HomeMy WebLinkAboutDrainage Reports - 05/08/2017 (2)TA I T
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September 14, 2016
City of Fort Collins Engineering Division
281 N College
Fort Collins, CO 80524
Drainage Letter for the Proposed Site Development located at
2860 E Harmony Road, Fort Collins, CO 80528
Lot 6, Front Range Village
Dear Rick Richter
. s
6163 E. County Rood 16, lo.elond, CO 80537
i
ter Utilities Redlln
Review
Date:
Sao Return with Res �.
City offt,, COOT pro ,Plans
Approved Sy
Date
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 55,922 square foot (1.28 acre) site
located in the southeast quarter of Section 32, Township 7 North, Range 68 West of the 60' Principal
Meridian, City of Fort Collins, County of Larimer, State of Colorado, on the northwest corner of Harmony
Rd and Zeigler Rd. The subject property lies on Lot 6 of the Front Range Village Subdivision. It is bound
to the South by Harmony Road, to the west by an existing Chase Bank, to the north by a private access
drive, and to the east by a Famous Dave's BBQ Restaurant.
Proposed improvements for this lot include a building constructed on the south side of the site with a total
footprint of about 8,540 square feet, consisting of a strip mall of two restaurants with a combined square
footage of 6,720 SF and a retail store that uses 1,820 SF. This site will have 51 parking spaces, paved
driveways, parking stalls, a trash enclosure, and landscape islands. The site consists of Type C Soils
Nunn clay loam, and existing backfill. 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 northeast side of the property where there is an existing
area 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 200, which has a
total area of 2.74 acres. Basin 200 has a C10 of 0.85, C100 of 0.85, Tc10 of 6.4 minutes, Tcloo of 5.0
minutes, and flows of Q1o=10.41 cfs and Q1oo= 27.24 cfs. Lot 6 has an area of 1.28 acres, so the weighted
flows for pre -developed Lot 6 are Q1o= 4.86 cfs and Q1oo=12.72 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 four 6" trench drain systems, each connecting to a 12" PVC storm drain pipe which will
convey runoff to the existing area inlet in the northeast corner of the site. At the same time, the parking
lot and sidewalk along the north face of the building will be conveyed via sheet flow and curb and gutter
to a curb cut in the northeast corner of the parking lot. This curb cut will allow flow to travel to the proposed
grass swale along the north landscaping area of the lot where it will discharge into the existing area inlet.
From this existing inlet, 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.
The post development property consists of six on -site sub -basins and two off -site basins. See drainage
sheets for additional information.
Post -development Sub -basin B1 consists of 0.20 acres of the proposed building. This basin is 90%
impervious. Runoff from this basin drains via roof and storm drains to the existing type B inlet where it is
piped into existing storm sewer infrastructure. Sub -basin 61 discharges at a rate of 0.85 cfs in the 10-
year storm event and 1.82 cfs in the 100-year storm event.
Post -development Sub -basin B2 consists of 0.64 acres of parking lot and landscaped area on the north
side of the property. This basin is 82% impervious. Runoff from this basin generally sheet flows to the
north where it is routed through a 3' curb cut and into the existing inlet. Sub -basin B2 has a discharge
rate of 2.52 cfs in the 10-year event and 5.56 cfs in the 100-year storm event.
Post -development Sub -basin 63 consists of 0.18 acres of paved walkway, paved road, and landscaped
area along the east side of the property. This basin drains offsite, where it sheet flows towards the existing
inlet on Lot 7 in accordance with existing conditions. This basin is 77% impervious. Sub -basin B3
discharges at 0.68 cfs in the 10-year event and 1.52 cfs in the 100-year storm event.
Post -development Sub -basin 64 consists of 0.08 acres of paved walkway and landscaped area on the
southeast corner of the property. This basin drains into a proposed trench drain inlet along the south side
of the proposed building. This basin is 53% impervious. Sub -basin B4 discharges at 0.23 cfs in the 10-
year event and 0.59 cfs in the 100-year storm event.
Post -development Sub -basin B5 consists of 0.08 acres of paved walkway and landscaped area on the
southwest corner of the property. This basin drains into a proposed trench drain inlet along.the south side
of the proposed building. This basin is 53% impervious. Sub -basin B5 discharges at 0.23 cfs in the 10-
year event and 0.59 cfs in the 100-year storm event.
