Rainbow Springs #1 at the headspring of Florida's Rainbow River
Hundreds of springs lie on the west coast of Central Florida. While some of these springs are isolated features, many are clustered into groups, or spring groups, of varying size and areal extent. Large spring groups, such as Rainbow Springs in southwestern Marion County, drain large areas, often draining tens or even hundreds of square miles.
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The Rainbow Springs group is the fourth largest spring system in terms of discharge in Florida. The group is the second largest spring group on the west coast of Central Florida. Rainbow Springs is generally considered to be the group of springs in the area that encompasses the first 1.5 miles of Florida's Rainbow River.
Form the Rainbow Group
Like many of the major springs in Florida, Rainbow Springs is composed of numerous vents distributed over a large area, rather than a single, very large discharge point. In addition to the springs at the head of the river, numerous springs discharge into the bed of the river through most of its length.
Rainbow Springs #4 on the Rainbow River, Florida
Rainbow Springs #4
Rainbow Springs #4 lies near the center of the Rainbow River about 250 feet south (downstream) of Rainbow Springs #1. The spring vent is elliptical in shape; about five feet long and three feet wide. The spring lies 10 feet below the surface of the pool, and is first encountered upon entering the head spring area from the south. The spring creates a pronounced boil on the surface of the spring pool. The spring is located within the boundaries of the Rainbow Springs State Park.
A number of small springs also feed Indian Creek, a tributary that flows southwest and intersects the Rainbow River about one mile south of the head spring area. Springs that comprise the Rainbow Springs group include: Bridge Seep North, Rainbow Springs #1, Rainbow Springs #4, Bubbling Spring, Rainbow Springs #6, and Rainbow Swamp Spring #3.
How Much Water Flows from
Rainbow Springs Group?
Historically, the average annual discharge at Rainbow Springs is approximately 459 million gallons per day (1,737,534,009 liters per day; that's nearly 2 billion liters per day). The total discharge of Rainbow Springs is represented by the cumulative discharge of springs in the head spring area, springs in the bed of the river, and springs along Indian Creek. That is a phenomenal amount of water boiling from the ground, daily.
Discharge of the Rainbow River is regularly measured by the United States Geological Surveyapproximately five miles downstream from the head spring area at the C.R. 484 bridge, and about one-half mile above the confluence of the Withlacoochee and Rainbow Rivers. Eighty-nine percent of the rivers discharge, as measured at the C.R. 484 bridge, enters the river in the first 1.5 miles. There's a park at the bridge where the river narrows and the flow there is quite strong. Photos of that park in a future blog post.
The Rainbow River, Florida
Seasonal High and Low Waters
Discharge exhibits significant seasonality, reaching a minimum at the end of the dry season in June and peaking in October, after the end of the summer wet season. This pattern indicates that the lag time between seasonal changes in rainfall and the response of the system is minimal.
The seasonal pattern also indicates that the circulation of ground water in the Floridan aquifer is open and vigorous and the springs are largely recharged by precipitation falling in close proximity (5-10 mile radius) of the springs.
Why is Rainbow Springs Water Always 72° (22° C)?
The temperature of spring waters throughout Florida reflects the average annual air temperature in the vicinity of the springs. Mean annual air temperatures in the Central Florida range from 22-23°C (71-74° F) from north to south across the peninsula of Florida. That is to say an average of all temperatures throughout the year (day and night, winter and summer).
Springs in the Rainbow area typically have temperatures that range from 73-75° F (23-25° C). The lowest spring temperatures are often found in the extreme northern portions of the Central Florida (e.g., Rainbow Springs) where recharged may be rapid and somewhat cooler in temperature.
The warmest spring temperatures, not counting Warm Mineral Springs in southern Sarasota County, occur in Central Hillsborough County at Sulphur and Lithia Springs. These springs have temperatures that are typically near 77° F (25°C) which is slightly elevated above the mean annual air temperature measured in Hillsborough County, 22° C (72° F). This difference in temperature may reflect slightly deeper flow paths taken by ground water through the Floridan aquifer.
Bubbling Spring is located about 1,500 feet southeast of the main spring pool in a small tributary on the eastern side of the Rainbow River. The spring lies 500 feet east of the river, and emanates from at least three fractures in the limestone floor of the run. The fractures in the limestone are in three feet of water and measure no more than four feet long and six inches wide. The spring boil is so vigorous that the sound of flowing water is clearly audible for some distance away from the spring. The spring is spectacular old Florida at its best.
Tritium as an Indicator
of Water Flow Times
Through the Aquifer
A number of investigations have determined that ground water in the shallow portion of the Floridan aquifer has entered the aquifer very recently. In the Rainbow Springs area, for example, tritium (a radioactive isotope of hydrogen) activities in wells and springs were as high as 174 TU at the same time (1966-68) that rainfall contained activities as high as 158 TU. In addition, tritium activities in Rainbow and Silver Springs ranged from 38 to 85 TU and 25 to 150 TU, respectively. This indicates that a large percentage of the water discharging from Rainbow and Silver Springs in 1966-68 could not have been in the flow system for more than 16 years. Those years were much wetter than today in Florida when winters can be exceptionally dry. For example this year we experienced only one rainfall event in February and it was not robust (generally less than 1 .00-inch across Central Florida).
