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Summary
As a result of conversations with local landowners, Bert Wilcher of Tampa Adventure
Sports became aware of a spring in the Dobes Hole area of the Withlachoochee River,
which is south-southwest of the town of Lacoochee in Pasco County, Florida. The
spring is located within the Green Swamp West parcel of Southwest Florida Water
Management District (SWFWMD) lands.
A cross-reference with other published literature did not identify any pre-existing
information about this spring. Given the absence of information, we have named the
spring as Dobes Spring for this report.
Reconnaissance, exploration and assessments were conducted between April and May of 2006.
At that time, water levels on the Withlacoochee River were low due to drought conditions.
Although there was no observed boil or water movement in the spring pool, ground-water
discharge from Floridan aquifer was apparent at the spring vent underwater. A discharge
measurement across the downstream opening of the pool, conducted by SWFWMD personnel during
a subsequent visit, resulted in an estimated flow rate of 15 cubic feet per second (cfs).
This discharge tentatively classifies Dobes Spring as a 2nd magnitude spring, but further
measurements will be necessary to fully assess the flow characteristics of the spring.
Access
Dobes Spring can be reached by two different routes. The northern access route requires
permission to travel through a private ranch which skirts the northern edge of the spring
basin. A southern route provides access on District lands to the southwest edge of the
broad body of water known locally as Dobes Hole. From there, a boat is required to continue
northward to the spring itself. Water levels across the Dobes Hole basin are typically quite
shallow (ranging from 0 to 2 feet in depth). However, the area around the spring cavern and
the short 'run' that join the spring pool to the larger Dobes Hole basin are distinctly
deeper. At the time of the reconnaissance, water depths in the circular pool above Dobes Spring
ranged from 10 to 12 feet.
Qualitative Assessments
Dobes Hole is a broad 'flood plain' fed by the Withlacoochee river from the south-eastern side
of the basin area; the river then converges back into a defined river on the north side of Dobes
Hole and continues flowing north and west from there.
Given the draught conditions the region was experiencing at the time of the initial exploration,
it was surprising to observe such a strong level of discharge. It appears that the water level
was substantially lower than usual when the site was visited in April of 2006; this assessment
was based on the water lines on nearby trees. Under normal conditions a surface disturbance
(boil/slick) from the spring would most likely not be evident. This is due to the combination of
the level of discharge, the morphology of the entrance and higher river stages that would conceal
the clear water. At the cavern entrance, which sits approximately 30-35 feet below the surface, the
water discharges horizontally to a slowly upward-sloping mud plane. These factors could make it
difficult to recognize the presence of a spring under most conditions.
Conversations with local property owners indicated that at times in the past, the spring has suddenly
reversed and drained the entire basin within the matter of a few hours. Thereafter, the spring began
to discharge again. Unfortunately, we were unable to identify any actual witnesses to these events or
get a date when one of these alleged 'reversals' occurred.
Exploration
During April of 2006, KUR divers performed two exploratory dives in the system. The teams have
gone approximately 500 feet in the system and reached a maximum depth of 123 feet fresh water
(ffw). Depth measurements were based on ambient water pressure, not land elevations. The following
discussion describes the observations and measurements compiled during the exploratory dives at
Dobes Spring, which are depicted in the included maps of the system.
This system contains several extremely restrictive areas, even by cave diving standards. Tanks must
be worn in a side-mount configuration to explore this cave system. All the water discharging from the
spring and entrance room comes from a vertical fracture that averages two feet across. This fracture
breaches another room at approximately 71 ffw. Thereafter, the cave spirals downward to level off at
approximately 120 ffw. This appears to be the primary depth where the cave conduit establishes a
consistent morphology. While the upper sections were typified by vertical fractures and large
'breakdown' piles of boulders and rocks, the deeper section has a floor of clastic materials, including
white sand, and detritus-like materials. Also, a large vertebra, possibly from an alligator skeleton, was
recovered from the cave conduit. These materials provide some circumstantial support to the stories of
the system's catastrophic 'reversals'.
Aside from the consideration of these 'instantaneous' reversals, this exsurgence may be more
appropriately classified as an estavelle due to the probable intermittent discharge when the spring is
under higher river stages. Both flow reversals during higher river stages or possible karst windows
(with direct connection to the conduit further upstream) could alternatively be responsible for the
presence of surface materials found in the 120-foot depth section of the system.
For further consideration, several subsidences – some recent/active, others being much older and
stabilized – where identified on land to the southwest, west and west-northwest of the spring. Since
the system was only explored a short distance, it is quite possible that the main trajectory of the
primary conduit could change its directional trend from the southeast trend that is currently mapped.
The tunnel continues on beyond what has been surveyed. Further exploration is recommended to
validate this apparent trajectory. However, exploration must be performed by experienced cave divers
using a side-mount configuration and be prepared for significant restrictions in the shallower section
of the cave.
For the section of system that has been explored to date, there does not appear to be multiple water
sources of inconsistent water quality converging in the system. It appears that all the water is Floridan
Aquifer and no surficial or deep intrusion is occurring under current conditions.
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