HomeMy WebLinkAboutHOMESTEAD AT CLARENDON HILLS - PDP190007 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTApril 10, 2019
DRAINAGE LETTER AND LID REPORT
HOMESTEAD AT CLARENDON HILLS
Fort Collins, Colorado
Prepared for:
Kenneth R. Mitchell
Mosaic Real Estate LLC
1021 Nightingale Drive
Fort Collins, Colorado. 80525
Prepared by:
301 North Mason Street, Suite 100
Fort Collins, Colorado 80524
Phone: 970.221.4158
www.northernengineering.com
Project Number: 1013-008
Drainage Letter and LID Report – Homestead at Clarendon Hills
Date: April 10, 2019
Project: Homestead at Clarendon Hills Project No. 1013-008
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 “Homestead at
Clarendon Hills”. The site is located in southwest Fort Collins and is bounded to the north by Front Range
Community College, to the east by existing Clarendon Hills Subdivision, to the south by Clarendon Hills Drive
and Langdale Drive, and to the west by South Shields Street. The project site is part of the Drainage Report for
Clarendon Hills by Stuart and Associates written in 1986. The proposed development consists of 8 low-density
single-family lots and a detention area. The project site also contains an existing irrigation ditch. This ditch will
be piped underground as part of the construction activities.
Since the project was included in the Clarendon Hills development Drainage Report, 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 Clarendon Hill drainage design divided the subdivision into 3 basins. The current project site is
split by two of these basins - Drainage Basin A draining to the north, and Drainage Basin B draining to the
south. Drainage Basin B flows into Clarendon Hills Drive and Langdale Drive and travels via gutter and pan
flow south along Clarendon Hills Drive. The flow is then collected by inlets at Clarendon Hills Drive and
Hinsdale Drive and conveyed to a series of existing detention ponds. Drainage Basin A generally flows to the
northeast onto the Front Range Community College site or to an existing irrigation ditch on the property. From
there, it flows through existing drainage ways east to Mail Creek, and eventually to Fossil Creek. An Existing
Drainage Exhibit has been provided in the appendices for reference, along with excerpts from the original report.
Proposed Drainage Patterns
The Homestead at Clarendon Hills project has divided the site into three proposed drainage basins that
essentially follow the established drainage patterns, as well as the drainage patterns approved with the
Drainage Report for Clarendon Hills. The site is composed of proposed Basin A, which encompasses the rear of
the lots, most of the expected buildings and roofs, and the detention area. Flows from the basin will drain to the
detention area and then will be released into the existing irrigation channel at historic 2-yr release rates. Basin
B will roughly match the existing area draining south to the existing Clarendon Hills ponds and will be limited to
the driveways and walks. All proposed roof drains will drain north to the proposed detention area. Additionally,
Basin OS1 has been defined on the east and the north sides of the site to quantify flows to the Front Range
Community College campus. The areas draining off-site undetained have been reduced in area but remain due
to restricted construction in the existing wetland area and maintaining desired trail connectivity between
Clarendon Hills and Front Range Community College. 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, what is already flowing to the ponds and what the
developed runoff coefficient of the site per the approved drainage report was compared for Basin B. Using this
approach, the existing site has an area of 0.68 acres draining south to the existing ponds (Basin B). In the
approved Drainage Report for Clarendon Hills, the developed runoff coefficient used was C=0.50. The
proposed site has an area of 0.63 acres draining south to the existing ponds (Basin B), a reduction in area from
existing. For calculations, an assumed runoff coefficient of C=0.55 was used per City of Fort Collins standards
for Low-Density development. But when driveways of a size similar to those in surrounding lots are included in
the calculations, the resulting runoff coefficient is calculated as C=0.47, a reduction from the approved report’s
assumed value, maintaining runoff to the ponds at or below previously approved flows. Runoff from Basin A will
release at the historic 2-yr rate by using a new detention pond with an outlet structure that will restrict flows.
Detention
As shown in the analysis of Site Imperviousness, the proposed project will maintain existing or slightly decrease
the previously approved imperviousness of the project site draining south (Basin B) to the existing detention
when compared to the originally approved project, thereby decreasing the runoff from the project site to the
existing Clarendon Hills ponds. Since detention from Basin B was accounted for in the original Clarendon Hills
drainage report and the detention required by this project is at or less than originally assumed, no additional
detention is required for the Clarendon Hills ponds as a part of this project, and no changes to the existing
facilities are proposed. Basin A, an area previously undetained, will now be detained in an onsite detention
area, and released into the existing irrigation ditch at or below historic 2-yr release rates.
