20170314 Ver 3_Supplement Form - Wet Pond B_20181113

WET POND LEY-15010 - Twin Lakes Center
2
Drainage area number Sub 1 to SWMF B
Total coastal wetlands area (sq ft) - Parking / driveway (sq ft)332605 sf
Total surface water area (sq ft) - Sidewalk (sq ft)55062 sf
Total drainage area (sq ft)638526 sf - Roof (sq ft)33755 sf
BUA associated with existing development (sq ft)33893 sf - Roadway (sq ft)
Proposed new BUA (sq ft)421422 sf - Other, please specify in the comment box below (sq ft)33893 sf
Percent BUA of drainage area 71.3%Total BUA (sq ft)455315 sf
Design rainfall depth (in)1.0 in
Minimum volume required (cu ft)36809 cf
Design volume of SCM (cu ft)36809 cf
#1 Is the SCM sized to treat the SW from all surfaces at build-out?Yes #7 If applicable, with the SCM be cleaned out after construction?Yes
#2 Is the SCM located on or near contaminated soils?No #8 Does the mainetenance access comply with General MDC (8)?Yes
#3 What are the side slopes of the SCM (H:V)?3:1 #9 Does the drainage easement comply with General MDC (9)?Yes
#3 Does the SCM have retaining walls, gabion walls or other engineered side slopes?Yes #10 If the SCM is on a single family lot, does the plat comply with General MDC (10)?
#4 Are the inlets, outlets, and receiving stream protected from erosion (10-year storm)?Yes #11 Is there an O&M Agreement that complies with General MDC (11)?Yes
#5 Is there a a bypass for flows in excess of the design flow?Yes #12 Is there an O&M Plan that complies with General MDC (12)?Yes
#6 What is the method for dewatering the SCM for maintenance?Pump (preferred)#13 Was the SCM designed by an NC licensed professional?Yes
#1 Method used SA/DA #6 Width of the vegetated shelf (feet)6 ft
#1 Surface area of the main permanent pool (square feet)17488 sf #6 Location of vegetated shelf Above Normal Pool
#1 Volume of the main permanent pool (cubic feet)51965 cf #6 Elevation of top of shelf (fmsl)349 ft
#2 Average depth of the main pool (feet)4 ft #6 Elevation of bottom of shelf (fmsl)348 ft
#2 Was the vegetated shelf included in the calculation of average depth?Yes #6 Slope of vegetated shelf (H:V)6:1
#2 Elevation of the bottom of the permanent pool (fmsl)342 ft #7 Diameter of drawdown orifice (inches)2.5 in
#2 Elevation of the top of the permanent pool (fmsl)348 ft #7 Drawdown time for the temporary pool (hours)67 hrs
#2 Elevation of the top of the temporary pool (fmsl)354 ft #7 Does the orifice drawdown from below the top surface of the permanent pool?Yes
#3 Depth provided for sediment storage (inches)12 in #8 Does the pond minimize impacts to the receiving channel from the 1-yr, 24-hr storm?Yes
#4 Are the inlet(s) and outlet located in a manner that avoids short-circuiting?Yes #9 Are fountains proposed?No
#9 If yes, is documentation provided per Wet Pond MDC (9)?No
#10 Is a trash rack or other device provided to protect the outlet system?Yes
#5 Volume of the forebay (cubic feet)9976 #11 Are the dam and embankment planted in non-clumping turf grass?Yes
#5 Is this 15-20% of the volume in the main pool?Yes #11 Species of turf that will be used on the dam and embankment Tall Fescue
#5 Depth of forebay at entrance (inches)48 in #11 Describe the planting plan for the vegetated shelf:
#5 Depth of forebay at exit (inches) in
#5 Does water flow out of the forebay in a non-erosive manner?Yes
#5 Clean-out depth for forebay (inches)12 in
#5 Will the forebay be cleaned out when the depth is reduced to less than the above?No
Break down of BUA in the drainage area (both new and existing):
COMPLIANCE WITH THE APPLICABLE STORMWATER PROGRAM
Stormwater program(s) that apply (please specify):
Stormwater Rules and Regulations found in 15A NCAC 02H .1053
ADDITIONAL INFORMATION
Please use this space to provide any additional information about this wet pond that you think is relevant to the review:
Other catergory in breakdown of BUA refers to all existing impervious area offsite of project area, but within the sub-basin.
GENERAL MDC FROM 02H .1050
THE DRAINAGE AREA
WET POND MDC FROM 02H .1053
#4 Describe any measures, such as berms or baffles, that will be taken to improve the flow path:
Forebay berm
Mixture of three shallow water and three shallow land species. Species to be planted: Arrow Arum, Bull Tongue, Joe Pye
Weed, Cardinal Flower, Lizard's Tail, Swamp Milkweed.
Wet Pond 3 10:15 AM 7/18/2018