This article sets forth requirements to protect public safety
through the proper design and operation of stormwater management basins.
This section applies to any new stormwater management basin.
A.
A trash rack is a device designed to catch trash and debris and prevent
the clogging of outlet structures. Trash racks shall be installed
at the intake to the outlet from the stormwater management basin to
ensure proper functioning of the basin outlets in accordance with
the following:
(1)
The trash rack shall have parallel bars, with no greater than six-inch
spacing between the bars.
(2)
The trash rack shall be designed so as not to adversely affect the
hydraulic performance of the outlet pipe or structure.
(3)
The average velocity of flow through a clean trash rack is not to
exceed 2.5 feet per second under the full range of stage and discharge.
Velocity is to be computed on the basis of the net area of opening
through the rack.
(4)
The trash rack shall be constructed and installed to be rigid, durable,
and corrosion resistant, and shall be designed to withstand a perpendicular
live loading of 300 pounds per square foot.
B.
An overflow grate is designed to prevent obstruction of the overflow
structure. If an outlet structure has an overflow grate, such grate
shall meet the following requirements:
(1)
The overflow grate shall be secured to the outlet structure but removable
for emergencies and maintenance.
(2)
The overflow grate spacing shall be no less than two inches across
the smallest dimension.
(3)
The overflow grate shall be constructed and installed to be rigid,
durable, and corrosion resistant, and shall be designed to withstand
a perpendicular live loading of 300 pounds per square foot.
C.
For purposes of this § 330-63C, "escape provisions" means the permanent installation of ladders, steps, rungs, or other features that provide easily accessible means of egress from stormwater management basins. Stormwater management basins shall include escape provisions as follows:
(1)
If a stormwater management basin has an outlet structure, escape provisions shall be incorporated in or on the structure. With the prior approval of the reviewing agency identified in § 330-64, a freestanding outlet structure may be exempted from this requirement.
(2)
Safety ledges shall be constructed on the slopes of all new stormwater management basins having a permanent pool of water deeper than 2 1/2 feet. Such safety ledges shall be comprised of two steps. Each step shall be four feet to six feet in width. One step shall be located approximately 2 1/2 feet below the permanent water surface, and the second step shall be located one foot to 1 1/2 feet above the permanent water surface. See § 330-65 for an illustration of safety ledges in a stormwater management basin.
(3)
In new stormwater management basins, the maximum interior slope for
an earthen dam, embankment, or berm shall not be steeper than three
horizontal to one vertical.
A variance or exemption from the safety standards for stormwater
management basins may be granted only upon a written finding by the
appropriate reviewing agency (municipality, county or department)
that the variance or exemption will not constitute a threat to public
safety.
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