FLOOD05988

• Designation Number: 311
• County: Arapahoe
• Community: Aurora
• Stream Name: Granby and Sable Drainageways
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Granby and Sable Drainageways
• Date: 9/1/1990
• Designation Date: 1/1/1991
• Floodplain - Doc Type: Floodplain Report/Masterplan

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II. PURPOSE AND SCOPE
This report was prepared to guide City officials in planning
the use and regulation of the 100-year floodplain. The report
includes information on past floods and the nature and extent of
probable future floods along a three mile study reach of Granby
Drainageway and a two mile study reach of Sable Drainageway.
The 100-year flood should be given appropriate consideration
before planning further development in the drainage basin, and
within the floodplain. The report provides a suitable basis for
the adoption of land use controls to guide floodplain management
and m~n~m~ze flood losses. Flood water surface elevations and
floodplain boundaries are often revised by road and bridge

and water surface elevations; 100-year flood water surface
elevation; top width of proposed floodway; floodway width on
left and right side of thalweg; floodway water surface
elevation; and mean velocities of 100-year flood for both
floodplain and floodway.

8.

The determination of a floodway based on an
encroachment which results in a total
elevation increase of no more than one foot.

equal degree of
water surface

construction, floodplain development, flood control improvements,

or natural processes. Prior to uti I ization of this report for

planning or design purposes, the user is advised to contact the

Ci ty, UDFCD, or CWCB to determine if the information in this

report has been amended.

This report was prepared under the current format of

District's Flood Hazard Area Delineation (FHAD) Reports.

the
The

Acknowledgements
This report was prepared by Kiowa Engineering Corporation of
Denver, Colorado, under contract with the UDFCD.-
Topographic mapping and digitized cross sections were
provided by Reids Aerial Mapping of Denver, Colorado. Original
mapp~ng was prepared with two-foot contour intervals at a scale
of I" = 100'. The final mapping will be reduced by 50 percent to
facilitate inclusion in this report.
The mapping was prepared according to the specifications of
the UDFCD, and meets National Map Accuracy Standards. Ground
control surveys for the topographic mapping were performed by BJI
Survey ing, Inc. Aeria 1 photography was prepared by Seha rf &
Associates, Inc., April, 1989.

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scope consists of the following items:

1. A summary of pertinent data or information.

2. Identification of major basin features.

3.

History of
description
or near the

the stream relative to
of various hazards associated
100-year floodplain.

flooding,
with the

and a
areas ~n

4. Hydrologic analysis including rainfall data, drainage basin
parameters, flood flows, and design hydrographs.

5. Hydraulic analysis and summary of hydraulic data.

6. Plan and profile information, including 100-year floodplain
limits, 10- and 100-year flood profiles showing the water
depths relative to the stream bed, typical cross-sections,
locations of all cross-sections utilized in hydraulic
computations, and design flows and velocities at appropriate
locations.

7. Tabulation of flood hazard information for each cross
section including section number; reference stationing;
thalweg elevation; 10-, 50-, 100-, and 500-year discharges

(