Tampa finally has come up with a formula to pay for much-needed improvements in storm drainage — one that is based, in part, on what portion of a property has been paved over. The new formula is rooted in reality: A typical city block — covered by sidewalks and driveways, parking lots and roofs — generates five times more runoff than a forested area of the same size, according to a study cited by West Virginia University.
In big ways and small, Tampa and its property owners can do more to stop adding to the expanse of ground we've already sealed over — and maybe even begin to reduce it.
Taking steps now might head off draconian measures later, like those the federal government has forced on Baltimore to protect the waters of Chesapeake Bay. The city, nearly half paved, is racing to pull up thousands of acres of pavement by December 2018, The Baltimore Sun reports.
The Tampa Bay area faces the same threat from the development all around it.
Street flooding that cuts off parts of the city during even typical rainfall, let alone the deluge Hurricane Hermine brought, is the major driver of the City Council's move to improve drainage. But the more devastating, long-term threat comes from the pollution that pours into the bay with each drop of rainwater sliding down dirty asphalt and concrete.
Capturing rain where it falls turns it from a liability to an asset. This can happen through engineering that's both passive and active — designing development to maximize natural surfaces or installing permeable cover, for example, and using dry wells or other means to send rainfall underground where it can filter and percolate into an aquifer that could use it.
Homeowners can swap concrete or asphalt slabs for paving stones or bricks, maybe alternating them with turf in a checkerboard pattern. Yanking out the middle of the concrete driveway allows for more percolation, too; two strips of pavement is all the tires need. For the truly ambitious, installing a French drain or grate at the bottom of the driveway keeps rainfall from running down the dirty street into storm drains and the bay.
Much cheaper than a French drain is good gutter management. A 1,000-square-foot roof can produce more than 600 gallons of runoff for every inch of rain that hits it, by some measures. Add an extension and point downspouts toward the yard rather than the street — or install a rain barrel or cistern to make use of the runoff later on the permeable landscape.
That said, low lying areas of South Tampa and other parts of the region were flooding to the point of submersion long before the earliest settlers laid down the first impermeable foundation. And all the barrels in Florida wouldn't slow the flow from rains falling as quick and heavy as Hermine's.
Like all coastal areas, we must learn to live with flooding.
Still, by our actions, we can reduce that portion of the flow that results from development. And we can make a big dent in how much it carries in the form of pesticides, fertilizer and plain old street trash.
The city's new storm drainage assessment — approved, coincidentally, as Hermine raged — factors in how much of a parcel is covered as well as its overall size. For the owner of a medium-sized home, the assessment starts at $45 per year and rises over five years to $89.
Like last summer, when the council backed away from imposing the full fee, this one has drawn opposition over its formula. Poor people still are paying too much, some have said, while others insist that property owners who try to capture their own runoff deserve an even bigger break.
Both arguments have merit. And, as Tampa Bay Times staff writer Richard Danielson has reported, the city staff is working on ways to address them.
But this community problem requires a communitywide solution. Even those who reduce their runoff to zero, if that were possible, still should pay a share toward the city's 30-year, $251 million program. Plans call for an estimated 150 neighborhood-scale drainage projects and five major projects designed to move water quickly out of larger basins.
Meantime, the more we move toward zero as individuals, the greater the chance this fix still will be taking care of our needs when the 30 years is up.