Old Tampa Bay Water Quality Improvement Project

The Florida Department of Transportation’s (FDOT) District 7 anticipated spending millions of dollars purchasing right-of-way for stormwater management for large transportation projects throughout Tampa Bay.

Developed properties would be demolished to build detention ponds to prevent construction runoff from entering the bay. While this traditional approach would prevent water quality from worsening due to the nearby improvements, FDOT needed something more innovative—a cost-saving solution that addressed the short-term construction needs while also improving the overall water quality for the area.

We performed an ecological feasibility study and created a detailed hydrodynamic model to evaluate the viability and benefits of a new approach which included restoring natural circulation patterns near causeways. With a proposal to construct a new channel through the Courtney Campbell Causeway (SR60) crossing Old Tampa Bay, the modeling and scientific site analysis confirmed the main factor to poor water quality and limited abundance of seagrass north of the causeway was reduced circulation. Fresh water inflows to the bay were settling, creating varying levels in salinity. The model showed that tidal flushing through the addition of a new opening would improve the conditions for restoration of the seagrass species and be equivalent to constructing over 200 traditional stormwater detention ponds.

After more than two years of on-site study, modeling and coordination with multiple agencies, our team and FDOT established a new channel and tidal connection through the Courtney Campbell Causeway. The channel enabled the flushing of the water north of the causeway which created an ecological uplift, cutting the time water sat stagnant to less than half, stabilizing salinity and lowering nitrogen levels in the bay.

A comprehensive water quality monitoring system was also developed to demonstrate project success and includes water quality gages and flow meters around the bridge opening. As such, a first-of-its-kind water quality credit bank was established which FDOT can apply to future projects that drain into the bay area. As water quality improvements continue to be recorded and thresholds met, additional water quality credits are released to FDOT. Early data showed immediate water quality improvements that offset approximately $50 million in future right-of-way costs by way of reduced requirements in traditional stormwater management. That savings accounts for only 20% of the water quality and seagrass mitigation credits that had been released. Based on more recent water quality data, it is expected that another 70% of credits will be released in the near future.

The project initiated new permitting and environmental policy and applied sound engineering principles to the study, design and criteria for success. Due in part to the success of this project, FDOT developed statewide guidance establishing the use of similar approaches as a best management practice and the first option over traditional stormwater management.

This project offset seagrass impacts associated with FDOT highway construction projects, offered substantial cost savings and improved water quality of Old Tampa Bay. It enhanced overall watershed water quality; reduced right-of-way requirements for associated upcoming FDOT projects; accelerated project delivery by eliminating the pond design phase; and mitigated sea grass impacts all while exceeding regional stormwater treatment criteria.

After three years, post-project water quality monitoring has shown significant improvements. In fact, success criteria of at least 50% improvement in nitrogen reduction was exceeded, actually reduced by 80%. Locals, news agencies and boaters have indicated a visible improvement in water clarity.

The Old Tampa Bay Water Quality Improvement Project received the Florida Institute of Consulting Engineers Outstanding Environmental Project Award (2017), the 2019 American Society of Civil Engineers (ASCE) Florida Project of the Year Award, the 2019 Federal Highway Administration (FHWA) Environment Excellence Award, and the Tampa Bay Regional Planning Council Natural Environment Award (2019).