FLOOD02983

• County: Arapahoe
• Community: Littleton
• Stream Name: Lee Gulch, Little Creek
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 9/1/1978
• Prepared For: Littleton
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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IV. HYDRAULICS

V. SELECTED ALTERNATIVES

The hydrological data was used to determine the 100-year water surface

profile for the 100-year storm for both the existing channel conditions and

the proposed flood control improvements. Cross sections of the existing

channel were taken and digitized by Bell Mapping Co. and these were modified

where channel improvements were proposed. These cross sections were used in

the computer program developed by the Corps of Engineers Hydrological En-

gineering Center and known as REC-II to define the flood profiles. Crossing

structures, both existing and proposed, were rated by hand. Manning's n

values used in this study varied from 0.023 to 0.035 for the channels and

0.035 to 0.10 for the overbanks.

The computed flood profile elevations are plotted on the Major Drainageway

Planning Plan and Profile sheets for both existing channel conditions and

for proposed improvements. All cross section information is presented looking

upstream.

ALTERNATIVES STUDIED

There were nine basic alternatives that were considered as viable pos-

sibilities for flood control improvements in the study area. These ranged

from flood plain zoning of the existing flood plain (the "do-nothing"

alternative) to installation of major conduits along the drainageway.

These alternatives were considered both singly and in combination within

reaches of the drainageways. Lee Gulch was divided into three reaches and

Little Creek into six reaches for evaluation of the basic alternatives.

These reaches were determined on the basis of similar improvement possibili-

ties, hydrological sub-basins, land use similarity, and political boundaries.

The alternatives were screened for each reach and only the most promising

selected for further evaluation. The alternates considered and the results

of the screening process are summarized in Figure 11.

A benefit-cost analysis of the alternative solutions selected during

the alternate screening phase was performed. Table III summarizes the costs

and benefits which were determined during the Phase A study of Lee Gulch and

Little Creek on a reach by reach basis.

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