The City of Edmond requested the services of Cabbiness Engineering to provide a detailed engineering feasibility study to replace the existing bridge over Opossum Creek at East Coffee Creek Road, just west of North Anderson Road.

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The dilapidated condition of the existing bridge and all of the sub-structure deterioration did not lend itself to the option of rehabilitation. It was not an option to completely replace this structure with a conventional single span, concrete bridge from a financial point or a constructability stand point if the City of Edmond or Oklahoma County forces and equipment were to be used. Thus, the Cabbiness team investigated two (2) separate design alternatives that would meet the following design and constructability criteria:

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1. Must not have any adverse impact to the FEMA floodplain and floodway for both the water surface elevation and footprint width.

2. Must have approximately the same channel flow conveyance for the more frequent rainfall events (approximately the 2, 5 and 10-year storms).

3. Must have the flexibility to be constructed with the City of Edmond and/or Oklahoma County forces and equipment.

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Both design alternatives - a 32-feet wide by 12-feet high aluminum metal arch box-type culvert and the use of multiple, large diameter pipes to replace the bridge - were costly but could have been installed by City and County forces and their equipment. The construction installation costs were included in the estimates to show the anticipated level of effort that would be required for both designs. As expected, installation of the aluminum arch design alternative was more than double that of the multiple pipe design. The overall difference between the aluminum arch construction cost and the multiple pipe alternative was $106,087.50 or 25.8% more.

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So, in conclusion, both design alternatives were feasible from:

• An engineering stand point where hydraulic modeling shows no loss in channel flow conveyance with frequent (2, 5 and 10 year) rainfall events.

• No adverse impact to the FEMA flood elevations or flood plain for the base flood frequency (100 year storm event).

• Can be constructed with City and/or County forces and equipment.