Post -development Sub -basin B6 consists of 0.07 acres of paved walkway and landscaped area on the
west side of the property. This basin drains into a proposed trench drain inlets along the west side of the
proposed building. This basin is 63% impervious. Sub -basin B6 discharges at 0.22 cfs in the 10-year
event and 0.52 cfs in the 100-year storm event.
Post -development Sub -basin OFF1 consists of 0.04 acres of paved walkway and landscaping south of
the property. The sub -basin is 48% impervious. Discharge from this area runs onto B5 and then follows
the same drainage patterns. Sub -basin OFF1 discharges at 0.11 cfs in the 10-year event and 0.30 cfs in
the 100-year storm event.
Post -development Sub -basin OFF2 consists of 0.08 acres of paved walkway and landscaping south of
the property. The sub -basin is 35% impervious. Discharge from this area runs onto B4 and then follows
the same drainage patterns. Sub -basin OFF2 discharges at 0.18 cfs in the 10-year event and 0.53 cfs in
the 100-year storm event.
The overall post -development site imperviousness is 67%, compared to the 95% pre -development
conditions. This imperviousness was calculated using 0.24 acres of landscape as pervious service. After
improvements, the site will discharge at a total rate of 11.44 cfs in the 100-year storm event, generating
1.28 cfs less than existing conditions.
In the 100 year event, the total site discharge rate will be 11.44 cfs, compared to 12.72 cfs in the originally
proposed condition. The site will discharge at 1.28 cfs less than the originally proposed condition as
determined in the master drainage report.
The overall drainage concept for this site is to convey flows via underground storm drain and sheet flows
to an existing inlet on the northeast corner of the property.
The proposed condition
reduction of runoff in the
in the Master Report.
Sincerely,
Alex Hoime, PE
Director
has 1.08 acres of impervious surface, 18% less than originally proposed, and a
100 year storm event of 1.28 cfs from the originally proposed design as shown
RUNOFF COEFFICIENT CALCULATIONS
Project Name: C01303B - Front Range Village - Lot 6
Calculated By: KV
Check By: AH
Date: 8/17/2016
RECOMMENDED RUNOFF COEFFICIENT AND PERCENT IMPERVIOUS'
Runoff Coefficients C-value
LAND USE
%IMPERVIOUS
10 YEAR 100 YEAR
LANDSCAPE
2
1
0.22
0.52
DRIVES AND WALKS
90
0.87
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 C110 C100
%
IMPERVIOUS
B7
0.00
0.00
0.20
0.20
0.87
0.91
90
B2
0.06
0.58
0.00
0.64
0.81
0.87
82
B3
0.03
0.15
0.00
- 0.18
0.77
0.85
77
B4
0.03
0.05
0.00
0.08
0.59
0.74
53
B5
0.03
0.05
0.00
0.08
0.59
0.74
53
B6
0.02
0.05
0.00
0.07
0.67
0.79
63
OFF1A
0.02
0.02
0.00
0.04
0.56
0.72
48
OFF2A
0.05
0.03
0.00
0.08
0.46
0.67
35
TOTAL: 1.37
WEIGHTED:
0.74
67
1 Runoff coefficients and percent impervious per Grand Junction Stormwater Management Manua
'CONTRIBUTING OFFSITE AREAS DRAINING INTO DETENTION BASIN BUT OUTSIDE OF PROPOSED PROPERTY.
10-YEAR INDIVIDUAL BASIN FLOWS
Project Name: C01303B - Front Range Village - Lot 6
Calculated By: NE
Check By: AH
Date: 8/22/2016
POST -DEVELOPMENT CONDITIONS:
SUB -BASIN DATA
DIRECT RUNOFF
CONTRIBUTING
BASINS
BASIN
AREA acre
C10
EFFECTIVE
AREA acre
I
in/hr
SUB BASIN'
Q cfs
Bi
0.20
0.87
0.17
4.87
0.85
B2
0.64
0.81
0.52
4.87
2.52
B3
0.18
0.77
0.14
4.87
0.68
B4
0.08
0.59
0.05
4.87
0.23
B5
0.08
0.59
0.05
4.87
0.23
B6
0.07
0.67
0.04
4.87
0.22
OFF1A
0.04
1 0.56
1 0.02
4.87
0.11
OFF2A
0.08
1 0.46
1 0.04
4.87
0.18
TOTAL:
5.02
I per City of Fort Coillins stormwater design standards.
