HomeMy WebLinkAboutFORTY THREE PRIME - PDP - PDP180014 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTNovember 14, 2018
DRAINAGE LETTER AND LID REPORT
FORTY-THREE PRIME
Fort Collins, Colorado
Prepared for:
Red Raven LLC
201 Commerce Drive Unit 2
Fort Collins, Colorado 80524
Prepared by:
301 North Mason Street, Suite 100
Fort Collins, Colorado 80524
Phone: 970.221.4158
www.northernengineering.com
Project Number: 1328-010
Drainage Letter and LID Report – Forty-Three Prime
Date: November 14, 2018
Project: Forty-Three Prime Project No. 1328-010
Preliminary Development Plan (PDP)
Fort Collins, Colorado
Attn: City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
To whom it may concern:
This letter serves to address the stormwater impacts of the proposed project known as “Forty-Three Prime”.
The site is located in southeast Fort Collins and is bounded to the north by East Trilby Road, to the east by
Brittany Drive, to the south by Candlewood Drive and to the west by Autumn Ridge Drive. The project site is
Tract A of the Provincetowne P.U.D. Filing 2, which was approved in 2001, and was included in the drainage
study by Manhard Consulting for that project. The proposed development consists of six (6) multifamily
buildings, a parking area, two carports and amenity areas for residents. The project site also contains a
detention area and drainage facilities that were designed and constructed as a part of the Provincetowne
development.
Since the project was included in the Provincetowne development, this letter is intended to show conformance
with the approved drainage design, including general drainage patterns and imperviousness. This letter also
documents how the project meets new Low Impact Development requirements that the City of Fort Collins has
implemented since the original project was approved.
Original Drainage Patterns
The original Provincetowne drainage design divided Tract A into 5 basins – Basins 212, 220, 221, 225 and
406. In general, all of the basins drained from south to north, where they were intercepted by a swale along
the north boundary. The exception was Basin 212, which drained west to Autumn Ridge Drive and then
collected by an inlet located on Trilby. Once captured, the flows from all of the basins were conveyed to the
northeast corner of Tract A and detained in Detention Pond 306. An Existing Drainage Exhibit has been
provided has been provided at the back of this report for reference, along with excerpts from the original report
in the appendix.
Proposed Drainage Patterns
The Forty-Three Prime project has divided the site into seven drainage basins that follow essentially the same
drainage patterns that were originally approved with the Provincetowne project. The proposed site is comprised
of Basin A, which encompasses the parking area, and Basins B1-B3, which define building and landscape
areas. Basin C encompasses areas outside of the main development, including the existing detention pond and
the swale along the north property line. All of the aforementioned basins drain to the existing detention pond
via swales and surface conveyance. Additionally, Basin OS1 has been defined on the west side of the project to
quantify flows to Autumn Ridge Drive that will be captured by the existing inlet located on Trilby and conveyed
to the existing detention pond via existing storm drains. Please see the Drainage Exhibit for more information.
Page | 3
Site Imperviousness
While the drainage patterns of the proposed project generally conform with the previously approved drainage
design, the drainage basins themselves do not have the same extents or areas. Since a direct comparison
cannot be made between the original and proposed basins, a weighted percent imperviousness has been
developed. Using this approach, we find that the original drainage plan had a Composite Percent
Imperviousness of 42.6% (C100=0.56) while the proposed project will have a Composite Percent
Imperviousness of 39.5% (C100=0.44). This is an overall imperviousness decrease of 3.1%, which will result
in decreased runoff from the project than the original report anticipated.
Detention
As shown in the analysis of overall Site Imperviousness, the proposed project will decrease the imperviousness
of the project site when compared to the originally approved project, thereby decreasing the runoff from the
project site. This decrease in imperviousness and runoff also results in a decrease in the required detention
volume identified in the original Provincetowne report. Since detention was accounted for in the original
drainage report and the detention required by this project is less than originally assumed, no additional
detention is required as a part of this project, and no changes to the existing facilities are proposed.
Inlets
Similar to the analysis performed for detention, all areas draining to existing inlets have a decrease in
imperviousness and area from what was projected in the original Provincetowne report. This results in
decreased runoff to the existing inlets that were designed and approved with the earlier project, so no additional
inlet calculations have been provided as a part of this report.
