HomeMy WebLinkAboutDrainage Reports - 08/27/2012City of Ft. Col)inspr ed Plar;>Cs
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design
700 Automation Drive, Unit I
Windsor, CO 80550
Phone: 970-686-6939
Fax:970-686-1188
April 4, 2012
Glen Schlueter
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522
RE: Mawson Lumber Parking
Dear Glen,
Mawson Lumber is converting the building at 350 Linden Street to a retail store for their
hardware sales. In conjunction with this, they are providing additional asphalt area for parking,
drives and sidewalks. Attached are the calculations showing the increased imperviousness from
44% to 88% and an increase in runoff in the 100 year storm event from 4.2 cfs to 6.7 cfs.
Detention is being proposed along the north property line and provides the required volume at
elevation 4968.8. Water quality for the runoff from the site is being addressed by two measures
that will be implemented on site. A portion of the runoff from the asphalt will be collected in a
swale with a subsurface perforated pipe along the south property and will be conveyed in a solid
pipe to the detention area. The remainder of the runoff flows directly to the detention area which
will be overexcavated by 12" and filled with large diameter rock to facilitate percolation into the
soil and ultimately to the groundwater table.
I certify that this report for the drainage design of the Mawson Lumber Parking was prepared in
accordance with the criteria in the City of Fort Collins Storm Drainage Manual. I appreciate
your time and consideration in reviewing this submittal. Please call if you have any questions.
Project Manager
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u II - II
fJU.° Q
MINOR DETENTION VOLUME BY FAA & MODIFIED. FAA METHOD,
(See: USDCM Volume I Runoff Chapter for description of method)
Project: Mawson lumber ` -
Basin ID: Basinill
(For catchments less than 160 acres only. For larger catchments, use hydrograph routing method)
(Note: for catchments larger than 90 acres, CUHP hydrograph and routing are recommended)
The user must fill in all of the blue cells for these sheets to function.
tment Drainage Imperviousness
tment Drainage Area
:velopmerd NRCS Soil Group
n Period for Detention Control
of Concentration of Watershed
tble Unit Release Rate (See Table A)
tour Precipitation
In Rainfall IDFFormula I=Ct•P7/(C2+Tc)AC3
icient One
icient Two
icient Three
I.=
i:::88.00:, r:::
percent
A=
1.0000 :ii::
acres
Type=i.ri=.iiiii
Bf:.;:I:iii
A, B, C, or
T=;::::-100:
iii:i
years(2, 5, 10, 25, 50, or 100)
Tc=.--
; i'9:iiii! aminutes
9
::iIl::cfs/acre
P, _ ;: i!:<:
2.61 : ::.—inches
C, =`:-i:=28i50:::::
C3=fii
0!79..:::
Runoff Coefficient
nflow, Peak Runoff Op -in =a 586 _.:;::.cfs
Movable Peak Outflow Rate Op -out = 4 20 �`: cfs
Ratio of Op-out/Op-in Ratio =0 72
Determination of MINOR Detention Volume Using FAA & Modified FAA Method'
':: `5.--: - <. Enter Rainfall Duration Incremental Increase Value Here e.. 5 for 5-Minutes
Rainfall
Rainfall
Inflow
Average
Outflow
Storage
Adjustment
Average
Outflow
Storage _
Duration
Intensity
Volume
Outflow
Volume
Volume
Factor
Outflow
Volume
Volume
minutes
inches / hr
cubic feet
(FAA, cfs)
(FAA, cf)
(FAA, cf)
(Modifed)
(Mod. cfs)
(Mod, e,
(Mod. ct;
iinDub
(out✓ut}
icutout"
ioulouf
rcutcuti
/aacW
(OUIDUI)
(ov ut1
foul":11
(cutout)
5. -
,_ 8.76 __
...:Z'07S'2i99
898
1.178'ar
xs1'i00 •*•x
•r z420
._`. 1260 '
:815`s•
FAA Minor Storage Volume (cubic ft.) •-1 512 Mod. FAA Minor Storage Volume (cubic ft.)
FAA Minor Storage Volume (acre-ft.) 0 0347 Mod. FAA Minor Storage Volume (acre-ft.)
UDFCD DETENTION VOLUME ESTIMATING WORKBOOK Version 2.02, Released January 2007
UD-Detentior_Mawsonxls, Modified FAA 41412012, 12:58 PM
MINOR DETENTION VOLUME BY FAA & MODIFIED FAA METHOD - -
(See. USDCM Volume 1 Runoff Chapter for description of method) ,
Protect:" wsonaumber:
Basin ID: a xBasinq
Inflow and Outflow Volumes vs. Rainfall Duration
Intersection of Modified and FAA Outilow Plots is at maximum detention volume
135,000
130,000
125,000
2#00
1 �6000
110,000
1 5,000
Ot I I I I
0 20 40 60 80 100 .120 140 160 180 200
Duration (Minutes)
UDFCD DETENTION VOLUME ESTIMATING WORKBOOK Version 2.02, Released January 2007
LID-Detention_Mamon.As, Modified FAA 4l4l2012, 12:58 PM
LOCATION:
PROJECT NO:
COMPUTATIONS BY
DATE:
Detpond_rev.xls
Detention Pond - Stage/Storage
Mawson Lumber
321.01
ppk
4/4/2012
V = 1 /3 d (A + B + sgrt(A"B))
where V = volume between contours, ft3
d = depth between contours, ft
A = surface area of contour
Detention Volume Required
1210 Cu-Ft
Stage
(ft)
Surface
Area
(ft2)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4967.0
340
4968.0
341
340
340
4968.8
1989
869
1210
4969.0
2334
1189
1530
4970.0
5764
3922
5451
<- Det Volume
<- Top of Berm
Detention Pond Outlet Sizing
(100 yr event)
LOCATION: Mawson Lumber
PROJECT NO: 321.01
COMPUTATIONS BY: ppk
SUBMITTED BY:
DATE: 4/4/2012
Submerged Orifice Outlet:
release rate is described by the orifice equation,
Qo = CoAo sgrt( 2g(h-Eo))
where Qo = orifice outflow (cfs)
Co = orifice discharge coefficient
g = gravitational acceleration =
Ao = effective area of the orifice (ft`)
Eo = geometric center elevation of the orifice
h = water surface elevation (ft)
Qo = 4.20 cfs
outlet pipe dia = D = 12.0 in
Invert elev. = 4967.00 ft
Eo = 4967.50 ft
h = 4968.80 ft - 100 yr WSEL
Co = 0.65
solve for effective area of orifice using the orifice equation
Ao = 0.706 *
= 101.7 in`
orifice dia. = d = 11.38 in
Use d = 11.35 in
A,, = 0.703 ft' _
Qmax = 4.18 cfs
Detpond_rev.xls
101.18 /n
32.20 ft/s