Underwater Cave and Cavern Research

The National Cave and Karst Research Institute (NCKRI)

How many people driving down US 19 are aware of the vast cavern system beneath them? Brett Hemphill and the Karst Underwater Research (KUR) Team know the system very well. Mr. Hemphill jokes that every time he drives a certain portion of US19, he holds his breath because he knows that the only thing between the car and a vast underwater cavern hundreds of feet deep and large enough to hold a jumbo airliner is just feet of limestone rock.

Mr. Hemphill is Director of Karst Underwater Research out of Dade City, a 501 organization. He has been cave diving for over 25 years. Early on in his explorations, he became amazed with the sanctums beneath the water's surface that still remain unexplored. His priority along with Karst Underwater Research is to protect these fragile spring and cave systems and learn about their intricate workings through scientific analysis so that we are aware of how best to protect them and our limited water resources.

Mr. Hemphill along with the Karst Research Team has successfully mapped the Weeki Wachee cavern and spring system. They also recently discovered the elusive connection between the Weeki Wachee Spring System and a nearby spring named Twin Dees, northwest of Weeki Wachee. Mr. Hemphill described the systems as "Two lovers [that were] lost in the fog." Understanding the connection of these intricate cavern and spring systems is essential to understanding how we can help improve our water and the preserve the aquifer system. The Karst Underwater Research team is devoted to this effort despite the difficulties of the work as well as the adversity and loss which they have recently faced.

In order to understand the spring systems and our aquifer, it is essential to know what karst actually refers to. Geologists have adopted the word karst to describe a landscape which features sinkholes, springs, caves and sinking springs. This type of landscape usually develops on limestone rock, but can also develop on dolostone, gypsum, and salt. Precipitation is absorbed into the ground and runs down from a higher elevation streaming to lower elevations. Naturally occurring weak acids in the rain and soil gradually dissolve the small fractures in the soluble bedrock, eventually forming a sinkhole.

Mr. Hemphill explained that sometimes Karst features come very close to the surface. Sand and sediment usually filter out a certain amount of nitrates and pollutants, but when karst features those found especially in the Brooksville area come close to the surface and connect directly into the spring conduit system not much can be filtered out. It is essential to recognize these features when we go to develop an area. Mr. Hemphill says the technology is there to evaluate this. Because karst features can occur very close to the surface, it is also important to realize that some locations are better than others for septic. Mr. Hemphill explained that you can have a septic field in one spot with good sedimentary layers and another could be close to a karst feature that poses more of a threat to contaminating the aquifer.

To provide an example, the massive conduit beneath US19 mentioned previously heads to the S/SE towards a group of man made lakes in which developments were built around them. These lakes were constructed in this location since there were already existing sink holes which help to keep the lakes full. However, the runoff from development is going directly into the aquifer since these lakes connect to it through the sinkholes. Mr. Hemphill emphasizes that there is a responsibility to know what is happening underground in terms of karst features before developing an area.

Mr. Hemphill describes the Florida aquifer as saturated limestone. It is not a gigantic room of water. Water does move through rock. Additionally, drinking water in Florida comes from a very thin layer of the aquifer somewhere above 200 and below 100 feet. If you go too deep it's salt- too shallow it hasn't had enough time to filter itself out. Mr. Hemphill states that the developing practices in Florida have to be more stringent in order to keep the aquifer healthy.

Many of the discoveries by the Karst Underwater Research team have been made through water sampling and fauna identification. There are some small life forms, crustacea such as crayfish that live inside the caverns. Karst Underwater Research also works in conjunction with other scientists collecting information but their big goal is to map the system and to try to understand what is happening and what is going on once the water has made its way inside. Researchers have found that some of the water that flows out of Weeki is days old and other samples are hundreds of years old.

In 2007, Florida was experiencing one of its worst long-term droughts. This enabled the researchers to have access to Weeki Wachee. Mr. Hemphill describes just getting into the spring as monumental. Then they had the challenges of figuring out how to explore it safely and effectively. The last time anyone made headway exploring the spring was in the 1980's when a team led by Sheck Exley laid 220' of line into the first room. Karst Researchers were able to tie into Exley's line and eventually explored Weeki Wachee Springs to a depth of 407 feet. Confirming what was already suspected, that Weeki Wachee is the deepest known spring in the United States. Since then KUR explored a spring in Texas to 455 feet.

They were able to explore Weeki Wachee on and off between 2007 and 2012 depending on rainfall. They had short windows of opportunity consisting of 1 to 2 weekends between June and July, before the start of the rainy season. According to Mr. Hemphill, one of their most interesting finds was the connection to another spring, Twin Dees, northwest of Weeki Wachee.

This type of diving is perilous as well as demanding. Some dives have reached up to 16 hours, close to full saturation diving. Diving to depths over 300 feet require at least 15 hours of decompression. Decompression is a stop at a shallower depth to allow the gases in your bloodstream to adjust to the decrease in pressure. Often divers must pass through very narrow crevices. In 2012, the Karst team suffered a major loss with the death of team member Marson Ashly Kay while researching the Weeki Wachee system. He reportedly became disoriented during the dive and got stuck in a tight cavern while trying to surface. It is possible that the flow of the spring contributed to the tragedy.

The water flow of the spring must be low enough to enter and maneuver safely. There has not been much opportunity for access to Weeki Wachee in 2015 since the water discharge rate has been very high- good news for the health of the aquifer, spring and its estuaries.

Waterflow at Weeki Wachee can reach an upwards of 200 cubic feet per second. During droughts, Weeki Wachee water flow has dropped as low as 98 cubic feet per second. Researchers are unable to enter the Weeki Wachee spring if water flow is above 110 cubic feet per second. Twin Dees on the other hand, can only be entered during times of very high flow. The researchers shift their explorations to Twin Dees when they are unable to access Weeki Wachee.

The opening to Twin Dees is quite narrow but at around 1300' into the cave system at around 200' deep, it opens up into an enormous space. This space called the Alph Tunnel, is directly under US 19 and 280 feet deep.

Source: Hernando Sun

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