Using a Global Positioning System to Measure Tidal Currents in Absecon Inlet, Atlantic City, N.J.

A Leica System 5000 dual frequency global positioning system receiver System 500 rover operating from a fixed base station was mounted in a drogue made from a $5\text{-}\mathrm{gal}$ (19 L) fisherman’s bucket and used to measure ebb and flood tidal currents in Absecon Inlet, Atlantic City, N.J., to provide data for the design of a marina. The drogue was deployed from a boat in the inlet channel during times of maximum ebb and flood currents. Nine deployments were made around the time of maximum ebb flow and six deployments around the time of maximum flood flow. The drogue was tethered to a boat by a slack line to prevent its loss. Drogue positions were determined at $3\text{-}\mathrm{s}$ intervals and used to calculate flow velocities which were then spatially averaged over travel distances of approximately $50\mathrm{ft}$ (15.2 m). No position had more than $0.54\mathrm{ft}$ (0.16 m) reported horizontal error, and the average of all errors was $0.06\mathrm{ft}$ (0.02 m) for the ebb tide and $0.08\mathrm{ft}$ (0.024 m) for the flood tide.