Water Levels and Flows
Spring Flow is the rate of volume of water discharging from a spring. This is dependant on several factors: the elevation of the water level in the source aquifer, the water level in the receiving water resource and to a lesser extent barometric pressure. What impacts the aquifer and surface waters will generally affects spring flow. Since recharge (rainfall) and withdrawals (pumping) from the source aquifer will impact that aquifer's water levels, these will also impact the spring flow. Also changes in a structure downstream from a spring such as a dam or weir will impact flow. Spring flows also provide base-flow to streams and rivers during dry seasons. As a note, a spring by definition must have flow to be a spring therefore a lake that does not have an outlet can not be a "spring-fed" lake.
Spring flow can be reversed should the receiving water resource have a higher water level than the source that supplies the spring.
Depending on the amount of discharge, the units of measurement may change. Larger springs are generally measured in millions of gallons per day (mgd) or cubic feet per second (cfs). Smaller spring may be measured in gallons per minute (gpm) or in even smaller quantities.
The location of a discharge measurement is critical. Whenever possible, a discharge measurement should be restricted to a single vent or seep. However, this is often impractical. For example, the only place to take a measurement may be in a spring run downstream where multiple springs have discharged into the run. For this reason, whenever a discharge measurement or water sample is taken, the springs (vents or seeps) included in the measurement need to be reported along with the exact location (section) of the discharge measurement. In the case of submerged springs that discharge directly into a lake or stream like Apopka or Island Springs, the flow measurement has to be taken underwater using SCUBA equipment. Spot measurements are taken across the measurement section with a rotating cup flow meter, a newer Doppler flow device or other accepted methods. These measurements are then combined with the area of the section measured to determine the overall flow.
Spring Magnitude1 is a flow category to be based on the discharge from a spring. Where multiple measurements are available, it is a weighted median value of all discharge measurements for the period of record. However, one discharge measurement is enough to place a spring into one of the eight magnitude categories. Springs have dynamic flows and a spring categorized as being categorized as one magnitude at one moment in time may not continue to remain in the same category.
The classification system used in Florida is based on Meinzer (1927).
||≥ 2.832 cms
||≥ 100 cfs (≥ 64.6 mgd)
||≥ 0.283 to 2.832 cms
||≥ 10 to 100 cfs (≥ 6.46 to 64.6 mgd)
||≥ 0.0028 to 0.283 cms
||≥ 1 to 10 cfs (≥ 0.646 to 6.46 mgd)
||≥ 0.0063 to 0.028 cms
||≥ 0.22 to 1 cfs (≥ 100 to 448 gpm)
||≥ 0.631 to 6.308 lps
||≥ 0.02 to 0.22 cfs (≥ 10 to 100 gpm)
||≥ 0.063 to 0.631 lps
||≥ 1 to 10 gpm (≥ 0.002 to 0.02 cfs)
||≥ 0.473 to 3.785 lpm
||≥ 1 pint/min to 1 gpm
||< 0.473 lpm
||< 1 pint/min
cms = cubic meters per second
cfs = cubic feet per second
mgd = million gallons per day
gpm = gallons per minute
lps = liters per second
pint/min = pints per minute
lpm = liters per minute
Historical Spring Magnitude is a special spring classification category based on the median volume of flow from a spring per unit time, based on discharge data obtained prior to the year 2001. It is recognized that historically, many springs in Florida have kept one magnitude category, even though the discharge may have changed considerably from when it was first assigned a magnitude. For this reason, a historical category is acceptable in the Florida Springs Classification System. For example, the discharge of a spring may have been taken in 1946. At that time it was classified as a first-magnitude spring. No other measurement was taken until 2001, when three discharge measurements were taken. The median value for the two annual medians reveals that the spring should be re-classified to a second-magnitude spring in 2001. Nevertheless, it can still be considered a historical first-magnitude spring.
 Spring Classification System and Spring Glossary – Florida Geological Survey Special Publication No. 52, 2003, revised 2005
To learn how water flow is measured, please read our Water Flow Learn More »