High Tides Affect Drainage Systems

OverviewStormwater outfall pipe enters into Cooper River, it has a duckbill type check valve, one that is being phased out for more efficient and effective in-line valves.

The height of the tide has one of the greatest impacts on how quickly stormwater will drain from the City because most of the outfalls of the City drain to water bodies that are tidally influenced.

At high tide, much of the stormwater collection system (the pipes and ditches) is already full of sea water leaving little room for the stormwater runoff. The stormwater that has collected on the surface has no place to go because the pipes and ditches are full and ponding occurs.  

The image to the right shows a stormwater outfall pipe that directs water into the Cooper River.  It has a duckbill type check valve on it to help prevent water from backing up into the system, the duckbill type is being phased out for more efficient and effective in-line check valves.

Low Tide and High Tide Scenario Graphic 

Delayed Drainage

When a high tide stays inland extra long, such as due to wind, the sea water will continue to remain in the outfalls of the stormwater collection system until the tide recedes. Rain events that occur within two hours of high tide will drain significantly slower than rain events that occur during other times. This time frame can be even longer, such as when rain events occur during a higher King Tide and/or when wind forces hold a high tide inland longer.

The longer the tide is high and much of the stormwater collection system is full of sea water, the longer time stormwater will pond on the surface with little or no place to go.

Learn More 

Learn more about how check valves are successfully preventing sea water from backing up into our stormwater systems.

Learn more about how major tunnel and pump drainage improvement projects successfully overcome high tide challenges.

Learn more about what causes flooding in the City of Charleston.

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