Inlets
Similar to the analysis performed for detention, all areas draining to existing inlets have matched or decreased
in imperviousness and area from what was projected in the previously approved Clarendon Hills report. This
results in matching or decreasing 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
Stormwater quality will be addressed by permanent Best Management Practices (BMPs) and Low Impact
Development (LID) requirements. City LID requirements specify that 50% of all single-family areas receive
water quality treatment from a LID facility. This project proposes to treat at least 50% of the new impervious
areas through a vegetated buffer located on the rear of the lots. Although exact impervious area is unavailable
at this preliminary stage, a majority of the lots area will drain across the vegetated buffer. It is also assumed
that the houses will be located in areas draining to the north across the vegetated buffer, leaving only the
driveway draining south untreated. A LID Treatment Exhibit is provided with this report details treatment area
and method.
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 matches the original drainage patterns. The site matches or decreases the
designed imperviousness draining to the existing Clarendon Hills ponds to the south making additional detention
in the ponds unnecessary. Onsite detention will be provided for the increased imperviousness of the area
draining to the existing irrigation ditch and will be released at or below existing 2-yr historic rates. Stormwater
quality has been provided and meets the city requirements for Low Impact Development treatment. Therefore,
it is my professional opinion that Homestead at Clarendon Hills 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,
Benjamin Ruch
Project Engineer
ATTACHMENT 1
HYDROLOGIC CALCULATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
1
Percentage
Impervious
1
Project:
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt …………………......................... ............................................................................... 0.95 100% Date:
Concrete ………………. ......................... ............................................................................... 0.95 100%
Gravel (packed) ………. ......................... ............................................................................... 0.50 40%
Roofs………………….. ......................... ............................................................................... 0.95 90%
Pavers…………………. ......................... ............................................................................... 0.50 40%
Recycled Asphalt ......................... ............................................................................... 0.80 80%
Lawns and Landscaping
Playgrounds 25%
Sandy Soil
Flat <2% ………….. ......................... ............................................................................... 0.10 2%
Average 2% to 7% ......................... ............................................................................... 0.15 2%
Steep >7% ………… ......................... ............................................................................... 0.20 2%
Clayey Soil
Flat <2% ………….. ......................... ............................................................................... 0.20 2%
Average 2% to 7% ......................... ............................................................................... 0.25 2%
Steep >7% ………… ......................... ............................................................................... 0.35 2% 2-year Cf
= 1.00 10-year Cf
= 1.00
USDA SOIL TYPE: C
Sub-Basin ID
Sub-Basin
Area
(sq. ft.)
Sub-Basin
Area
(ac.)
Area of Asphalt
& Concrete
(ac.)
Area of Roofs
(ac.)
Area of Gravel
(ac.)
Area of
Landscaping
2% to 7%
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Existing A 103,755 2.38 0.25 0.25 0.31 2%
CHARACTER OF SURFACE:
Runoff
Coefficient
1
Percentage
Impervious
1
Project:
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ………………… ......................... ............................................................................. 0.95 100% Date:
Concrete ………………. ......................... ............................................................................. 0.95 100%
Gravel (packed) ………. ......................... ............................................................................. 0.50 40%
Roofs………………….. ......................... ............................................................................. 0.95 90%
Pavers…………………. ......................... ............................................................................. 0.50 40%
Recycled Asphalt ......................... ............................................................................. 0.80 80%
Lawns and Landscaping
Playgrounds 25%
Sandy Soil
Flat <2% ………….. ......................... ............................................................................. 0.10 2%
Average 2% to 7% ......................... ............................................................................. 0.15 2%
Steep >7% ………… ......................... ............................................................................. 0.20 2%
Clayey Soil
Flat <2% ………….. ......................... ............................................................................. 0.20 2%
Average 2% to 7% ......................... ............................................................................. 0.25 2%
Steep >7% ………… ......................... ............................................................................. 0.35 2% 2-year Cf = 1.00 10-year Cf = 1.00
USDA SOIL TYPE: C
Sub-Basin ID
Sub-Basin Area
(sq. ft.)
