FLOOD09085

• Designation Number: 97
• County: Adams
• Community: Thornton
• Stream Name: Grange Hall Creek
• Basin: South Platte
• Title: Major Drainageway Planning - Grange Hall Creek, Phase B, Thornton, Adams County
• Date: 12/1/1977
• Designation Date: 1/19/1978
• Floodplain - Doc Type: Floodplain Report/Masterplan

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INFLATED CONSTRUCTION COSTS*
(Present Worth -- Thousand of Dollars)
Year Adams County Northglenn Thornton
1977 8.1 1101.8 635.3
1978 8.7 1189.9 686.1
1979 9.4 1285.1 741.0
1980 10.2 1388.0 800.3
1981 11.0 1499.0 864.3
1982 11.9 1618.9 933.5
*Does not include Fiscal and Admin. Costs and Operation and Maintenance Costs.

CHAPTER V
CONCLUSIONS AND RECOMMENDATIONS

As can be seen from the table, significant increases in improvement costs can occur.

Hawever, the net benefits derived from the improvements should remain approximately

the same since damage costs (benefits) would also increase at the same inflationary rate.

The purpose of the Major Drainageway Planning Study for Grange Hall Creek basin

and its main tributaries was to delineate the drainage problems of the basins, evaluate

several solutions to the problems, determine the best alternative plan by economic, legal,

and environmental criteria, and prepare preliminary design drawings for the selected

alternative plan so that flood plain regulations may be administered and planning for

future development call be accomplished. The results and conclusions of the study are:

A. Selected Alternative

The recommendations for improvements jn the Phase-A study were reviewed by
Adams County, Northglenn, Thornton, and the Urban Drainage and Flood Control District
and the accepted plan for each reach was identified. There were several reaches where

the selected alternative indicated more improvements than were originally recommended

ill the Phase A study. One notable example is the draillage improvements in Reach 8G on

Grange Hall Creek hetween Grant Drive and Washington Street. For this reason and due

to increased costs due to inflation, some of the improvement costs by reach are higher in

the Phase B study than in the Phase A study.

B. Master Plan Drawings

Master plan drawings were prepared on mylar plan and profile sheets at a horizontal

scale of I" = I 00' and a vertical scale of I" = I 0'. The drawings are presented in the

appendix of this report at a reduced scale. The plans present the I DO-year flood plain for

existing and improved channel conditions for the runoff from a totally developed basin

based on future land use. The drainage facilities required for the selected alternative are

depicted on the drawings with detai Is of the improvements shown at larger scales.

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