
minimal, as well.

Probtem Area 6. The improved channel for this sub-reach uses a 400ft bottom-width
channel along the existing channel alignment with a slope of 0.00134 and 1:3 sideslopes, and a
less sinuous interior channel with an 85-ft bottom width on a slope of 0.000859. The