Featured Project: Tidal Tributary Restoration by Modification of Salinity Control Structures

Tidal tributaries are important to the ecological health of Tampa Bay. The Tampa Bay Estuary Program (TBEP) estimates that there are over 300 named and unnamed tidal creeks and tributaries that enter Tampa Bay. These tidal systems serve as a nexus between freshwater inputs and tidally influenced salinity regimes. As such, they serve as major areas of productivity and habitat for the diversity of the greater estuary. Tidal creeks also serve as nursery habitat for many of the estuary’s fish species.

Many of the tidal creeks have evidence of anthropogenic impacts, including barriers which restrict tidal movement, resulting in “flashiness” in the system whereby nutrient-rich pulses of freshwater enter the tidal creeks, overriding the system’s ability to naturally assimilate the nutrients, as well as preventing a consistent oligohaline zone. To address these issues in Tampa Bay, the Southwest Florida Water Management District , and TBEP contracted with GPI to look at candidates for modification to restore the natural hydrologic connectivity.

Tributaries that were chosen for a pilot modification study were Channels A and G and Rocky Creek (collectively referred to as the Channel A & G complex for this study). The Channel A & G complex is located in western Hillsborough County, just west of Tampa International Airport. It’s a freshwater and tidal tributary system bisected by two salinity control barriers owned and operated by the District. The system suffers from excessive, nuisance submerged aquatic vegetation (e.g. Hydrilla) growth and low dissolved oxygen and nutrient TMDLs.

In June of 2014 the salinity control barrier gates were fully raised to allow for free tidal movement throughout the system (the gates remain open as of May 2016). The study compared the baseline and post-modification data for a variety of parameters. The results of the study showed how the system is starting to function as a true tidal tributary, with improved water quality data indicating a shift to an oligohaline system, decrease in nuisance algal mats coupled with an increase in salt-tolerant vegetation, and an increase in salt tolerant fish species in the previously freshwater sections of the system.