Site Location and Environment
The Maple Leaf (8DU8032) is located in Section 26, Township 4S, Range 26E, Duval County, Florida. The vessel sank at a prominent bend in the St. Johns River off Mandarin Point, approximately twelve miles south of downtown Jacksonville, Florida (Figure 1). The hull lies near the east side of the navigation channel, with the bow pointing to the east, perpendicular to stream flow. Water depth is 21 ft. at high tide.
The wreck is almost completely buried under sediment and very little structural material protrudes above the river bottom to indicate the site. The largest component is a section of the paddle wheel shaft that rises from the bottom and is partially obscured by a large log. This feature identifies the amidships area and is oriented north-south. West of the paddle wheel shaft, the rudder post marks the stern and confirms the east-west orientation of the vessel. This alignment is consistent with historical accounts of the loss (Board of Survey 1864). No structural components protrude above the bottom to mark the bow.
The St. Johns River is the longest river in Florida, unusual in North America for its northward flow. Its headwaters lie in the marshes of St. Lucie and Indian River Counties and flow 480 km north along the Atlantic coast dropping only 8 meters along the way (DeMort 1991:97-99). The river occupies a lagoonal valley formed as a result of fluctuating sea levels during Pleistocene glaciation. The valley began as a lagoon behind a long barrier island during a time of higher sea levels associated with the interglacial periods. As sea level dropped, the St. Johns River formed in the shallow stranded valley. The large lakes that characterize the present river formed in depressions of the lagoon (Clewell 1991:19).
Peat marshes that give rise to the river also supply the tannins that give blackwater streams a dark color. As decaying vegetation accumulates in the marshes, rain water percolates through, leaching out tannin and other decomposition products. This water acquires a dark-reddish brown hue and collects as a surface flow, draining into the river or one of its tributary streams. Tannic water is often nutrient-poor, low in dissolved oxygen, and strongly acidic (Clewell 1991:23). These factors are moderated at the site area by tidal influences.
The St. Johns is a tidal river with a tidal reach over 59% of its total length. The astronomical tides affecting Florida's Atlantic coast are semidiurnal with two highs and two lows per tidal day. Flow reversal occurs with each change and is influenced by wind, water density, freshwater inflow and channel configuration (McPherson and Hammett 1991:32-35). These factors also affect the current strength present at the site location. Water velocity was measured at the site on April 27, 1987, under the astronomical phase corresponding to mean tidal conditions. The measured and estimated current for both ebb and flood tide was 1.4 ft./sec. (.83 knots/hr.)(Bodge 1987:6-7). The highest tides, and subsequently the strongest currents, occur during full and new moon phases. These maximum current velocities have not been measured.
Vertical stratification is often present in tidal rivers like the St. Johns because of the density difference between sea water and freshwater. A dense saltwater wedge flows upstream along the bottom with the tide, mixing with the fresh river water above. The rate and amount of mixing is dependent on wind and freshwater inflow. This often creates a broad transition zone from fresh to salt water (McPherson and Hammett 1991:37). Wind is an important factor on the broad stretches of the St. Johns where the open fetch can extend several miles. Brackish water is normally present at the site location with salinity ranging from 1.0 ppt at low tide to 5.0 ppt at high tide in the Orange Park/Mandarin area (DeMort 1991:105). Salinity directly affects the shipwreck through chemical processes occurring on exposed structure and by determining the type of marine organisms able to exist in the esturine environment. A concern is the corrosion of the iron paddle wheel shaft and ship worm damage evident on the bow rail now on display at the Jacksonville Museum of Science and History.
The river bottom surrounding the site area is a flat featureless plain of very soft sediment. A sample of the material contains 25% sand size particles and 75% silt and clay size particles (Bodge 1987:12). In addition, a suspended silt layer, 12 to 18 in. thick, flows across the bottom with the changing tidal currents. Sediment depth over the deck varies between 4 and 9 ft. This sediment goes into suspension very easily and affects visibility conditions on the site.
Visibility in the water column is dependent on dissolved tannin and suspended silt with wind and tidal flow direction having a strong impact. Natural light penetration can exceed 15 ft. under ideal conditions but normally fails about 10 ft. below the surface. Artificial light penetration is dependent on diver activity and suspended silt. It can range from nil to 5 ft. Near the bottom silt layer, visibility is totally obscured and the problem is compounded when bottom sediments are suspended by disturbances such as dredging. As a result, all excavation work on the site is hampered by zero visibility unless the suspended silt layer is diverted from the area.