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

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GRANGE HALL CREEK MAJOR DRAINAGEWAY PLANNING

SYNOPSIS

drainageways and flood plains. The problem areas and the flood damage potentials in the

basins were then identified. Subsequently, a series of drainage alternatives were

determined and evaluated by a rating criteria, based in part on cost-benefit aspects plus

legal and environmental impact considerations. Finally, an alternative plan for alleviating

the potential flood damages was recommended and presented in the interim Phase A

report. The alternative plan was then reviewed and accepted with certain modifications

by Northglenn, Thornton, and Adams County, and notice to proceed on the Phase B portion

of the analysis was transmitted to Hydro-Triad, Ltd.

The second part of the analysis, Phase B, included performing final hydrologic and

hydraulic studies that were used in the preliminary design of the drainage facilities

required for the selected alternative. Preliminary design drawings were then prepared on

plan and profile mylar, presenting the selected alternative and the flood plain information

for existing channel conditions. A detailed cost estimate was prepared and the

benefit/cost comparison was made. A final report was then prepared in one volume

containing the narrative description and the plan and profi Ie drawings showing the

improvements reduced to the II" x 17" report size.

The alternative plan chosen for each reach for Grange Hall Creek and the North,

Northeast, South, and Southeast tributaries to Grange Hall Creek is identified in the

following table:

This report presents the results of the detailed hydrologic, hydraulic and design
analysis for the Grange Hall Creek Major Drainageway Planning Study as performed by
Hydro- Triad, Ltd. under contract with the Urban Drainage and Flood Control District
(U.D. and F.C.D) Sponsoring governmental agencies in addition to the U.D. and F.C.D.
are Adams County and the cities of Thornton and Northglenn.
Copies of this report are available for reference and purchase at the office of U.D.
and F.C.D. Copies of the Phase A portion of the study, as well as technical addenda to

the reports, also are available for review at the U.D. and F.C.D. office.

The Grange Hall Creek basin lies within the northern portion of the Denver

Metropolitan area and is a west bank tributary of the South Platte River. At the present

time II percent of the basin is within Adams County, 36 percent within the City of

Thornton, and 49 percent within the City of Northglenn. The remaining 4 percent is

within Federal Heights and Westminster.

The major drainageway storm runoff problems in the basin are due primarily to the

construction of various facilities such as streets, railroads, buildings and houses

concomitant with the urbanization of the area.
The natural flood plain has been changed and modified, particularly in the upper
reaches of Grange Hall Creek and the main tributaries, due to urbanization and the

construction of storm sewers.
The analysis waS performed in two parts. The Phase A study evaluated the

hydroloqical and hydraulic aspects of the drainage basins with primary focus on the major