Minimum flows and levels

State law (Paragraph 373.042(2), Florida Statutes (F.S.), mandates that the District adopt minimum flows and levels (MFLs) for all first magnitude springs. First magnitude springs are those springs with a long-term average flow of at least 100 cubic feet per second (cfs) or 65 million gallons per day (mgd).

Additionally, Blue Spring was named as a water course to be prioritized for the establishment of MFLs in a 1995 Settlement Agreement between the District and the organizations Concerned Citizens of Putnam County For Responsive Government, Inc., and Citizens For Water, Inc.

The adoption of a minimum flow regime for Blue Spring protects the spring from a reduction in flows that could threaten its water resource values and functions, including its use as a reliable winter warm-water refuge by manatees.

The long-term average flow of Blue Spring is 157 cfs (101 mgd). This average flow was calculated from 654 instantaneous manual flow measurements collected and compiled by the U.S. Geological Survey (USGS) and the District over a 75-year period of record (POR).

Yes. Blue Spring’s flow is primarily driven by climatic conditions. Alternating cycles of drought and abundant rainfall affect flows throughout the year and also from year to year.

The minimum flow regime was developed through a three-part approach. First, the District calculated a minimum flow that will protect the use of Blue Spring as a refuge to accommodate expansion of the West Indian manatee population. Second, the District evaluated the water resource values in Rule 62-40.473, F.A.C., relevant to Blue Spring. Third, the District considered whether these values would be protected under the minimum flow regime for Blue Spring, and determined they also would be protected.

The minimum flow regime defines the minimum long-term mean flow in five-year increments until 2024. The minimum flow increases over time. The first increment would have allowed a temporary reduction in the long-term mean flow from 157 cfs (101 mgd) to 133 cfs (86 mgd) for the period of time from the date of rule adoption to March 31, 2009. This 15-percent decrease in flow would have represented the maximum allowable reduction in the Blue Spring long-term mean flow during this five-year period. Currently, the allowable long-term minimum mean flow is 142 cfs (until March 31, 2019). Under the regime, the minimum long-term mean flow will be raised during each of two subsequent five-year intervals to the following:

• 148 cfs (from April 1, 2019, through March 31, 2024)
• 157 cfs (after March 31, 2024)

The phased approach was developed to accommodate the increasing number of manatees using Blue Spring Run as a winter warm-water refuge. The model used to estimate future manatee use of Blue Spring is based on the projected increase in the manatee population that will use Blue Spring.

By law the District is required to calculate minimum flows and levels using the best information available. After careful consideration of existing scientific information, the District used the best available information to calculate minimum flows for Blue Spring, and these calculations show that a long-term average flow of 157 cfs will be needed by the manatee population by 2024.

Manatees frequent Blue Spring Run at any time of the year. However, the most intensive use occurs during the colder months of each year, when manatees seek warm-water refuge. Manatees seek refuge in the warmer waters of the Blue Spring Run when the temperature of the river drops below 68°F (20°C). Manatees typically begin congregating in the spring run in November and leave in March, which is referred to as the “manatee season.” Manatees typically leave the run each day to feed in the St. Johns River. No food resources are available to the manatees in Blue Spring Run.

Manatee use of Blue Spring Run as a winter warm-water refuge has increased dramatically since 1978, when routine manatee counts were begun. For information about manatees at Blue Spring, visit the Blue Spring State Park website. The Save the Manatee Club routinely counts manatees at Blue Spring and maintains webcams to view manatees in the spring and springrun.

Since 1978, Blue Spring State Park biologists have tracked individual manatees’ occurrence within the spring run. Daily surveys are performed during the manatee seasons from the confluence of the spring run with the St. Johns River to the spring boil. Surveys are usually conducted in the morning, when the manatees are in greatest attendance. The field observation sheet for recording manatee data divides the spring run into 22 zones, based on landmarks located along the bank. The biologists record the locations of individual manatees within the 22 spring run zones on the field datasheets as they paddle a canoe upstream. River and spring run water temperatures and the location of the dark water intrusion are also recorded. This information is then entered into computer files for future data analysis.

