By Daniel Lauricello & Ginger Creighton – Environmental
What if the FDOT could fund a project which is a win, win, win? What if the Department could accomplish the Department’s mission, to provide “a safe transportation system that ensures the mobility of people and goods, enhances economic prosperity and preserves the quality of our environment and communities;” and also reduces the project’s right‐of‐way foot print, and not only meets water quality rules and regulations, but exceed them? Through the efforts of the Department staff and Consultant partners, the District Seven Drainage and Environmental Permitting office is working to make these lofty goals a reality.
In 2012, the Florida Legislature passed Florida Statute 373.413 (6), which allows the FDOT and the Water Management Districts to work together on stormwater treatment concepts that provide “the most cost‐efficient and effective method of achieving the treatment objectives.” Simply put, this allows us to “zoom out” and look at stormwater management from a regional watershed perspective rather than on a project by project basis.
In 2014, the Department created an initiative known as Environmental Look Arounds or “ELAs.” The aim of this initiative is to gather “the right people, from the right agencies, at the right time, in the same room, creatively focusing on the missions of all agencies present. (1)” Department Drainage Engineers across the state have been striving to work toward making this initiative a reality.
Much of the Tampa Bay Metropolitan area is part of the Tampa Bay Watershed. Tampa Bay was designated an “estuary of national significance” by Congress in 1990. However, Tampa Bay is considered to be polluted according to the State of Florida’s Impaired Waters Rule (2). The Tampa Bay National Estuary Program (TBNEP) was established in 1991, and since 1998, the Program has been working diligently towards restoration of Tampa Bay through reduction of nitrogen and phosphorous loads. The success of reducing these pollutants has been a measureable increase in seagrass density in the Bay. However, several isolated areas have not seen similar increases in seagrass. Research in the last decade or so suggests Bay‐wide circulation is inhibited due to the two traversing causeways (I‐275 and SR 60).
Additionally, congestion in “the Tampa metro area was rated the 11th worst in the nation for traffic congestion by the 2014 TomTom Traffic Index. (3)” This puts Tampa just behind larger metropolitan areas like Orlando, Atlanta, and Houston. To add to this Tampa, along with Miami, Orlando, and Jacksonville, is projected to see a population growth of 80 % from 2010 to 2050 (5). With population projections like these, the need for transportation infrastructure improvements for increased vehicular usage and mass transportation opportunities is a certainty. To address traffic congestion and projected population growth, the Department is preparing for a large managed lane improvement project consisting of eight segments on I‐275, and I‐4 traversing Hillsborough and Pinellas Counties. Much of the planned improvements will be centered in the heavily urbanized downtown Tampa and Westshore area.
With the impairment classification of Tampa Bay, capacity projects that greatly increase the amount of impervious pavement and pollutant load require extremely large stormwater ponds to meet water quality regulations for the removal of nitrogen. Current regulations require that projects which discharge to an impaired waterbody must provide additional or ‘enhanced’ treatment to not increase levels of nitrogen discharged or actually reduce the daily load of pollutants to the Bay. Nitrogen removal has been of particular challenge in areas with high water tables, such as in the Tampa metropolitan area.
Stormwater facilities with a permanent water pool are known as “wet ponds”. These types of stormwater management facilities have been found to have limited removal efficiency of nitrogen (6). Targeted levels of nitrogen removal are extremely difficult if not impossible to obtain with wet ponds and much larger ponds are required to meet the criteria. Alternatives such as dry ponds that can remove a higher percentage of nitrogen often are not an option due to high water table in the area.
In highly urbanized areas, such as downtown and the Westshore area of Tampa, there are very few undeveloped parcels for large stormwater management facilities that will be required. Traditionally, the Department would acquire developed sites to meet this need, and in a developed area like the westshore area there are many multi‐story office buildings. This will add a huge expense to project right‐of‐way costs.
In the summer of 2014, Department staff was presented with a proposal by its consultants (Atkins and ESA) to complete a baseline study of Old Tampa Bay, located in the extreme northeast side of the Bay and north of SR 60 (the Courtney Campbell Causeway (CCC)). The theory was that by improving the circulation in this portion of Old Tampa Bay, there would be a corresponding improvement in water quality. The Department embraced the concept because it is exactly in line with the intent of the Florida Statute 373.413 and the ELA concept. In addition, the success of increased circulation from essentially cutting a ‘hole’ in the eastern part of the causeway could be measured by water quality sampling and a monitoring for a subsequent response of seagrass growth.
The overall goal of the TBNEP management plan calls for achieving seagrass levels that existed in the 1950’s when measurements were first taken; but seagrass coverage was not good everywhere back in 1948. The CCC was constructed in the mid 1930’s and circulation in Old Tampa Bay was cut off from the rest of the Bay at that time.
In general, impacts from installation of causeways across a water body include reduced flushing rates and increased water residence times due to their impact to the natural circulation patterns. This creates an increase in water quality problems. Other causeway removal projects completed in Florida (Lake Surprise in Monroe County‐D6, Rose Bay in Volusia County‐D5, and Ft. DeSoto in Pinellas County‐D7) have had good results in improving salinity regimes, decreases in Chlorophyll‐A levels, lower nitrogen levels, and increase habitat response including the diversity, areal extent, and abundance of seagrass species when found.
Department consultants collected baseline data on surface and near bottom water quality, sediment characterizations, seagrass and macroalgal presence, depth to the deep edge of seagrass meadows, and made flora and fauna observations. No fatal flaws surfaced to contradict reestablishing the circulation would result in improvements of seagrass distribution and abundance. From the study, it was determined that the current higher nitrogen levels north of SR 60 is mostly due to the variable salinity regimes and not pollutants from upstream (7). Phase 2 of the study established a coastal hydrodynamic numerical model that included additional data being collected including currents and water levels, bathymetry, topography, and the results from dissolution rate experiments. The model was used to lower water residence times, increase flushing, and to find the optimum width of ‘cut’ opening through the causeway to ultimately improve water quality and sea grass distribution.
Model results showed that by installing a 200 foot wide cut in the eastern portion of the causeway, the residence time was reduced by 50% after 7 days (8). Based on the results it appears that hydrologic restoration of circulation has a greater potential to increase water quality and the coverage of seagrass in Old Tampa Bay than any number of stormwater ponds located upstream. It is anticipated the project will improve conditions in about 80 acres of seagrass habitat north of the CCC. This acreage could be equivocated to approximately the removal of 10,439 lbs of total nitrogen from this location in the Bay.
How does all of this benefit Old Tampa Bay, SWFWMD, and the Department? By causing a net nutrient improvement to the impaired waterbody (Tampa Bay) directly instead of traditionally treating water upstream in small amounts (ponds) indirectly. This is water quality compensatory treatment to the max. In this case, the Department constructs this restoration project in the receiving waterbody and is allowed to reduce pond sizes associated with the project. It is important to note, ponds are still required for stormwater management but this project dramatically reduces their footprint. This translates to cost savings on right of way purchases, especially within downtown Tampa and the Westshore area. The magnitude of the right‐of‐way savings have been estimated in the order of $50 Million while the preliminary cost of the bridge is estimated at $15 million.
1 FDOT Pond Design Course (April 2015)
2 Chapter 62‐303 F.A.C. Total Maximum Daily Loads (TMDL) Program
7 Old Tampa Bay Water Quality Improvements Phase 1 Feasibility Study
8 Old Tampa Bay Water Quality Improvements Phase II Hydrodynamic Modeling Report