HomeMy WebLinkAboutDrainage Reports - 05/08/2017{
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4118" to 1.1 i�4lNN1
September 14, 2016
City of Fort Collins Engineering Division
281 N College
Fort Collins, CO 80524
6163 E. County Rood 16. to-Oand, CO $0537 ,
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Drainage Letter for the Proposed Site Development located at
2740 E Harmony Road, Fort Collins, CO 80528
Lot 4, Front Range Village
Dear Rick Richter,
This drainage letter is to convey the proposed site development conforms to the overall report, which is
titled Final Drainage and Erosion Control Study for Front Range Village, Fort Collins, Colorado
prepared by Stantec Consulting Inc. 209 South Meldrum, Fort Collins, Colorado 80521 (February,
2007), and will hereafter be referred to as the Master Report.
The subject property is currently an undeveloped lot. The lot is a 35,043 square foot (0.80 acres) site
located in the southeast quarter of Section 32, Township 7 North, Range 68 West of the 611 Principal
Meridian, City of Fort Collins, County of Larimer, State of Colorado, on the northeast corner of Harmony
Rd and Corbett Drive. The subject property lies on Lot 4 of the Front Range Village Subdivision. It is
bound to the South by Harmony Road, to the east by an existing Chase Bank, to the north by a private
access drive, and to the west by Corbett Drive.
Proposed improvements to the site include a building to be constructed on the south side of the site
with a total footprint of about 6,500 square feet. The site will have 34 parking spaces, 2 of which are
ADA accessible parking spaces, internal sidewalks, utility services and landscaping. The site consists
of Type C Soils, Nunn clay loams, and existing fill from previous development rough grading. This site
is located in flood Zone X, "Areas determined to be outside the 0.2% annual chance floodplain."
Existing drainage patterns convey flows to the north side of the property where there is an existing type
R inlet. The Master Report was calculated using an overall imperviousness of 95-percent for this basin.
The proposed lot is accounted for in the Final Drainage Report as a portion of Basin 160, which has a
total area of 1.63 acres. Basin 160 has a C,00f 0.85, C,00 of 0.85, Tc,o of 5.4 minutes, Tc,000f 5.0
minutes, and flows of Q,o=6.55 cfs and Q1oo=16.23 cfs. Lot 4 has an area of 0.80 acres, so the
weighted averages of the flows for pre -developed Lot 4 are Clio = 3.21 cfs and Q1oo=7.97 cfs. The post
developed site will discharge at rates less than or equal to these flows in the 10 and 100 year storm
events.
Post -development drainage will be conveyed via a private, on -site storm drainage network which will be
composed of three 6° trench drain systems connecting to a 12" PVC storm drain pipe which will convey
runoff to the proposed inlet on the north median of the site. At this point, runoff will be conveyed from
the inlet to the proposed manhole in the northeast corner of the site via an 18" PVC storm drain pipe.
From this manhole, the runoff from the site will be conveyed to an existing detention pond within the
Front Range Village system prior to the ultimate discharge of the runoff into the Cache la Poudre. Pipe
sizing calculations are attached to this letter for reference.
Post -development conditions consist of a proposed building consisting of retail and restaurant usage
that includes associated parking lot and landscaped areas. The post development property consists of
five on -site sub -basins and four off -site basins. See drainage sheets for additional information.
Post -development Sub -basin All consists of 0.15 acres of proposed building rooftop. This basin is 90%
impervious. Runoff from this basin drains to the south of the building where it will be conveyed to a 12"
PVC pipe collecting from the south end of the site. Sub -basin Al discharges at a rate of 0.64 cfs in the
10-year storm event and 1.36 cfs in the 100-year storm event.
Post -development Sub -basin A2 consists of 0.49 acres of parking lot and landscaped area on the north
portion of the property. This basin is 76% impervious. Runoff from this basin drains into a proposed 4'
curb inlet with vertical opening and proposed storm drain infrastructure. The storm drain drains into the
existing infrastructure. Sub -basin A2 discharges at a rate of 1.82 cfs in the 10-year storm event and
4.12 cfs in the 100-year storm event.