Water Quality/LID Conformance
Although stormwater quantity detention is not required, stormwater quality will be addressed by permanent Best
Management Practices (BMPs) and Low Impact Development (LID) requirements. City LID requirements
specify that either 75% of all newly added impermeable areas are provided LID treatment OR 50% LID
treatment by which 25% of drivable surfaces are treated by permeable pavers. This project proposes to treat at
least 75% of the new impervious though a combination of a large rain garden on the east side of the project site
and a grass swale on the north side of the site. Both treatment methods are recognized as LID treatment
methods by Urban Drainage.
The rain garden will treat 77,772 square-feet of impervious area on the site. This is 80.2% of the total
impervious area within the project area, which exceeds the amount of LID treatment required by City Code
without further treatment. The rain garden will be designed as a single feature that will treat the majority of the
parking lot, concrete flatwork and rooftops by conveying flows from the parking area into the rain garden. The
facility will allow 12” of ponding as allowed by Urban Drainage, at which point stormwater will flow out the
east side of the facility, down a reinforced rundown and into the existing detention pond.
The grass swale will treat an additional 14,940 square-feet of impervious area on the site, which constitutes
15.4% of the impervious areas on the site. The grass lined swale is being provided along the north side of the
project to collect and treat runoff from the north sides of Buildings A thru D as well as the associated concrete
flatwork in those areas. The swale will be vegetated with blue grass to the west of the proposed sidewalk and
native grasses to the east. The swale bottom will be sloped at 2%, which conforms with Urban Drainage
requirements for vegetation and slope. These areas should see relatively low pollutant loads since they are non-
vehicular areas, making the grass swale an excellent treatment option.
When combined, 92,712 square-feet of total impervious area will be treated by these two methods, which
equates to 95.6% of the project areas. A LID Treatment Exhibit is provided with this report detailing the
treatment areas and methods.
Page | 4
Erosion and Sediment Control
During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards for
erosion and sediment control. Since more than 10,000 sf will be disturbed as a part of this project, a
comprehensive Stormwater Management Plan will be prepared for this project at final design. Post construction
water quality and erosion control will be achieved by a fully established and stabilized site. All areas disturbed
during construction will receive permanent hardscape, landscape, or building structure.
Floodplains
There are no regulatory floodplains associated with the project.
Conclusions
The proposed grading concept closely matches the original drainage patterns and decreases overall site
imperviousness and additional detention is proven to be unnecessary. Stormwater quality has been provided
and meets the city requirements for Low Impact Development treatment. Therefore, it is my professional
opinion that Forty-Three Prime satisfies all applicable stormwater criteria and will effectively limit potential
damage associated with its stormwater runoff.
Please do not hesitate to contact me if you have questions or require additional information.
Sincerely,
Andy Reese
Project Manager
ATTACHMENT 1
HYDROLOGIC CALCULATIONS
SITE IMPERVIOUSNESS COMPARISON
Basin ID
Basin Area
(ac)
Composite % Imperv.
100-year
Composite Runoff
Coefficient
212 0.68 33% 0.71
220 0.52 45% 0.74
221 2.18 45% 0.74
224 0.08 96% 1.00
225 1.30 39% 0.73
406 0.11 45% 0.74
Total Site 4.87 42.6% 0.56
Basin ID
Basin Area
(ac)
Composite % Imperv.
100-year
Composite Runoff
Coefficient
OS1 0.23 40% 0.69
A 1.62 80% 1.00
B1 0.15 68% 0.97
B2 0.03 59% 0.89
B3 0.15 39% 0.69
B4 0.45 39% 0.69
C 2.23 8% 0.39
Total Site 4.87 39.5% 0.44
EXISTING MASTER PLANNED COMPOSITE % IMPERVIOUSNESS
PROPOSED COMPOSITE % IMPERVIOUSNESS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Forty-Three Prime
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: B. Ruch
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40%
Roofs …….…….………………..……………….…………………………………………….0.95 . 90%
Pavers…………………………...………………..…………………………………………….0.40 . 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….0.15 . 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf = 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
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.
