St. Pete Prepares with a New Stormwater Master Plan
We are now well into the 2023 hurricane season, though St. Petersburg thankfully has not seen a direct hit since 1921. Known as the Tarpon Springs Hurricane, the 1921 hurricane was a Category 4 while over the Gulf, with winds declining to a Category 3 by landfall. A six-to-eleven-foot storm surge flooded low-lying areas throughout Pinellas County, including St. Petersburg. Since then, there have been many near misses, two of the most recent being Hurricane Irma in 2017 and Hurricane Ian just last year. Irma, a Category 5 over water, brushed St. Petersburg with a negative surge that emptied the bay. Ian did the same.
St. Pete continues to “get lucky” by avoiding a direct hit, but that’s only part of the threat. Not only does our city need to plan for more frequent and stronger storms, but we also need to review how we deal with more intense rainfall and sea-level rise due significantly to global warming. In 2017 Hurricane Harvey dumped more than 40 inches of rain over Houston and eastern Texas, with peak accumulations of nearly 61 inches in one area. Rainfall generally is becoming more intense, including flash floods. Recently nearly 26 inches of rain fell on Ft. Lauderdale over 12 hours.
As the atmosphere warms, there is increased evaporation and more water generated when it rains, causing more intense rainfall and related flooding. A 2022 study by Ryan Harp of Northwestern University and others has documented that for 17 climate regions in the United States, rainfall generally has become more intense over a 30-year period. For the eastern United States, including Central Florida and Tampa Bay, researchers documented a 4.5% to 5.7% increase in average daily rainfall.
Parts of Tampa Bay have witnessed record-breaking temperatures in the past few years. In the case of our cross-the-bay neighbor, Tampa experienced nine out of ten of its warmest years in the past decade. Climate Check, a real estate climate risk assessment research group, notes that in a typical year between 1985-2005, St. Petersburg experienced about seven days above 93.4ºF in a year. They predict that by 2050, St. Petersburg is likely to experience an average of approximately 80 days per year over 93.4ºF. The Gulf of Mexico warmed by 0.6F between 1982 and 2006. As water warms it expands, contributing to sea level rise. Studies by climate scientists at the Universities of Arizona and Tulane report that from 2010 to 2022 Gulf of Mexico sea levels rose nearly five inches, twice as fast as previously predicted.
In 2015 and again in 2016 St. Petersburg experienced several days of record-breaking rainfall. This overwhelmed the city’s wastewater collection system and resulted in discharge of millions of gallons of wastewater and effluent into the bay and other areas. Subsequently, the state Department of Environmental Protection issued a “consent order” mandating overhaul of the city’s wastewater system and levying an $810,000 fine. In addition to the state consent order three environmental non-profits successfully sued the city in federal court seeking more stringent corrective actions than those contained in the state order.
Following the major rain events of 2015-2016 the city committed to allocate $326 million to improve its sewage system and has since spent approximately $16 million a year doing so. The city also increased its wastewater disposal capacity by 74.7 million gallons a day, and rehabilitated over 800,000 feet of pipe and over 5,500 manholes, resulting in an infiltration and intrusion reduction of 47%.
As a result of the state and federal orders, the city undertook development of a comprehensive plan known as the St. Pete Water Plan. The plan is a strategic document addressing our city’s aging water infrastructure in the areas of potable (drinking) water, reclaimed water, wastewater, stormwater, and natural water bodies such as the bay and lakes. A new Stormwater Master Plan (SMP) is part of this larger comprehensive plan.
The SMP is limited to mitigate flooding due to rainfall. It does not address flooding caused by surge due to hurricanes or storms. That will be addressed through a “Citywide Vulnerability Study,” which will simulate surges to identify the relative risks of surge impact areas and recommend climate resilience measures such as improved seawalls, living shorelines, related pumping, and other measures. St. Pete’s stormwater drains are not connected to the sanitary sewer system or treatment plants, so rainwater flows directly from storm drains into creeks and stormwater ponds to undergo treatment, and ultimately discharge into Tampa Bay and the Gulf. The wastewater drainage system is a separate component of the overarching St. Pete Water Plan.
