HomeMy WebLinkAbout556 CAJETAN ST - DUPLEX & CARRIAGE HOUSE - FDP230003 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
1
November 17, 2022
Attn:
Dan Mogen, Civil Engineer
City of Fort Collins
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
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
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
2
the site is located in the 500-yr floodplain, floodplain requirements do not apply to the site. Reference
sheet C-2 in the 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 accessory dwelling unit (ADU)
above the garages = 80 ft2 footprint, an ADU above garages = 769 ft2, drive/parking surface with
concrete and pavers, Landscaping including low impact development (LID) features. Reference sheet C-3
in the drawing set for proposed site plan.
The calculated proposed imperviousness for the entire developed site is approximately 73%, with a
Composite Runoff Coefficient of 0.78 for type C Soils per Urban Storm Drainage Criteria Volume 1.
• Pavers = 366 ft2 (6.1%) @ 50%
• Roofs = 2,522 ft2 (42.1%) @ 95%
• Concrete = 1,558 ft2 (26.0%) @ 95%
• Landscaping = 1,544 ft2 (25.8%) @ 20%
• Total Area = 5,990 ft2 (100%)
Per the Utility Plans for Old Town North Fourth Filing, the northern half of the site is located in Sub-Basin
3A, which is 0.50 acres in size with a composite runoff coefficient of 0.78. Per the Utility Plans for Old
Town North Filing, the southern half of the site is located in Sub-Basin 14, which is 0.78 acres in size with
a composite runoff coefficient of 1.00. The composite runoff coefficient for developing the entire site
was calculated at 0.78, which is in compliance with the overall Old Town North Master Drainage Plan.
Sub-Basins Onsite:
The developed site will have three Sub-basins for stormwater runoff drainage. Reference sheet C-5 in
the drawing set for grading & drainage information.
Sub-basin 1:
Sub-Basin 1 includes: Garage/ADU roofs, the eastern unit in duplex roof, landscaping on the east side of
site, concrete walkway between duplex and garages, majority of driving/parking surface, and the rain
garden. Sub-Basin 1 is that area that contributes stormwater runoff to the rain garden, which is
discussed in further detail below. A portion of the stormwater runoff generated in Sub-Basin 1 will reach
the inlet in the curb (Design Point 1) and will travel into a riprap protected rundown into the rain
garden. The other portion of the stormwater runoff generated in Sub-Basin 1 will reach the swale in the
landscape area (Design Point 2) east of the proposed duplex. Sub-Basin 1 is approximately 0.08 acres in
size and has an impervious value of 78%.
Sub-Basin 2:
Sub-Basin 2 includes: 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
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
3
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 69%.
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 either flows south through the drainage swales located on the east and west sides 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 65%.
The proposed development of the site requires a Low Impact Development (LID) design. The
implementation of LID systems requires one of the following two options:
1) 50% of the newly added or modified impervious area must be treated by LID techniques and
25% of new paved (vehicle use) areas must be pervious.
2) 75% of all newly added or modified impervious area must be treated by LID techniques.
Option 1 will be utilized, the development of the site will implement bioretention (rain garden) and
permeable pavers to satisfy LID requirements. The proposed newly added impervious area for the entire
site includes roofs (2,522 ft2) + concrete (1,558 ft2) = 4,080 ft2. The rain garden must treat 50% of 4,080
ft2 = 2,040 ft2. The area contributing to the rain garden (Sub-Basin 1) has an impervious surface area of
2,448 ft2 (roofs = 1,615 ft2 + concrete = 833 ft2). The impervious area being treated with the rain garden
is 2,448 ft2, which is 20% over the required percentage for treatment of impervious surfaces.
The proposed vehicle use area of the site is 1,631 ft2 and the permeable pavers area is 366 ft2. The
permeable pavers area 366 ft2/1,631 ft2 = 22.4% of the vehicle use area. 22.4% is less than the required
25%, however the rain garden is designed at 20% over the required treatment percentage of impervious
surfaces, which makes up for the shortage of pavers. Per discussions with Stormwater Engineer Dan
Mogen, the LID design for the site satisfies LID requirements from the City of Fort Collins. Reference
sheets C-3 & C-4 in the drawing set for all design details pertaining to the LID system.