OS1 0.23 0.04 0.03 0.03 0.00 0.00 0.13 0.55 0.55 0.69 40%
A 1.62 0.75 0.38 0.23 0.00 0.00 0.27 0.83 0.83 1.00 80%
B1 0.15 0.00 0.01 0.11 0.00 0.00 0.04 0.78 0.78 0.97 68%
B2 0.03 0.00 0.00 0.02 0.00 0.00 0.01 0.71 0.71 0.89 59%
B3 0.15 0.00 0.01 0.05 0.00 0.00 0.09 0.55 0.55 0.69 39%
B4 0.45 0.00 0.03 0.17 0.00 0.00 0.25 0.56 0.56 0.69 39%
C 2.23 0.00 0.07 0.12 0.02 0.00 2.02 0.31 0.31 0.39 8%
Total Onsite 4.64 0.75 0.49 0.70 0.02 0.00 2.68 0.54 0.54 0.68 40%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf = 1.00
Overland Flow, Time of Concentration:
Project: Forty-Three Prime
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt
= L / 60V
Tc
= Ti
+ Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
Rational Method Equation: Project: Forty-Three Prime
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
C2 C10 C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
Flow,
WQ
(cfs)
OS1 OS1 0.23 5 5 5 0.55 0.55 0.69 2.85 4.87 9.95 0.4 0.6 1.6 0.18
A A 1.62 10 10 10 0.83 0.83 1.00 2.21 3.78 7.88 3.0 5.1 12.8 1.50
B1 B1 0.15 5 5 5 0.78 0.78 0.97 2.85 4.87 9.95 0.3 0.6 1.5 0.17
B2 B2 0.03 5 5 5 0.71 0.71 0.89 2.85 4.87 9.95 0.1 0.1 0.2 0.03
B3 B3 0.15 8 8 8 0.55 0.55 0.69 2.40 4.10 8.59 0.2 0.4 0.9 0.10
B4 B4 0.45 10 10 10 0.56 0.56 0.69 2.21 3.78 7.88 0.6 0.9 2.5 0.28
C C 2.23 26 26 25 0.31 0.31 0.39 1.40 2.39 5.04 1.0 1.7 4.4 0.49
DEVELOPED RUNOFF COMPUTATIONS
B. Ruch
September 26, 2018
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Q = C f ( C )( i )( A )
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Composite
% Imperv.
Flow,
WQ
(cfs)
Flow,
Q2
(cfs)
Flow,
Q100
(cfs)
OS1 10136 0.23 40% 0.18 0.36 1.59
A 70765 1.62 80% 1.50 3.00 12.79
B1 6750 0.15 68% 0.17 0.34 1.50
B2 1190 0.03 59% 0.03 0.06 0.24
B3 6718 0.15 39% 0.10 0.21 0.92
B4 19613 0.45 39% 0.28 0.55 2.46
C 97043 2.23 8% 0.49 0.97 4.38
Rational Summary (Proposed)
ATTACHMENT 2
LID/WATER QUALITY CALCULATIONS
MAIL
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RAINGARDEN
REQUIRED VOLUME: 1,333 CU. FT.
PROVIDED VOLUME: 1,496 CU. FT.
TREATMENT AREA: 76,464 SF
GRASS SWALE
TREATMENT AREA: 14,940SF
FORTY-THREE PRIME
SHEET NO:
D:\PROJECTS\1328-010\DWG\DRNG\1328-010_LID.DWG
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
ENGINEER ING
N O R T H E RN
PHONE: 970.221.4158
www.northernengineering.com
DRAWING REFERENCE:
LID TREATMENT EXHIBIT B. Ruch
1 in = 60 ft
November 14, 2018 LID-1
DRAWN BY:
SCALE:
ISSUED:
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 68.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.680
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.21 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 75,091 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 1,333 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 1021 sq ft
D) Actual Flat Surface Area AActual = 1496 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 1496 sq ft
F) Rain Garden Total Volume VT= 1,496 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
B. Ruch
Northern Engineering
November 13, 2018
Forty-Three Prime
Fort Collins, CO
UD-BMP (Version 3.06, November 2016)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.06_Rain Garden WQVol.xlsm, RG 11/13/2018, 3:49 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
PROVIDE A 30 MIL (MIN) PVC LINER WITH CDOT CLASS B
GEOTEXTILE ABOVE IT. USE THE SAME GEOTEXTILE BELOW
THE LINER IF THE SUBGRADE IS ANGULAR
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
B. Ruch
Northern Engineering
November 13, 2018
Forty-Three Prime
Fort Collins, CO
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
UD-BMP_v3.06_Rain Garden WQVol.xlsm, RG 11/13/2018, 3:49 PM
ATTACHMENT 3
PREVIOUS REPORT EXCERPTS
This unofficial copy was downloaded on Aug-14-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
ATTACHMENT 4
DRAINAGE EXHIBITS
ST
ST
ST
ST
C
C
T
F
E
S
F
E
S
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
CONTROL
IRR
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IRR
CONTROL
IRR
F
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LID
LID LID
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D
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D
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D
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D
MAIL
6YD
ST
ST
ST
ST
C
C
T
V.P.
