Main Street Ocean Outfall

In the early evening of August 27, the city of North Myrtle Beach received upwards of three inches of rain in about a two hour period, resulting in flooding of the Main Street, Horseshoe, Ocean Boulevard area. The flooding event has led some people to wonder if there is something wrong with the recently completed Main Street Ocean Outfall project, which was designed to collect storm water from a large area of the city and expel it about a quarter-mile offshore through a huge underground storm water discharge pipe.

The ocean outfall project was designed and installed correctly, and it functions correctly. However, the membrane filters that the City was required by federal permit to install at each of the storm water catch basins that are part of the project were overwhelmed with debris carried to them by the flowing storm water. The membrane filters are made of a fine material that collects anything that may enter the catch basins during a rain event, including sand, dirt and all forms of litter.

The filters were not required as part of the four ocean outfall projects previously constructed by the city. Those projects were constructed under a blanket national permit. Permitting requirements changed prior to the design and installation of the Main Street Ocean Outfall project, and the filters are now required.

The membrane filters are located within each of the 12 catch basins located in the area of the intersection of the Horseshoe and Ocean Boulevard, in each of the 14 catch basins going north along Ocean Boulevard, and in each of the 16 catch basins going south along Ocean Boulevard.

The federal permit requires the membrane filters to be cleaned once each quarter. That has worked to date but the sheer amount of rain experienced on August 27, and the large amount of debris that it carried into the catch basins overwhelmed the filters, backing up the discharge of storm water into the ocean. As a result, the City will now check and clean each filter every other week in order to ensure that they are not blocked and that storm water can flow through them.

The current reconstruction status of the Horseshoe also contributed to the scenario. The Horseshoe parking lot base is currently sand and coquina. A permanent surface will be constructed this fall and winter. A lot of the sand and coquina currently located within the Horseshoe entered the catch basins located in the Horseshoe area, adding to the clogging of the filters.