010= C*I*A
100-YEAR INDIVIDUAL BASIN FLOWS
Project Name: C01303B - Front Range Village - Lot 6
Calculated By: NE
Check By: AH
Date: 8/19/2016
POST -DEVELOPMENT CONDITIONS:
SUB -BASIN DATA
DIRECT RUNOFF
CONTRIBUTING
BASINS
BASIN
AREA acre
C100
EFFECTIVE
AREA acre
I
in/hr
SUB BASIN
Q cfs
B1
0.20
0.91
0.18
9.95
1.82
B2
0.64
0.87
0.56
9.95
5.56
B3
0.18
0.85
0.15
9.95
1.52
B4
0.08
0.74
0.06
9.95
0.59
B5
0.08
0.74
0.06
9.95
0.59
B6
0.07
0.79
0.05
9.95
0.52
OFFM
0.04
0.72
0.03
9.95
0.30
OFF2A
0.08
0.67
0.05
9.95
0.53
TOTAL: 11.44
I per City, of Fort Coillins stormwater design standards.
Q100= C*I*A
Culvert Report
Hydraflow Express Extension for Autodesk@ AutoCAD® Civil 3D® by Autodesk, Inc.
12-inch PVC Storm Drain Analysis
Invert Elev Dn (ft)
Pipe Length (ft)
Slope (%)
Invert Elev Up (ft)
Rise (in)
Shape
Span (in)
No. Barrels
n-Value
Culvert Type
Culvert Entrance
Coeff. K,M,c,Y,k
Embankment
Top Elevation (ft)
Top Width (ft)
Crest Width (ft)
S. ml
id 00
107 M
TM00
106W
10. o0
IM M
10$.00
'Q DD
100.00
W00
= 100.00
= 400.00
= 1.00
= 104.00
= 12.0
= Circular
= 12.0
= 1
= 0.012
= Circular Concrete
= Square edge w/headwall (C)
= 0.0098, 2, 0.0398, 0.67, 0.5
= 107.00
= 395.00
= 395.00
�Neme>
GrMVGd M L Em k
Calculations
Qmin (cfs)
Qmax (cfs)
Tailwater Elev (ft)
Highlighted
Qtotal (cfs)
Qpipe (cfs)
Qovertop (cfs)
Veloc Dn (ft/s)
Veloc Up (ft/s)
HGL Dn (ft)
HGL Up (ft)
Hw Elev (ft)
Hw/D (ft)
Flow Regime
Wednesday, Sep 14 2016
= 4.35
= 4.35
_ (dc+D)/2
= 4.35
= 4.35
= 0.00
= 5.69
= 5.54
= 100.94
= 105.70
= 106.42
= 2.42
= Outlet Control
H D.M m
4.00
3A0
I.00
1.00
0.00
4.00
-z.00
-900
4.00
.500
Ra 00
Channel Report
Hydraflow Express Extension for Autodesk@ AutoCAD® Civil 3D8 by Autodesk, Inc.
3-foot Curb Cut Analysis
Rectangular
Bottom Width (ft)
= 3.00
Total Depth (ft)
= 0.50
Invert Elev (ft)
= 100.00
Slope (%)
= 1.00
N-Value
= 0.013
Calculations
Compute by:
Known Q
Known Q (cfs)
= 5.56
Elev (ft)
101.00 -
100.75
100.50
100.25
100.00
99.75
Section
Wednesday, Sep 14 2016
Highlighted
Depth (ft)
= 0.37
Q (cfs)
= 5.560
Area (sgft)
= 1.11
Velocity (ft/s)
= 5.01
Wetted Perim (ft)
= 3.74
Crit Depth, Yc (ft)
= 0.48
Top Width (ft)
= 3.00
EGL (ft)
= 0.76
0 .5 1 1.5 2 2.5 3 3.5 4
Reach (ft)
Depth (ft)
1.00
0.75
0.50
0.25
-0.25 1
u anmm• P !♦
K
11
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UNAUTHORIZED CHANGES & USES
THE ENGINEER PREPARING THESE PLANS WILL NOT BE RESPONSIBLE FOR OR UABLE FOP.
