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North ernEngineering.com // 970.221.4158
NORTHERN
E N G: N E E R N G
Arrowhead Cottages
EROSION CONTROL REPORT
A comprehensive Erosion and Sediment Control Plan (along with associated details) has
been included with the final construction drawings. It should be noted, however, that any
such Erosion and Sediment Control Plan serves only as a general guide to the Contractor.
Staging and/or phasing of the BMPs depicted, and additional or different BMPs from those
included may be necessary during construction, or as required by the authorities having
jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are
properly maintained and followed. The Erosion and Sediment Control Plan is intended to
be a living document, constantly adapting to site conditions and needs. The Contractor
shall update the location of BMPs as they are installed, removed or modified in conjunction
with construction activities. It is imperative to appropriately reflect the current site
conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be
implemented during construction, as well as permanent erosion control protection. Best
Management Practices from the Volume 3, Chapter 7 — Construction BMPs will be utilized.
Measures may include, but are not limited to, silt fencing and/or wattles along the disturbed
perimeter, gutter protection in the adjacent roadways and inlet protection at existing and
proposed storm inlets. Vehicle tracking control pads, spill containment and clean-up
procedures, designated concrete washout areas, dumpsters, and job site restrooms shall
also be provided by the Contractor.
To ensure stormwater quality is achieved long after the construction of the project, one
permanent Stormwater Quality BMP is included within the design. Located at the northern
portion of the project site, an Extended Detention Basin (EDB) is being proposed. This
measure will treat all of the runoff draining through the property prior to reaching the
historic outfall.
The Final Public Improvement Construction Plan contains a full-size Erosion Control Plan as
well as a separate sheet dedicated to Erosion Control Details. In addition to this report and
the referenced plan sheets, the Contractor shall be aware of, and adhere to, the applicable
requirements outlined in any existing Development Agreement(s) of record, as well as the
Development Agreement, to be recorded prior to issuance of the Development Construction
Permit. Also, the Site Contractor for this project may be required to secure a Stormwater
Construction General Permit from the Colorado Department of Public Health and
Environment (CDPHE), Water Quality Control Division — Stormwater Program, before
commencing any earth disturbing activities. Prior to securing said permit, the Site
Contractor shall develop a comprehensive StormWater Management Plan (SWMP) pursuant
to CDPHE requirements and guidelines. The SWMP will further describe and document the
ongoing activities, inspections, and maintenance of construction BMPs.
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APPENDIX C
EROSION CONTROL REPORT
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APPENDIX 6.2
INLETS
NorthernEngineering.com // 970.221.4158
APPENDIX 6.1
STORM SEWERS
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APPENDIX B
HYDRAULIC COMPUTATIONS
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DEVELOPED RUNOFF COMPUTATIONS
same ]-6
Rational Method Equation: awzzoewz ,arxm rMCQUENCY aomsa VACi Project: Arrowhead Cottages
Q = C (C)I(i)(A) . �tt m �iea ,� reocox Calculations By: D. Weber
l Date: March 25, 2016
From Section 3.2.1 of the CFCSDDC 2 to 10 1.06
11 Co 25 1.Ic
26 to SO 20
71 to Igo 1.25
Rainfall Intensity: Noce: the product of C tlsex C, shell dot exceed :.--
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Design
Point
Basin(s)
Area, A
(acres)
2-yr
T,
(min)
10-yr
T.
