Kiawah’ s Pond System
Story by Matt Hill, Lakes Supervisor, Kiawah Island Community Association( KICA)
Water is no stranger to Kiawah Island— it surrounds us. One would be hard-pressed to visit this sea island and not notice the many ponds that dot its landscape, 124 to be exact. These ponds offer Kiawah Island much more than an attractive aesthetic. They are linked together by a series of pipes creating the Island’ s storm water drainage system. The ponds’ primary function by design is to catch and hold storm water runoff before directing the water to the creeks and tributaries around the Island via outfall structures.
There are nine primary outfall structures located at Beachwalker, Bass, Egret, Pintail, Canvasback, Ibis, Willet, Snowy Egret, and Blue Heron Ponds. These outfall structures have flap gates and risers that allow the water levels to be controlled and adjusted. For instance, in a storm situation, the ponds can be drained or lowered to increase their holding capacity for runoff. The gates are normally set in a way that allows water transfer in and out of the ponds at high tide. In general though, the water levels regulate themselves. High tides can flow in, slightly raising the water level. As the tide falls, the pond level falls too until it reaches the set height of the weir wall in the outfall structure. Once the set height is reached, the water stops exiting the pond and is maintained at the normal pool height.
A common misunderstanding regarding Kiawah’ s pond system is its salinity. The outfalls mentioned above are directly connected to the tidal fluctuations of the Kiawah River. During the majority of the high tides, the tidal amplitude is great enough to bring water into the pond system. This creates a situation where the pond closest to an outfall has a salinity measure similar to the river or creek, sometimes ranging as high as 32 parts per thousand( ppt). For reference, ocean salinity is typically 35 ppt.
As you move toward the center of the Island, the ponds become fresher due to rainwater runoff slowing salinity infiltration. These ponds have salinities ranging from 1 ppt to 20 ppt and are considered brackish. No ponds on the Island technically qualify as freshwater, although some freshwater species do reside in a few of the ponds. Freshwater is classified as having a salinity of 0.5 ppt or less. Though salinity may be within this range at certain times of the year,
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Photo by Kathy Keane