Post -development Sub -basin A3 consists of 0.07 acres of landscaped area along the west side of the
property. This basin drains offsite and where it sheet flows easterly towards an existing area inlet where
it ultimately connects to the proposed manhole in the northwest corner of the site. This basin is 27%
impervious. Sub -basin A3 discharges at a rate of 0.14 cfs in the 10-year storm event and 0.44 cfs in the
100-year storm event.
Post -development Sub -basin A4 consists of 0.09 acres of paved walkway and landscaping on the south
side of the property and is 69% impervious. Discharge from this area drains into a proposed trench
drain along the center of the patio area and drains into the proposed storm drain infrastructure. Sub -
basin A4 discharges at a rate of 0.32 cfs in the 10-year storm event and 0.75 cfs in the 100-year storm
event.
Post -development Sub -basin A5 consists of 0.01 acres of paved walkway and landscaping on the south
side of the property and is 90% impervious. Discharge from this area drains into proposed trench drain
along the west side of the 5' sidewalk adjacent to the west side of the building and drains into the
proposed storm drain infrastructure. Sub -basin A5 discharges at a rate of 0.04 cfs in the 10-year storm
event and 0.09 cfs in the 100-year storm event.
Post -development Sub -basin OFF1 consists of 0.09 acres of landscaping to the south of the property
and is 10% impervious. Runoff from this basin flows onto Sub -basin A4 and then follows the same
drainage patterns. Sub -basin OFF1 discharges at a rate of 0.12 cfs in the 10-year storm event and 0.48
cfs in the 100-year storm event.
Post -development Sub -basin OFF2 consists of 0.10 acres of landscaping to the west of the property
and is 2% impervious. Runoff from this basin flows onto Sub -basin A2 and then follows the same
drainage patterns. Sub -basin OFF2 discharges at a rate of 0.11 cfs in the 10-year storm event and 0.52
cfs in the 100-year storm event.
Post -development Sub -basin OFF3 consists of 0.03 acres of landscaping to the west of the property
and is 2% impervious. Runoff from this basin flows onto Sub -basin A5 and then follows the same
drainage patterns. Sub -basin OFF3 discharges at a rate of 0.03 cfs in the 10-year storm event and 0.16
cfs in the 100-year storm event.
Post -development Sub -basin OFF4 consists of 0.02 acres of landscaping to the west of the property
and is 2% impervious. Runoff from this basin flows onto Sub -basin A4 and then follows the same
drainage patterns. Sub -basin OFF4 discharges at a rate of 0.02 cfs in the 10-year storm event and 0.10
cfs in the 100-year storm event.
The overall post -development site imperviousness is 58%, compared to the 95% imperviousness that
was assumed with the original drainage report. After improvements, the site will discharge at a total rate
of 2.96 cfs in the 10 year storm event, generating 0.25 cfs fewer than anticipated conditions, which was
3.21 cfs.
In the 100 year event, the total site discharge rate will be 6.75 cfs, compared to 7.97 cfs from the
original development build -out. Generating 1.22 cfs less than anticipated conditions, which was 7.97
cfs.
There is no required detention for this site as the overall imperviousness of the site will be decreased
from the anticipated conditions assumed in the original drainage report for the subdivision.
Overall the site will see a reduction of 0.30 acres of impervious surface, a decrease of 37%
imperviousness, and a total runoff in the 100 year storm event of 6.75 cfs, which is 1.22 cfs less than
the anticipated 7.97 cfs. Water quality will be provided via sheet flow across landscaped areas in
conjunction with the detention ponds that were constructed with the overall development.
Sincerely,
Alex Hoime, PE
Director
RUNOFF COEFFICIENT CALCULATIONS
Project Name: C01303A - Front Range Village - Lot 4
Calculated By: KV
Check By: AH
Date: 8/24/2016
RECOMMENDED RUNOFF COEFFICIENT
AND PERCENT IMPERVIOUS'
Runoff Coefficients, C-value
LAND USE
°� IMPERVIOUS
70 YEAR
100 YEAR
LANDSCAPE
2
0.22
0.52
DRIVES AND WALKS
90
0.87
1
0.91
ROOFS
90
0.87
0.91
POST -DEVELOPMENT CONDITIONS:
AREA
DESIGN
A(LAND.)