(min)
100-yr
Tc
(min)
C2
CIO
Clop
Intensity,
i2
(in/hr)
Intensity,
ilo
(in/hr)
Intensity,
i100
(in/hr)
Flow,
Q2
(cfs)
Flow,
010
(cfs)
Flow,
Q100
(cfs)
Al
Al
0.03
5.0
5.0
5.0
0.57
0.57
0.72
2.85
4.87
9.95
0.0
0.1
0.2
A2
A2
0,03
5.5
5.5
5.0
0.47
0.47
0.59
2.85
4.87
9.95
0.0
0.1
0.2
A3
A3
0.05
5.0
5.0
5.0
0.78
0.78
0.97
2.85
4.87
9.95
0.1
0.2
0.5
A4
A4
0.04
5.0
5.0
1 5.0
0.72
0.72
0.90
2.85
4.87
9.95
0.1
0.1
0.4
A
A
0.07
5.0
5.0
5.0
0.62
0.62
0.78
2.85
4.87
9.95
0.1
0.2
0.5
A
A6
0.17
5.0
5.0
5.0
0.85
0.85
1.00
2.85
4.87
9.95
0.4
0.7
1.7
A
A
0.08
5.0
5.0
5.0
0.81
0.81
1.00
2.85
4.87
9.95
0.2
0.3
0.8
A8
A8
0.03
5.0
5.0
5.0
0.70
0.70
0.87
2.85
4.87
9.95
0.1
0.1
0.3
B1
Bl
0.04
5.3
5.3
5.0
0.25
0.25
0.31
2.85
4.87
9.95
0.0
0.0
0.1
B2
B2
0.03
5.0
5.0
5.0
0.47
0.47
1 0.59
2.85
4.87
9.95
0.0
0.1
0.2
63
83
0.15
5.0
5.0
5.0
0.87
0.87
1.00
2.85
4.87
9.95
0.4
0.6
1.5
B4
B4
0.04
5.0
5.0
5.0
0.25
0.25
0.31
2.85
4.87
9.95
0.0 1
0.0
0.1
B5
B5
0.10
6.8
6.8
6.3
0.26
0.26
0.32
2.60
4.44
9.31
0.1
0.1
0.3
C
C
0.08
5.0
5.0
5.0
0.84
0.84
1.00
2.85
4.87
9.95
0.2
0.3
0.8
D
D
0.38
5.0
5.0
5.0
0.81
0.81
1.00
2.85
4.87
9.95
0.9
1.5
3.8
E
E
1 0.19
5.0
5.0
5.0
0.62
0.62
0.77
2.85
4.87
9.95
0.3
0.6
1.5
F
F
1 0.65
13.4
13.4
12.0
0.38
0.38
0.47
1.98
3.39
7.16
0.5
0.8
2.2
G
G
0.19
9.5
9.5
9.3
0.25
0.25
0.31
2.30
3.93
8.03
0.1
0.2
0.5
OS1
O51
0.03
5.0
5.0
5.0
0.44
0.44
0.55
2.85
4.87
9.95
0.0
0.1
0.2
OS2
OS2
0.11
6.6
6.6
5.8
0.35
0.35
0.44
2.60
4.44
9,63
0.1
0.2
0.5
D:IProjectsl374-0181Drainagel Hydmtogyl374-018_ RationaLxtsxl Direct -Runoff
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Overland
Flow, Time of Concentration:
l .�% �I
-, - C
* Cf L
sable S_•
Project:
Arrowhead
Cottages
7- -
Calculations
By:
D. Weber
'
S 13
���� KTeco encoOttnCr AoiwTmlxT ■ACTcas
Date:
March 25,
2016
Gutter/Swale
Flow,
Time of Concentration:
All Netara Parlod
Frequency
Feat=
T, = L /
60V
t'M`a)
E-
Tc = T,
+ T, (Equation
RO-2)
2 to 10
1.00
Velocity
(Gutter Flow), V = 20-Sv`
(Equation
RO-4)
11 to 25
26 to SO
1.10
1.20
Velocity
(Swale Flow), V = 15-S"
51 to 100
1.25
Note: She product
of C class Cr stall not exceed 1.00
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Overland Flow
Gutter Flow
Swale Flow
Time of Concentration
Deign
Basin
C*Cf
C*Cf
C*G
Length,
Slope,
T,
T,
T,
Length,
Slope,
Velocity,
