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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hydrological and hydraulic feasibility study of various scenarios to
determine what improvements must be made to accomplish City goals. The
report was completed in March 1991 and accepted by the City of Central in
April 1991, and in the summer and fall of 1991, proposed improvements were
made. This report was prepared as a follow-up to improvements, and
presents detailed hydrological and hydraulic information used in defining
current floodplain limits.

II. KEY COMPONENTS

Central City is built along and over Eureka Gulch, Nevada Gulch, Spring
Gulch, and Gregory Gulch. Eureka Gulch begins west of City 1 imits and
enters town from the west. Nevada Gulch begins southwest of City limits
and enters town from the south. Spring Gulch begins south to southeast of
town and joins Nevada Gulch prior to the Nevada Gulch confluence with
Eureka Gulch, which is where Gregory Gulch begins. Gregory Gulch continues
east toward Blackhawk.

The four major gulches in Central City are identified on Exhibit "A". Also
shown are flumes or pipes placed in gulches to convey flows underneath
developed areas. The flume in Eureka Gulch, commonly referred to as the
Opera House flume, begins west of the main business district and continues
to Gregory Gul ch. The fl ume is made of various materi a 1 s and shapes,
including circular corrugated metal pipe (CMP) and reinforced concrete pipe
(RCP) up to six (6) feet in diameter and rocked archways. Some of the
oldest and largest buildings in Central City are located above the Opera
House flume. Nevada flume is made of RCP and CMP up to six (6) feet in
diameter and a bridge section, and passes under parking lots and streets.
Minor flows from Spring Gulch are conveyed through a 36-inch diameter RCP
to the Nevada flume. This pipe is referenced herein as the Spring Gulch
fl ume .

The largest watershed above the City contributes to Eureka Gulch, which
parallels much of the City business district. Several facilities and
crossings are worth discussing.

In addition to gulches and flumes, the other primary facil ities for
conveying flows are streets. Eureka Gulch overflows to Eureka Street which
dra i ns to Ma in Street. Nevada Gul ch overflows to Nevada Street whi ch
drains to Main Street. Accumulated flows in Main Street passes through
" Gregory Street, joining with overflow from Spring Gulch coming down Spring
Street, and on to Gregory Gulch, which generally contains runoffs.

The gulches, flumes and streets are the key components of runoff conveyance
in town. Other minor drainage facilities exist, all of which contribute
to the key components.

III. EXISTING CONDITIONS

A. Eureka Gulch Watershed

West of town is the newly constructed detention pond. Fourteen (14)
acre feet of freeboard volume is provided over a small recreational
pond with a low-level outlet and spillway. The detention pond is sized

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