Rain Garden:
The rain garden will be located on the east side of the site just south of the two parking stalls and
northeast of the duplex. A portion of the stormwater runoff generated in Sub-Basin 1 will reach the inlet
in the curb (Design Point 1) and will travel into a riprap protected rundown into the rain garden. The
other portion of the stormwater runoff generated in Sub-Basin 1 will reach the swale in the landscape
area (Design Point 2) east of the proposed duplex. The rain garden will be constructed per City of Fort
Collins Stormwater Construction Detail D-53. The Stormwater Best Management Practice Design
Workbook, Version 3.07 was used to design the rain garden.
Design components of the Rain Garden include:
• Effective imperviousness of rain garden tributary area = 78%
• Contributing watershed area (including rain garden) = 3,371 ft2
• Required Rain Garden Volume = 66 ft3, actual Rain Garden Volume = 73 ft3
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
4
• Rain Garden Depth = 7 inches
• Rain Garden Side Slopes = 4:1
• Minimum Flat Surface Area = 53 ft2, actual flat surface area = 55 ft2
• Area at design depth (top surface area) = 206 ft2
• 4” Ø PVC underdrain pipe
Design Point 1:
The peak flow runoff for a 100-yr storm event at Design Point 1 (Curb inlet into the rain garden area)
was calculated using the Rational Method to design the riprap rundown into the rain garden.
The Rational Method is based on the Rational Formula:
Q = CIA, in which:
• Q = the maximum rate of runoff (cfs)
• C = a runoff coefficient that is the ratio between the runoff volume from an area and the
average rate of rainfall depth over a given duration for that area
• I = average intensity of rainfall in inches per hour for a duration equal to the time of
concentration, Tc.
• A = area (acres)
C = 0.84 @ 87% imperviousness, Type C soils
I = 12.3 in/hr @ assumed Tc of 5 minutes
A = 0.05 acres
Q100 = 0.84 x 12.3 in/hr x 0.05 acres = 0.52 cfs
The Rock Chute Design Data Spreadsheet, Version WI-July-2010, was used to design the riprap
protection of the rain garden rundown, not to design the actual rundown. Reference Detail 1 on Sheet
C-6 in the drawing set for rundown details.
Design components of Rain Garden Rundown at Design Point 1:
• Type VL Riprap will be used, D50 = 6”, Thickness = 12”
• Rundown width = 3’, Bottom width = 1’
• Side slopes = 3:1, Bed slope = 4:1
• Approximate riprap area = 16 ft2
Design Point 2:
The peak flow runoff for a 100-yr storm event at Design Point 2 (Drainage swale) was calculated using
the Rational Method to ensure the swale can handle flows from a 100-yr storm event.
Q = CIA
C = 0.80 @ 77% imperviousness, Type C soils
I = 12.3 in/hr @ assumed Tc of 5 minutes
A = 0.02 acres
ALLES TAYLOR & DUKE, LLC 3610 35TH AVE. UNIT #6
LICENSED PROFESSIONAL ENGINEERS EVANS, 80620
LICENSED PROFESSIONAL LAND SURVEYORS 970-330-0308
5
Q100 = 0.80 x 12.3 in/hr x 0.02 acres = 0.20 cfs
The UDFCD Open Channel Design Workbook, Version 1.05 was used to perform a capacity check for the
drainage swale to see if it can handle flows from a 100-yr storm event.
Design components of Swale at Design Point 2:
• Channel Invert Slope = 0.02 ft/ft
• Side slopes = 4:1
• Design water depth = 0.19’ @ Q100 = 0.20 cfs
• Froude Number = 0.82
• Flow Velocity = 1.43 fps
The swale can handle a 100-yr storm event at Design Point 2. The water flow depth for a 100-yr storm
event is 0.19’ (2.28 inches). The overall depth of the swale at Design point 2 is 0.64’ (7.7”).
Permeable Pavers:
The permeable pavers will be in the northeast area of the site where the two parking stalls will be
located. Storm water runoff in the permeable pavers area will infiltrate directly into the ground, with
any excess runoff reaching the curb inlet for the rundown into the rain garden. The south, east, and
north edges of the pavers will have a concrete curb and gutter edge restraint and the west edge will
have a concrete apron edge restraint. Permeable Interlocking Concrete Pavers will be constructed per
City of Fort Collins Stormwater Construction Detail D-54.
Underdrain Pipe:
A 4” PVC underdrain Pipe will be utilized to convey filtered storm water runoff in the rain garden and
permable pavers area to the Storm Sewer Man Hole located east of the site on Tract A. The invert of the
4” underdrain pipe will be 2” higher than the crown of the 30” storm sewer pipe. Reference Detail 1 on
sheet C-7 for Underdrain pipe details.