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LID
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221
220
406
224
221
225
224
0.08 AC
221
2.18 AC
225
1.30 AC
212
0.68 AC
220
0.52 AC
406
0.11 AC
EAST TRILBY ROAD
CANDLEWOOD DRIVE
BRITTANY DRIVE
AUTUMN RIDGE DRIVE
EXISTING
EXISTING STORM DRAIN
STORM DRAIN
EXISTING
STORM DRAIN
EXISTING
STORM DRAIN
EXISTING INLET
EXISTING INLET
EXISTING INLET
EXISTING INLET
EXISTING INLET
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
NORTH
DR2
EXISTING DRAINAGE EXHIBIT
18
A
1.62 AC
LEGEND:
EXISTING STORM SEWER
EXISTING CONTOUR
EXISTING CURB & GUTTER
PROPERTY BOUNDARY
EXISTING INLET
DESIGN POINT A
FLOW ARROW
DRAINAGE BASIN LABEL
DRAINAGE BASIN BOUNDARY
PROPOSED SWALE SECTION
1 1
NOTES:
1. REFER TO THE PRELIMINARY DRAINAGE LETTER AND LID REPORTFOR
FORTY-THREE PRIME, DATED NOVEMBER 14, 2018 BY NORTHERN ENGINEERING
SERVICES, INC AND THE FINAL DRAINAGE AND EROSION CONTROL REPORT FOR
PROVINCETOWNE PUD FILING TWO, DATED MARCH 22, 2001 BY MANHARD
CONSULTING, LTD., FOR ADDITIONAL
2. THE NATURAL HABITAT BUFFER ZONE IS INTENDED TO BE MAINTAINED IN A NATIVE
LANDSCAPE. PLEASE SEE SECTION 3.4.1 OF LAND USE CODE FOR ALLOWABLE
USES WITHIN THE NATURAL HABITAT BUFFER ZONE.
BENCHMARK
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK 24-94
NORTHEAST CORNER OF EAST TRILBY RD AND PORTNER DR., ON TOP OF THE
WEST END OF A CONCRETE HEADWALL.
ELEV. = 4960.69
CITY OF FORT COLLINS BENCHMARK 25-94
NORTHWEST CORNER OF EAST TRILBY RD. AND SOUTH LEMAY AVE, ON TOP OF THE
SOUTHEAST EDGE OF THE CONCRETE RING TO AN ELECTRIC MANHOLE.
ELEV. = 4913.16
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM.
SURROUNDING DEVELOPMENTS HAVE USED NGVD29 UNADJUSTED FOR THEIR
VERTICAL DATUMS.
IF NGVD29 UNADJUSTED DATUM IS REQUIRED FOR ANY PURPOSE, THE
FOLLOWING EQUATION SHOULD BE USED:
NGVD29 UNADJUSTED = NAVD88 - 3.19'
BASIS OF BEARINGS
THE BASIS OF BEARINGS IS THE NORTH LINE OF THE NORTHEAST QUARTER OF
SECTION 13-6-69 AS BEARING NORTH 88° 11' 32" WEST (ASSUMED BEARING).
EXISTING PLANNEDCOMPOSITE % IMPERVIOUSNESS
Basin ID Basin Area (ac) Composite % Imperv.
