HomeMy WebLinkAboutDrainage Reports - 05/30/20191
May 10, 2018
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NORTHERN
EfVGINEERING
Mr. Was Lamarque
City of Fort Collins
700 Wood Street
Fort Collins, Colorado 80522
RE: Final Drainage Memorandum for 1st Stop Plaza Second Filing
Fort Collins, Colorado
Dear Wes:
City of Ft Ctf Plans.
Approved �
Date S-3r� r.q
Northern Engineering Services is pleased to submit this Final Drainage Memorandum for 1st Stop Plaza
Second Filing. Asa result of the recent design improvements to the intersection of Sunige Drive and College
Avenue, the driveway access for Lots 1 and 2 of 1st Stop Plaza will be relocated. The existing driveway is a
full -service access from College Avenue. In conjunction with the improvements to Suniga Drive, the access on
College Avenue will become right turn in and out only and relocated 60 feet north of the current location. A
three-quarter access will be provided from Suniga Drive 390 feet east of College Avenue. A shared driveway
will be constructed to allow vehicular movement between the two new access locations.
As part of the improvements for Suniga Drive and College Avenue intersection, Interwest Consulting Group
prepared a drainage memorandum to North East College Corridor Outfall (NECCO) Design Report dated
August:13, 2018. tots 1 and 2 of 1st Stop Plaza Second Filing coincide with Basin B of the Interwest
Drainage Memorandum. Interwest assumed an impervious area of 44.4% and a runoff coefficient of 0.53 for
Lots 1 and 2 of 1st Stop Plaza. The impervious area with the, proposed. driveway improvements is 33% and,
the runoff coefficient is 0.57. The proposed driveway improvements comply with assumptions. used in the
Interwest Drainage: Memorandum for Suniga Drive.
Detention for the site is part of the North East College Corridor Outfall (NECCO), but the project does not meet
the City's water quality and LID requirements. Upon redevelopment of Lots 1 and 2 for l° Stop Minor
Subdivision, the developer will need to provide the necessary water quality and LIDimprovements for that
portion of the driveway, asphalt, parking lot, and concrete of this project that fails within their property. Table
1 below summarizes the required volumes necessary to satisfy the City's water quality requirements for this
project
Table 1: Required Water Quatil i Volume
Description
Water Quality
Volume (ft3)
Water Quality
Volume (Acres)
Lot 1
669
0.015
Lott
285
0.007
FORT COLLINS:301 North Howes Street, Suite 100, 80521 1 970.221.4158
GREELEY-820 8'" Street, 80631 1970.395.98801 WEB: www.northemengineering.com
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NORTHERN
ENGINEERING
Interest Consulting Group assumed the entire flow from this site will flow towards a CDOT Type-D inlet at
the southeast comer of the project: Due to the necessary grading improvements to connect the proposed
driveway into the Suniga Road Improvements, the site was divided into four basins: Basin B1, B2, OS1, and
OS2.
Basin B1 sheet flows from the northwest comer of the project site towards the southeast comer of the site per
Interest Consulting GrouWs assumptions. The CDOT Type-D inlet will collect stonnwater from Basin B1 and
discharge into the NECCO storm sewer system.
Basin B2 flows from the northwest comer of Lot 2 to Inlet B2 along the south side of the project. Inlet B2
will discharge into a 30" storm sewer provided as part of the Suniga Road Improvements, and as an extension
of the NECCO storm sewer system.
Basin OS1 will sheet flow into the curb and gutter provided by he.Suniga Road Improvements. The curb and
gutter discharges into a storm inlet located on Suniga Road, provided by the Suniga Road Improvements, at.
the upstream location of the same storm sewer collecting drainage from Basin B2.
Basin OS2 follows historic patterns and discharges into the curb and gutter along. North College Avenue.
Drainage from North College Road ultimately discharges into the same storm sewer inlet collecting drainage
from Suniga Road and Basin OSl.
' We feel the current proposed drainage plan for 1st Stop Plaza Second Filing is in compliance with the
concepts shown in the NECCO Design Report and the interwest'Drainage Memorandum for Suniga Drive and
College Avenue. Upon redevelopment of Lots 1 and 2 of 15t Stop Minor Amendment, the developer will need
to provide water quality and LID Improvements for that portion of the driveway improvements that fall within
their property. If you have any questions, please feel free to contact me at;your earliest convenience.
NORTHERN ENGINEERING SERVICES, INC.
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Q�'•.
Frederick S. Wegert, PE
Project Engineer
FORT COLLINS:301 North Howes Street, Suite 100, 80521 1970.221.4158
GREELEY: 820 8" Street, 80631 l 970.395.9880 WEB: www riorthemengineering.com
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50% On -Site Treatment by LID Requirement
New Impervious Area
0.187 Ac.
Paver Area
0.048 Ac.
Traditional Pavement Area
0139 At.
Other Impervious Surfaces (Roofs, Concrete Walks, etc.)
0.000 Ac.
Required Minimum Impervious Area to be Treated
0.094 Ac.
Paver LID Treatment
Paver area
0.048 Ac.
Run-on area for Pavers (parking area)
0.125 Ac.
Run-on area for Pavers (other - concrete walks, etc.)
