SW6231109_Design Calculations_20240315

PROJECT
50130756-Barker Laydown Yard
Dewberry
CLIENT Duke Energy Progress, LLC
CALCULATION SHEET TITLE Rational Method Peak Flow
Designer DLS Reviewer DAR Sheet No.
Date 3/12/2024 Date 3/12/2024 1 of 2
Post-Development Ditch 1 (PD-1)
Land Use Area(acres) C-Value
Impervious 3.00 0.95
C-Values found using the
Agricultural Land (Crop) 0.00 0.40 information provided by the
NCDEQ.
Cumulative 3.00 0.95

PROJECT
e r
�e50130756-Barker Laydown Yard
CLIENT Duke Energy Progress, LLC
CALCULATION SHEET TITLE Rational Method Peak Flow
Designer I DLS Reviewer DAR I Sheet No.
Date 3/12/2024 Date 3/12/2024 2 of 2
Post-Development Ditch 2(PD-2)
Land Use Area(acres) C-Value
Impervious 2.47 0.95
C-Values found using the
Agricultural Land (Crop) 0.00 0.40 information provided by the
NCDEQ.
Cumulative 2.47 0.95

Project:50130756-Barker Laydown Yard Dewberry®
Client:Duke Energy Progress,LLC •
Title:Level Spreader Design www.dewberry.com
Date:3/13/2024
LS-FS MDC 1:Level Spreader Length
The level spreader shall be a minimum often feet in length per one cubic foot per second of stormwater flow that is directed to it.
PD1
C= 0.95 10-Yr Storm(5-min Tc)
Design Storm l ntensity= 0.75 in/hr �in/hr
A= 3 acres
Q=F 2.14 cfs 22.80 cfs
L=LLE5 LF 228 LF
PD2
C= 0.95 10-Yr Storm(5-min Tc)
Design Storm Intensity=W.75 in/hr -in/hr
A= 2.47 acres
Q=F 1.76 cfs 18.77 cfs
L=LIL599 LF 187.72 LF
Combined
C= 0.95 10-Yr Storm(5-min Tc)
Design Storm Intensity= 0.75 in/hr -
A= 5.47 acres
Q= 3.90 cfs
L=L38.974 LF <=TARGET REQUIRED LENGTH
L= 226 LF 418 LF <=PROPOSED LENGTH
MDC Met?Yes
Comments: PD1 and PD2 represent the edge swales that will convey runoff to the blind swale(BS)and level spreader(LS).The combined
calculations combines PD1 and PD2 to determine final target length of the LS.The BS will be flat to promote ponding and
uniform overflow.The BS is sized based on the combined flow,both edge swales are designed based on the max flow in PD1.
The LS is oversized to more closely mimic the low lying area on site where the filter strip will be placed;and,to promote
longevity and provide reslience
LS-FS MDC 2:Required Storm Intensity and Bypass
The required storm intensity and bypass system shall be based on the source of the
stormwater:
(a) A level spreader that receives flow directly from the drainage area shall be sized based
on the flow rate during the 0.75 inch per hour storm,with a flow bypass system for
larger storm events;or
(b) A level spreader that receives flow from an SCM shall be sized based on the draw
down rate of the design volume,with a flow bypass for larger storm events.
MDC Met?Yes
Comments:There are no storm outfalls and no other SCMs.The LS-FS lengths have been designed for the 0.75
in/hr storm event
LS-FS MDC 3:Exception from Flow Bypass Requirement
A flow bypass system is not needed if the level spreader is sized to handle the flow during 10-year storm event.
MDC Met?Yes
Comments:Sized for 10-Yr Storm.See MDC 4 calcs
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Project:50130756-Barker Laydown Yard Dewberry®
Client:Duke Energy Progress,LLC •
Title:Level Spreader Design www.dewberry.com
Date:3/13/2024
LS-FS MDC 4:Blind Swale
Immediately upslope of the level spreader,there shall be a blind swale or other method of ponding water.The blind swale shall be
designed to provide for uniform overtopping of the level spreader.
Permissible shear stress,
Ta up(Ib/ft2) 0.33 (No.57 Stone) 0.45 (Jute Liner)
Design storm LS-FS MDC
