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.