Sub-Basin Area
(ac.)
Area of Asphalt
& Concrete
(ac.)
Area of Roofs
(ac.)
Area of Gravel
(ac.)
Area of
Landscaping
2% to 7%
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Proposed A 106,608 2.45 0.55 0.55 0.69 0%
Proposed B 27,254 0.63 0.55 0.55 0.69 0%
Proposed OS1 8,749 0.20 0.000 0.000 0.000 0.201 0.25 0.25 0.31 2%
PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Homestead at Clarendon Hills
Project: Homestead at Clarendon Hills
Calculations By:
Date:
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Existing A Existing A No 0.25 0.25 0.31 6.2 6.2 5.8 1.38 8.0 14.2 14.2 13.8
Existing B Existing B No 0.25 0.25 0.31 6.0 6.0 5.6 3.01 1.8 7.8 7.8 7.4
Existing OS1 Existing OS1 No 0.25 0.25 0.31 14.5 14.5 13.5 N/A N/A 14.5 14.5 13.5
Existing OS2 Existing OS2 No 0.25 0.25 0.31 5.4 5.4 5.0 N/A N/A 5.4 5.4 5.0
EXISTING TIMES OF CONCENTRATION COMPUTATIONS
B. Ruch
April 10, 2019
Design
Point
Sub-Basin
Overland Flow Gutter/Swale Flow Time of Concentration
Velocity (Gutter Flow), V = 20·S½
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Overland Flow, Time of Concentration:
Gutter/Swale Flow, Time of Concentration:
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
Project: Homestead at Clarendon Hills
Calculations By:
Date:
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Proposed A Proposed A No 0.25 0.25 0.31 6.5 6.5 6.0 1.52 6.8 13.4 13.4 12.9
Proposed B Proposed B No 0.35 0.35 0.44 5.3 5.3 4.7 3.01 1.8 7.1 7.1 6.5
Proposed OS1 Proposed OS1 No 0.00 0.00 0.00 10.8 10.8 10.8 N/A N/A 10.8 10.8 10.8
Tt = L / 60V
PROPOSED TIME OF CONCENTRATION COMPUTATIONS
Overland Flow, Time of Concentration:
B. Ruch
April 10, 2019
Gutter/Swale Flow, Time of Concentration:
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Design
Point
Sub-Basin
Overland Flow Gutter Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Project:
Calculations By:
Date:
Existing A Existing A 2.38 14 14 14 0.25 0.25 0.31 1.92 3.29 6.82 1.14 1.96 5.07
Existing B Existing B 0.68 8 8 7 0.25 0.25 0.31 2.46 4.21 8.80 0.42 0.72 1.88
Existing OS1 Existing OS1 0.15 15 15 13 0.25 0.25 0.31 1.90 3.24 6.92 0.07 0.12 0.32
Existing OS2 Existing OS2 0.06 5 5 5 0.25 0.25 0.31 2.85 4.87 9.95 0.05 0.08 0.20
Rainfall Intensity:
EXISTING RUNOFF COMPUTATIONS
Rational Method Equation: Homestead at Clarendon Hills
B. Ruch
April 10, 2019
Flow,
Q100
(cfs)
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Design
Point
Sub-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)
Q = C f ( C )( i )( A )
Project:
Calculations By:
Date:
Proposed A Proposed A 2.45 13 13 13 0.55 0.55 0.69 1.98 3.39 7.04 2.67 4.56 11.85
Proposed B Proposed B 0.63 7 7 6 0.55 0.55 0.69 2.52 4.31 9.31 0.87 1.48 4.00
Proposed OS1 Proposed OS1 0.20 11 11 11 0.25 0.25 0.31 2.17 3.71 7.57 0.11 0.19 0.48
April 10, 2019
Intensity,
i10
(in/hr)
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
B. Ruch
Homestead at Clarendon Hills
PROPOSED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Sub-Basin(s)
Rational Method Equation:
Rainfall Intensity:
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Q = C f ( C )( i )( A )