0.000 Ac.
Impervious Area Treated by LID Pavers
6.173 Ac.
Rain. Garden -Treatment
Rain Garden Area
0.000 Ac.
Run-on area for Rain Garden
0.000 Ac.
Impervious Area Treated by Rain Gardens
0.000 Ac.
Total Impervlous Area Treated
0.173 Ac.
Percent of Impervious Area Treated
92.38 %
25% Permeable_ Pavement.Requlre
merit_
New Pavement Area
8,165 .S . Ft.
Required Minimum Area of Permeable Pavement
2,041 Sq. Ft.
Total Permeable Pavement Area
2,099 Sq. Ft.
Actual % of Permeable Pavement Provided
25.7 %
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Area Inlet Performance Curve:
Existing Inlet at Basin B1
Governing Equations:
At low flow depths, the inlet will act like a weir governed by the following equation:
' where P = 3.1416'Dia. of grate
• where H corresponds to the depth of water above the flowline
Q = 3.0P H's
At higher flow depths, the inlet will act like an orifice governed by the following equation: ^ = 0.67 A G g'H ) 115
QJ
` where A equals the open area of the inlet grate
• where H corresponds to the depth of water above the centroid of the cross -sectional area (A)
The exact depth at which the inlet ceases to act like a weir, and begins to act like an orifice is unknown.
However, what is known, is that the stage -discharge curves of the weir equation and the orifice equation
will cross at a certain flow depth. The two curves can be found below:
Stage - Discharge Curves
90.00
80.00
70.00
+Weir Flow
mF--.-•Orifice Flow
-- -
60.00
50.00
m
40.00
u
30.00
20.00
10.00
0.0o
0.00 0.20 0.40 0.60 0.8o 1,00 1.20 1.40 1.60 1.80
Stage (ft)
If H > 1.792 (A/P), then the grate operates like an orifice; otherwise it operates like a weir.
Input Parameters:
Type of Grate:
MOT Ty
Diameter of Grate (ft):
3.8
Open Area of Grate (ft2):
24.70
Rim Elevation 1
4966.430
Reduction Factor:
50%
vs. Flow:
Shallow
Orifice
Actual
Elevation
Weir Flow
Flow
Flow
Depth Above Inlet (ft)
(ft)
(cfs)
(cfs)
(cfs)
0.00
4966.43
0.00
0.00
0.00
0.20
4966.63
1.60
29.68
1.60
0.40
4966.83
4.53
41.98
4.53
0.53
4966.96
6.83
48.14
6.83
0.60
4967.03
8.32
51.41
8.32
0.80
4967.23
12.81
59.36
12.81
1.00
4967.43
17.91
66.37
17.91
1.20
4967.63
23.54
72.71
23.54
1.40
4967.83
29.66
78.53
29.66
1.60
4968.03
36.24
83.95
36.24
1.80
4968.23
43.24
89.05
43.24
100-Year Design Flow = 6.86 cfs
10-Year Design Flow
= 2.69 cfs
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1108 N. COLLEGE AVENUE
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1 EXISTING BUILDING
1" N. COLLEGE AVENUE MATCH ITSSITTING
1� VM
FISTEDLIP �D,TER
ses ONTRAM LOT 21 ST STOP PLAZA l O e 1
W CONCRETE SECOND FILINGVALL
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QED OS2 Fm 1 ~ SECOND FILING 1 WIDE _ - 31FA9EIE r�
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III i DRUVE IMPROVEMENTS PREPARED IIIINTERWE TxOGROUP I _ 1` ���- � � � �mow- -mp
GONE BYa 1
IGHT", c PROPOSED STORM INLET I REINVEST w
DRIVE IMPROVEMENTS PREPARED
1
ccxSULnUUIi4n CONSULTING
IMPRUVEMENTS PREPARED By INTERWIST_ - %i..
tWP't GONwt GGROUPT - - - _
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PROPOSEDNFRASTRUCTMEeIGTRMs
PRO
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PROPOSED N.IORmNTow —eo--
wONSEDMINORCOxTdw —74
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PROADNED STORM SEWER
PERMANENT BMPS
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NOTES
s. F.a..NNrs INNFONF. T
PLAN wpPoSED.NO VACATED
REQUIRED WATER QUALITY VOLUME
OESUi, tPTION
WATERODULDS
VCl FI
W=(WMITY
VOL (ACRES)
THIS PROJECT WES NOT MEET THE CTB LID REQUIREMENTS. UPON
REDEVELOPMENT OF LOT$ t 83 FOR 1ST $TOP MINOR $UBONISION,
THE DON OF PERTHE DRIVEWAY
PROVIDE LID PARKING LOT,
FOR THAT
PoRTIFA OF IT DRIVEWAY, ASPHALT.PARKING LOT, AND CONCRETE
THAT FALLS WITHIN THEIR PROPERTY.
OFFSITE DRAINAGE FROM THE NORTH MUST BE MAINTgINED
CONVEYED OR NE ROUTED TO FLOW INTO THE NORTH E0.ST COLLEGE
CORRIDOR OUTALL STORM SEWER SYSTEM W(THINS EGA p=
DI1wTILm XOIRCAATTIGN CENTER OF
COLO
KRow MVlS below.
wWE ME xX. WINDrtymALL 7 ANNUAL AD, I MI��III
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
ROSE
BY,
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