HomeMy WebLinkAboutMEYERS SUBDIVISION - FDP190006 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE RELATED DOCUMENTKEEFE CIVIL, LLC
825 Union Street
Golden, Colorado 80401
(970) 215-6808
April 4, 2019 Keefe Civil Project Number: 2018-025
Shane Boyle
Development Review Engineer
Stormwater Engineering & Development Review Division
City of Fort Collins Utilities
700 Wood Street
Fort Collins, Colorado 80522
RE: Meyer Subdivision, FDP190006 Drainage and Erosion Control Memo
Dear Shane:
The purpose of this letter is to address the drainage impacts to the existing 2.21 acre residential
lot at 2200 Kechter Road due to the proposed site improvements (Appendix A –Grading,
Drainage, and Erosion Control Plan). The site is located 0.1 mile east of South Timberline Road,
on the north side of Kechter road, and is bound by urban estate residential properties to the west,
north, and east.
The existing site is a developed urban estate residential lot with two residential homes, a gravel
driveway, two existing water wells, and several outbuildings. The vegetation is sparse and the soil
consists of Fort Collins loam and Nunn clay loam per the NRCS Soil Survey of Larimer County
(Appendix B).
Per the flood insurance rate map (Appendix C), the lot is located within Zone X. Zone X is defined
as an area of minimal flood hazard and does not have a base flood elevation associated with it.
The local topography generally slopes from the south to north behind the existing right-of-way
fence. The total existing impervious area is 14,577 square feet (sf) or 18%.
The proposed grading and drainage design for the site (Appendix A) follows the existing drainage
patterns and does not result in concentrated flow leaving the property. One of the single-family
residences and an outbuilding will be relocated offsite. The total impervious area will increase
slightly to 18,791 sf or 20%.
Hardscape or Hard
Surface
Historic
Area (sf)
Developed
Area (sf)
Change in
Impervious Area (sf)
Asphalt, Concrete 100 843
Rooftop 4,917 6,717
Fire Lane 0 9,746
Gravel 9,560 1,485
Total Impervious Area 14,577 18,791 4,214
Meyer Subdivision, FDP190006 Keefe Civil Project No.: 2018-025
Page 2 of 2 April 4, 2019
The composite C values and basin flow calculations for the historic and developed site are
included in the enclosed tables (Appendix D). Using the Fort Collins Stormwater Criteria Manual,
the estimated site runoff increases will be negligible with the 2-year, 10-year, and 100-year flows.
2-year 10-year 100-year
Historic runoff 0.79 cfs 1.36 cfs 3.63 cfs
Developed runoff 0.93 cfs 1.59 cfs 4.28 cfs
Based on these calculations, Keefe Civil respectfully requests no detention and water quality
requirements be imposed on this development.
Erosion Control Measures
The structural practices for the site will consist mainly of silt fence, vehicle tracking control pad,
and concrete washout area. The locations of these structural practices are shown in Appendix A.
The corresponding construction control measures fact sheets are included in Appendix E.
After construction has been completed at the site, all disturbed areas shall be seeded with native
plant seed or landscaped. The anticipated disturbed area is estimated at 0.54 acre. The City of
Fort Collins erosion and sediment control escrow calculations for the site are included in Appendix
F.
Thank you for the opportunity to submit this drainage and erosion control memo. Please do not
hesitate to reach out to me if you have any questions or comments regarding the above items.
