Overview of New Infrastructure
Project One is in the area of the Kiawah Island Parkway and Sea Marsh Drive near the west end of the island. Sea Marsh Drive floods in this location. Water from the road is designed to shed into Pond 21, but the water level in this pond stays too high due to insufficient capacity to drain, so there is no place for water to be displaced. The solution is to add another pipe from Pond 21 to its neighboring pond, to increase its capacity to flow through the pond system and out through the drainage system. This will significantly reduce rainfall flooding on Sea Marsh Drive.
Project Two is in the area of the Kiawah Island Parkway and Sea Forest Drive near the fire station. On at least an annual basis, the Kiawah Island Parkway floods in this location with 12 inches of water, the height of some car tailpipes, which could prevent access to most of island. There is no possible detour in this area, so it is critical to maintain access here. Overall drainage capacity issues also contribute to significant flooding (up to 26 inches) on Sea Forest Drive and many side streets.
The solution is add a new outfall to the marsh at an existing inlet and raise an existing berm at that inlet to prevent tidal water from flooding the parkway. Currently, one outfall at Inlet Cove drains all of the ponds on the west end of the island up to the V-gate, 37 ponds and over three miles of drainage. A new outfall will drain The Settlement neighborhood on the north side of the parkway, relieving the Inlet Cove outfall from draining this one-mile section. The additional outfall helps keep the Kiawah Island Parkway clear, and alleviates hazardous flooding in The Settlement neighborhood and throughout West and East Beach areas. This is a critical and impactful project.
In two independent digital hydrologic models of Kiawah Island, simulations confirm the new outfall will effectively relieve the Beachwalker Drainage Basin with no negative impact to the existing inlet and surrounding properties. As a precaution, KICA has surveyed this inlet, and will continue to survey and analyze it annually to monitor any impact of the new outfall.
Project Three is in the area of the Kiawah Island Parkway and Green Dolphin Way. At this location, the Kiawah Island Parkway’s elevation dips, creating a bowl, and it floods with several inches of water. The solution is to raise 450 feet of the parkway to eliminate the bowl so that water does not collect in this area. There is no possible detour in this location, so maintaining a passable road is imperative.
Project Four is in the area of the Vanderhorst Gate (V-gate). This area is also low and can hold water from rainfall. In some cases, a nearby pond can push excess water onto the road through curb drainage, compounding flooding. There is no possible detour in this area, so it is a priority to maintain traffic flow in this location. The solution is to add a flap gate to the pipe from the nearby pond, so that water cannot be pushed up into the intersection, and install a pump so that water can be pumped out from the V-gate area, keeping it passable for cars. The pump can also alleviate Governors Drive flooding in the Project Five area.
Project Five is in the area of Governors Drive and Halona Lane (across from the Turtle Point maintenance facility). A tidal inlet at the end of Halona Lane can cause flooding on Governors Drive. A weir, a low barrier to reduce the infiltration of minor tides, and flap gate on the end of the pipe will reduce flooding in Indigo Park and on Governors Drive. A new dry detention area next to Governors Drive will collect excess rainwater. The pump at the V-gate could also be connected to this section of Governors Drive to relieve road flooding, as there is no detour in this area.
Project Six is in the area of Governors Drive, between the Vanderhorst Mansion (across from Flyway Drive) and Persimmon Court. Blocked pipes and an inefficient drainage configuration cause flooding on Governors Drive. The solution involves adding pipes, reconfiguring pipes and raising the level of pipes so that water efficiently drains from the road and area ponds into the inlet. The inlet will also be dredged, to remove several decades of deposited sediment, and flap gates on pipes will prevent water from coming in with tides. A weir will be added to the end of Pond 56, to prevent tidal water from infiltrating and overflowing the pond.