Alline Avenue features a brick street with large yards and stately live oaks.
Residents surrounding Alline Avenue in Tampa, Florida, enjoy large yards, tasteful landscaping, historic homes, and proximity to Hillsborough Bay. What they don’t enjoy is flooding.
Several times each year, rain events, combined with high tide surges from the bay and exacerbated by the area's low elevation, cause salt-laden water to flow into the brick street and landscaped lawns. The water often stands for extended periods of time, creating driving hazards and damaging the landscaping.
Rain events, combined with high tide surges from nearby Hillsborough Bay, can flood the area's outdated stormwater system very quickly. Photo courtesy of City of Tampa
The City of Tampa is addressing the situation by building a stormwater pumping station on Alline Avenue. The objective is to alleviate the street flooding and function as a quiet neighbor that blends in with the community. The residents, reports Al Hoel, PE, design division head of Tampa's Stormwater Division of the Department of Public Works, are "thrilled."
The Right Property at the Right Time
The City knew that a pumping solution was required to solve the flooding situation in the Alline Avenue area, but pumping stations are typically industrial buildings that do not blend well with a tight community of single-family homes. In 2007, the City got lucky, says Hoel. The property with the lowest elevation within the bowl-shaped area came up for sale.
The City of Tampa bought this property in 2007 as the site for the Alline Avenue stormwater pumping station. The property is situated at the lowest elevation—four feet—on the street, making it an ideal spot for the new facility.
"An in-house engineering analysis was performed, which included peak flow rate determination, preliminary pump selection and strategy, emergency generator sizing, and control building space requirements. Based on this analysis, the City went ahead and purchased this property," says Hoel. "We then hired an architect to conceptualize the control building. This is a nice residential neighborhood, so [the building] had to blend in as opposed to looking like most pump stations, typically an industrial building."
The resulting concept was a control building designed to look like a single-family home. The design and cost estimate were presented to the City administration, which approved the project to move ahead in 2011. At the City-led public meetings, residents heartily embraced the improvements, which led to a successful rezoning of the property.
A Pumping Station That’s a Good Neighbor
Once the initial concepts were approved, McKim & Creed led the team of Greeley and Hansen, Applied Sciences and Tagliarini Architectural Group (TAG) and worked with the City to study drainage conditions and prepare a Basis of Design Report. In the report, modeling results were presented, as well as the design concepts for an upgraded collection system and the basic design for the pumping station.
The team modeled three different stormwater conditions to determine the necessary improvements. After examining the modeling scenarios, the City opted to replace an existing 27-inch elliptical culvert with a 36-inch equivalent and build a pumping station that provides a capacity of 54 cubic feet per second (cfs).
The City of Tampa bought this property in 2007 as the site for the Alline Avenue stormwater pumping station. The property is situated at the lowest elevation—four feet—on the street, making it an ideal spot for the new facility.
A new gravity stormwater system will replace a portion of the old pipes that were constructed in the 1920s. A triplex pump station with two operating and one rotating standby submersible 90-hp pumps will provide the capacity, and a 36-inch stormwater force main will be installed to the existing seawall via direct bury.
The design team planned and designed the Alline Avenue stormwater pumping station.
Variable frequency drives will minimize pump starts by matching flow within the pump/drive capability, and a 250 KW standby generator will supply power for the pumping equipment during a power loss.
Two nutrient separator baffle boxes, upstream of the station bar screen, will reduce pollutants and debris entering Hillsborough Bay, providing a Best Management Practice (BMP) solution.
“An energy dissipation box installed at the bay will reduce velocities to below two feet per second and, coupled with gates over the outfall to prevent entrance by manatees, will help protect aquatic life,” says Matt Love, PE, project manager with McKim & Creed.
The control building is a two and a half-story “house” that encloses and protects pump station equipment capable of moving approximately 35 million gallons per day (mgd) of stormwater flow. Because of the building’s proximity to residences, the design incorporates several noise-reducing elements, including sound-attenuating concrete block construction, false windows to prevent the escape of noise, heavy-duty gasketed doors, a false chimney to direct sound upward from the generator motor exhaust, and acoustic curtain material in the generator room.
Completion Set for 2012
The existing stormwater system discharges into Hillsborough Bay, which is adjacent to Alline Avenue. In conjunction with the new Alline Avenue stormwater pumping station, an energy dissipation box will be installed to reduce stormwater velocities to below 2 feet per second into the bay. This will help protect the bay’s aquatic life.
The City plans to begin construction of the $6.2 million facility in August 2011, with completion scheduled for August 2012. “The neighbors love us coming in and doing this,” says Hoel. “We anticipate getting excellent bids. We couldn’t be doing this at a better time.”