Based on 28 years of observed manatee season maximum daily counts, the manatee population using Blue Spring as a winter, warm-water refuge grew at a rate of 6.6 percent per season. However, the District’s model used to project maximum daily manatee growth rate in future manatee seasons used a 7.02 percent growth rate. The use of this higher growth rate recognized the potential increase in the number of manatees using Blue Spring as a winter, warm-water refuge that may result from the future closure of artificial warm-water refuges (e.g., electrical energy power plants) in the St. Johns River and along Florida’s east coast. Using this higher growth rate, the manatee season maximum daily count was projected to increase from 158 manatees in the 2006 season, to 558 manatees by the 2024 season.

The minimum flow regime is designed to protect Blue Spring as a winter, warm-water refuge critical to the survival of a growing manatee population. The regime is designed to provide adequate warm water from the spring in winter months, including during catastrophic cold-weather conditions. Catastrophic conditions are defined as the simultaneous occurrence of the lowest St. Johns River water level, the coldest river water temperature, and the lowest spring flow that would be expected to occur only once every 50 years, lasting for three or more consecutive days. The time period of 50 years is based on the long life span of the manatee and the three-day duration is based on laboratory studies of manatee tolerance to cold water.

No. While the adequate protection of manatee habitat was the controlling factor in establishing the Blue Spring minimum flow regime, the minimum flow regime also will protect other water resource values.

Rule 62-40.473(1), F.A.C., directs water management districts to consider the following water resource values:

• Recreation in and on the water
• Fish and wildlife habitats and the passage of fish
• Estuarine resources
• Transfer of detrital material
• Maintenance of freshwater storage and supply
• Aesthetic and scenic attributes
• Filtration and absorption of nutrients and other pollutants
• Sediment loads
• Water quality
• Navigation

These values were evaluated in a report entitled, Human Use and Ecological Evaluation of the Recommended Minimum Flow Regime for Blue Spring and Blue Spring Run, Volusia County. Based on this report, the District concluded that these ecological and human use values would be protected by the Blue Spring minimum flow regime.

Applicants seeking environmental resource permits (ERP) or a consumptive use permits (CUP) are required to provide reasonable assurance that the Blue Spring minimum flow regime will continue to be achieved by a proposed water withdrawal or the construction or operation of a proposed surface water management system. In addition, the District includes the Blue Spring minimum flow regime in the regional water supply planning process as a constraint in developing sustainable water supply options to meet existing and future water supply needs.

The establishment of a minimum flow regime for Blue Spring limits the continued availability of groundwater to meet the increasing regional water supply demands. However, future water supply development in the area is also limited by other factors. Eventually, the Blue Spring minimum flow regime is expected to become the greatest limitation on groundwater use in the area.

The minimum flow regime constrains or limits regional groundwater pumping for future water supply development. Over the next 20 years this minimum flow regime will create the greatest limitation on groundwater development. As a result, the primary impact of the minimum flow regime is to create the need for water users to develop alternative water supply projects to supplement groundwater in meeting existing and future water supply needs.

Regulatory and water supply planning tools help to ensure that the increasing minimum flow regime will be met. The District includes conditions on consumptive use permits, requiring that permit holders plan and develop alternative water supply sources to meet future water supply needs. The District is strongly supportive of and is assisting water suppliers in the timely development of conservation initiatives, reuse of reclaimed water and alternative water supply projects that will be needed to reduce water withdrawals in time to meet the increasing minimum flow requirement.

No, the change is not perceptible to the eye. The water level in the spring run is almost totally determined by the level of the St. Johns River, not the magnitude of flow in the spring. The variability (range) of Blue Spring Run surface water levels is relatively small as compared to the water level variability of the adjacent St. Johns River. Even a large spring flow of 212 cfs (137mgd) results in only 1.5 inches (0.13 feet) of rise in the surface water level of the run from the mouth of the spring run to the spring boil. By contrast, the water level of the St. Johns River in winter ranges over 6 feet.

Yes. The District continues to work in coordination and partnership with other agencies to enhance existing data collection. This additional information and the District’s work in other areas (e.g. refinement and improvement of groundwater and hydrodynamic models) will be used by the District to determine whether rule amendments are warranted in the future.