Prepared by Dan Campbell Mark A. Taylor
EIT 74322 Registered Professional Engineer
State of Colorado No. 46065
Job Name
Job No.22-071
Date 11/17/2022
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 366 ft2 0.95
Roofs 2522 ft2 0.20
Concrete 1558 ft2
Landscaping 1544 ft2 =0.14 AC Soil Type = Type C
0.73 = 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 366 ft2 0.95
Roofs 1615 ft2 0.20
Concrete 833 ft2
Landscaping 557 ft2 =0.08 AC Soil Type = Type C
0.78 = i Nunn Clay Loam
Site Area =888 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 584 ft2
Landscaping 304 ft2 =0.02 AC Soil Type = Type C
0.69 = i Nunn Clay Loam
Site Area =1731 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 0 ft2 0.95
Roofs 907 ft2 0.20
Concrete 140 ft2
Landscaping 684 ft2 =0.04 AC Soil Type = Type C
0.65 = i Nunn Clay Loam
Site Area =2079 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 366 ft2 0.95
Roofs 880 ft2 0.20
Concrete 833 ft2
Landscaping 0 ft2 =0.05 AC Soil Type = Type C
0.87 = i Nunn Clay Loam
Site Area =960 ft2 From Table 3.2-2. Surface Type - Runoff Coefficients
Pavers 0.50
Site Conditions Roofs 0.95
Pavers 0 ft2 0.95
Roofs 735 ft2 0.20
Concrete 0 ft2
Landscaping 225 ft2 =0.02 AC Soil Type = Type C
0.77 = i Nunn Clay Loam
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS ENTIRE SITE
Concrete
Landscaping
Percent Imperviousness (Calculated)
Concrete
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS DESIGN POINT 2 (Swale)
Concrete
PERCENT IMPERVIOUS SB-1 (AREA CONTRIBUTING TO BIORETENTION)
Concrete
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS DESIGN POINT 1 (Curb Inlet)
IMPERVIOUS CALCULATIONS
556 Cajetan St
Constant or linked from boxes above
Calculated value
Value that seldom changes
Concrete
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS SB-2
Concrete
Landscaping
Percent Imperviousness (Calculated)
PERCENT IMPERVIOUS SB-3
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1.Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =78.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.780
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV =0.25 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area)Area =3,371 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 =0.40 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =66 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2.Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =7 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical)Z =4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =53 sq ft
D) Actual Flat Surface Area AActual =55 sq ft
E) Area at Design Depth (Top Surface Area)ATop =206 sq ft
F) Rain Garden Total Volume VT=73 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3.Growing Media
Per City of Fort Collins Rain Garden
4.Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
Dan Campbell - EIT
Alles Taylor & Duke, LLC
November 17, 2022
556 Cajetan St
Fort Collins, CO 80524
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.07 (2).xlsm, RG 11/17/2022, 1:26 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5.Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6.Inlet / Outlet Control
A) Inlet Control
7.Vegetation
8.Irrigation
NO SPRINKLER HEADS ON FLAT SURFACE
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
Dan Campbell - EIT
Alles Taylor & Duke, LLC
November 17, 2022
556 Cajetan St
Fort Collins, CO 80524
Choose One
Choose One
Choose One
Sheet Flow-No Energy Dissipation Required
Concentrated Flow-Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
UD-BMP_v3.07 (2).xlsm, RG 11/17/2022, 1:26 PM
Project: County:
Designer: Checked by:
Date: 11/17/2022 Date:
Minimum Enter
Design Values Plan Values
3.3 D50 dia. =6.00 % Passing Rock =4
6.7 Rockchute thickness =12.00 D100 Geotextile (WCS-13)b =18
2 Inlet apron length =10.00 D85 Bedding =0
4 Outlet apron length =4.00 D50 Excavation =0
7 Radius =17 D10 Earthfill =0
Will bedding be used?No Seeding =0.0
Degree of angularity = 1
1 50% angular, 50% rounded
2 100 % rounded
Inlet apron elev. = 65.58 ft.
6 - 9 (15 - 52)
9 - 12 (52 - 122)
Rock Gradation Envelope Quantities a
5 - 8 (8 - 34)
Rock Chute Design - Plan Sheet
(Version WI-July-2010, Based on Design of Rock Chutes by Robinson, Rice, Kadavy, ASAE, 1998)
556 Cajetan Street, Fort Collins Larimer
Dan Campbell
Diameter, in. (weight, lbs.)
