FLOOD03149

• County: Gilpin
• Community: Central City
• Stream Name: Eureka and Nevada Gulches
• Basin: South Platte
• Title: FEMA LOMR Application Hydrologic and Hydraulic Study
• Date: 10/1/1991
• Prepared For: Central City
• Prepared By: RMC
• Floodplain - Doc Type: Floodplain Report/Masterplan

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VI.

turbul ent fl ow wi th non-homogeneous fl ui d, and safety factor,
particularly in the older and more critical Opera House flume.

diagrams were obtained from Fluid
(See Reference No. 16 in the

Viscosity values and Moody
Mechanics and Hydraulics.
Bibliography.)

4. Appendi x "G", Exi st i ng Hydraul ics (HEC-2 Output)

The HEC-2 model is based on the CWCB model. Minor changes fall
into one of several categories:

a. Manni ng "n" values were generally increased per criteri a
previously presented;

b. Flows and flow changes were modified to reflect HEC-l output
contained in this study;

c. Culverts less than 8.0 feet in diameter were not considered
part of a "bridge" opening. Flows over the surface at these
locations were surface flows, not total flows;

d. The location of Section 16 was moved to facilitate analyzing
street flow capacities;

e. Sections 2 through 5 on Nevada Gulch were eliminated, with
ca 1 cul at ions performed by hand for the street and pavement
sections involved; and

g. Notes were added to clarify procedures.

5. Appendix "H", Existing Channel Hydraulics (Hand Calculations)

Hand calculations of flow for street and pavement sections which
are steep and flows are not subject to backwater conditions.

6. All floodplain delineation was performed within City limits based
1" . 100' mapping with 2' contours.

RESULTS

A. Hydrology

Three (3) previous studies have presented information from hydrological
analyses. The CWCB report presented estimated peak runoff flows from
Eureka Gulch (referred to therein as Gregory Gulch at the confluence
with Nevada Gulch), Nevada and Spring Gulches combined, and Gregory
Gulch at the lower City limit. The Hydrodynamics report used the same
data providing essentially identical answers, with the addition of
dividing Eureka Gulch to observe the impact of a proposed detention
facil ity. However, results were not provided for runoff up to the
detention pond; only the resultant flows downstream with it in place.
Additionally, the proposed detention facility analyzed by Hydrodynamics
is considerably different than the actual detention facility

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