Reviving the Hillsborough River: Restoring Flows

by Mary Kelley Hoppe

48 Hours
It was a last ditch gambit by a small group of residents racing against the clock. In December 1999, the Southwest Florida Water Management District mandated a minimum freshwater flow to resuscitate the lower Hillsborough River below the Tampa dam. A letter from Tampa Mayor Dick Greco to then District Executive Director Sonny Vergera the year before made plain the city's stance: water from the reservoir would not be tapped to satisfy a minimum flow, lest it compromise the needs of some 440,000 water customers.

The lower Hillsborough River ’Äì once fresh, now salty ’Äî was dying for a drink. Prior to the district ruling, there was no mandated minimum flow. The lower river subsisted largely on freshwater spillover from the dam and stormwater runoff in rainy seasons when water was ample. While the new minimum flow of 10 cubic feet per second (cfs), or roughly 6.5 million gallons of freshwater per day, could only help, river advocates decried the decision, arguing it was merely a temporary stay of execution based on political expediency and not scientific evidence.

Worse, critics charged, the minimum flow added no new fresh water, relying instead on slightly saline water re-routed from Sulphur Springs and pumped 2.5 miles upriver to the base of the dam.

With just 48 hours to appeal, Tampa residents mobilized to fight the decision. Incorporating overnight, the ’ÄúFriends of the River’Äù filed a challenge in state court. Months later and moments before the appeal was to be heard, the water management district and city offered a settlement. The agency would study the river for five more years and reevaluate the minimum flow based upon study findings. Meanwhile, the city would meet its responsibilities by pumping water upriver to the dam.

New Day, New Flow
Fast forward six years. In 2006, following an intensive five-year study, Swiftmud released its recommendation for a revised minimum flow of 20 cfs, or 13 million gallons per day, double the existing threshold. Its goal: ’Äúto provide a minimum flow that would extend a salinity range of less than 5 parts per thousand (ppt) from the Hillsborough Reservoir dam toward Sulphur Springs.’Äù

The once-pristine Hillsborough River has shouldered its share of burdens at the hands of development, retaining in places its breathtaking beauty and fecundity, while coming under increasing attack from pollution in stormwater runoff and withdrawals of its very lifeblood ’Äì fresh water.

Two of its chief problems ’Äì too much nitrogen and too little dissolved oxygen ’Äì feed one another. Excess nutrients fuel the growth of algal blooms that cut off sunlight to underwater plants and deplete dissolved oxygen levels. In the stagnant waters, fish and crabs either die or are driven away.

Downstream, Tampa Bay also suffers. The bay depends on a steady freshwater diet to create the highly fertile nursery areas and low-salinity habitats that the estuary’Äôs ecosystems and celebrated sport fisheries require.

Deconstructing the Flow
The district’Äôs minimum flows study included a series of experimental releases in the 10 to 30 cfs range, along with computer modeling to simulate outcomes.

The primary ecological driver affecting flows at the base of the dam is salinity. The Swiftmud recommendation focuses primarily on the salinity needs of benthic or bottom dwelling organisms, not fish.

Even with a constant minimum flow, the report notes, salinities vary considerably on a daily basis as a result of tides, winds, rainfall and stormwater runoff ’Äì so maintaining salinities of under 5 ppt will be difficult.

The river’Äôs health also is threatened by low levels of dissolved oxygen. DO generally improves with increased flows but less predictably than salinity. Fish, like humans, need oxygen to breathe; when dissolved oxygen levels plummet, hypoxic conditions can lead to ’Äúdead zones’Äù devoid of marine life.

Increasing freshwater flows to improve DO levels nearest to the dam may actually depress DO downstream, according to Swiftmud. Still, the agency acknowledges that the significant improvements in low-salinity portions of the river resulting from increased DO would far outweigh any slight decreases elsewhere.

The agency says the revised flow will reduce occurrences of low DO concentrations, those below 2.5 milligrams of oxygen per liter. While that falls well short of the state DO standard of 4 mg/l for rivers, Swiftmud data suggests it is sufficient to support fish in the lower Hillsborough.

Opposition mounts
Critics say the study ignores the Tampa Bay Estuary Program’Äôs 1997 recommendation to establish and maintain a freshwater zone and complete salinity gradient. They also believe that flows should be based on the needs of both benthic organisms and fish, not benthos alone as Swiftmud has done.

’ÄúWe chose to focus on low-salinity habitats because those have been disproportionately lost in Tampa Bay,’Äù says Marty Kelly, who directed the minimum flows study for Swiftmud. Additionally, Kelly notes, some ’Äúfreshwater’Äù fish species, such as bluegill and largemouth bass, can tolerate low and mid-range salinities.

