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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I engineers. planners . surveyors

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May 16, 1991

Mr. Brian R. Hyde
Senior Water Resource Specialist
Flood Control and Floodplain Management
COLORADO WATER CONSERVATION BOARD
721 Centennial Building
1313 Sherman Street
Denver, Colorado 80203

Section

RE:

Central City
RMC Reference No. 1671.001.00

Dear Brian:

We appreciate recelvlng
floodplain information.
for which we would like

a copy of the CWCB's rules and regulations regarding
Having perused through it, two (2) issues were found
to request a variance.

The first issue is concerning Rule 5-A-3, Ground Control. The elevation
information used in RMC's feasibility study and LOMR Study was the 2' contour
mapping performed by Ray and Associates in July of 1975, which is based on
U.S.G.S. datum. Additionally, CWCB surveyed several bridges and critical
sections which were slightly adjusted to match the 2' contour map upon which
flood areas would be delineated.

Accuracy of the vertical and horizontal ground control, which was performed by
others, is unknown. However, inasmuch as all vertical and horizontal
information was derived from or adjusted to the map, and floodplain
information is placed on the same map from which the floodplain ordinance will
be administered, and having determined in the field by observation the
relative accuracy of the map, we request acceptance of the ground control as
submitted.

The second issue relates to Rule 5-A-6, or spot elevations. These can be
extremely helpful, and even necessary in many locations to help determine flow
patterns. They were not available nor obtained because they were felt
unnecessary for this study. Central City gulches, channels, flumes, streets,
and parking lots all have grades of at least 5%, and are generally in the
range of 7%-11%. Flow patterns are readily observed as a result. Approval of
the study without the aid of spot elevations is requested.

It appears from reading the literature and our discussion clarifying several
rules that our study conforms to all other rules and regulations required by
CWCB.

I Rocky Mountain Consultants, Inc.
8301 East Prentice Avenue No 101, Englewood, CO 80111 [phone]
Offices also In Longmont . Boulder. and Estes Park, CO

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