Rice field trunks play a big role in controlling water movement in many of the South Carolina areas I explore. Once used for growing rice, private land owners and the SC Department of Natural Resources currently manage thousands of acres of wetlands using this time-tested method. Dikes separate what was a rice field from a major body of water and the trunk is used to move water back and forth.
Last week the water had been let out of the Magnolia Plantation & Gardens boat pond, so named because they give nature tours by boat around the pond. To give you an idea of the size, the perimeter of the pond is about 1.75 miles (3 KM). The pond is a mixture of open water and cat tails / reed clumps. Two years ago the boat channel was dredged and the water seen in the first image is in that channel.
With the low water I was able to get some images of the trunk parts that are normally under water.
There is a wooden box creating a culvert under the dike (think cereal box laying on its side). I have read that these are called trunks because in colonial times hollowed tree trunks were used to conduct the water.
The lower paddle ends of the flaps, which pivot at the top, are adjusted to manage the water flow.
The Ashley River is tidal, so with both ends of the trunk wide open at low tide the water drains out of the pond. Then with at least one end of the trunk closed as the tide turns the water in the pond will remain low. The seals on either end are not tight and there is always some water movement.
Leaving the trunks ends open will refill the pond as the tide raises the water level in the river. Sometimes they are left open for days to wash out the pond or change the salinity level.
The bonus to all this for the nature photographer is that wading and shore birds are attracted to the lower water. Fish are concentrated in a smaller volume making hunting easier and they can poke around in the mud.