Both the Friends of the River and Hillsborough County’Äôs Environmental Protection Commission believe the district’Äôs own data supports a 30 to 40 cfs minimum flow.

’ÄúWe’Äôve put this day off for six or seven years now,’Äù says Phil Compton, spokesman for Friends of the River. ’ÄúAnd when it comes down to what the ecology of the river requires, they’Äôve missed the boat.’Äù

River advocates say the management goal of extending a salinity range of less than 5ppt from the dam ’Äútoward Sulphur Springs’Äù is vague. They want to know what size salinity zones the flow will produce and for how long, particularly for freshwater (less than 0.5 ppt) and the zone most vital for juvenile fish (less than 2 ppt).

Even more troubling, they contend, are provisions for ’Äúseasonal adjustments’Äù ’Äì dry or drought periods in which the City of Tampa may be relieved from meeting minimum flows, essentially turning off the freshwater spigot when the river needs fresh water most.

As it is, the current minimum flow of 10 cfs for the lower Hillsborough River is required for only 165 days, or less than half a year on average. For the rest of the year, there is no flow over the dam.

Taken together, says EPC in a letter to the district, ’Äúthe proposed minimum flow would continue depressed DO levels and elevated salinities,’Äù preventing the maintenance of a healthy lower Hillsborough River, while failing to meet state DO standards under most conditions.

Adds Compton: ’ÄúFailure to acknowledge such ’Äòinconvenient truths’Äô may lead Swiftmud to adopt a minimum flow that perpetuates significant harm to the river, in violation of state law and the city’Äôs own water use permit.’Äù

Kelly disagrees. ’Äú’ÄòSignificant harm’Äô is not defined anywhere in Florida statute. Our data shows that 95% of low DO concentrations occur at flows less than 20 cfs.’Äù

The proposed minimum flow rule will be presented to Swiftmud’Äôs Governing Board for adoption as early as April, once findings from an independent peer review panel are evaluated. The agency has already begun evaluating a minimum flow for the upper Hillsborough River.

Turning up the Faucet
Meanwhile, the big question is where the additional water will come from to meet minimum flows on the lower Hillsborough.

’ÄúTo write the rule will be relatively easy, but to come up with a recovery strategy ’Äì to find those additional sources of water ’Äì that’Äôs going to be the trick,’Äù says Kelly.

Water to make up the minimum flows will likely come from a variety of sources, including Sulphur Springs and Blue Sink, northernmost in chain of historically connected sinkholes located between Fowler and Florida avenues. An earlier proposal to reuse treated wastewater being discharged to the bay from the Howard Curren wastewater treatment plant was ultimately rejected because of the water’Äôs high nutrient content.

’ÄúIt took us over 30 years to get down to the business of proposing minimum flows for the Hillsborough River,’Äù says Alan Wright of the Hillsborough County City-County Planning Commission. ’ÄúIf it takes more time to do it right, to find the water for the flows that will replenish the river, let’Äôs do it ’Äì but start now.’Äù

Tapping additional water sources could mean a hike in water rates for Tampa residents, who enjoy some of the lowest water rates in the state. A typical city homeowner pays less than a half-penny per gallon for clean water delivered directly to their tap, or less than $5 per month for 7,000 gallons.
’ÄúI think the decision comes down to what we value,’Äù says Tampa Councilwoman Linda Saul Sena. ’ÄúIf you look only at the per-unit cost of water, you might be tempted to skimp on minimum flows. If you value the health of the river and seek a ’Äútriple bottom line’Äù ’Äì what’Äôs best for our people, the river, and consider the cost of water ’Äì then you make different choices. I think we have a responsibility to look at the triple bottom line.’Äù

’ÄúWe send 45 million gallons of treated wastewater per day into the bay,’Äù says Compton. ’ÄúIf half that could be used to replace potable water now used in industry and irrigation, we’Äôd have the equivalent of a minimum flow that everyone would agree is sufficient to restore the river.’Äù

Desal is another option to supplement the city’Äôs needs, Compton adds. ’ÄúIf we’Äôre always going for the cheap way, what happens is we wind up cheating ourselves out of water and a healthy river.’Äù

Side note: From its freshwater origins in the Green Swamp to its salty terminus at Tampa Bay, the Hillsborough River meanders for 40 miles before reaching the Hillsborough Reservoir Dam at Rowlett Park. Below the dam, the 10-mile-long lower Hillsborough River winds through quiet neighborhoods and urban landscapes on its way to downtown Tampa.