CN-2013-00155-1.tif Allen Schoemaker
From: brett @napiereng.com
Sent: Monday, July 22, 2013 1:12 PM
To: Allen Schoemaker
Cc: Mark Abeln
Subject: Blair NE Dollar General
Attachments: Storm Water Management.pdf; Storm Water Management- Exhibit A.pdf
Al - Please find attached the Storm Water Management Letter and Exhibit for the proposed Dollar
General. The 100 -year runoff will be decreased by 0.11 cfs due to the increase in green space.
Let me know if you need further information or revisions.
Thanks,
Brett
BRETT NAPIR, P. E.
NAPIEP ENGINEE IN
207 SOUTH 5TH STPEET
LEAVErNWOPTH, KS 66046
OFFICE - (913) 632 -3
CELL - (913) 375-0482
brett@nap
1
Tue,23 Jul 2013 8:42:22
i
207 South 5th Street
Leavenworth, KS 66048
July 22, 2013
Al Schoemaker
Director of Public Works
City of Blair, NE
218 South 16' Street
Blair, Nebraska 68008
RIE: Dollar General, 693 Washington St ®, Blair, NE
a Storm Water Management Plan
Dear Al:
The proposed Dollar General to be located at 69' ) Washington Street will be constructed on a 0.795
acre parcel that was the site of a former McDonald's Restaurant. The existing storm structures on
the site will be reutilized to convey storm water runoff. (See Exhibit 4)
The site currently has approximately 0.075 acres of green space and approximately 0.72 acres of
impervious area (includes asphalt & concrete pavement, buildings, etc.). The existing runoff
coefficient "C" for the site is 0.92. The 100-year runoff for the existing condition is 9.44 cubic feet
per second (cfs). (See Exhibit A for Drainage Calculations)
The proposed Dollar General will increase the green space area to 0.094 acres and decrease the
impervious area to 0.701 acres. The proposed runoff coefficient "C" for the proposed site is 0.91.
The 100-year runoff for the proposed condition is 9.33 efs. (See Exhibit A for Drainage
Calculations)
Due to the decrease in runoff of 0.11 efs for the 100-year storm event, no detention will be required
for this development.
Please feel free to contact me for additional information at (913) 375-0482.
Sincerely,
CIV/
Arett A. Napier, P.E. RE A.
NAPIER
E-1456.4
OF N
Tue,23 Jul 2013 8:41:40
Exhibit A
Drainage Areas
-- — --- - - - - -- — _ \ & Calculations
_ Washington Street /h hwa 30
_Washington Street /Iighway 3 0 \\ - -- -- g - y - -- - -
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_______ __ ___ _____ 1[65 n Space �____ - __
rainage
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Green Space Item �,1., .< —.c._ } _. _ `� �- ! 063 Q J
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Total Area = 0.795 Ae
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Total Area =0.795 Ae St'
77 y ' r Pro�otype C J
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— — � 212.27'
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Green Space
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' 207 S. 5th Slrect
Leavenworth, KS 66048 '..
913.375 0482
breltr'- napiereng.com
GA 4 2940
Renewal 2/11/2015
Date of Preparation/
Exist. Total Drainage Area = 0.795 Ac Total Drainage Area = 0.795 Ac Revision:
Exist. Green Space Area = 0.075 Ac Green Space Area = 0.094 Ac
Exist. Impervious Area = 0.72 Ac. Impervious Area — 0.701 Ac. July 22, 2013
Ex st. Runoff Coefficient "C" = [(0.075 *0.35) + (0.72 *0.98)] / 0.795 = 0.92 Proposed Runoff Coefficient "C" _ [(0.094 *0.35) + (0.701 *0.98)]
Exist. 100 -Yr Runoff: Q — CIAK, where Proposed 100 -Yr Runoff: Q =CIAK, where o,
Q = cubic feet per second (cfs) Q = cubic feet per second (cfs)
C = Runoff Coefficient C = Runoff Coefficient a
I = Rainfall intensity in inches per hour = 10.32 in/hr (te =5.0 min) I = Rainfall intensity in inches per hour =10.32 inAlr (tc =5.0 min) W
A = Drainage area in acres = 0.795 Ac. A = Drainage area in acres = 0.795 Ac. o
K = Antecedent precepitation factor= 1.25 K = Antecedent precepitation factor =1.25
Q100= 0.92 *10.32 *0.795 *1.25 =9.44 cfs 20 0 10 20 Q100= 0.91 *10.32 *0.795 *1.25 =9.33 cfs 20 0 10 20 —
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1 =20' 1
Existing Drainage Area & Q100 Calculation Proposed Drainage Area & Q100 Calculation z,
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