Length,
Slope,
Velocity,
2-yr
10-yr
100-yr
Point
Is Length
(2-yr
(10-yr
(100-yr
L
S
2-yr
10-yr
100-yr
L
S
V
T
'
L
S
V
T '
T,
T,
T,
>50017
Cr=1.00)
Cf=1.00)
C,=1.25)
(ft)
(%)
(min)
(min)
(min)
(f)
(%)
ON
(min)
(ft)
(%)
NO
(min)
(min)
(min)
(min)
AT--
Ai
No
0.57
0.57
0.72
7
1.8
1.8
1.3
0.0
0.0
N/A
42
,2
2.68
0.3
5.0
5.0
5.0
A2
A2
No
0.47
0.47
0.59
34
2.2
5.3
5.3
4.3
0
0.0
0.00
N/A
22
1.5
1.84
0.2
5.5
5.5
5.0
A3
A3
No
0.78
0.78
0.97
34
33.3
1.1
1.1
0.4
0
0.0
0.00
N/A
10
5.0
3.35
0.0
5.0
5.0
5.0
A4
A4
No
0.72
0.72
0.90
49
5.3
2.8
2.8
1.5
0
0.0
0.00
N/A
0
0.0
0.00
N/A
5.0
5.0
5.0
A5
A5
No
0.62
0.62
0.78
44
7.0
3.1
3.1
2.1
0
0.0
0.00
N/A
0
0.0
0.00
N/A
5.0
5.0
5.0
A6
A6
No
0,85
0.85
1.00
48
2.3
2.4
2.4
1.0
76
0.6
1.55
0.8
0
0.0
0.00
N/A
5.0
5.0
5.0
A7
A7
No
0,81
0.81
1.00
32
33.3
1.0
1.0
0.3
0
0.0
0.00
N/A
22
2.6
2.42
0.2
5.0
5.0
5.0
A8
A8
No
0.70
0.70
0.87
48
2.3
3.9
3.9
2.2
76
0.6
1.55
0.8
0
0.0
0.00
N/A
5.0
5.0
5.0
Bl
Ell
No
0.25
0.25
0.31
35
5.6
1 5.3
5.3
4.9
0
0.0
0.00
N/A
0
0.0
0.00
N/A
5.3
5.3
5.0
B2
B2
No
0.47
0.47
0.59
29
6.0
3.5
3.5
2.8
0
0.0
0.00
N/A
0
0.0
0.00
N/A
5.0
5.0
5.0
E13
B3
No
0.87
0.87
1.00
26
2.0
1.7
1.7
0.8
99
0.5
1.41
1.2
0
0.0
0.00
N/A
5.0
5.0
5.0
B4
B4
No
0.25
0.25
0.31
5
5.0
2.1
2.1
1.9
0
0.0
0.00
N/A
32
5.0
3,35
0.2
5.0
5.0
5.0
B5
65
No
0.26
0.26
0.32
48
4.7
6.5
6.5
6.0
0
0.0
0.00
N/A
28
1.5
1.84
0.3
6.8
6.8
6.3
C
C
No
0.84
0.84
1.00
26
2.0
2.0
2.0
0.8
58
0.5
1.41
0.7
0
0.0
0.00
N/A
J 5.0
5.0
5.0
D
D
No
0.81
0.81
1.00
25
2.0
2.2
2.2
0.7
179
1.1
2.10
1.4
0
0.0
0.00
N/A
5.0
5.0
5.0
E
E
No
0.62
0.62
0.77
26
33.3
1.4
1.4
1.0
0
0.0
0.00
N/A
106
1.0
1.50
1.2
5.0
5.0
5.0
F
F
No
0.38
0.38
0.47
95
2.0
10.5
10.5
9.1
244
0.5
1.41
2.9
0
0.0
0.00
N/A
13.4
13.4
12.0
G
G
No
0.25
0.25
0.31
17
20.0
2.4
2.4
2.2
0
0.0
0.00
N/A
285
0.2
0.67
7.1
9.5
9.5
9.3
OS1
0S1
No
0.44
0.44
0.55
10
2.0
1 3.1
3.1
2.6
0
0.0
0.00
N/A
0
0.0
0.00
N/A
5.0
5.0
5.0
OS2
OS2
No
0.35
0.35
0.44
35
2.0 1
6.6
6.6
5.8
0
0.0
C.00
N/A
0
0.0
0.00
N/A
6.6
6.6
5.8
D9ProjactsU74-0181DrainagelHydro)ogyl374-018_Raeonal.x1sxlTc-2-yr S_f00-yr
DEVELOPED COMPOSITE % IMPERVIOUSNESS
AND RUNOFF COEFFICIENT CALCULATIONS
CHARACTER OF SURFACE:
Streets, Parking Lots, Roofs, Alleys, and Drives:
Asphalt................................................................................................