(970) 215-6808
Best regards,
Megan L. Keefe, PE / Manager
Keefe Civil, LLC
Enclosures
Cc: Adam Meyer, Owner
Kim Rose, Rose Custom Homes
APPENDIX A
APPENDIX B
Soil Map—Larimer County Area, Colorado
(Meyer Subdivision)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/18/2019
Page 1 of 3
4484270 4484290 4484310 4484330 4484350 4484370 4484390 4484410 4484430
4484270 4484290 4484310 4484330 4484350 4484370 4484390 4484410 4484430
496790 496810 496830 496850 496870 496890 496910
496790 496810 496830 496850 496870 496890 496910
40° 30' 38'' N
105° 2' 16'' W
40° 30' 38'' N
105° 2' 11'' W
40° 30' 32'' N
105° 2' 16'' W
40° 30' 32'' N
105° 2' 11'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 40 80 160 240
Feet
0 10 20 40 60
Meters
Map Scale: 1:864 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
36 Fort Collins loam, 3 to 5
percent slopes
0.9 37.9%
73 Nunn clay loam, 0 to 1 percent
slopes
1.5 59.1%
74 Nunn clay loam, 1 to 3 percent
slopes
0.1 3.0%
Totals for Area of Interest 2.5 100.0%
Soil Map—Larimer County Area, Colorado Meyer Subdivision
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/18/2019
Page 3 of 3
APPENDIX C
USGS The National Map: Orthoimagery. Data refreshed October, 2017.
National Flood Hazard Layer FIRMette
0 250 500 1,000 1,500 2,000 Feet
Ü
105°2'32.52"W
40°30'46.53"N
105°1'55.06"W
40°30'19.17"N
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
HAZARD SPECIAL AREAS FLOOD
Without Zone A, V, Base A99 Flood Elevation (BFE)
With BFE or Depth Zone AE, AO, AH, VE, AR
Regulatory Floodway
0.of 2% 1% Annual annual Chance chance Flood flood with Hazard, average Areas
depth areasdrainage of less less than than one one foot square or with mile
Zone X
Future ChanceAnnual Conditions Flood Hazard 1%
Zone X
Area Levee.to with See Reduced Notes. Flood Risk due
Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood Hazard Zone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This digital map flood complies maps if with it is FEMA's not void standards as described for the below. use of
The accuracy basemap standards shown complies with FEMA's basemap
The authoritative flood hazard NFHL information web services is derived provided directly by FEMA. from This the map
was reflectnot exported changes on or 2/amendments 19/2019 at 1:subsequent 56:49 AM to and this does date and
time. becomeor The superseded NFHL and effective by new data information over time. may change
This elementsmap map image do not is appear: void if basemap the one or imagery, more of flood the following zone labels,
legend, FIRM panel scale number, bar, map and creation FIRM effective date, community date. Map identifiers,images for
unmapped regulatoryfor purposes. and unmodernized areas cannot be used
Legend
OTHER FLOOD AREAS HAZARD OF
OTHER AREAS
STRGUECNTUERREASL
FEATURES OTHER
MAP PANELS
8
1:6,000
B 20.2
The point pin selected displayed by the on the user map and is does an approximate not represent
an authoritative property location.
APPENDIX D
Composite C Values
Meyer Subdivision
Surface Type
Runoff
Coefficients1
Historic Area
(sf)
Minor (2-yr)
Historic
Composite C2
Major (100-yr)
Historic
Composite C2
Developed
Area (sf)
Minor (2-yr)
Developed
Composite C2
Major (100-yr)
Developed
Composite C2
Hardscape or Hard Surface
Asphalt, Concrete 0.95 100 843
Rooftop 0.95 4,917 6,717
Fire Lane 0.80 0 9,746
Gravel 0.50 9,560 1,485
Total Impervious Area 14,577 18,791
Landscape or Pervious Surface
Lawns, Clayey Soil, Avg Slope 2-7% 0.25 0 8,815
Undeveloped
Greenbelts, Agriculture 0.20 78,890 65,861
Total Drainage Basin Area 93,467 0.27 0.34 93,467 0.31 0.39
Notes:
1. Runoff Coefficients per Fort Collins Stormwater Criteria Manual Table 3.2-2.
2. Frequency adjustment factor per Fort Collins Stormwater Criteria Manual Table 3.2-3.
Meyer - drainage.xlsx
Basin Flow Calculations
Meyer Subdivision
Length
(ft)
Slope
(%)
Minor to
(min)
Major to
(min)
Length
(ft)
Slope
(%)
Channel
Type
Velocity
(fps)
tt
(min)
Minor Tc
(min)
Major Tc
(min)
2-yr 10-yr 100-yr 2-yr 10-yr 100-yr
1 A 2.146 0.27 0.34 485 2 27.1 24.9 NA 27.1 24.9 1.37 2.34 5.00 0.79 1.36 3.63
1 A 2.146 0.31 0.39 485 2 25.9 23.3 NA 25.9 23.3 1.41 2.40 5.17 0.93 1.59 4.28
Notes:
