Panama City Beach, Florida, purchases all of its potable water from Bay County. It's received through two delivery points, West Bay and Hathaway Bridge. Near each of these points, the city operates a large storage and pump station (West Bay and McElvey) with the ability to convey water to the east and west side of the city. When Hathaway Bridge was constructed in 2003 to replace the Saint Andrews Bay Bridge, a 24-inch ductile iron pipe was constructed and supported within the bridge spans. In early 2018, a water leak developed in the 24-inch ductile iron transmission main near the east end of the bridge, which raised concerns for both Bay County and Panama City Beach. As a result, under an emergency work order, Bay County contracted with Dewberry and Marshall Brothers Construction to evaluate feasible alternatives to construct a temporary bypass transmission water main that would allow Bay County to evaluate the extent of the water leak and alternatives for repairs, while at the same time provide a back-up water supply.

Creating a Specialized, Above-Ground Solution

As part of a design-build team, we designed the temporary bypass line to convey peak water demand to the Panama City Beach McElvey storage pump station, evaluated various pipe materials for construction, and developed construction drawings. The proposed alignment for the temporary bypass transmission main included approximately 6,000 feet of water main with a portion of the water line to be buried, but the majority of the pipe to be laid on top of the concrete sidewalk and pedestrian bridge deck along the bridge span. Pipe expansion joints were also incorporated near the bridge expansion joints.

We used Water Cad Model Software to evaluate the maximum flow required to maintain proper water storage at the McElvey storage tank farm. With the use of the model, we determined that with a flow of seven million gallons per day (MGD), the water level in the tanks remained within its minimum and maximum operating range. Therefore, a 16-inch diameter pipe was selected, which provided a maximum velocity of approximately 7.2 feet per second.

Certa-lok Yelomine PVC, AWWA C900 PVC, and ductile iron pipe were evaluated. Because of its ability to be disassembled, reassembled, and used on other temporary projects, we ultimately selected ductile iron pipe and mechanically restrained each pipe joint. The proposed 16-inch water transmission main was connected to the existing 24-inch water main at each end of the bridge, using a 24-inch tapping saddle and valve. The 16-inch diameter ductile iron pipe was cradled along the bridge deck with six- by six-inch treated lumber. Pipe clamps were installed at each pipe support to minimize longitudinal movement. Jersey barriers were also used at each bend to resist thrust forces.

Meeting a Tight Schedule

Our team—Cliff Wilson, Alex Rouchaleau, Steven Ray, and myself—was able to perform all of the above tasks and develop final construction drawings within 14 days from the time we were given a notice to proceed. Marshall Brothers Construction was then able to use the construction drawings and complete the temporary bypass 16-inch water transmission main within 30 calendar days, including pressure and disinfection testing. The temporary 16-inch transmission water main has been in operation for more than four months and is currently in operation in parallel with the existing 24-inch transmission main. The temporary 16-inch transmission main is expected to remain in service until early 2019, when a more permanent solution will be designed and built.

As the project continues to unfold, we'll expand on this project and the ultimate, permanent fix.