Required Flow,Q(cfs) 41.57 22.80 PD1 Required Flow-Edge Conditions,Q(cfs)
Unit weigt of water,y(lb/ft') 62.4 18.77 PD2 Required Flow-Edge Conditions,Q(cfs)
Channel slope,s(ft/ft) 0.003
m � m
V-Shaped v v Y s > U U
v a v a - b:m
0 0 0 T ¢ ;
E `�° E� �
o v x o v o a a . o' o) o o
3 d = U a n > > U C7 U U n U
(ft) (ft) (ft2) (ft) (ft) (ft) (lb/ft2) (ft/s) (cfs) (lb/ft2)
Q �
J
W
Z CO
PD1 3 0 1.5 9.0 6.75 9.49 0.71 3.56 0.022 0.45 2.96 U 19.96 > 0.28 0
U W
W Of
z
z
PD2 3 0 1.47 8.8 6.48 9.30 0.70 3.49 0.022 0.45 2.92 U 18.91 0 0.28 0
U
W
Of o
`m A
v a t0 a > � 0)
V -c L K U a+ o), N 4) 4)
V-Shaped-BS o o z v _ N = N > a 0
a -No.57 Stone " "~ y
x g a �Y �o � 2 o o c, L L�
Check N N o f `° o o 0 0-.. o o
(ft) (ft) (ft2) (ft) (ft) 5 (lb/ft2) (ft/s) (cfs) (lb/ft2)
Q O o
z w
71,
F F -ml
w
z CO
PD1 3 0 1.5 9.0 6.75 9.49 0.71 3.56 0.022 0.33 2.96 U 19.96 > 0.28 0
U W
W Of
}
z
PD2 3 0 1.47 8.8 6.48 9.30 0.70 3.49 0.022 0.33 2.92 U 18.91 0 0.28 0
U
W
>
MDC Met?Yes
Comments:The V-Shaped channel calculations confirm capacity and velocity based on a jute liner during the
10-Yr storm. Note that PD1 does not meet the target Q10 of 22.8 CFS--the drainage areas for PD1
and PD2 are highly conservative in that roughly 50%of the drainage areas actually flow directly to
the blind swale;therefore,the velocity and capactiy check are considered valid for meeting the 10-
Yr MDC.The BS will be at a constant 0.0%slope to allow ponding and overtopping.The BS No.57
Stone check is used to confirm that the No.57 Stone liner in the BS can withstand the entrant shear
stresses from PD-1 and PD-2.
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Project:50130756-Barker Laydown Yard Dewberry®
Client:Duke Energy Progress,LLC •
Title:Level Spreader Design www.dewberry.com
Date:3/13/2024
LS-FS MDC 6:Level Spreader Shape
The level spreader shall be straight or convex in plan view.
MDC Met?Yes
Comments:See plan
LS-FS MDC 7:Transition Zone
Immediately downslope of the lev re shall be a one to three-inch drop followed by a transition zone that is protected from
erosion via aggregate or high pert nforcement matting.The transition zone shall be a minimum of 12 inches wide.
MDC Met?Yes
Comments:Transition zone consists of No.57 stone see detail
LS-FS MDC 8:Minimum Width of the Filter Strip
The minimum width of the filter strip shall be 30 feet,measured perpendicular to the level spreader lip.
Filter Strip Provided:30 LF
MDC Met?Yes
Comments:
LS-FS MDC 9:No Draws or Channels in the Filter Strip
The filter strip shall not contain draws or channels.
MDC Met?Yes
Comments:
LS-FS MDC 10:Filter Strip Specifications
(a) Filter strips shall be graded with a uniform transverse slope of eight percent or less;
(b) The pH,compaction and other attributes of the first 12 inches of the soil shall be adjusted if necessary to promote plant
establishment and growth;
(c) The filter strip and side slopes shall be planted with non-clumping,deep-rooted grass sod;and
(d) Soils shall be stabilized with temporary means such as straw or matting until the permanent vegetative cover has taken root or
the runoff shall be directed elsewhere until vegetation has been established.
(a)Max Slope: 3.50%
(b)pH Requirements: See Plans
(c)Sod Regs: See Plans
(d)Stabilization: See Plans
MDC Met?Yes
Comments:The LS detail calls for 8%maximum slope to ensure contractor flexibility for meeting grades if site
conditions differfrom plans;however,anticipated slope based on surveyed and observed
conditions is 1.7%
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