FLOOD01607

• County: Gilpin
• Community: Central City
• Stream Name: Eureka and Nevada Gulches
• Title: Master Drainage Study
• Date: 2/12/1988
• Prepared For: Central City
• Prepared By: HydroDynamics
• Floodplain - Doc Type: Floodplain Report/Masterplan

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CENTRAL CITY MASTER DRAINAGE STUDY

9

SECTION 3. HYDROLOGY AND HYDRAULICS

3.1 General

Hydrology for Eureka Gulch and Nevada Gulch was simulated by the
same model utilized by the Colorado Water Conservation Board
(CWCB) in development of their 1987 floodplain report for Central
City. Once calibrated, hydrographs were generated by the model
not only for the lOa-year event but also for the 2-year, la-year
and 50-year events. The following precipitation distributions
were utilized in evaluating the hydrology for each basin.

Table 3.1.1. Accumulated Precipitation (in Inches) .
Hour 2-Year 10-Year 50-Year lOa-Year
1 0.10 0.15 0.21 0.22
2 0.28 0.43 0.59 0.63
3 0.84 1. 30 1. 79 1. 94
4 1. 00 1. 54 2.12 2.30
5 1.11 1.71 2.36 2.54
6 1. 20 1. 85 2.55 2.75
3.1.1 Eureka Gulch

As indicated above, hydrology was simulated to match the values
presented in the CWCB Report. For this analysis, Eureka basin
was separated into two sub-basins having the following watershed
characteristics (see Figure 1.1.1).

Table 3.1.2. Eureka Gulch Watershed Characteristics.

"

Watershed
Characteristics
Drainage Area
Slope
'Hydraulic Lengt.h
Time of Concentration
Curve Number

Above
Dorothy Lee
708 acres
18.4%
8,800 feet
0.32 hours
81

Below(l)
Dorothy Lee
510 acres
17.3%
10,880 feet
0.41 hours
81

, (1) Tributary to Eureka Gulch at the confluence of Nevada Gulch

In order to simulate the hydrology for Eureka Gulch to match
CWCB hydrology, it was necessary to lag above Dorothy Lee by 30
minutes.' The hydrograph nearly matched that presented in the
CWCB report. As a result, hyd~aulic evaluations of flows
simulating what will happen when the Dorothy Lee detention pond
routs flood flows can be completed. Further discussion on the
impact to hydrology due to constructing the Dorothy Lee reservoir
and the resulting hydraulics are presented in Section 3.2.

3.1. 2

Nevada Gulch

Hydrology for Nevada Gulch
presented in CWCB (1987) due
as evident in Eureka Gulch.

w~s not changed from what was
to lack of detention storage sites
Section 5 provides discussion on

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