Concrete..............................................................................................
Gravel................................................................................................
Roofs.................................................................................................
Concrete Pavers.....................................................................................
Lawns and Landscaping
SandySoil...........................................................................................
Clayey Soil..........................................................................................
Runoff
Coefficient
Percentage
Impervious
Project: Arrowhead Cottages
Calculations By: D. Weber
Date: March 25, 2016
2-rear G = 1.00 10-year C, = 1.00 100-year G = 1.25
0.95
100
0.95
90
0.50
40
0.95
90
0.40
22
0.15
0
0.25
0
Runoff Coefficients are taken from the City
of on Collins Storm Drainage Desi n Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Al
1,334
0.03
0.00
0.00
0.01
0.00
0.00
0.02
0.57
0.57
0.72
41.5
A2
1.244
0.03
0.00
0,01
0.00
0.00
0.00
0.02
0.47
0.47
0.59
28.4
A3
2,034
0.05
1 0.00
0.02
0.01
0.00
0.00
0.01
0.78
0.78
0.97
68.1
A4
1,780
0.04
0.00
0.01
0.02
0.00
0.00
0.01
0.72
0.72
0.90
60.7
A5
2,841
0.07
0.00
0.01
0.02
0.00
0.00
0.03
0.62
0.62
0.78
47.6
A6
7,364
0.17
0.00
0.15
0.00
0.00
0.00
0.02
0.85
0.85
1.00
77.5
A7
3,293
0.08
0.00
0.01
0.05
0.00
0.00
0.02
0.81
0.81
1.00
71.4
A8
1,323
0.03
0.00
0.00
0.02
0.00
0.00
0.01
0.70
0.70
0.87
57.6
B1
1,623
0.04
0.00
0.00
0.00
0.00
0.00
0.04
0.25
0.25
0.31
0.0
B2
1,163
0.03
0.00
0.01
0.00
0.00
0.00
0.02
0.47
0.47
0.59
28.7
63
6,615
0.15
0,00
0.09
0.04
0.00
0.02
0.00
0.87
0.87
1.00
80.0
B4
1,546
0.04
0.00
0.00
0.00
0.00
0.00
0.04
0.25
0.25
0.31
0.0
B5
4,157
0.10
0.00
0.00
0.00
0.00
0.00
0.09
0.26
0.26
0.32
0.7
C
3,666
0.08
0.00
0.02
0.05
0.00
0.02
0.00
0.84
0.84
1.00
76.1
D
16,696
0.38
0.00
0.18
0.12
0.00
0.00
0.08
0.81
0.81
1.00
71.8
E
8,350
0.19
0.00
0.01
0.09
0.00
0.00
0.09
0.62
0.62
0.77
47.0
F
28,449
0.65
0.00
0.02
0.10
0.00
0.00
0.54
0.38
1 0.35
1 0.47
1 16.1
G
8,448
0.19
0.00
0.00
0.00
0.00
0.00
0.19
0.25
0.25
0.31
0.0
OS1
1510
0.03
0.00
0.01
0.00
0.00
0.00
0.03
0.44
0.44
0.55
24.4
CS2
4,913
0.11
0.00
0.02
0.00
0.00
0.00
0.10
0.35
0.35
0.44
12.6
TOTAL
108,349
2.49
0.00
0.56
1 0.54
0.00
0.04
1.35
0.56
0.56
0.70
40.1
D: Projects 074-0 1 8iDrainage I Rydrologyl374-018_ Rabonal.xlsxlC-Values
■� NORTHERN
ENGINEERING
s •; r 4 ,,w
r•�r�
N NORTHERN
ENGINEERING
Arrowhead Cottages
approximately 47,885 SF. For this reason, no modifications to the existing detention pond
are proposed.