AC
A(D&W)
AC
A(ROOFS)
AC
A(TOTAL)
AC
C10 C100
%
IMPERVIOUS
Al
0.00
0.00
0.15
0.15
0.87
0.91
90
A2
0.08
0.41
0.00
0.49
0.77
0.85
76
A3
0.05
0.02
0.00
0.07
0.41
0.63
27
A4
0.02
0.07
0.00
0.09
0.72
0.82
69
A5
0.00
0.01
0.00
0.01
0.87
0.91
90
OFF1
0.08
0.01
0.00
0.09
0.28
0.56
10
OFF2
0.10
0.00
0.00
0.10
0.22
1 0.52
2
OFF3
0.03
0.00
0.00
0.03
0.22
0.52
2
FF4
0.02
0.00
0.00
0.02
0.22
0.52
2
TOTAL: 1.05
WEIGHTED:
0.70
58
1 Runoff coefficients and percent impervious per Urban Drainage and Flood Control District, Volume 1 - Dated January 2016
*CONTRIBUTING OFFSITE AREAS DRAINING INTO DETENTION BASIN BUT OUTSIDE OF PROPOSED PROPERTY.
10-YEAR INDIVIDUAL BASIN FLOWS
Project Name: C01303A - Front Range Village - Lot 4
Calculated By: KV
Check By: AH
Date: 8/24/2016
POST -DEVELOPMENT CONDITIONS:
SUB -BASIN DATA
DIRECT RUNOFF
CONTRIBUTING
BASINS
BASIN
AREA acre
C10
EFFECTIVE
AREA acre
I
in/hr
SUB BASIN
Q cfs
Al
0.15
0.87
0.13
4.87
0.64
A2
0.49
0.77
0.37
4.87
1.82
A3
0.07
0.41
0.03
4.87
0.14
A4
0.09
0.72
0.07
4.87
0.32
A5
0.01
0.87
0.01
4.87
0.04
OFF1
0.09
0.28
0.02
4.87
0.12
OFF2
0.10
0.22
0.02
4.87
0.11
OFF3
0.03
0.22
0.01
4.87
0.03
OFF4
0.02
0.22
0.00
4.87
0.02
1= (28.9*P10,1)/[(10+Tc)"0.786]
TOTAL: 3.23
TOTAL ONSITE: 2.96
I MAX ALLOWED: 3.21
Q10= C*I*A Point Intensities determined using NOAA Atlas 14 values per NOAA website stating:
NOAA Atlas 2 values superseded by NOAA Atlas 14 values for Colorado as of April 19,
2013
100-YEAR INDIVIDUAL BASIN FLOWS
Project Name: C01303A - Front Range Village - Lot 4
Calculated By: KV
Check By: AH
Date: 8/24/2016
POST -DEVELOPMENT CONDITIONS:
SUB -BASIN DATA
DIRECT RUNOFF
CONTRIBUTING
BASINS
BASIN
AREA acre
C100
EFFECTIVE
AREA acre
I
in/hr
SUB BASIN
0 cfS
Al
0.15
0.91
0.14
9.95
1.36
A2
0.49
0.85
0.41
9.95
• 4.12
A3
0.07
0.63
0.04
9.95
0.44
A4
0.09
0.82
0.07
9.95
0.75
A5
0.01
0.91
0.01
9.95
0.09
OFF1
0.09
0.56
0.05
9.95
0.48
OFF2
0.10
0.52
0.05
9.95
0.52
OFF3
0.03
0.52
0.02
9.95
0.16
OFF4
0.02
0.52
0.01
1 9.95
0.10
I= (28.9*P100,1)/[(10+Tc)^0.786]
TOTAL: 8.00
TOTAL ONSITE: 6.75
1 MAX ALLOWED: 7.97
0100= C*I*A Point Intensities determined using NOAA Atlas 14 values per NOAA website stating:
NOAA Atlas 2 values superseded by NOAA Atlas 14 values for Colorado as of April 19,
2013
Channel Report
Hydraflow Express Extension for Autodesk@ AutoCAD9 Civil 3138 by Autodesk, Inc.