100-year
Composite Runoff
Coefficient
212 0.68 33% 0.71
220 0.52 45% 0.74
221 2.18 45% 0.74
224 0.08 96% 1.00
225 1.30 39% 0.73
406 0.11 45% 0.74
Total Site 4.87 42.6% 0.56
Sheet
FORTY-THREE PRIME These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
REVIEW SET
E NGINEER ING
N O R T H E RN
FORT COLLINS: 301 North Howes Street, Suite 100, 80521
GREELEY: 820 8th Street, 80631
970.221.4158
northernengineering.com
of 18
6YD
6YD
6YD
UD
UD
UD
C
OS1
B1
B2
B3
B4
C
A
OS1
B1
B2
B3
B4
OS1
0.23 AC
A
1.62 AC
B1
0.15 AC
B2
0.03 AC
B3
0.15 AC
B4
0.45 AC
C
2.23 AC
EXISTING
EXISTING STORM DRAIN
STORM DRAIN
EXISTING
STORM DRAIN
EXISTING
STORM DRAIN
PROPOSED
AREA DRAIN
PROPOSED
AREA DRAIN
PROPOSED
AREA DRAIN
EXISTING INLET
EXISTING INLET
EXISTING INLET
EXISTING INLET
EXISTING INLET
PROPOSED
PROPOSED 2' RAIN GARDEN
CONCRETE CHASE
PROPOSED
RAIN GARDEN
PROPOSED
UNDERDRAIN
PROPOSED
1'SIDEWALK
CHASE
PROPOSED
1' SIDEWALK
CHASE
PROPOSED
1' SIDEWALK
CHASE
PROPOSED
7.5' SIDEWALK
CULVERT
PROPOSED
CULVERTS
EAST TRILBY ROAD
CANDLEWOOD DRIVE
BRITTANY DRIVE
AUTUMN RIDGE DRIVE
LOT 2
TRACT A
LOT 1
BLDG A
BLDG B
BLDG C
BLDG D
BLDG E
BLDG F
PROPOSED
CULVERT FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
HYDROLOGY SUMMARY
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
NORTH
LID SUMMARY
Sheet
FORTY-THREE PRIME These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
REVIEW SET
E NGINEER ING
N O R T H E RN
FORT COLLINS: 301 North Howes Street, Suite 100, 80521
GREELEY: 820 8th Street, 80631
970.221.4158
northernengineering.com
of 18
DR1
DRAINAGE EXHIBIT
17
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Composite
% Imperv.
Flow,
WQ
(cfs)
Flow,
Q2
(cfs)
Flow,
Q100
(cfs)
Treatment
Area
(sf)
OS1 10136 0.23 40% 0.18 0.36 1.59 4315.00
A 70765 1.62 80% 1.50 3.00 12.79 59061.24
B1 6750 0.15 68% 0.17 0.34 1.50 5103.00
B2 1190 0.03 59% 0.03 0.06 0.24 784.00
B3 6718 0.15 39% 0.10 0.21 0.92 2921.16
B4 19613 0.45 39% 0.28 0.55 2.46 8565.00
C 97043 2.23 8% 0.49 0.97 4.38 9091.00
PROPOSED COMPOSITE % IMPERVIOUSNESS
FORTY-THREE PRIME ON-SITE LID TREATMENT
Project Summary
Total Impervious Area 96,936 sf
Target Treatment Percentage 75%
Minimum Area to be Treated by LID
measures 72,702.00 sf
Rain Garden
Total Rain Garden Treatment Area 77,772 sf
Grass Swale
Total Rain Garden Treatment Area 14,940 sf
Total Treatment Area 92,712 sf
Percent Total Project Area Treated 95.6%
Basin ID Basin Area (ac) Composite % Imperv.
100-year
Composite Runoff
Coefficient
OS1 0.23 40% 0.69
A 1.62 80% 1.00
B1 0.15 68% 0.97
B2 0.03 59% 0.89
B3 0.15 39% 0.69
B4 0.45 39% 0.69
C 2.23 8% 0.39
Total Site 4.87 39.5% 0.44
A
1.62 AC
LEGEND:
PROPOSED CONTOUR
PROPOSED STORM SEWER
PROPOSED SWALE
EXISTING CONTOUR
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED INLET
DESIGN POINT A
FLOW ARROW
DRAINAGE BASIN LABEL
DRAINAGE BASIN BOUNDARY
PROPOSED SWALE SECTION
1 1
NOTES:
1. REFER TO THE PRELIMINARY DRAINAGE LETTER AND LID REPORTFOR
FORTY-THREE PRIME, DATED NOVEMBER 14, 2018 BY NORTHERN ENGINEERING
SERVICES, INC AND THE FINAL DRAINAGE AND EROSION CONTROL REPORT FOR
PROVINCETOWNE PUD FILING TWO, DATED MARCH 22, 2001 BY MANHARD
CONSULTING, LTD., FOR ADDITIONAL INFORMATION.
