Stormwater | Project Profile

The Bayside Bridge is not only an important arterial roadway that parallels US 19 and connects Largo to Clearwater, FL, but it also spans a sensitive Florida waterway. As part of its ongoing maintenance activities, the Environmental Division of Pinellas County Public Works Department set out to rehabilitate the existing stormwater pond that provides water-quality treatment to the bridge's north end.

"We were having two specific problems with the stormwater pond," explains Mike Maroney, P.E., senior engineer for the Surface Water Division of Pinellas County Public Works. "First off, the current system was providing treatment but not at the level we would like; it was Œshort circuiting' and sending water back into Old Tampa Bay sooner than we'd like. Second, trash and sediment were washing off the bridge, collecting along the side, and eventually going into the retention pond, filling it up. As Old Tampa Bay is a Designated Aquatic Habitat and an Outstanding Florida Water, it's supposed to have the highest level of treatment possible."

Left: Runoff from the Bayside Bridge in Pinellas County, Fl, collects in a retention pond before eventually flowing into Old Tampa Bay. Right: Debris from the bridge collects inside a separation chamber that was installed to rehabilitate the pond.

Pinellas County considered its options. "Large fiberglass pipes under the bridge take the stormwater, but once a large treatment volume came in, it was going right into Old Tampa Bay," Maroney continues. "We looked at different alternatives, but there was nowhere to expand the pond, and we couldn't put a treatment plant on the bridge. We also needed to keep stormwater off the bridge; we didn't want hydroplaning cars."

The county installed a stormwater treatment device designed by CDS Technologies that uses continuous deflective separation. "We've used other such units down here, and they work well," Maroney says. "We don't use a lot of CDS units, but probably more than other areas of the state."

One of CDS's engineers, David Ziegler, P.E., met with county staff on-site to discuss design-related issues and fully understand the county's project objectives. After that meeting, the design phase of the project was initiated; the county's staff supplied available design information from their files, which included preliminary pond reconstruction plans, survey data, and study reports.

CDS engineers reviewed these documents to extract the pertinent site-specific data needed to design the device. The initial task: evaluating the application's hydrology to identify the device that would treat the 13 acres of bridge deck. As more than one CDS device is often feasible for an application, CDS presented relevant information on several of its devices to the county (unit specifications, template drawings, budgetary information) to aid in its decision. After considering the all the options, Pinellas County selected the CDS PSW70_70, which has a rated treatment capacity of 26 cubic feet per second. The device was selected based on its ability to treat the first inch and a half of runoff, which mimics the level of service provided by the stormwater pond. Once the device was chosen, CDS engineers prepared final design and drawings within a day or two.

As the project neared construction, CDS engineers coordinated closely with the county to assist with the preparation of the final bid documents. During construction, CDS coordinated with the successful contractor, Keystone Excavating Inc., to have a representative available on-site while the device was being installed. This onsite guidance not only ensured that the device was installed properly but also provided immediate feedback to any questions the contractor might encounter to help minimize the potential for construction delays. Installation of the device began March 30, and the majority of the work was completed that day. In subsequent days, pipe connections were made and field-cast concrete work completed by the contractor.

The overall project is still under way. Maroney outlines some of the problems Pinellas County faces: "This is the most highly-developed county in Florida, even more than the Miami area. The area has a relatively high water table, and, with all the construction that took place in the 1960s and '70s, when there were no retention ponds required, a lot of the county is covered with impervious pavement. We have a lot of streams and creeks which are now eroding, then depositing sediment into the bay."

Pinellas County received state funding assistance for the Bayside Bridge project.

"Florida has five water-management districts, and ours, Southwest Florida Water Management Department, gave us funding. It assists us with most of our stormwater projects, and we get 50% funding if the project has something to do with water quality.

"We're very proud of our surface-water program, and we should be," Maroney concludes. "However, we're always fighting projects built in the '60s and '70s, when the goal was to get the water to the Gulf ASAP! Who knew about environmental impacts then?"

SW November/December 2004

Home + About + Subscribe + News + Calendar + Glossary
Talk + Images + Advertise + Contact Us + Search + Email + Services