FLOOD07093

• 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: 8/1/2001
• Prepared For: CWCB
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

The results of the HEC-2 hydraulic models were imported into SAM and used to describe
a set of hydraulic parameters for sediment transport calculations. This was accomplished by
specifying a portion of each sub-reach as representative of the hydraulic conditions and
calculating average values for velocity, depth, width, and energy slope for each discharge value.
These parameters were then used, along with bed material particle distribution information, to
generate sediment transport rating curves for the sub-reaches. The "Bent's Fort" particle
distribution from the geomorphological assessment completed in 1997, discussed in 3.1
GEOMORPOLOGICAL ASSESSMENT, was used for the bed material parameters. This
particle distribution closely matched the "Highway 207" distribution, located 30 miles upstream,
from the same report suggesting uniform bed material throughout the reach. The Brownlie
sediment transport equation was used to calculate transport. This equation was used because the
Stable Channel geometries are calculated with this equation, thus preserving theoretical
consistency. The Brownlie sediment transport equation would not necessarily be the first choice
for transport calculation, but it is applicable to sand-bed rivers such as the Lower Arkansas.

Three groups of conditions were analyzed. The reach-averages from each problem area
were used to indicate current conditions. Because of the length of Problem Area 1, it was broken
into 4 parts. The sediment transport rates for this condition are listed in Table 3.5. The second
condition analyzed used only the HEC-2 cross-sections with a capacity of at least 1,000 cfs. The
results are shown in Table 3.6.

Table 3.5. Existin~ sediment transport rates (reach averaged hydraulic narameters).
Discharge Problem Problem Prob. Area Prob. Area Prob. Area Prob. Area
Area 3 Area 2 1, Part 1 1, part 2 1, part 3 I; part 4
(cfs) (tld) (tld) (Vd) (tld) (tld) (tld)
100 2.35 1.38 0.41 4.53 2.52 4.81
200 16.66 13.23 7.25 26.58 17.20 29.14
300 43.93 37.93 23.69 64.30 43.05 71.59
500 131.32 119.00 79.57. 163.13 113.52 206.64
750 293.11 264.82 184.90 321.62 229.28 43328
1,000 510.75 445.83 327.46 500.01 394.78 720.64

Table 3.6. In-channel sediment transport rates (at least 1,000 cfs canacitv).
Discharge Problem Problem Prob. Area Prob. Area Prob. Area Prob. Area
Area 3 Area 2 1, part 1 1, part 2 1, Dart 3 1, part 4
(cfs) (tld) (tld) (tld) (tld) (tld) (tld)
100 4.31 10.91 5.13 9.24 44.37 15.16
200 27.91 57.73 20.81 48.26 166.04 69.38
300 74.07 137.22 45.95 113.61 356.00 156.09
500 232.66 360.24 128.99 315.07 960.48- 400.71
750 557.81 746.22 331.43 694.00 1,628.24 818.97
1,000 1,028.76 1,218.29 603.32 1,481.66 3,611.55 1,406.84

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