There are a number of waterfalls around the Rainbow River. More on these waterfalls in a future blogpost.
Rainbow Spring #6
Rainbow Spring #6 is located about one-half mile downstream of the head spring area in a limestone- floored depression approximately 100 feet across. The spring lies in the channel of the Rainbow River in about 15 feet of water. The spring does not produce a strong boil at the water surface, however, swimmers report that a very strong flow emanates from the spring vent. The spring vent is elliptical in shape; about five feet long and two feet wide.
Declining Water Quality in
Due to Relentless Development
Encroaching on the Springshed
Ground water discharging at Rainbow Springs is fresh, typically containing less than 200 mg/l TDS. Water quality varies slightly across the spring group; sulfate concentrations increasing from less than 10 mg/l in the head spring area to greater than 30 mg/l in springs near the confluence of Rainbow River and Indian Creek. Chloride concentrations in the springs are generally less than 10 mg/l indicating that the springs are recharged by precipitation falling in close proximity to the springs.
Turtles do it in the water.
A pair of Yellow-bellied Sliders engaged in coitus in the Rainbow River
Nitrate concentrations at Rainbow Springs are significantly elevated above background concentration measured in the Floridan aquifer due primarily to encroaching agricultural development and septic tanks, golf courses, etcetera associated with massive development in the area of the springs.
Rainbow Springs is at the bottom of this map.
The highlighted area is the springshed (inside dash marks)
representing over 700 square miles of drainage into the springs
Bridge Seep North
Bridge Seep North is one of two seeps located on the west side of the main spring pool. The spring discharges horizontally from beneath a small outcrop of limestone, and flow from the spring discharges into a short spring run that flows under a foot bridge into the head spring area. The combined flow from Bridge Seep North and another seep 20 feet east of the spring (Bridge Seep South) averaged 3 cubic feet per second for two flow measurements taken in 1996.
Rainbow Springs #1
Rainbow Springs #1 is located on the north side of the head spring area in close proximity to two other vents in the spring pool. The spring, as well as two others, emanates from one of the largest vents in the group (30-50 feet in length). The spring vent is located just outside the boundary of a designated swimming area in approximately 10-15 feet of water. Discharge is not concentrated, however, faint boils can sometimes be seen on the pool’s surface above the vents.
Rainbow Swamp #3
Rainbow Swamp Spring #3 is located along Indian Creek, a small and heavily wooded spring run that lies about 200 yards upstream from the Rainbow Springs State Park Campground. The spring lies at the bottom of an oval-shaped pool in about 10-15 feet of water, and is situated approximately 50 feet to the northeast of Rainbow Swamp #4. Three other springs occur along Indian Creek, and when combined, discharge ~5 mgd to the Rainbow River.
Aerial view of the many springs that make up the Rainbow Springs Group and the pointless development ongoing all along and around the springs and river.
Future for Florida's Springs is Bleak
Water-quality studies conducted by the Southwest Florida Water Management District (SWFWMD) have shown that nitrate concentrations have been increasing in a number of springs throughout the northern portions of the District. This nitrate, derived primarily from inorganic fertilizers, has leached into the Upper Floridan aquifer within the last 20 years and is now being discharged at springs across the region. With population in the SWFWMD expected to exceed 15 million by the year 2020, this situation can only become more serious.
It is estimated that springs in the SWFWMD discharge more than 1,000 million gallons per day (one billion gallons per day) of water from the Floridan aquifer, and that prior to development, accounted for over 80% of the ground-water discharge from the Floridian aquifer. That water nurtured vast river and swamp ecosystems that are now imperiled. As development has accelerated discharge has greatly decreased due to ground-water withdrawals in the region (for housing, golf courses, farms, etcetera) coupled with climate change which has left peninsular Florida drier than historical averages.
Read More about Florida's Imperiled Springs
Of Florida's 700 artesian springs, Silver Springs shimmered the brightest. Its fresh water was so translucent that the white sand and tiny shells at the bottom glistened, giving the river and springs a beautiful tint from above. That was then, today, except for a few patches, the bottom of Silver Springs and Silver River are no longer visible, covered by invasive weeds and coated with algae.
Separated by less than 20 miles along Highway 19 in Florida's Ocala National forest are two of Florida's first magnitude (more than 100 cubic feet per second flow) springs. They offer a tale of two Floridas; one natural, protected, and respected, while the other is trashed by increasingly numerous and disorderly humans.
De Leon Springs State Park is a slice of old Florida that is thankfully far enough away from major highways to preserve some of the area's character and discourage human visitation.