Pond No :
Proposed A
100-yr
0.69
13.00 min 17847 ft3
2.45 acres 0.41 ac-ft
Max Release Rate = 1.14 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 5046 1.00 1.14 342 4704
10 7.720 7830 1.00 1.14 684 7146
15 6.520 9920 0.93 1.06 958 8962
20 5.600 11360 0.83 0.94 1129 10232
25 4.980 12628 0.76 0.87 1300 11328
30 4.520 13754 0.72 0.82 1471 12283
35 4.080 14484 0.69 0.78 1642 12843
40 3.740 15174 0.66 0.76 1813 13361
45 3.460 15793 0.64 0.73 1984 13809
50 3.230 16381 0.63 0.72 2155 14226
55 3.030 16903 0.62 0.70 2326 14578
60 2.860 17405 0.61 0.69 2497 14909
65 2.720 17933 0.60 0.68 2668 15265
70 2.590 18389 0.59 0.68 2839 15551
75 2.480 18866 0.59 0.67 3010 15856
80 2.380 19312 0.58 0.66 3181 16132
85 2.290 19743 0.58 0.66 3352 16392
90 2.210 20174 0.57 0.65 3523 16652
95 2.130 20524 0.57 0.65 3694 16831
100 2.060 20895 0.57 0.64 3865 17030
105 2.000 21300 0.56 0.64 4036 17265
110 1.940 21645 0.56 0.64 4207 17439
115 1.890 22046 0.56 0.63 4378 17668
120 1.840 22396 0.55 0.63 4549 17847
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
ATTACHMENT 2
LID EXHIBIT
VAULT
ELEC
E ELEC
E
VAULT
ELEC
CONTROL
IRR
CONTROL
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IRCRONTROL
IRR
CONTROL
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ATTACHMENT 3
PREVIOUS REPORT EXCERPTS
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
This unofficial copy was downloaded on Nov-02-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA
APPROXIMATE
LOCATION OF
HOMESTEAD AT
CLARENDON HILLS
PROJECT
ATTACHMENT 4
DRAINAGE EXHIBITS
VAULT
ELEC
E ELEC
C
T C
T C
E
VAULT
ELEC
CONTROL
IRR
CONTROL
IRR CONTROL
IRCRONTROL
IRR
CONTROL
IRR
CONTROL
IRR CONTROL
IRR CONTROL
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TT
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VAULT
ELEC
E ELEC
C
T C
T C
E
VAULT
ELEC
CONTROL
IRR
CONTROL
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CONTROL
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CONTROL
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CLARENDON HILLS DRIVE
LANGDALE DRIVE
EXISTING 4' SIDEWALK
EXISTING 4' SIDEWALK
12' UTILITY
EASEMENT
15' UTILITY
EASEMENT
FRONT RANGE
COMMUNITY COLLEGE
CLARENDON HILLS
FIRST FILING
EX B
EX A
EX OS2
EX OS1
EX B
0.68 ac
EX A
2.38 ac
EX OS1
0.15 ac
EX OS2
0.07 ac
TELECOMMUNICATION
EASEMENT
EXISTING 18"
RCP IRRIGATION
EXISTING
IRRIGATION
STRUCTURE
EXISTING 18"
STEEL IRRIGATION
EXISTING 30" VERTICAL
CURB & GUTTER
EXISTING 31" DRIVE-OVER
CURB & GUTTER
EXISTING 6'
CROSS-PAN
EXISTING
IRRIGATION DITCH
EXISTING
LANDSCAPE WALL
EXISTING
WETLAND AREA
EXISTING
WETLAND AREA
8' UTILITY EASEMENT
8' UTILITY EASEMENT
DR2
EXISTING DRAINAGE EXHIBIT
9
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
( IN FEET )
1 inch = ft.
30 0 30 Feet
30
60 90
Sheet
HOMESTEAD AT CLARENDON HILLS 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 9
LEGEND:
DESIGN POINT A
FLOW ARROW
DRAINAGE BASIN LABEL
EXISTING DRAINAGE BASIN BOUNDARY
NOTES:
1. REFER TO THE PRELIMINARY DRAINAGE LETTER FOR HOMESTEAD AT CLARENDON HILLS, DATED
APRIL 10, 2019 FOR ADDITIONAL INFORMATION.
