20021500 Ver 1_COMPLETE FILE_20020911

BARBARA H.MULKEY ENGINEERING,INC.
STORMWATER MANAGEMENT PLAN
Lake Boone Trail Extension
from Edwards Mill Road Extension
to Existing Lake Boone Trail
Wake County
Prepared by: Barbara H. Mulkey Engineering, Inc.
For City of Raleigh, North Carolina
Project Manager: Jenny S. Fleming, PE
Design Engineer: Karen E. Ellis, El
3/18/2003
6750 Tryon Road ♦ Cary, NC 27511 ♦ Phone:[phone] ♦ Fax: [phone] ♦ www.bhme.com
PO Box 33127 ♦ Raleigh, NC 27636

STATION 12+25 TO 13+45-L- Lt.
(Plan Sheet 4)
Runoff from the proposed roadway is being treated with a grassed swale that
parallels the roadway and spills into an existing "draw" to the perennial stream.
The total drainage area to this swale is 2.26 Acres with 1.18 Acres of impervious
area. Based on Division if Water Quality guidelines, the swale must provide 100
linear feet/acre of impervious area and velocities of less than 2 ft/s in the 2-year
event.
DA: 2.26 Acres
Impervious Area: 1.18 Acres
Grassed Swale:
2 foot base
3:1 side slopes
Longitudinal slope: 1.2%
Length: 120 feet
Q2: 8.06 cfs
V2: 1.36 ft/s
STATION 14+70-L- Lt.
(Plan Sheet 4)
Runoff from the proposed roadway is being diffused through a level spreader.
The total discharge for the 10-year event is 3.07 cfs. Based on Division of Water
Quality guidelines on level spreaders, the length is 13'/cfs for a total length of 40
ft. The area between the level spreader and the stream is heavily grassed
pasture with an overland slope of approximately 2.5%.
DA: 0.6 Acres
Q10: 3.07 cfs.
Level Spreader:
Length= 3.07 x 13 = 39.91 ft. 4 40' provided
3:1 sides with 4' base (15" outlet pipe)

STATION 18+50 - L- Lt.
(Plan sheet 5)
Runoff from the proposed roadway is being diffused through a level spreader.
The total discharge for the 10-year event is 8.57 cfs. Based on Division of Water
Quality guidelines on level spreaders, the length is 13'/cfs for a total length of 120
ft. The area between the level spreader and the stream is heavily grassed
pasture with an overland slope of approximately 8.0%.
DA: 2.08 Acres
Q 10: 8.57 cfs.
Level Spreader:
Length= 8.57 x 13 = 111.4 ft. 4 120' provided
3:1 sides with 4.5' base (18" outlet pipe)