FLOOD08330

• County: Gilpin
• Community: Central City
• Stream Name: Gregory Gulch, Nevada Gulch
• Basin: South Platte
• Title: Flood Hazard Identification Report - Gregory Eureka Gulch and Nevada Gulch
• Date: 2/1/1987
• Prepared For: Central City
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
!I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

STUDY AREA DESCRIPTION

Drainage Basin Characteristics

Gregory Gulch and Nevada Gulch both flow through Central City
part 1y in channels and part 1y in underground cu1 verts (in the downtown
area). Headwaters of both Gregory and Nevada Gulches begin on the same
sma~l mountain (Bald Mountain) with the peak at elevation 9994 feet above
mean sea 1 eve 1 .

Elevation of Gregory Gulch at the downstream corporate limit of
Central City is at 8150 feet. Gregory Gulch heads easterly for its
entire length with only minor tributaries. The hydraulic length of the
gulch is approximately 3.7 miles. The drainage area of Gregory Gulch to
Central City's downstream corporate limit is 3.4 square miles; to just
above its confluence with Nevada Gulch the drainage area is 1.9 square
miles. (See Basin Map, Plate 1).

E 1 evat ion of Nevada Gu 1 ch at its confl uence with Gregory Gu 1ch
(just downstream from Spring St. in the center of town) is at 8410 feet.
Nevada Gu 1 ch heads easter 1y unt i1 it reaches town; then it heads in a
northerly direction. The hydraulic length of the gulch is approximately
2.6 miles. The drainage area of Nevada Gulch to its confluence with
Gregory Gulch is 1.1 square miles.

Study Reach Description

The study reach a long Gregory Gulch extends the entire corporate
limit of Central City. Technically this gulch is named Eureka Gulch
upstream from station 55+42 (upstream from its confluence with Nevada
Gulch); however for simplicity of discussion the entire reach will be
referred to as Gregory Gulch. The study reach covers a length of 1.6
miles. There is extensive development directly over the gulch's culverts
in town.

The study reach along Nevada Gulch is only the 1000 feet upstream
from its confluence with Gregory Gulch. This study reach covers the
downtown area only.

The study reaches were included in the Federal Insurance
Administration's Flood Hazard Boundary Map (FHBM) for Central City
(Community No. 080077, map effective August 30, 1974). The FHBM, derived
using approximate methods, is shown in Exhibit 2. Central City entered
the regular phase of the National Flood Insurance Program (NFIP) with
this map on January 23, 1986. This floodplain study is being performed
using detailed methods that gives the town a more accurate map of
flooding limits that includes flood elevations. Central City could
appeal to the Federal Emergency Management Agency (administrators of the
NFIP) with this report and its maps requesting that they become the
official floodplain maps (once converted to proper format by FEMA).

3