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
C
PROPOSED CONTOUR
EXISTING CONTOUR
PROPERTY BOUNDARY
PROPOSED STORM DRAIN / IRRIGATION
EXISTING CURB AND GUTTER
PROPOSED SWALE
PROPOSED LOT LINE
EASEMENT
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
Existing A Existing A 2.38 0.25 0.31 14.2 13.8 1.14 5.07
Existing B Existing B 0.68 0.25 0.31 7.8 7.4 0.42 1.88
Existing OS1 Existing OS1 0.15 0.25 0.31 14.5 13.5 0.07 0.32
Existing OS2 Existing OS2 0.06 0.25 0.31 5.4 5.0 0.05 0.20
Proposed A Proposed A 2.45 0.55 0.69 13.4 12.9 2.67 11.85
Proposed B Proposed B 0.63 0.55 0.69 7.1 6.5 0.87 4.00
Proposed OS1 Proposed OS1 0.20 0.25 0.31 10.8 10.8 0.11 0.48
BENCHMARK
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK 5-02
1/2 MILE SOUTH OF HARMONY ROAD, APPROXIMATELY 200 FEET NORTH OF WOODED CREEK COURT, ON
THE WEST SIDE OF SHIELDS STREET, ON THE NORTHWEST CORNER OF A STORM INLET.
ELEV. = 5089.11
CITY OF FORT COLLINS BENCHMARK 8-13
SOUTHEAST CORNER OF HARMONY RD. AND SHIELDS ON THE NORTHEAST CORNER OF A CONCRETE
TRAFFIC SIGNAL BASE.
ELEV. = 5086.71
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS
HAVE USED NGVD29 UNADJUSTED (PRIOR CITY OF FORT COLLINS DATUM) FOR THEIR VERTICAL DATUMS.
IF NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) IS REQUIRED FOR ANY PURPOSE,
THE FOLLOWING EQUATION SHOULD BE USED:
NGVD29 UNADJUSTED (PRIOR CITY OF FORT COLLINS DATUM) = NAVD88 - 3.20'
BASIS OF BEARINGS
THE BASIS OF BEARINGS IS THE WEST LINE OF SECTION 2-6-69 AS BEARING NORTH 00° 17' 10" EAST
(ASSUMED BEARING).
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CLARENDON HILLS DRIVE
LANGDALE DRIVE
9' UTILITY EASEMENT
EXISTING 4' SIDEWALK
9' UTILITY EASEMENT
EXISTING 4' SIDEWALK
12' UTILITY
EASEMENT
15' UTILITY
EASEMENT
FRONT RANGE
COMMUNITY COLLEGE
CLARENDON HILLS
FIRST FILING
20' SANITARY
EASEMENT
20' IRRIGATION
EASEMENT
10' UTILITY
EASEMENT
3' DRAINAGE
EASEMENT (TYP.)
ACCESS EASEMENT
LOT 1
LOT 2
LOT 3
LOT 6
LOT 5
LOT 7
LOT 8
LOT 4
TRACT A
A
2.40 ac
OS1
0.20 ac
CONNECT TO EXISTING
IRRIGATION PIPE
PROPOSED
IRRIGATION
PROPOSED
OUTLET STRUCTURE
PROPOSED 2'
CONCRETE PAN
B
A
OS1
B
0.63 ac
PROPOSED
VEGETATED BUFFER
PROPOSED
VEGETATED BUFFER
TELECOMMUNICATION
EASEMENT
EXISTING 18"
RCP IRRIGATION
EXISTING
IRRIGATION
STRUCTURE
EXISTING 18"
STEEL IRRIGATION
EXISTING 30" VERTICAL
CURB & GUTTER
EXISTING 31" DRIVE-OVER
CURB & GUTTER
EXISTING 6'
CROSS-PAN
EXISTING
IRRIGATION DITCH
EXISTING
LANDSCAPE WALL
EXISTING
WETLAND AREA
EXISTING
WETLAND AREA
DR1
DRAINAGE EXHIBIT
8
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
( IN FEET )
1 inch = ft.
30 0 30 Feet
30
60 90
Sheet
HOMESTEAD AT CLARENDON HILLS 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 9
LEGEND:
DESIGN POINT A
FLOW ARROW
DRAINAGE BASIN LABEL
PROPOSED DRAINAGE BASIN BOUNDARY
NOTES:
1. REFER TO THE PRELIMINARY DRAINAGE LETTER FOR HOMESTEAD AT CLARENDON HILLS, DATED
APRIL 10, 2019 FOR ADDITIONAL INFORMATION.
