Degrove recently completed a Hydrographic Survey of Lake Panasoffkee for the Southwest Florida Water Management District (SWFWMD). The area surveyed included the open water within Lake Panasoffkee and the centerline of open water portions of Little Jones Creek, Big Jones Creek, Shady Brook spring runs, and the Lake Panasoffkee Outlet River that flows west to the Withlacoochee River. The survey was completed using RTK/GPS with cellular modems at the base and on the boat. Lake cross-sections were surveyed every 1000 feet, and two transect lines were surveyed the length of the lake – perpendicular to the cross-sections. The data from these crossing lines was used to calculate precision statistics for the hydrographic data.
Lake Panasoffkee is a large (over 3200 acres) lake, but very shallow and heavily vegetated. These conditions forced us to use non-typical processing procedures for the hydrographic data collected. Due to the extreme amounts of vegetation, we had to view the echogram of each cross-section line individually, in order to determine and manually digitize the lake bottom – a tedious process. Electronic soundings could not be achieved in some areas, either because the vegetation was too matted for electronic soundings, or floating vegetation was too thick for an outboard motor. In these areas, field crews collected bottom shots using an airboat and a GPS receiver on a 25 foot rod. The base of the rod was equipped with a six-inch plate, which was allowed to come to rest in the silt and mud. This allowed for a consistent lake bottom to be determined. Bottom shots were also taken near the shorelines, where the lake became too shallow for electronic readings or outboard motors. Crews overlapped rod shots with electronic soundings to ensure continuity in the data of each cross-section line. The image seen at the top of this page depicts the data collected. The magenta lines depict hydrographic data, and the yellow lines depict data collected with the airboat and rod.
SWFWMD intends to use the data collected to support decision making in the long-term management of Lake Panasoffkee, and more specifically how the District operates the Wysong-Coogler Water Conservation Structure.
The photographs below illustrate some of the field procedures and conditions. Notice the photo of the floating vegetation.