The current SMP has not been updated since 1994. That plan established 26 drainage basins (with 1,186 subbasins; the new plan includes 12,682) throughout the city and listed 338 needed drainage projects. Approximately one-third of these projects were planned for accomplishment over a 20-year period and have been largely completed.
Updated weather event goals or standards for the new plan have been adopted. These are referred to as Level of Service (LOS). The 1994 plan referenced a standard of a 10-year storm with a one-hour duration resulting in 3.2 inches of rainfall. The new plan proposes multiple LOS standards based on 24 hours of rainfall: 10-year/24-hour/7.5 inches of rain; 25-year/24-hour/9 inches of rain; 100-year/24-hour/12 inches of rain.
Another parameter directing the plan is projected sea-level rise. The plan is based on meeting the Federal National Oceanic and Atmospheric Administration’s Intermediate Sea Level Rise projections. These projections estimated a 1.44-foot sea-level rise in the Tampa Bay area by 2050. All new development projects will need to meet the new LOS standards as part of the permitting process and be required to show that they will not contribute to any flooding when completed.
A major part of the plan is development of a new floodplain map. This new map does not replace FEMA flood maps used for evacuation and insurance purposes, but addresses the 10-, 25-, and 100-year design storm intensities as well as the 2050 sea-level rise standard. To further refine map accuracy, the city has installed water-level gauges in the stormwater system and used data from the flow meters compared to recorded rain events.
The new plan also proposes 76 major stormwater capital projects to be accomplished over a period of 20 years at a cost of $760 million. High priority areas such as Shore Acres and Lake Maggiore already have projects underway. Based on the current stormwater utility rates that all water users pay, there will be sufficient funding to cover approximately 60% of the proposed projects over the next 20 years. These projects include expansion of the pipe system, new box culverts, street improvements to better handle stormwater, and others.
In addition to work on the new plan, the city is revising codes to promote Limited Impact Design to mitigate the effect of new construction on potential flooding. This includes incentives for underground stormwater vaults, pervious pavements, greywater systems, and vegetative swales. Other code revisions considered include better enforcement of development projects like right-of-way encroachment, damage due to unpermitted work, and illegal dumping of construction materials.
The SMP is an element included in the Community Rating System, which determines flood insurance rates for the public. Completion of the new SMP may improve St. Petersburg’s rating under the Community Rating System of the National Flood Insurance Program. The city has a current rating of 5, which equates to a 25% discount on federal insurance policies. With the successful completion of the SMP, the city has the potential to achieve a rating of 4, which would equate to a 30% discount.
So, what about extreme weather events like what happened in Texas and more recently Ft. Lauderdale? Bresjesh Prayman, director of engineering and capital improvements for the city, says, “It’s impossible to financially design for an event like that. Our goal is to design a system that will cover rainfall scenarios over the next 25 years that are extreme but feasible to accomplish.”
The city has shared the draft plan with the Tampa Bay Regional Planning Council and the Florida Flood Hub, both of which expressed agreement with the plan’s model and assumptions. Justin Bloom of Suncoast Waterkeeper, one of the previously mentioned nonprofits that successfully sued the city following the 2015-2016 wastewater spills, said after reviewing a recent update on the new Stormwater Master Plan presented to city council, “On its surface, the Stormwater Master Plan appears to be a healthy commitment by the city to significant flood prevention and mitigation.” Hopefully the new SMP can be accomplished in time to deal with the 10-, 25-, and 100-year floods it is designed to mitigate.
The city’s Stormwater Master Plan design team includes Bresjesh Prayman, Daniel Sanders, Roger Johnson, and Fatima Sahrabi. Senior Professional Engineer Daniel Saunders worked for the city for 49 years and extended his retirement plans to see the SMP completed. Regretfully he passed away just before his retirement.
The city is soliciting public comment on the draft plan. Email comments to stormwater.masterplan.update@stpete.org. View relevant documents and learn more at stpete.org/stormwatermasterplan.
Will Michaels is a former director and trustee of the St. Petersburg Museum of History and a member of the City Community Planning and Preservation Commission. He is the author of The Making of St. Petersburg and The Hidden History of St. Petersburg. Reach him at wmichaels2222@gmail.com.
