DEVELOPMENT OF MINIMUM FLOWS AND LEVELS FOR BLUE SPRING, MADISON COUNTY, FLORIDA

Madison Blue Spring (MBS) is a first-magnitude spring located on the Withlacoochee River in Madison County, Florida. The Suwannee River Water Management District sought to protect this natural resource by establishing a minimum flow and level (MFL), though little hydrologic data for the spring was available. Nearby gauges on the Withlacoochee River were also significantly lacking in data. To overcome this, a time-series of data for the river and spring were synthesized, utilizing all other available and relevant hydrologic data.

MBS is an estavelle; the spring is flooded as the river rises and backflows into the aquifer during large river floods. An analysis of Withlacoochee River gauge data shows a complex relationship between surface water-groundwater interactions, stage, and the fall. The range of inflows to or outflows from the river increases with increasing stage. The range of fall along this reach also increases with increasing river stage. For a given stage, the river experiences an influx from the aquifer below some level of fall, and discharges water to the aquifer above that level of fall.

Flow duration analysis of the measured and synthesized spring and river data was utilized to determine the duration of low flows and the relative contributions of spring discharge to the river during low-flow events. At low river stage, MBS contributes up to 25 percent of the base flow in the river. Therefore, reductions in MBS discharge may create adverse consequences to river water quality or ecological conditions.

In the absence of a driving ecological factor within the spring itself, the spring’s ability to maintain flow in shoal habitats in the river was considered the driving factor for MFL development. These shoal habitats constitute important aquatic habitat for benthic invertebrates and algae and flow over them is critical for fish passage. Six representative shoals in the river downstream from MBS were surveyed and utilized in conjunction with historic and simulated discharge and stage data to determine low-flow conditions on the shoals for a range of MBS discharges. A critical, low-flow MFL was identified for the spring that will prevent significant harm to shoal habitats and protect the passage of fish during low flow in the river.