FLOOD07680

• County: Logan
• Community: Sterling
• Basin: South Platte
• Title: Cost Proposal and Oral Presentation - Sterling
• Date: 12/4/1995
• Prepared For: CWCB
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Miscellaneous

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3) Where improvements are necessary to nummlZe severe flooding problems along said
drainageways, modify HEC-2 analysis to match the preliminary design of said improvement
as prepared for this study and prepare resulting residual floodplain delineations.

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b. Existing Outfall Systems Capacity: The capacity of the existing outfall systems for Sand
Creek, Pawnee Creek, and Pioneer Ditch System will be evaluated utilizing applicable hydraulic
analysis methodology.

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I) Analyze, prepare and verify hydraulic parameters for all outfall facilities identified during
the field investigations as well as from the topographic mapping (i.e. street hydraulics)

2) Verify said facilities and parameters with the City/CWCB.

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3) Prepare hydraulic analysis of said facilities (i.e. physical capacity, culvert headwater depths,
detention facilities storage and flow capacities, etc.)

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4) Provide capacity analysis to the City/CWCB for review and comment.

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c. Alternatives Hydraulics: Initial comparative hydraulic analysis will be performed on all
alternative outfall systems for facility sizing and feasibility checking. WRC has found that a
detailed hydraulic analysis of the alternative systems is not necessary to fully evaluate the
comparable benefits and costs of said systems since intangible items will control the alternative
selection where cost differences are small.

7. EXISTING PROBLEMS IDENTIFICATION/VERIFICATION

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a. Obtain input from CWCB, City staff, citizens and others who have observed flooding problems
in the study area.

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b. Review results of the hydraulic analyses for existing conditions and identify capacities and
inefficiencies of the existing drainage conveyance systems.

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c. Determine areas of drainage system where there is additional available capacity or lack of
capacity to convey existing and future design flows.

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d. Compare empirical data with reported problem areas to determine perceived and real drainage
problems.

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e. Prioritize problem areas based upon assessment of potential damage to property, effect on
percentage of population, emergency vehicle access, approximate improvement cost versus
benefits (cost effectiveness) and citizen reaction.

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8, ALTERNATIVE EVALUATIONS

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Alternative Evaluations is a very critical and important phase of the development of the work. The
results of this effort essentially determines the direction of the improvements for the next several
years.

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The WRC approach to this work will be to involve all professional staff members in informal work
sessions to assist in the development of creative solutions. Techniques that will be considered for
improving and controlling of drainage patterns include construction of outfall systems, interception
and diversion of runoff, replacement of deteriorating or undersized existing facilities, introducing
properly sized new infrastructure and stormwater detention facilities. In addition to these structural
solutions, non-structural alternatives such as regular maintenance and repair programs will also be
evaluated.

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CITY OF STERLINGlC" CIl 5 WRC ENGINEERING, INC.

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