North Carolina Administrative Code › Title 15A - Environmental Quality › Chapter 02 - Environmental Management › Subchapter H - PROCEDURES FOR PERMITS: APPROVALS › Section .1000 - STORMWATER MANAGEMENT › Section 02H .1054 - MDC FOR STORMWATER WETLANDS

Current through Register Vol. 39, No. 2, July 15, 2024
The purpose of this Rule is to set forth the design
					 requirements for stormwater wetlands that are constructed to meet the
					 requirements of this Section.
(1)
				  TEMPORARY PONDING DEPTH. The ponding depth for the design volume shall be a
				  maximum of 15 inches above the permanent pool.
(2) PEAK ATTENUATION DEPTH. The wetland may
				  be designed to temporarily pond peak attenuation volume at a depth exceeding 15
				  inches.
(3) SURFACE AREA. The
				  surface area shall be sufficient to limit the ponding depth to 15 inches or
				  less. The surface area specifications in Items (6) through (9) of this Rule are
				  based on the wetland at its temporary ponding depth.
(4) SOIL AMENDMENTS. The pH, compaction, and
				  other attributes of the first 12-inch depth of the soil shall be adjusted if
				  necessary to promote plant establishment and growth.
(5) LOCATION OF INLET(S) AND OUTLET. The
				  inlet(s) and outlet shall be located in a manner that avoids short
				  circuiting.
(6) FOREBAY. A forebay
				  shall be provided at the inlet to the stormwater wetland. The forebay shall
				  comprise 10 to 15 percent of the wetland surface area. The forebay depth shall
				  be 24 to 40 inches below the permanent pool elevation. The forebay entrance
				  shall be deeper than the forebay exit. If sediment accumulates in the forebay
				  in a manner that reduces its depth to 15 inches, then the forebay shall be
				  cleaned out and returned to its design state.
(7) NON-FOREBAY DEEP POOLS. Deep pools shall
				  be provided throughout the wetland and adjacent to the outlet structure to
				  prevent clogging. The non-forebay deep pools shall comprise 5 to 15 percent of
				  the wetland surface area and shall be designed to retain water between storm
				  events. The deep pools at their deepest points shall be at least 18 inches
				  below the permanent pool elevation.
(8) SHALLOW WATER ZONE. The shallow water
				  zone shall comprise 35 to 45 percent of the wetland surface area. The shallow
				  water zone shall be zero to nine inches below the permanent pool
				  elevation.
(9) TEMPORARY INUNDATION
				  ZONE. The temporary inundation zone shall comprise 30 to 45 percent of the
				  wetland surface area. The temporary inundation zone shall be between 0 and 15
				  inches above the permanent pool elevation.
(10) DRAWDOWN TIME. The design volume shall
				  draw down to the permanent pool level between two and five days.
(11) PROTECTION OF THE RECEIVING STREAM. The
				  wetland shall discharge the runoff from the one-year, 24-hour storm in a manner
				  that minimizes hydrologic impacts to the receiving channel.
(12) LANDSCAPING PLAN. A landscape plan shall
				  be provided and shall include the following:
(a) delineation of planting zones;
(b) plant layout with species names and
				  locations; and
(c) total number and
				  sizes of all plant species.