HomeMy WebLinkAbout556 CAJETAN ST - DUPLEX & CARRIAGE HOUSE - FDP230003 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
1
May 18, 2023
Attn:
Dan Mogen, Civil Engineer
City of Fort Collins
281 North College Avenue
Fort Collins, CO 80524
Subject:
Drainage Narrative – Lot 1 of Old Town North Fourth Filing
556 Cajetan Street
Fort Collins, CO 80524
Erik Haagenson (Owner) is proposing to develop Lot 1 of Old Town North Fourth Filing, recorded with
the Larimer County Clerk & Recorder on December 20, 2018, at Reception No. 20180077798. The
address of the subject property (site) is 556 Cajetan St, Fort Collins, CO 80524, and is located within the
Southwest Quarter (SW 1/4) of Section 1, Township 7 North, Range 69 West of the 6th Principal
Meridian, City of Fort Collins, County of Larimer, State of Colorado. The site is bounded on the south by
Cajetan Street and is approximately 60’ west of Redwood St. A vicinity map is included in Figure 1 below
with the site outlined for reference.
Figure 1. Vicinity Map
The site is approximately 5,990 ft3 (0.138 acres) in size and is currently undeveloped with bare ground
and weeds. Lot 2 to the west has been developed with a single-family residence. Tract A to the east is
vacant and will eventually be developed per the Old Town North Fourth Filing Landscaping Plan. Vehicle
access to the site will be from the 12’ Alley that is adjacent to the north side of the site.
A topographic survey was performed by Alles Taylor & Duke (ATD) for the site and surrounding features
on September 2, 2022. Elevations provided are based on the National Geodetic Survey (NGS) Benchmark
Designation A 402, PID LL1017, which has an elevation of 4962.47’ (NAVD 88). Stormwater runoff
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
2
generated onsite flows to the north, east, and south at approximately 1-2 % slopes. Per Web Soil
Survey, the entire site is comprised of Nunn Clay Loam – Hydrologic Soil Group C. The southern half of
the site is located in the 500-yr floodplain, floodplain requirements do not apply to the site. Reference
sheet C-2 in the Civil drawing set for Existing Site Conditions.
The proposed development of the site includes: a side by side duplex (Unit 1 = 766 ft2 footprint, Unit 2 =
735 ft2 footprint), 3 separate garages (Garage 1 = 230 ft2 footprint, Garage 2 = 240 ft2 footprint, Garage 3
= 288 ft2 footprint) with a stairway adjacent to Garage 1 that leads to the carriage house above the
garages = 80 ft2 footprint, a carriage house above the garages = 769 ft2, drive/parking surface with
concrete and pavers, a concrete walk between the duplex and garages/carriage house, and Landscaping.
Reference sheet C-3 in the Civil drawing set for proposed site plan.
Sub-Basins Onsite:
The developed site will have three Sub-basins for stormwater runoff drainage. Reference sheet C-6 in
the Civil drawing set for grading & drainage information.
Sub-basin 1:
Sub-Basin 1 includes: Garage/carriage house roofs, the eastern unit in duplex roof, landscaping on the
east side of site, a portion of the concrete walkway between the duplex and garages, and the majority of
the driving/parking surface. Stormwater generated in Sub-Basin 1 will sheet flow to the East onto Tract
A. Sub-Basin 1 is approximately 0.08 acres in size and has an impervious value of 79%.
Sub-Basin 2:
Sub-Basin 2 includes: a portion of the concrete walkway between the duplex and garages, a landscaping
strip on the west side of the site and a portion of the concrete drive surface. Stormwater runoff
generated in the landscaping area will flow north through the drainage swale until reaching the concrete
drainage pan on the south side of the alley. Stormwater runoff generated in the concrete drive surface
will sheet flow north until reaching the same drainage pan. Stormwater runoff that reaches the drainage
pan flows to the northeast, eventually reaching the storm sewer inlet located on the south side of
Osiander Street. Sub-Basin 2 is approximately 0.02 acres in size and has an impervious value of 76%.
Sub-Basin 3:
Sub-Basin 3 includes: landscaping areas on the west, south, and east sides of the site, the western unit in
duplex roof, and the concrete walk/stairs into the two duplex units. Stormwater runoff generated in
Sub-Basin 3 either flows south through the drainage swale located on the west side of the site or sheet
flows to the south until reaching the curb and gutter on the north side of Cajetan Street. Stormwater
runoff that reaches the curb and gutter flows east and then north, eventually reaching the storm sewer
inlet located on the south side of Osiander Street. Sub-Basin 3 is approximately 0.04 acres in size and
has an impervious value of 67%.
Job Name
Job No.2022-071
Date 4/4/2023
Input value or note
Site Area =5990 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 557 ft2 0.95
Roofs 2522 ft2 0.20
Concrete 1638 ft2
Landscaping 1273 ft2 =0.14 AC Soil Type = Type C
0.75 = i Nunn Clay Loam
Site Area =3371 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 498 ft2 0.95
Roofs 1615 ft2 0.20
Concrete 833 ft2
Landscaping 425 ft2 =0.08 AC Soil Type = Type C
0.79 = i Nunn Clay Loam
Site Area =893 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 0 ft2 0.95
Roofs 0 ft2 0.20
Concrete 663 ft2
Landscaping 230 ft2 =0.02 AC Soil Type = Type C
0.76 = i Nunn Clay Loam
Site Area =1725 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 59 ft2 0.95
Roofs 907 ft2 0.20
Concrete 140 ft2
Landscaping 619 ft2 =0.04 AC Soil Type = Type C
0.67 = i Nunn Clay Loam
PERCENT IMPERVIOUS ENTIRE SITE
Concrete
Landscaping
Percent Imperviousness (Calculated)
Concrete
Landscaping
Percent Imperviousness (Calculated)
IMPERVIOUS CALCULATIONS
556 Cajetan St, Fort Collins, CO 80524
Constant or linked from boxes above
Calculated value
Value that seldom changes
PERCENT IMPERVIOUS SB-1
Concrete
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS SB-2
Concrete
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS SB-3