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

2

SECTION 1. INTRODUCTION

1.1 Purpose and Scope

This report was prepared to provide Central City with specific
recommendations regarding feasible drainage structures and
reconstruction of existing drainage facilities to reduce
potential flood and sediment damage. There are existing drainage
structures on both Eureka and Nevada Gulches (see Figure 1. 1.1)
that convey only high-frequency storms. Infrequent storms, such
as 20,50 and 100-year events will, under present conditions,
cause street flow, substantial damage to existing structures and
impede traffic and safety.

The report presents conceptual designs and cost estimates that
enabled the author assess the economics related to construction
costs. Floods ranging from the mean annual (50 percent
probability of exceedance) to the lOa-year (1 percent probability
of exceedance) were necessary to determine the economic impact of
improvements. To obtain these storms, Colorado Water
Conservation Board hydrology was expanded to these other
,frequencies. An extensive discussion of the Colorado Water
Conservation Board hydrologic analysis is included in the
technical addendum to CWCB (1987).

1.2

Location and site Characteristics

Gregory and Nevada Gulches are two main drainages upon which
Central City is built. Central City is 30 miles northwest of
Denver on Colorado Highway 279. The Town of Black Hawk abuts the
eastern city limit.

Eureka Gulch becomes Gregory Gulch below the confluence with
Nevada qulch, immediately east of downtown Central City. Eureka
Gulch is an easterly flowing creek. Nevada Gulch, above the
confluence with Eureka Gulch, flows in a generally north
northeasterly direction. Be low the conf 1 uence, Gregory Gu lch
flows east to Black Hawk. Eureka Gulch drains 1185 acres
with upper elevations of 9994 feet. The elevation in downtown
Central City at the confluence of Nevada Gulch is 8380 feet.

The upper _ reach of the Eureka Gulch basin is characterized by
wooded mountain area with meadows near the Eureka channel. From
the western city limit, the area to the north of the channel has
very few trees. This characteristic continues through Central
City to Black Hawk. The Eureka Gulch channel is confined between
roads and buildings and eventually is piped through the downtown
area in a fl ume .

West of
Dorothy
1.1.1) .
purposes.

Central City corporate limits on Eureka Gulch is the
Lee placer dam site oWf)ed by Central City (see Figure
A small embankment impounds water for recreational

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HydroDynamics Incorporated