8 - 11 (34 - 89)
Inlet apron 12 in.
10 ft.
Radius =17 ft. Outlet apron
elev. =65 ft.
Sta.Elev. (Pnt)
Slope = 0.05 ft./ft.
Stakeout Notes
0+00.0 65.58 ft. (1)
0+07.9 65.58 ft. (2)4 Outlet apron
0+10.0 65.5 ft. (3)2 ft.4 ft.d =0 ft.
0+12.0 65.1 ft. (4)
0+12.3 65 ft. (5)Profile Along Centerline of Rock Chute **Note : The outlet will not
0+16.3 65 ft. (6) function adequately
0+16.3 65 ft. (7)
3 ft.
Class I non-woven
0 ft.
Rock gradation envelope can be met with 0.29 ft.Rock Chute
DOT Light riprap Gradation 3 Bedding
Rock Chute Cost Estimate 1 ft.12 in.
Unit Unit Cost Cost
Rock $10.00 $40.00 B' = 1.3 ft.
Geotextile $12.00 $216.00 Rock Chute Cross Section
Bedding $12.00 $0.00
Excavation $12.00 $0.00
Earthfill $1.00 $0.00
Seeding $2.00 $0.00
Total $256.00
Date File Name
556 Cajetan Street, Fort Collins
Drawing Name
Larimer County
Sheet ___ of ___
Slope = 0.001 ft./ft.
Profile, Cross Sections, and Quantities
Dan Campbell
Checked
Approved
Drawn
Upstream
Downstream
Channel
Channel
1Geotextile
Berm
*
Geotextile
Use Hp throughout chute
but not less than z2.
*
2.5
1
ft.
ft.
in.
ft.yd3
yd3
acres
in.
y =
Top width =
1
Rock thickness =
Freeboard =
Rock thickness =
yd3
yd3
yd2
/yd3
/yd3
/ac.
/yd3
/yd3
/yd2
Notes: a Rock, bedding, and geotextile quantities are determined
from the x-section below (neglect radius).
b Geotextile Class I (non-woven) shall be overlapped
and anchored (18-in. min. along sides and 24-in. min. on the ends).
---------
---------
---------
---------
Rock Chute Station1 2 3
4
5 6
7
ft.
ft.
in.
ft.
in.---------
O
Natural Resources Conservation Service
United States Department of Agriculture
Designed
Page 1 of 1
Project:
Channel ID:
Design Information (Input)
Channel Invert Slope So =0.0200 ft/ft
Manning's n n =0.030
Bottom Width B =0.00 ft
Left Side Slope Z1 =4.00 ft/ft
Right Side Slope Z2 =4.00 ft/ft
Freeboard Height F =0.00 ft
Design Water Depth Y =0.190 ft
Normal Flow Condtion (Calculated)
Discharge Q =0.207 cfs
Froude Number Fr =0.82
Flow Velocity V =1.43 fps
Flow Area A =0.14 sq ft
Top Width T =1.52 ft
Wetted Perimeter P =1.57 ft
Hydraulic Radius R =0.09 ft
Hydraulic Depth D =0.10 ft
Specific Energy Es =0.22 ft
Centroid of Flow Area Yo =0.06 ft
Specific Force Fs =0.00 kip
Normal Flow Analysis - Trapezoidal Channel
556 Cajetan St, Fort Collins
Design Point 2 (Channel Capacity)
UD-Channels_v1.05.xls, Basics 11/17/2022, 1:29 PM
Project:
Channel ID:
Design Information (Input)
Bottom Width B =0.00 ft
Left Side Slope Z1 =4.00 ft/ft
Right Side Slope Z2 =4.00 ft/ft
Design Discharge Q =0.20 cfs
Critical Flow Condition (Calculated)
Critical Flow Depth Y =0.17 ft
Critical Flow Area A =0.12 sq ft
Critical Top Width T =1.36 ft
Critical Hydraulic Depth D =0.09 ft
Critical Flow Velocity V =1.73 fps
Froude Number Fr =1.05
Critical Wetted Perimeter P =1.40 ft
Critical Hydraulic Radius R =0.08 ft
Critical (min) Specific Energy Esc =0.22 ft
Centroid on the Critical Flow Area Yoc =0.03 ft
Critical (min) Specific Force Fsc =0.00 kip
Critical Flow Analysis - Trapezoidal Channel
UD-Channels_v1.05.xls, Basics 11/17/2022, 1:29 PM