Home Methods of Study Bathymetry Freshwater Flow Specific Conductance Summary & References

Methods of Study

Transects were run diagonally from shoreline to shoreline, when possible, and also down the main channel. Many of the shallow areas near shore are not navigable and were measured with a tape and weight to confirm depths. Boat coordinates, time, and mean water depth were recorded about every 30 to 60 seconds on a paper scroll. Continuous data from the recording fathometer were available for interpolation between recorded measurements. Depths were considered accurate within 0.5 ft, whereas the horizontal position was considered accurate within 100 ft. The combined margin of error for the depth contours was about 1.0 ft.

Five continuous tidal-stage recorders were used to make observations of the tidal stage every 15 minutes at Bokeelia, Indian Field, Matlacha, Parrots Perch, and Camelot Lock (figs. 2 and 3). Records from these stations were evaluated to determine time lag and changes in amplitude of tidal waves. Depth data were adjusted to sea level based on the tidal stage from the nearest recorders at the stations (figs. 4-8).

Figure 4. (above) High and low tidal stage at Bokeelia. [larger image]	Figure 5. (above) High and low tidal stage at Indian Field. [larger image]
Figure 6. (above) High and low tidal stage at Matlacha. [larger image]	Figure 7. (above) High and low tidal stage at Parrots Perch. [larger image]
Figure 8. (above) High and low tidal stage at Camelot Lock. [larger image]

The average time lag varied at high and low tides between Bokeelia (in the northern end of Matlacha Pass) and Matlacha (in the middle of the pass) and between Matlacha and Parrots Perch (in the southern end of the pass). The average time lag was about 45 minutes between Bokeelia and Matlacha and between Matlacha and Parrots Perch during high tide. The average time lag was about 1 hour and 45 minutes between Bokeelia and Matlacha and about 1 hour between Matlacha and Parrots Perch during low tide.

The average range in tidal waves between the high and low tides throughout Matlacha Pass was about 1.62 ft. At Bokeelia, Matlacha, Parrots Perch, and Camelot Lock for the 1990-92 water years and at Indian Field for the 1991-92 water years, the average range in tidal waves between the high and low tides was: 1.77 ft at Bokeelia, 1.87 ft at Indian Field, 1.77 ft at Matlacha, 1.17 ft at Parrots Perch, and 1.52 ft at Camelot Lock. The small tidal average at Parrots Perch might have been because of dampening of wave action as this gage is located in protected waters.

Freshwater flow into Matlacha Pass was measured at streamflow-gaging stations on the major canals in Cape Coral (figs. 2 and 3). A stage-discharge relation was established for each canal. The daily mean discharge was computed from this relation.

Water samples were collected and specific conductance was measured at about 90 sites in the freshwater canals, spreader canal systems, and in Matlacha Pass during 1984 (La Rose and Sheftall, 1984). That extensive study provided an excellent data base for determining the distribution of freshwater flow into Matlacha Pass under wet- and dry-season conditions. Continuous monitoring for specific conductance was conducted about 2 ft below the surface and about 2 ft above the bottom in the main channel near State Road 78 (fig. 2).

A geographic information system (GIS) was developed to store, analyze, and plot spatial data for this study. From the bathymetric surveys, Universal Transverse Mercator coordinates, time, depth, and other information (such as location of sandbars and oyster beds) were stored in the GIS. The canal system, roads, sandbars, and mangroves of the pass were digitized from U.S. Geological Survey 1:24,000 scale topographic maps. Adjusted depth data were plotted on large-scale digitized maps, and depth contours were digitized into the GIS. Vegetative features and aerial photography were used to modify the depth contours in areas where depth data were unavailable.