FLOOD06965

• County: Adams
• Community: Northglenn, Thornton
• Stream Name: Grange Hall Creek
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 12/1/1977
• Prepared For: Adams County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
.
I
I
I
I
I
I
t
,
I
I
I
t
I

Upon acceptance of this report by the Urban Drainage and Flood Control District

and the designation and approval of this report by the Colorado Conservation Board, the

areas described as being inundated by the 100-year flood (Intermediate Regional Flood)

can be designated as flood hazard areas and their use regulated accordinagly.

The study was performed in two parts, Phase A and Phase B. The purpose of the

Phase A portion of the study can be summarized as follows:

Perform an in-depth evaluation of the hydrological and hydraulic factors of the

storm drainage for the Grange Hall Creek basin, with primary focus on the major

drainageways and flood plains, such that the current and future problems can be identified

and that a series of drainage improvement alternatives can be developed and compared.

The comparison or rating criteria is based, in part, on cost-benefit aspects, plus legal and

environmental impact considerations. A recommended plan for the major drainageways to

accommodate the storm runoff up to the 100-year recurrence interval values was defined

and presented in the Phase A report.

The Phase A report was submitted to the U.D. and F.C.D. on October II, 1976. The

report was reviewed by the participating entities and a notice to proceed on the Phase B

design of the recommended alternative was received on April 20, 1977.

The purpose of the Phase B portion of the study can be summarized as follows:

Prepare a preliminary design of improvement for the subject drainage courses for

the selected alternative plan. The design shall be of adequate detail to permit U.D. and

F.C.D., Northglenn, Thornton, and Adams County to properly plan bridges and culverts for

new vehicular thoroughfare construction. The plan is also in sufficient detail to permit

the acquisition of needed channel right-of-way and to permit the planning of new

subdivisions and buildings with full knowledge of future channel and flood plain locations

and characteristics. The drawings shall show the plan and profile of the 100-year flood

plain under existing and improved channel conditions for full developed flows, in sufficient

detail to allow administration of the flood plain regulations.

C. Mappinq and Surveys
The contour maps were prepared by Bell Mapping Company under a separate
mapping contract with the U.D. and F.C.D. The maps have been compiled and prepared at
a scale of I" = I 00'. The ground topography in the area along Grange Hall Creek and the
main tributaries to Grange Hall is represented by elevation contours at two foot intervals.
The maps were prepared photogrammetrically from aerial photographs of the area taken
on January 14, 1976. The maps have been prepared using U.S.G.S. elevation datum and
generally portray the actual ground elevation within one foot.
The mapper also obtained digitized cross sections which were used in the delineation
of the flood plain. The Engineer also obtained additional cross sections by use of the
topographic maps. Culverts, irrigation structures, and other facilities located along the
major drainageways in this study were field surveyed by Bell Mapping Company. This field
information was the basis of the hydraulic studies completed for the flood plain
delineation.

Various control points used in the mapping are shown on the maps. No permanent

benchmarks were established in the field for the purpose of future reference.

D. Acknowledqments

The assistance and cooperation of the agencies, organizations and firms listed below

are appreciated and acknowledged.

Urban Drainage and Flood Control District

Adams County

City of Northglenn

City of Thornton

Colorado State Highway Department

Lind Engineering

Bell Mapping Company

4