BRADENTON -- Stormwater runoff projections have come a long way since the 1973 construction of the Desoto Square mall parking lot inadvertently caused flooding in a historic Ware's Creek neighborhood by sending too much overflow into Ware's Creek headwaters.
Engineers have a much better handle today on runoff from a large-scale development, but Bradenton officials still must consider water quality and quantity as stormwater traverses the city drainage system.
The city is now using a $349,500 matching grant from the Southwest Florida Water Management District to develop a stormwater model to address several issues citywide.
"It's something we've been working on for several years and we submitted the application about a year ago," said Public Works Director Claude Tankersley. "What the model will do is allow us to have a better understanding of how the entire stormwater system works throughout the city."
Tankersley said once the 2-year project is complete, the model will address water quantity and quality "to better understand how we can control anything that might be discharging from our system into local rivers and bays."
Retention ponds have successfully filtered stormwater before it reaches local bodies of water, but older areas of the city were built well before retention pond tech
nology came into play and stormwater still flows directly into other bodies of water. Tankersley said the model won't eliminate the need for existing retention ponds, but can create an environment where future retention ponds, which are expensive and take property out of development, won't be needed.
"Retention ponds have been a great and traditional way to treat stormwater for the last 25 years," said Tankersley. "But looking at older parts of the city and downtown as an example, we can't build a retention pond in the middle of downtown. New techniques are being developed using smaller facilities and sometimes it's just a manhole using baffles that would allow for the collection of trash and we come along later and clean it all up so it's not getting into the stormwater system."
Tankersley said that's one small example of a broader model where: "We can make sure that once the rainwater reaches the rivers and bays that we have done our job and been good stewards."
Tankersley said the city is in good shape in addressing flooding.
"But because our system is so integrated, just like our streets are on a grid system, sometimes we may experience localized flooding on a street, but the cause of that flooding may be four or five blocks over. We wouldn't know that without modeling the whole system," he said.
The city uses a similar method on a much smaller scale for localized projects. Tankersley cited the $370,000 10th Street West drainage project -- completed Thursday ahead of schedule and $30,000 under budget -- as an example.
"We created a smaller model with the 10th Street project than what we are proposing now," he said. "That model looked at all the pipes in that specific area, whether the stormwater was going to Ware's Creek or Manatee River, and looked at any restrictions that were causing the flooding in the first place. If we are reducing flooding in one area, we want to make sure we aren't transferring the flooding down the street, so it will be nice to have one model available for every project we do."
Jim McLellan, city engineering section manager, said the 2-year $699,000 citywide drainage model project will "define our problem areas and create possible solutions. Basically, the model that is developed also will mean that anyone who develops property in the city will have to use that model to ensure that future development will not create regional flooding problems."
Tankersley also said developers will be required to use the finished model in site plans to show the city how their developments will affect stormwater flow at their project sites and throughout the city.
The Southwest Florida Water Management District will fund half of the model development with the city portion coming from stormwater utility fees.
Tankersley said the city will be reimbursed when the project is complete. To help with the model and pinpoint problem areas, public works is asking citizens experiencing localized flooding to call 941-708-6300, ext. 222.
Mark Young, Herald urban affairs reporter, can be reached at 941-745-7041 or follow him on Twitter @urbanmark2014.