3. Per Fort Collins Stormwater Criteria Manual Section 3.3.4.
2. Per Fort Collins Stormwater Criteria Manual Section 3.3.3.
1. Per Fort Collins Stormwater Criteria Manual Section 3.3.2.
4. Per IDF Table for Rational Method, Table 3.4-1 Fort Collins Stormwater
5. Per Fort Collins Stormwater Criteria Manual Equation 5-1.
Initial/Overland Time1 Travel Time2
Historical
Developed
Final Tc
3 Intensity (in/hr)
4
Design
Point
Basin
Area
(acres)
Minor
Composite C
Major
Composite C
Basin Flow (cfs)
5
Meyer - drainage.xlsx
APPENDIX E
Concrete Washout Area (CWA) MM-1
November 2010 Urban Drainage and Flood Control District CWA-3
Urban Storm Drainage Criteria Manual Volume 3
MM-1 Concrete Washout Area (CWA)
CWA-4 Urban Drainage and Flood Control District November 2010
Urban Storm Drainage Criteria Manual Volume 3
Silt Fence (SF) SC-1
November 2010 Urban Drainage and Flood Control District SF-3
Urban Storm Drainage Criteria Manual Volume 3
SC-1 Silt Fence (SF)
SF-4 Urban Drainage and Flood Control District November 2010
Urban Storm Drainage Criteria Manual Volume 3
Stockpile Management (SP) MM-2
November 2010 Urban Drainage and Flood Control District SP-3
Urban Storm Drainage Criteria Manual Volume 3
MM-2 Stockpile Management (SM)
SP-4 Urban Drainage and Flood Control District November 2010
Urban Storm Drainage Criteria Manual Volume 3
Vehicle Tracking Control (VTC) SM-4
November 2010 Urban Drainage and Flood Control District VTC-3
Urban Storm Drainage Criteria Manual Volume 3
SM-4 Vehicle Tracking Control (VTC)
VTC-6 Urban Drainage and Flood Control District November 2010
Urban Storm Drainage Criteria Manual Volume 3
APPENDIX F
Project: Disturbed Acres: 0.54
EROSION CONTROL BMPs
Estimated
Quantity Units
Unit
Price
Total
Price
425 LF $2.00 $850.00
1 EA $500.00 $500.00
1 EA $500.00 $500.00
Sub-Total: $1,850.00
1.5 x Sub-Total: $2,775.00
Amount of security: $2,775.00
Total Acres x Price/acre: $390.08
$720.00 Sub-Total: $390.08
1.5 x Sub-Total: $585.12
Amount to Re-seed: $585.12
Minimum escrow amount: $1,500.00
Erosion Control Escrow: $2,775.00
Miniumum Escrow Amount
Meyer Subdivision
Unit Price of Seeding per acre:
“The amount of the security must be based on one and one-half times the estimate of the cost to install the approved measures, or one and one-half times
the cost to re-vegetate the disturbed land to dry land grasses based upon unit cost determined by the City's Annual Revegetation and Stabilization Bid,
whichever is greater. In no instance, will the amount of security be less than one thousand five hundred dollars ($1,500) for residential development or three
thousand dollars ($3,000) for commercial development”
Concrete Washout Area (CWA)
Final Escrow Amount
Erosion and Sediment Control Escrow/Security Calculation
for The City of Fort Collins
BMP Amount
Silt Fence (SF)
Vehicle Tracking Control (VTC)
Reseeding Amount
4/4/2019 8:34 AM https://d.docs.live.net/0e018cb1e76890ea/Documents/Keefe Civil/25-Meyer Subdivision/Erosion Control Report/Meyer_Escrow.xls
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 13, Sep 10, 2018
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Sep 20, 2015—Oct
21, 2017
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Larimer County Area, Colorado
(Meyer Subdivision)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/18/2019
Page 2 of 3