Executive Summary Introduction Study Area & Objective Methods Results >Summary & Recommendations Acknowledgements & References Statement of Work Appendix A Appendix B PDF Version

More than 68 line-mi of data were collected from 8 major canals plus the canal adjacent to the ECPL. Quality of profile data varied between good to moderate and poor depending on numerous variations in canal structure and subsurface lithology. Depth of acoustic returns varied greatly from 10 to 260 ft, but generally there are usable data to 100 ft below sea level. Approximately 80 per cent (52 mi) of the canals provided usable data. The canals that did not have usable data include C-4 Canal, Bird Drive Canal, and the Snapper Creek Canal extension.

In all canals surveyed the Holocene sediment and Pleistocene Miami Limestone were removed during canal construction. The bottom of most canals has an acoustically transparent layer of undifferentiated muck. The first solid reflection recorded is the original surface left from canal construction within the Pleistocene Fort Thompson Formation. The Fort Thompson Formation is a vuggy, with poor to good induration, and has moderate stratigraphic variability that is conformable around much of the Lake Belt study area. Thickness of this unit varies from ~1 to ~25 m (~3 to ~80 ft). Beneath the Fort Thompson Formation is the Tamiami Formation with irregular alternating layers of sand, silt and limestone. The interpretations discussed in this report are best used as inferred features without direct verification to indicate trends and changes in the geology associated with porosity, and rock hardness.

In the upper 50 ft of most canals, the seismic profiles reveal several continuous reflections and numerous vertical features that are inferred to represent shallow solution pipes or vugs. The solution pipes or large vugs frequently penetrate through more than one horizon and may be conduits for vertical ground-water flow through the formation. The Tamiami Formation has numerous similar inferred features that may represent solution pipes and collapse structures. An exception to the general description of Fort Thompson and Tamiami Formations in these canals is the C-6 Canal with seismic profiles that do not show flat continuous reflections, instead there is an irregular, but fairly continuous reflection. This reflection is probably produced by a lithologic contact within the Fort Thompson between a weak limestone (poor induration) above and a moderate to hard limestone (good to moderate induration) below. This reflection is distinctive and not recognized beneath other canals.

In general, it is postulated that the highly variable depositional lithology of the area does impact ground-water flow due to the formation of the inferred post-depositional dissolution that could provide pathways and conduits for ground-water to flow between units, both laterally and horizontally. The post-depositional solution-enlarged pore spaces vary as a result of depositional textures, diagenesis in a meteoric-water system, and vertical position within the lithofacies of upward-shallowing cycles. It been demonstrated by Cunningham and Aviantara (2001) that each depositional facies has unique solution features that are characteristic of the rock units. This would indicate that even though the rock-fabric facies within the Fort Thompson Formation stratigraphic cycles is moderately variable it is characteristically conformable within much of the Lake Belt study area. Using high-resolution seismic data to identify trends of post-depositional dissolution features provides valuable information about the mechanics of differential ground-water flow.

The objective of this study is to improve the understanding of the geology and hydrogeology underlying the Lake Belt Area by conducting a high-resolution seismic reflection survey of area canals. Acquiring continuous high-resolution seismic profiles from shallow freshwater lakes and canals in Florida has had varying degrees of success. In most cases it has been very useful in combination with core descriptions, gamma logs, and other data in describing the shallow geology. In this study, the objective was successful because we now have better information about the extent and variability of subsurface units, but the quality of data acquired did not have adequate penetration to span the entire thickness of rocks and sediments that comprise the surficial aquifer. Perhaps, in future studies modifications of acquisition techniques, hydrophone spacing, or acoustic output (power) might provide better results in canals such as the C-4 Canal. Other modifications, such as configuring hydrophones and source to be laid on the canal bottom or to be towed near the bottom to minimize reflections from canal walls, and to develop a method to shield receivers from top and side reflections. Canals similar to the Bird Drive Canal are the most challenging of canals due to the shallow and narrow nature of the canal prohibits data collection.