2. THE NATURAL HABITAT BUFFER ZONE IS INTENDED TO BE MAINTAINED IN A NATIVE
LANDSCAPE. PLEASE SEE SECTION 3.4.1 OF LAND USE CODE FOR ALLOWABLE
USES WITHIN THE NATURAL HABITAT BUFFER ZONE.
PROPOSED UNDERDRAIN UD
BENCHMARK
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK 24-94
NORTHEAST CORNER OF EAST TRILBY RD AND PORTNER DR., ON TOP OF THE
WEST END OF A CONCRETE HEADWALL.
ELEV. = 4960.69
CITY OF FORT COLLINS BENCHMARK 25-94
NORTHWEST CORNER OF EAST TRILBY RD. AND SOUTH LEMAY AVE, ON TOP OF THE
SOUTHEAST EDGE OF THE CONCRETE RING TO AN ELECTRIC MANHOLE.
ELEV. = 4913.16
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM.
SURROUNDING DEVELOPMENTS HAVE USED NGVD29 UNADJUSTED FOR THEIR
VERTICAL DATUMS.
IF NGVD29 UNADJUSTED DATUM IS REQUIRED FOR ANY PURPOSE, THE
FOLLOWING EQUATION SHOULD BE USED:
NGVD29 UNADJUSTED = NAVD88 - 3.19'
BASIS OF BEARINGS
THE BASIS OF BEARINGS IS THE NORTH LINE OF THE NORTHEAST QUARTER OF
SECTION 13-6-69 AS BEARING NORTH 88° 11' 32" WEST (ASSUMED BEARING).
EXISTING NATURAL HABITAT BUFFER ZONE
PROPOSED NATURAL HABITAT BUFFER ZONE
EXISTING WETLAND
%
& ' !! %
(") #$*" & +
%
& ' !! %
(") #$*" & +
%
& ' !! %
(") #$*" & +
( IN FEET )
0
1 INCH = 60 FEET
60 60
LEGEND
UNTREATED AREA
RAIN GARDEN AREA
RAIN GARDEN
TREATMENT AREA
FORTY-THREE PRIME ON-SITE LID TREATMENT
Project Summary
Total Impervious Area 96,936 sf
Target Treatment Percentage 75%
Minimum Area to be Treated by LID measures 72,702.00 sf
Rain Garden
Total Rain Garden Treatment Area 77,772 sf
Grass Swale
Total Rain Garden Treatment Area 14,940 sf
Total Treatment Area 92,712 sf
Percent Total Project Area Treated 95.6%
GRASS SWALE
TREATMENT AREA
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
OS1 OS1 No 0.25 0.25 0.31 0 N/A N/A N/A N/A 99 4.88% 4.42 0.4 0 NA N/A N/A 5 5 5
A A No 0.25 0.25 0.31 23 22.78% 2.7 2.7 2.5 563 0.50% 1.41 6.6 91 1.79% 2.01 0.8 10 10 10
B1 B1 No 0.25 0.25 0.31 0 N/A N/A N/A N/A 143 0.50% 1.41 1.7 21 2.00% 2.12 0.2 5 5 5
B2 B2 No 0.25 0.25 0.31 0 N/A N/A N/A N/A 61 0.50% 1.41 0.7 20 4.85% 3.30 0.1 5 5 5
B3 B3 No 0.25 0.25 0.31 53 6.64% 6.2 6.2 5.7 138 0.50% 1.41 1.6 76 1.96% 2.10 0.6 8 8 8
B4 B4 No 0.25 0.25 0.31 23 22.78% 2.7 2.7 2.5 563 0.50% 1.41 6.6 91 1.79% 2.01 0.8 10 10 10
C C No 0.25 0.25 0.31 140 0.91% 19.4 19.4 17.9 513 0.40% 1.26 6.8 0 NA N/A N/A 26 26 25
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
B. Ruch
September 26, 2018
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
= −
September 26, 2018