6-inch PVC Trench Drain Connection (South)
Circular
Highlighted
Diameter (ft)
= 0.50
Depth (ft)
Q (cfs)
Area (sqft)
Invert Elev (ft)
= 100.00
Velocity (ft/s)
Slope (%)
= 5.00
Wetted Perim (ft)
N-Value
= 0.013
Crit Depth, Yc (ft)
Top Width (ft)
Calculations
EGL (ft)
Compute by:
Known Q
Known Q (cfs)
= 1.33
Elev (ft)
101.00
100.75
100.50
100.25
100.00
99.75
0 1
Wednesday, Sep 14 2016
= 0.45
= 1.330
= 0.19
= 7.14
= 1.25
= 0.50
= 0.30
= 1.24
Section
Reach (ft)
1
Channel Report
Hydraflow Express Extension for AutodeskS Auto CAD® Civil MR by Autodesk, Inc.
6-inch PVC Trench Drain Connection (West)
Circular
Highlighted
Diameter (ft)
= 0.50
Depth (ft)
Q (cfs)
Area (sqft)
Invert Elev (ft)
= 100.00
Velocity fts)
Slope (%)
= 5.00
Wetted Perim (ft)
N-Value
= 0.013
Crit Depth, Yc (ft)
Top Width (ft)
Calculations
EGL (ft)
Compute by:
Known Q
Known Q (cfs)
= 0.25
Elev (ft)
101.00
100.75
100.50
100.25
100.00
99.75
0 1
Wednesday, Sep 14 2016
= 0.16
= 0.250
= 0.05
= 4.59
= 0.60
= 0.26
= 0.47
= 0.49
Section
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3138 by Autodesk, Inc.
8-inch Roof Drain Connection
Circular
Highlighted
Diameter (ft)
= 0.67
Depth (ft)
Q (cfs)
Area (sqft)
Invert Elev (ft)
= 100.00
Velocity (ft/s)
Slope (%)
= 2.00
Wetted Perim (ft)
N-Value
= 0.013
Crit Depth, Yc (ft)
Top Width (ft)
Calculations
EGL (ft)
Compute by:
Known Q
Known Q (cfs)
= 1.36
Elev (ft)
101.00
100.75
100.50
100.25
100.00
99.75
0 1
Wednesday, Sep 14 2016
= 0.45
= 1.360
= 0.25
= 5.39
= 1.29
= 0.55
= 0.63
= 0.90
Section
Reach (ft)
t
Channel Report
Hydraflow Express Extension for AutodeskO AutoCADO Civil 3M by Autodesk, Inc.
12-inch PVC Storm Drain Analysis
Circular
Diameter (ft) = 1.00
Invert Elev (ft)
= 100.00
Slope (%)
= 1.00
N-Value
= 0.013
Calculations
Compute by:
Known Q
Known Q (cfs)
= 2.94
Elev (ft)
102.00
101.50
101.00
100.50
100.00
1
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section
2
Wednesday, Sep 14 2016
= 0.70
= 2.940
= 0.59
= 5.00
= 1.98
= 0.74
= 0.92
= 1.09
Depth ( I
2.00
1.50
1.00
0.50
M
-0.50
3
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk@ AutoCADR Civil 3D9 by Autodesk, Inc.
18-inch PVC Storm Drain Analysis
Circular
Diameter (ft) = 1.50
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 7.58
Elev (ft)
102.00
101.50
101.00
100.50
100.00
99.50
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section
Wednesday, Sep 14 2016
= 1.26
= 7.580
= 1.59
= 4.78
= 3.48
= 1.07
= 1.10
= 1.62
0 1 2 3
Reach (ft)
U
UNAUTHORIZED CHANGES & USES:
THE MOM PREPARING THESE PLANS WILL NOT BE RESPONSIBLE FOR, OR MARE FOR.
UMAUHR6ZED CHANGES M OR USES OF THESE PLANS ALL CHANCES OF THESE PLANS MUST BE IN
WRITING AND MUST BE APPROVED BY THE PREPAHER OF THESE PUNS PRIOR TO CONSTRUCTION.
