I’d Rather Have Been Wrong
Fox News 13 reported Plant City faced “unprecedented” flooding due to Hurricane Milton. City Manager Bill McDaniel, in a Facebook live update, stated that over a foot of rain fell during the storm. Many roads became impassable, with water reaching the door level of several vehicles. The heavy rainfall in such a short period often leads to street flooding and significant challenges for low-lying properties, which are abundant in this region. The City of Lakeland reported over 12+ inches of rain during the storm, straining its stormwater systems. While this level of rainfall is impactful on its own, the situation worsens with riverine flooding, where volumes accumulate from across the watershed.
In 2017, this area experienced a similar “outlier” event when Hurricane Irma brought over 11 inches of rain shortly after another tropical system had saturated the ground. In January, hundreds of rural residents from unincorporated Hillsborough and Polk Counties presented images and testimonies of flooding from that storm. Residents opposed a land-use change for a 250-acre parcel located on a critical drainage area along the county line, emptying into Itchepackesassa Creek. Hearings extended late into the night, with a capacity crowd of concerned landowners speaking. Technical concerns were presented by multiple credentialed community members, along with evidence including past engineering studies of the system, historic communication between jurisdictional governments, and opinion statements from a water scientist as well as a PhD level stormwater engineering expert. The project advanced, with one commissioner voting against parts of the application. In the following weeks, the city announced the city manager was empowered to lead a multi-jurisdictional task force to address the issue, especially after seeing the impact along Charlie Taylor Rd on potential future Plant Citians. The city should be commended for committing to tackle a long-standing issue known since the late 1980s it has historically owned. However, the City should reflect on past decisions in this area and assess challenges the Itchepackesassa problem presents to safely executing its master plan.
The Plant City Master Plan includes a village-themed residential community in the northeast quadrant. Much of this land was historically unincorporated Hillsborough County and classified as rural or agricultural due to its low elevation. Several parcels in this area were marked “unsuitable for development” in county maps. What was once 1,008 acres of pastureland north of Knights Griffin Rd and west of Charlie Taylor became “Varrea,” a mixed-use development with over 2,000 residential units, 345,000 square feet of commercial space, and 50,000 square feet of offices. It is one of the largest developments in Plant City, and its first residents moved in by 2023. In January, multiple residents shared accounts of new or significantly amplified flooding following construction of this development. Hurricane Debby brought 7 inches of rain, flooding many adjacent properties. Residents reported abnormally slow drainage and large-scale fish kills in the flooding. Following this event, engineers were dispatched by the developer to investigate their system as well as the flow readings of the Creek. This is just one example where development adversely impacted conditions on surrounding properties, despite best engineering efforts.
Fast forward to Hurricane Milton: Rural residents along Charlie Taylor Rd experienced flooding far worse than during Irma. Homes that previously saw minor yard flooding were inundated. Some are expecting total loss of homes and structures. Even properties not designated as being in flood zones experienced flooding. On the Polk side, conditions were also worse than Irma, with floodwaters estimated to be about 1 foot deeper. While severe, accounts suggest something more drastic changed on the Hillsborough areas of this system. Below is an image of Charlie Taylor and Knights Griffin. Earlier this year Hillsborough County Engineering stated this bridge had never completely flooded over road.
How can engineering fail? System behavior was consistent with what I and countless others argued in January. Overflow conditions for Itchepackesassa system are extreme. During Milton, backflow was observed nearly 4 miles south of Itchepackesassa Creek, along the county line, a major drainage basin shared by several established Polk communities and a future industrial site. Backflow is a condition where waterflow is reversed from its natural flow, in this case moving upstream into “tributaries” such as my community’s drainage system. The creek collects runoff from upstream watershed areas, and drainage competes with runoff from downstream areas. Eventually the water pressure in the main river exceeds the pressure in the tributary, resulting in reverse flow in those elements. The scale of the Itchepackesassa overflow is unimaginable and the area is highly sensitive to topographical changes. Last week several thousand acres became part of Itchepackesassa Creek. Every foot of water on an acre equates to several hundred thousand gallons, and much of the area held multiple feet. Engineering designs are theoretical and rely on a current, accurate model to simulate conditions. This system model is dated and incomplete, making it impossible to confidently simulate conditions reflecting the impact of substantial development in the watershed. There are also serious limitations to cup-for-cup methodology in a floodplain with heavy water movement, as excavation will not always compensate for lost flood storage. Large-scale changes within this “pool” can change flow and displace water to neighboring areas, despite the best efforts of site-level engineering controls. Established communities were constructed several decades ago, built to the elevation standards of that time, much lower than new construction. This concern is frequently expressed in development debates, but it carries a new level of seriousness when properties exist in a shared floodplain with a major stream for flooding.
I hope Plant City succeeds in spear-heading an effort to find an effective risk mitigation solution for the region. Until then, Hillsborough, Polk, and Plant City commissioners must recognize that Itchepackesassa Creek is critical infrastructure to facilitate development in this flood-prone area. It is an understatement to say that we are lacking infrastructure in this system. Authorities evaluating land-use and zoning changes required by development have a fundamental responsibility to demand there be adequate infrastructure to support changes.
Brian Holbrook, MBA, MS