UNAUTHORIZED CHANGES TO ON USES OF THESE RANI ALL CHANGES OF THESE BANS MUST BE N
WITHIG AND MUST BE APPROVED BY THE PREPARER OF THESE BANS PRIOR TO CONSTRUCTION
CONSTRUCTION CONTRACTOR AGREES THAT N ACCORDANCE WITH GENERALLY ACCEPTED
CONSTRUCTION PRACTICES, CONSTRUCTION CONTRACTOR WILL BE REQUIRED TO ASSUME SCE AND
COMPLETE RESPONSIBILITY FOR JOB SITE CONDITIONS DURING THE COURSE OF CONSTRUCTION OF THE
PROJECT, INCLUDING SAFETY OF ALL PERSONS AND PROPERTY. THAT THIS FEOIREYENT SHALL BE
MADE TO APPLY CONTIWOUSLY AND NOT BE WTED TO NORMAL WORKING HOURS AND
CONSTRUCTION CONTRACTOR FURTHER AGREES TO DEFEND, INDEMNIFY AND HOD DESIGN
PROFESSIONAL HARMLESS FROM ANY AND ALL UABUTY, REAL OR ALLEGED, N CONNECTION WITH
THE PERFORMANCE OF WORK ON THIS PROECT. EXCEPTING UABUTY ARI9NG FROM THE SCE
NEGLIGENCE OF DESIGN PROFESSIONAL
ENGINEERS NOTE TO CONTRACTOR
THE DOSITNCE AND LOCATION OF ANY UNDERGROUND UTUTIES, PIPES, AND/OR STRUCTURES
mom ON THESE PLANS WERE OBTAINED BY A SEARCH OF AVALABLE RECORDS THERE MAYBE
EXISTING UTILITIES NOT SHOWN ON TIES RANB THE CONTRACTOR SHALL ASCERTAIN THE TRUE
VERTICAL AND HORIZONTAL LOCATION OF THOSE UNDERGROUND UTILITIES TO BE USED PRIOR TO
CUISRUCTHN AND SHALL BE RESPONSIBLE FOR ANY DAMAGE TD ANY PUBLIC OR PRIVATE
UMUES. SHOWN OR NOT SHOWN HEREON.
GENERAL NOTE:
ANY FUTURE LAND DISTURBANCE, INCREASE IN IMPERVIOUS AREA,
AND/OR CHANGE IN RUNOFF CONDITIONS ON THIS SITE MAY
REQUIRE ADDITIONAL STORM WATER MANAGEMENT PER MSD
REGULATIONS IN PLACE AT THAT TIME (INCLUDING TOTAL LAND
DISTURBANCE AND/OR IMPERVIOUSNESS ADDED ON THIS PLAN).
STORMWATER RUNOFF NOTES:
TOTAL LOT AREA: 1.28 ACRE
TOTAL DISTURBED AREA: 1.30 ACRE
PRE -DEVELOPMENT % IMPERVIOUS: 2%
POST -DEVELOPMENT % IMPERVIOUS: 67%
POST -DEVELOPMENT 10-YR STORM RUNOFF: 6.77 CFS
POST -DEVELOPMENT 1DO-YR STORM RUNOFF: 11.44 CFS
i1 A = BASIN DESIGNATION
Ei B = AREA IN ACRES
C = % IMPERVIOUSNESS
SUMMARY RUNOFF TABLE
BASIN ID
AREA TONG
ACRES
C VALUE
t00YR
PEAK
YR
(CFS)
100YR
(CFS)
B1
0.20
0.91
0.85
1.82
82
0.64
0.87
3.04
5.56
83
0.18
0.85
0.96
1.52
B4
0.08
0.74
0.37
0.59
B5
0.08
0.74
0.42
0.59
86
0.07
0.79
0.44
0.52
OFFi
0.04
0.72
0.26
0.30
OFF2
0.08
0.67
0.44
0.53
< rs BEARNGL ALIwNT711 CAP 30 NEST OF CORBETT DRIVE ON TOP OF
BEARNIGS ARE BASIS ON THE NORTH LOT LINE OF LOT 1, FRONT CONCElE WAll OF RHGATION STRUCRM CITY OF FORT
GE VW,GE AS SOUTH 90' DO 00' EAST ACCORDING TO THE COLLINS BENCHMARK 12-94.
TIDE➢ RAT. NAGW 29 ELEVATION 4950.1 FEET.
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