CRNSTRUCIION CONTRACTOR AGF E THAT N ACCORDANCE WiN GERRNLY ACCEPTED
CONSTRUCTION PRACTICES, CONSTRUCTION CONTRACTOR WILL BE IEQXa TO ASSUME SOLE AND
CRNPLETE RESPONSIBILITY, FOR " STE CONDITIONS DURING TIE CRAP OF CONSTRUC110N CF THE
PRO,ECT, walo G SAFETY OF ALL PERSONS AND PROPERTY. THAT TIWS REQUIREMENT SHALL BE
MADE TO APPLY CONTINUOUSLY AND NOT BE OPTED M NORMAL WORKING HOURS. AND
CCNSTRUCBCN CONIENG i FDRNER AQM M DEFEND, WW41FY AND HOLD DESIGN
PROFESSIONAL HARMLESS FROM ANY AND ALL UABUTY, REAL OR ALLEGED. N CONNECTION NTH
THE PERFORMANCE OF W CH THIS PROFCT, EXCEPTING LABILITY ARISING FROM THE SOLE
NEOLICENCE OF DESIGN PROFESSIONAL
.PROPOSED MANHOLE
FL-4941.4S
MV(N)-4933.21'
NV(E)-493a61'
NV(SW)-493.161'
ENGINEERS NOTE TO CONTRACTOR:
111E DOS104CE AND LOCATION OF ANY UIDOWC ND UMEM PPFS', MID/OR STRUCTINES
SHOWN ON THESE PUNS TREK OBTAINED BY A SEARCH OF AVAILABLE RECORDS THEE MAYBE
E3GSTNG UTUTIES NOT SHOWN FN THESE PLANS, THE CONTRACTOR SHALL ASCERTAIN THE TRUE
VERTICAL AND HORIZONTAL LOCATION OF THOSE UNDERGROUND UTUTES TO BE USED PRIOR TO
CONSTRUCTION AND SHALL BE WSPONSHE FOR ANY DAMAGE M ANY PUBLIC OR PRIVATE
UTILITIES, SHOWN OR NOT SHOWN HEREON.
'N
I
0_ r at
SCALE: V=20'
BASIS OF BEARMGS
THE BEARINGS; ARE BASED CN TEE NORTH L07 UNE OF LOT 1. FRONT
RANGE VILLAGE AS SOUTH 9Q 00' W EAST ACCORDING TO THE
RECORDED PUT.
GENERAL NOTE:
ANY FUTURE LAND DIS7URBANCE, INCREASE N IMPERVIOUS AREA
MG/Ri CHANGE IN RIMRF COIDIT10N5 RN THIS STE MAY REOURE
ADDITIONAL STOW WATER MANACaENT PER MSD REGULATIONS N
PUCE AT THAT HIE (INCLUDING TOTAL LAND DISTURBANCE AND/OR
IBDMOIDESS ADOED ON THIS PLAN).
STORMWATER RUNOFF NOTES:
TOTAL LOT AREA 0.60 ARE
TOTAL DISYURI EDD AREA 0.86 ARE
PRE -DEVELOPMENT W IMPERVIOUS: 2
POST -DEVELOPMENT W IPERNOUS 55
POST -DEVELOPMENT 10-YR STORM RUNOFF: 2.96 CFS
PoST-DEVELOPMENT ID6-YR STORM (RUNOFF: 6.76 CIS
A = BASIN DESIGNATION
� B =AREA INNACRES
Ef C = % IMPERVIOUSNESS
SUMMARY RUNOFF TABLE
BAN! III
CONTRIBUTING
( PLEAACRES
C VALUE
TOOYR
�
PEAK
BOYER
ORS)
Al
0.15
0.91
0.64
1.36
A2
0.0
0.65
1.62
4.12
A3
0.07
0.63
0.14
0.44
A4
0.09
0.62
(132
0.75
AS
0.01
0121
0.04
0.09
CFll
BOB
0.56
0.12
0.48
OFF2
0.10
0.52
0.11
M52
OFF3
0.03
0.S2
0.03
0.16
OFF4
0.02
0.52
002
0.10
ALUMINUM! CAP 3DO' WEST OF CCRIEM DIM ON TOP OF
CRRC" WALL OF IRRIGATION STRUCTUM CITY OF FORT
COLLINS BDICKMAM /2-94.
PREPARED UNDER THE SUPERVISION OF
TNT W ASSOCIATE$ INC.
-PRELIMINARY-
NOT FOR
NSTRUCT
DR1