HomeMy WebLinkAboutBUCKING HORSE FIRST FILING - PDP - PDP120010 - REPORTS - DRAINAGE REPORT (3)`
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PROPOSED MAST It GUTTER
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NOTES:
1. RERA TO THE 'DRAINAGE k ER09ON CONTROL REPORT LETTER FOR
BUCKING HORSE TOWNHOMES' BY NORTHERN ENCINEERINO. DATED MARCH
Xth. 2012 FOR ADDITIONAL INFORMATION,
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
W L UTLIT Y NO TKGATKIN CENTER OF
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City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
APPROVED:
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NORTHERN � °
ENGINEERING Btu G HORSE
C-Value Comparison
Project: Bucking Horse Townhomes
Calculations By: A. Reese
Date: April 4, 2012
Bucking Horse Townhomes
Sidehill
- Filing Two
Basin ID
2-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Basin ID
2-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Al
0.54
0.68
102
0.69
0.86
A2
0.54
0.67
126
0.63
0.78
B1
0.55
0.69
125
0.63
0.79
B2
0.60
0.75
124
0.63
0.79
C1
0.56
0.70
133
0.58
0.73
C2
0.61
0.76
136
0.64
0.81
Drainage Letter Report D:IProjectsl687-0021DrainagelTownhomeslHydrologyl687-002 TH C-Values.xlsxlC-Values Comparison
11C� I NORNHERN BttK1NG HORSE
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
CHARACTER OF SURFACE:
Streets, Parking Lots, Roofs, Alleys, and Drives:
Asphalt......................................................................................................
Concrete....................................................................................................
Gravel.......................................................................................................
Roofs........................................................................................................
Pavers.......................................................................................................
Lawns and Landscaping
SandySoil.................................................................................................
Clayey Soil.................................................................................................
Runoff
Coefficient
Percentage
Impervious
2-year Ci = 1.00
Project:
Calculations By:
Date:
10-year C, = 1.00
Bucking Horse Townhomes
A. Reese
April 4, 2012
100-year Cf = 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 Fort Collins Storm Drainage Design 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
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Al
39,984
0.92
0.00
0.13
0.25
0.00
0.54
0.54
0.54
0.68
37.3
A2
101,246
1 2.32
1 0.00
1 0.33
0.62
0.00
1 1.37
0.54
0.54
0.67
37.0
B1
115,348
2.65
0.00
0.39
0.74
0.00
1.52
0.55
0.55
0.69
38.4
B2
10,208
0.23
0.00
0.04
0.08
0.00
0.12
0.60
0.60
0.75
44.5
C1
33,498
0.77
0.00
0.11
0.23
0.00
0.43
0.56
0.56
0.70
39.5
C2
105,004
2.41
0.00
0.31
0.91
0.00
1.19
0.61
0.61
0.76
45.6
TOTAL
405,287
9.30
0.00
1.31
2.83
0.00
5.16
0.56
0.56
0.70
40.06
Drainage Letter Report D:IProjects1687-0021DrainagelTownhomesViydrologyl687-002_TH_C-Values.xlsxlC-Values
■� NORTHERN B G HORSE*
ENGINEERING
The Bucking Horse Townhomes have been divided into 6 basins, designated as Basins Al, A2, 61,
B2, and C1 & C2. These new basins roughly correspond with the previously approved Basins 102,
126, 125, 124, 133, and 136, respectively. Due to a decrease in the overall density of the
proposed townhomes when compared to the previously approved plans, the C-values for the new
townhomes are less than the previously approved plans. A table comparing the previous C-values
with the new C-values has been provided for your reference.
The lower C-values result in lower peak runoff rates and stormwater volumes. The site grading
proposed with the Bucking Horse Townhomes development is in substantial compliance with the
drainage patterns originally approved with Sidehill — Filing Two. Therefore, stormwater runoff from
the Bucking Horse Townhomes project will not have any adverse impact on either the existing
drainage infrastructure, or that to be constructed according to the Phase 2 SF2 design.
Feel free to contact me if you have any questions or require additional information.
Sincerely,
Nicholas W. Haws, PE, LEED AP
enc.
Drainage Letter Report
J
NORTHERN
ENGINEERING
Drainage Letter Report
Date: April 4, 2012
ADDRESS: PHONE:970.221.4158 WEBSITE:
200 S. College Ave. Suite 10 www.northernengineering.com
Fort Collins, CO 80524 FAX: 970.221.4159
Project: Bucking Horse Townhomes Project No. 687-002
Replat of portions of Sidehill, Filings Two and Three
Fort Collins, Colorado
Attn: Mr. Wes Lamarque
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
Mr. Lamarque:
This letter is intended to address the stormwater impacts associated with the proposed Bucking
Horse Townhomes, which are a Replat of Sidehill, Filing Three, and Lots 40-45, Block 1; Block 2,
and Block Three; Lots 8-16, Block 11; and a portion of Outlot C of Sidehill — Filing Two. More
specifically, it serves to confirm that the proposed drainage patterns and runoff are in compliance
with the approved drainage plan for the overall Sidehill subdivision, which is now known as Bucking
Horse.
The document entitled, "Final Drainage & Erosion Control Report, Sidehill — Filing Two" dated May
27, 2005 by JR Engineering was used for the final design and analysis of the stormwater
infrastructure at Sidehill (aka, Bucking Horse). The drainage facilities included therein were sized to
accommodate the peak flow attenuation as well as the water quality treatment for the build -out of
the entire subdivision. The Phase 1 infrastructure, as outlined in the approved construction plans
for Sidehill — Filing Two (SF2,) have already been installed and certified by others.
The Bucking Horse Townhomes project will realign two existing storm lines due to conflicts with the
proposed site plan. Said realignments can be found on Sheet ST2 of the Bucking Horse Utility
Plans, with Storm Drain E1 and E2 corresponding to Line H and Lateral H5, respectively, from the
approved SF2 plans. Additionally, the remainder of storm sewer Line H (per SF2) in Scarecrow
Road and Blackbird Drive will constructed with the townhomes, as indicated on Sheet ST1 (Storm
Drain 1). The design is exactly as it was approved with the 03-22-07 plan revision to SF2.
The remaining drainage improvements will be constructed as part of the Bucking Horse Residences
project, essentially utilizing the Phase 2 plans previously approved with SF2. These facilities will
need to be built with, or before, Bucking Horse Townhomes as they provide the necessary
downstream conveyance, detention storage, and water quality treatment for portions of the
developed runoff from the townhome project.