North Inlet-Winyah Bay Reserve, South Carolina

North Inlet-Winyah Bay Reserve, South Carolina

Tidal Range

The Reserve experiences a regular semi-diurnal tidal pattern. Mean tidal amplitude is on the order of 1.4 meters at the ocean end of Winyah Bay and North Inlet, and 1 meter at the Sampit River (1.6 m and 1.2, respectively on the spring tide.) Maximum amplitude near the ocean is about 2.2 meters. Due to its shallow character, North Inlet is thoroughly flushed by the tides, with about 50 percent of its water ebbing into the ocean twice per day.

In Winyah Bay, a salt wedge effect occurs as heavier salt water moves up-estuary along the bottom with the flooding tide, even though the overlying fresh water may be flowing toward the ocean. During periods of low freshwater inflow, flooding tides move salt water more then 15 miles upstream of the Highway 17 bridges, but under average river flow, the penetration is usually within a mile of the bridges. Differences between surface and bottom salinities during these periods may be more than 20 ppt.

River Flow

Fresh water input into Winyah Bay estuary ranges from 2,000 to about one million cubic feet per second (cfs), and the mean runoff is approximately 15,000 cfs. Riverine influence is strong enough to limit ocean water penetration to the lower bay, especially during winter and spring.