River Recovery Status Report released

Figure 1 shows the number of days per year of no flow in the Hillsborough river near the Tampa Dam from 1995 to 2020. The number of days without flow has been trending down since the last high of over 275 days in 2006December 2021 – The Southwest Florida Water Management District released the Lower Hillsborough River Recovery Strategy Implementation Annual Update Report for 2021. The report provides an annual update regarding implementation of projects outlined in the Hillsborough River Recovery Strategy that are needed to recover minimum flows adopted for the Lower Hillsborough River (LHR). As required by statute, if the actual flow of a water course is below an adopted minimum flow or is projected to fall below a minimum flow over the next 20 years, a recovery or prevention strategy is developed as part of the minimum flows establishment process.

The currently adopted minimum flows for the LHR are 20 cubic feet per second (cfs) freshwater equivalent flow from July 1 through March 31, and 24 cfs freshwater equivalent flow from April 1 through June 30 at the base of the Hillsborough River Dam, as adjusted based on a proportionate amount that flow at the U.S. Geological Survey (USGS) Hillsborough River gauge near Zephyrhills, Florida is below 58 cfs. For purposes of the minimum flows rule and its implementation, freshwater equivalent means water that has a salinity concentration of 0.0 ppt for modeling purposes. The minimum flows for the LHR are based on extending a salinity range less than 5 ppt from the dam toward Sulphur Springs. The goals of the minimum flows are to effectively supply a total of 20 or 24 cfs of freshwater to the base of the Hillsborough River Dam during the two seasonal periods identified in the rule.

The LHR recovery strategy outlines six potential projects and a timeline for their implementation. Four projects are identified for joint-funding by the District and the City of Tampa (City) and two are to be implemented by the District. Implementation of specific projects is subject to applicable diagnostic/feasibility studies and contingent on obtaining any required permits. Projects to be jointly funded by the District and the City include the:

  1. Sulphur Springs Project (Lower Weir Modifications and Sulphur Springs Pool Upper Weir and Pump Station Modifications);
  2. Blue Sink Analysis and Project;
  3. Transmission Pipeline Evaluation and Project; and the 187
  4. Investigation of Storage or Additional Supply Options.

In addition, the District was required to initiate implementation of two projects, including the:

  1. Tampa Bypass Canal (TBC) and Hillsborough River Reservoir Diversions; and the
  2. Morris Bridge Sink Project.

The report discusses the progress of the six projects.  On average, water did not flow over the dam for 151 days each year (range: 9 to 315 days, based on days from 1995 through 2020 when flows were less than 1 cfs; in 2020, no flow occurred 115 days out of 365 days measured). Without this flow, salinity below the dam is relatively high and no low salinity habitat exists for much of the year. Implementation of recovery strategy projects has helped mitigate this condition and address minimum flow requirements for the LHR.  The report concludes that all activities and projects proposed in the adopted LHR recovery strategy are either underway, completed, or have been determined to not be viable. Important components of the strategy are currently in operation or available, including facilities or plans for the use of Sulphur Springs, Blue Sink, the TBC and Morris Bridge Sink as recovery flow sources.  The report also concludes that results from recent years suggest that the desired goal of creating low-salinity habitat below the Hillsborough River Dam can be sustained through minimum flows implementation.

For more information:  https://www.swfwmd.state.fl.us/projects/mfls/minimum-flows-the-lower-hillsborough-river

Source: SWFWMD, 2021

View the rest of this month's Connections to Tomorrow articles