The impoundment system that visitors see along the Laurel Hill Wildlife Drive was originally build as rice fields by plantation owners using slave labor in the 17 and 18 hundreds.
Growers looked for land that had sufficient tidal fresh water to permit a system of rice cultivation that was practiced in West Africa. The land was cleared, then fields were laid out and surrounded by hand-dug earthen dikes that included one or more "rice trunks". Rice trunks were wooded boxes that penetrated the dikes allowing fresh water form man-made canals or from natural streams to flow in or out of the field as needed.
The trunks had gates at either end that could be adjusted to allow water to flow into the field as the tide rose, or to flow out as the tide fell. Maintenance of the dikes and trunks was critical, since water entering or leaving the field at the wrong time could destroy an entire year's crop of rice.
The dikes have been enlarged to allow vehicle traffic, and the rice trunks replaced with modern materials, but the water levels are still controlled using the power of the tides.