BENCHMARK
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
C
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK 5-02
1/2 MILE SOUTH OF HARMONY ROAD, APPROXIMATELY 200 FEET NORTH OF WOODED CREEK COURT, ON
THE WEST SIDE OF SHIELDS STREET, ON THE NORTHWEST CORNER OF A STORM INLET.
ELEV. = 5089.11
CITY OF FORT COLLINS BENCHMARK 8-13
SOUTHEAST CORNER OF HARMONY RD. AND SHIELDS ON THE NORTHEAST CORNER OF A CONCRETE
TRAFFIC SIGNAL BASE.
ELEV. = 5086.71
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS
HAVE USED NGVD29 UNADJUSTED (PRIOR CITY OF FORT COLLINS DATUM) FOR THEIR VERTICAL DATUMS.
IF NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) IS REQUIRED FOR ANY PURPOSE,
THE FOLLOWING EQUATION SHOULD BE USED:
NGVD29 UNADJUSTED (PRIOR CITY OF FORT COLLINS DATUM) = NAVD88 - 3.20'
BASIS OF BEARINGS
THE BASIS OF BEARINGS IS THE WEST LINE OF SECTION 2-6-69 AS BEARING NORTH 00° 17' 10" EAST
(ASSUMED BEARING).
PROPOSED CONTOUR
EXISTING CONTOUR
PROPERTY BOUNDARY
PROPOSED STORM DRAIN / IRRIGATION
EXISTING CURB AND GUTTER
PROPOSED SWALE
PROPOSED LOT LINE
EASEMENT
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
Existing A Existing A 2.38 0.25 0.31 14.2 13.8 1.14 5.07
Existing B Existing B 0.68 0.25 0.31 7.8 7.4 0.42 1.88
Existing OS1 Existing OS1 0.15 0.25 0.31 14.5 13.5 0.07 0.32
Existing OS2 Existing OS2 0.06 0.25 0.31 5.4 5.0 0.05 0.20
Proposed A Proposed A 2.45 0.55 0.69 13.4 12.9 2.67 11.85
Proposed B Proposed B 0.63 0.55 0.69 7.1 6.5 0.87 4.00
Proposed OS1 Proposed OS1 0.20 0.25 0.31 10.8 10.8 0.11 0.48
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CLARENDON HILLS DRIVE
LANGDALE DRIVE
VEGETATED BUFFER
TREATMENT AREA: 50,362 SF
HOMESTEAD AT CLARENDON HILLS
SHEET NO:
D:\PROJECTS\1013-008\DWG\DRNG\1013-008_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
April 10, 2019 LID-1
DRAWN BY:
SCALE:
ISSUED:
( IN FEET )
0
1 INCH = 60 FEET
60 60
LEGEND
UNTREATED AREA
VEGETATED BUFFER
VEGETATED BUFFER
TREATMENT AREA
HOMESTEAD AT CLARENDON HILLS ON-SITE LID TREATMENT
Project Summary
Total Delveloped Site Area 76,079 sf
Target Treatment Percentage 50%
Minimum Area to be Treated by LID
measures 38,039.50
sf
Vegetated Buffer
Total Vegetated Buffer Treatment Area 50,362 sf
Total Treatment Area 50,362 sf
Percent Total Project Area Treated 66.2%
1013-008
Clarendon
Project Number :
Project Name :
Detention Pond A
C Cf L
Ti
= −
S
C Cf L
Ti
= −
B. Ruch
April 10, 2019
1) Runoff coefficients are taken from the Fort Collins Stormwater Criteria Manaual, Table 4.1-3and Table 3.2-2.
100-year Cf = 1.25
Composite Runoff Coefficient with Adjustment
Low Density, C = 0.55
Low Density, C = 0.55
Existing B 29,782 0.68 0.25 0.25 0.31 2%
Existing OS1 6,442 0.15 0.25 0.25 0.31 2%
Existing OS2 2,805 0.06 0.25 0.25 0.31 2%
Open Space (undeveloped), C = 0.25
Open Space (undeveloped), C = 0.25
1) Runoff coefficients are taken from the Fort Collins Stormwater Criteria Manaual, Table 4.1-3and Table 3.2-2.
EXISTING COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Homestead at Clarendon Hills
B. Ruch
April 10, 2019
100-year Cf
= 1.25
Composite Runoff Coefficient with Adjustment
Open Space (undeveloped), C = 0.25
Open Space (undeveloped), C = 0.25