1997-05-28_REVISION - M1981302 ‎(4)‎

• Permit No: M1981302
• IBM Index Class Name: Revision
• Doc Date: 5/28/1997
• Doc Name: TR-06 MODIFICATION OF BERM WESTERN MOBILE DEEPE PIT FN M-81-302
• From: DMG
• To: HART ENVIRONMENTAL
• Type & Sequence: TR6
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
of
Department of Natural Resources
1313 Sherman St., Room 215 Ily`
Denver,Colorado 80203 IIr
Phhonon e:(303)8fi6-6-3567
FAX:[phone]
DEPARTMENT OF
NATURAL
RESOURCES
DATE: May 26 , 1997 Roy Romer
y Governor
James S.Lochhead
TO: File No. M-81-302 Executive Director
Michael B.Long
FROM• Allen Sorenson Division Director
RE: Guidelines for Floodplain Evaluation
TECHNICAL GUIDELINES
The stream channel and floodplain are both integral parts of the
natural conveyance of a stream. The floodplain carries flow in
excess of the channel capacity and the greater the discharge, the
further the extent of flow over the floodplain.
The first step in any floodplain analysis is to collect data,
including topographic maps, flood flow data from nearby gauging
stations, and surveyed cross sections and channel roughness
estimates at a number of points along the stream.
It is my understanding that there is an accepted flood discharge
for the 100-year flood on So. Boulder Creek, so the next step is to
determine the profile of water surface elevation along the channel .
This analysis can be carried out assuming steady, gradually-varied,
nonuniform flow using a one-dimensional model such as HEC-2 (U.S .
Army Corps of Engineers, 1982) .
After the water surface elevations have been determined, the area
covered by the floodplain is delineated. The lateral extent of the
floodplain is determined by finding ground points on both sides of
the stream that correspond to the flood profile (water surface)
elevations . Ground elevations in the floodplain are determined
from topographic maps; the floodplain is determined by following
the contour line that corresponds to the flood profile elevation
for a particular area . The floodplain delineation is only as
accurate as the topographic maps used, so some verification through
field survey is advisable .
REGULATORY ASPECTS
In order to provide a standard national procedure, the 100-year
flood has been adopted by FEMA as the base flood for purposes of