HomeMy WebLinkAbout630 S HOWES ST EXTRA OCCUPANCY RENTAL - FDP190007 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTKEEFE CIVIL, LLC
825 Union Street
Golden, Colorado 80401
(970) 215-6808
April 17, 2019 Keefe Civil Project Number: 2019-006
Dan Mogen
Development Review Engineer
Stormwater Engineering & Development Review Division
City of Fort Collins Utilities
700 Wood Street
Fort Collins, Colorado 80522
RE: 630 South Howes Street Extra Occupancy Drainage Memo
Dear Dan:
The purpose of this letter is to address the drainage impacts to the existing 9,500 square foot (sf)
residential lot at 630 South Howes Street due to proposed site improvements required for extra
occupancy (Exhibit A –Grading and Drainage Plan). The site is located on the east side of South
Howes Street between Myrtle Street and Laurel Street. The lot is bound by residential properties
to the north and south, a dirt parking lot to the southeast, and an alley with commercial properties
to the east.
The existing site is a developed residential lot with one residential home, concrete driveway,
garage, and concrete sidewalks. vegetation is sparse with areas of gravel and the soil consists of
Fort Collins loam per the NRCS Soil Survey of Larimer County (Exhibit B).
The Basin A topography generally slopes from the east to the west starting approximately 45 feet
behind the Howes Street right-of-way. No site improvements are planned for Basin A. Basin B
slopes from the west to the east into the alley and will have an additional 543 sf of impervious
area with the driveway expansion and three parking spaces.
Hardscape or Hard
Surface
Basin B Historic
Area (sf)
Basin B Developed
Area (sf)
Change in
Impervious Area
(sf)
Concrete 825 1,368
Rooftop 932 932
Pavers 0 0
Total Impervious Area 1,757 2,300 543
Per the flood insurance rate map (Exhibit 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 proposed grading and drainage design for the site (Exhibit A) follows the existing drainage
630 S Howes St Extra Occupancy Keefe Civil Project No.: 2019-006
Page 2 of 2 April 17, 2019
patterns and does not result in concentrated flow leaving the property.
The composite C values and basin flow calculations for the historic and developed site are
included with this memo (Exhibit 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
Basin B Historic Runoff 0.22 cfs 0.38 cfs 1.12 cfs
Basin B Developed Runoff 0.25 cfs 0.42 cfs 1.23 cfs
Based on these calculations, Keefe Civil respectfully requests no detention and water quality
requirements be imposed on this development.
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: Robert Kulikowski, Owner
Kate Penning, Assoc. AIA, LEED Green Assoc.
Soil Map—Larimer County Area, Colorado
(630 South Howes Street)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/11/2019
Page 1 of 3
4492004 4492012 4492020 4492028 4492036 4492044 4492052
4492004 4492012 4492020 4492028 4492036 4492044 4492052
493165 493173 493181 493189 493197 493205 493213 493221 493229 493237 493245
493165 493173 493181 493189 493197 493205 493213 493221 493229 493237
40° 34' 45'' N
105° 4' 50'' W
40° 34' 45'' N
105° 4' 47'' W
40° 34' 43'' N
105° 4' 50'' W
40° 34' 43'' N
105° 4' 47'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 15 30 60 90
Feet
0 5 10 20 30
Meters
Map Scale: 1:370 if printed on A landscape (11" x 8.5") 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
35 Fort Collins loam, 0 to 3
percent slopes
0.4 100.0%
Totals for Area of Interest 0.4 100.0%
Soil Map—Larimer County Area, Colorado 630 South Howes Street
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/11/2019
Page 3 of 3
Composite C Values
630 South Howes Street
Surface Type
Runoff
Coefficients1
Basin A
Historic and
Developed
Area (sf)
Minor (2-yr)
Historic
Composite C2
Major (100-yr)
Historic
Composite C2
Basin B
Historic Area
(sf)
Minor (2-yr)
Historic
Composite C2
Major (100-yr)
Historic
Composite C2
Basin B
Developed
Area (sf)
Minor (2-yr)
Developed
Composite C2
Major (100-yr)
Developed
Composite C2
Hardscape or Hard Surface
Concrete 0.95 528 825 1,368
Rooftop 0.95 736 932 932
Pavers 0.50 97 0 0
Total Impervious Area 1,361 1,757 2,300
Landscape or Pervious Surface
Unlandscaped Ground, Hard-Packed 0.50 887 5,495 4,952
Total Drainage Basin Area 2,248 0.75 0.94 7,252 0.61 0.76 7,252 0.64 0.80
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.
Howes - drainage.xlsx
Basin Flow Calculations
630 South Howes Street
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
B 0.17 0.61 0.76 125 1 10.3 7.1 NA 10.3 7.1 2.21 3.78 8.80 0.22 0.38 1.12
B 0.17 0.64 0.80 125 1 9.6 6.2 NA 9.6 6.2 2.30 3.93 9.21 0.25 0.42 1.23
Notes:
3. Per Fort Collins Stormwater Criteria Manual Section 3.3.4.
4. Per IDF Table for Rational Method, Table 3.4-1 Fort Collins Stormwater
5. Per Fort Collins Stormwater Criteria Manual Equation 5-1.
1. Per Fort Collins Stormwater Criteria Manual Section 3.3.2.
2. Per Fort Collins Stormwater Criteria Manual Section 3.3.3.
Initial/Overland Time1 Travel Time2 Final Tc
3 Intensity (in/hr)
4
Basin Area (acres)
Minor
Composite C
Major
Composite C
Basin Flow (cfs)
5
Howes - drainage.xlsx
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
(630 South Howes Street)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/11/2019
Page 2 of 3