In conclusion, this addendum has been prepared in accordance with the Fort Collins
Stormwater Criteria Manual (FCSCM) and complies with assumptions from previous
drainage reports.
Page13
NORTHERN
ENGINEERING
Arrowhead
The Arrowhead Cottages project is a Major Amendment to the Centre Avenue Residences
site plan, previously submitted and approved by the City of Fort Collins. This addendum is
intended to document the associated stormwater impacts of the revised site development
plan on the existing and proposed storm drainage systems.
The project area has been previously studied as part of the Amended Master Drainage Plan
for the Centre for Advanced Technology (dated February 1987), the Final Drainage Report
for the Seventh Filing of the Centre for Advanced Technology (dated August 1988), and
the Final Drainage and Erosion Control Report for Centre Avenue Residences (dated
October 2009). The drainage plan for this proposed project will conform to these
previously approved reports.
Historically, the majority of the site sheet flowed north to an existing detention pond located
in the northern portion of the site. A small area of the site along Centre Avenue and
Worthington Circle sheet flowed into the adjacent curb and gutter where it was routed to an
existing inlet at the intersection between Centre Avenue and Worthington Circle.
The proposed site will follow similar drainage patterns as historical. The majority of the site
basins will be collected by existing and proposed storm sewer systems, where the flows will
be routed to the existing detention facility. The basin which do not directly flow to the
existing detention pond are described below:
Basin OS1 is a small basin along the Worthington Circle Right -of -Way. Historically, flow
from this basin sheet drained north directly to the existing detention pond. As proposed,
the runoff will enter the Worthington Circle curb and gutter where it will be routed north to
the existing detention pond. Runoff from this basin is considered negligible (0.2 cubic feet
per second [cfs] for 100-yr event) and, therefore, the existing storm sewer system is not
analyzed. This is similar to the previously approved Centre Avenue Residences
development plan, labeled Basin D3 in that report.
Basins OS2 and E are the southern -most basins along the Centre Avenue and Worthington
Circle Right -of -Ways. Historically, flow from these basins sheet drained south or west into
either Worthington Circle or Centre Avenue Right -of -Ways, where it was collected by an
existing inlet on the north side of Centre Avenue. Stormwater runoff from Basin E will pass
through an engineered bio-swale designed to provide water quality measures and attenuate
the flows for minor events. This proposed bio-swale will treat a larger area of runoff then
the previously approved rain garden. Additionally, the total off -site runoff has slightly
increased during the 100-yr event from the Centre Avenue Residences developed site to
the Arrowhead Cottages developed site, from 1.9 cfs to 2.0 cfs, respectively. This is
assuming no attenuation caused by the proposed bio-swale.
Stormwater detention is provided by an existing detention facility constructed with the
Seventh Filing of the Centre for Advanced Technology and certified with the Final
Drainage and Erosion Control Report for Centre Avenue Residences. The total impervious
area for the previously approved Centre Avenue Residences site plan was approximately
48,787 square feet (SF). Through the use of permeable pavers located along the driveway
north of building 2, the Arrowhead Cottages site plan results in a total impervious area of
Page12
NORTHERN
ENGINEERING
March 25, 2016
Wes Lamarque
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
RE: Preliminary Drainage Addendum to the
Final Drainage and Erosion Control Report for Centre Avenue Residences
Mr. Lamarque:
Northern Engineering is pleased to submit this Drainage Addendum for your review. This
addendum serves to outline the drainage design for the Arrowhead Cottages project, and to
show compliance with overall drainage concepts outlined in previous reports and studies.
This addendum has been prepared in accordance with the Fort Collins Stormwater Criteria
Manual (FCSCM) and serves to document the stormwater impacts associated with the
proposed project. We understand that review by the City is to assure general compliance
with standardized criteria.
If you should have any questions as you review this addendum, please feel free to contact
US.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Danny Weber, PE
Project Engineer
Ryan Banning, PE
Project Manager
301 N. Howes Street, Suite 100, Fort Collins, CO 80521
970.221.4158 I www.northernengineering.com