FLOOD01211

• County: Pueblo
• Community: Pueblo
• Stream Name: Fountain Creek
• Title: Pueblo Flood Control Project
• Date: 1/1/1990
• Prepared For: Pueblo County
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

.

.

:.
I
-'';

of the General Design Conference held 7 December 1983 prompted several design
changes from the plan presented in the Phase I Report.

3-10. Hvdraulic Design-Procedural Summarv. A channel baseline was set and
appropriate bridge data coded and inserted into the cross section data to, form
the basic HEC-2 model. Encroachment stations were added to the model to
simulate the location of the levees proposed in the Phase I study. Numerous
trials involving excavation and levee alternatives to finalize the Phase II
design are discussed in subsequent paragraphs.

3-11. Hvdraulic Losses. Mannings' roughness factors used in this study were
the same as used in the Phase I report. Left overbank values ranged from 0.08
to 0.10; right overbank values ranged from 0.05 to 0.06. Channel values from
0.03 to 0.035. After a site visit to Pueblo, it was found that these values
Were a little high. Additional HEC-2 backwater runs were made using a maximum
n value of 0.07 in the overbanks and 0.03 in the channel. The sensitivity of
stage and velocity to the roughness factors proved negligible, with water
surface elevations decreasing an average of only 0.03 feet. Contraction and
expansion coefficients used between cross sections On Fountain Creek were 0.1
and 0.3, respectively, which apply to gradual transitions. Bridge sections
used contraction and expansion coefficients of 0.3 and 0.5, respectively.
Because changes in the direction of flow are more abrupt at the confluence
withfhe Arkansas River, values of 0.3 and 0.6 were used for the cross
sections at the Highway 227 bridge.

3-12. Standard Pro;ect Flood. Pre-Pro;ect Conditions. Since the proposed
channel improvement provides less than SPF protection, the consequences of
flows exceeding the channel capacity, up to and including the SPF, were
investigated. The standard project flood is 152,000 cfs for Fountain Creek at
Pueblo. The existing condition analysis indicated that 44,000 cfs split from
the main flow around 13th Street and headed through downtown Pueblo. The
split flow traveled through the downtown area to the Arkansas River, where it
joined with a coincidental flow of 8,000 cfs a short distance above the mouth
of Fountain Creek.

3-13. Standard Pro;ect Flood. Post-Pro;ect Conditions. The proposed project
greatly reduces flooding from the SPF. A "worst case" scenario was ana lyzed
in which levees broke above the 8th Street and Atchison Topeka and Santa Fe
(ATSF) bridges. Flow broke out of the channel at 13th Street where 1700 cfs
went under 1-25 to the west. The east levee above the 8th Street broke for a
distance of 500 feet downstream from its start. A flow of 10,000 cis went
into the east overbank from this break. Immediately above 8th Street bridge
the earthen levee On the west side broke and sent 14,500 cfs to the west. The
soil-cement levee On the east side was overtopped and experienced failure of
the parapet wall. A flow of 6500 cfs joined the 10,000 cfs already on the
east side. About 1,800 feet upstream of the AT&SF bridge the east levee was
overtopped and partially eroded, sending 6500 cfs into the east overbank.
Immediately above the AT&SF bridge the east levee broke for a distance of 100
feet sending 2,800 cfs to the east. In the area of the Missouri Pacific
Railroad (MPRR) bridge, flow overtopped the tracks running parallel to the
creek on the west bank. The 16,200 cfs which split off to the west flowed
through the downtown area and on down to the Arkansas River just above the
mouth of Fountain Creek. The 25,800 cfs which split off to the east stayed
between the levee and high ground to the east. This flow ran parallel to the

III-3