HomeMy WebLinkAboutPACIFIC COAST SUPPLY WAREHOUSE - FDP200019 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL REPORT
FOR
PACIFIC COAST SUPPLY
A TRACT OF LAND LOCATED IN THE SOUTHWEST QUARTER OF SECTION 3,
TOWNSHIP 7 NORTH, RANGE 68 WEST OF THE 6TH P.M.,
CITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADO
ZP#: Z19-050
September 2, 2020
FINAL DRAINAGE AND EROSION CONTROL REPORT
FOR
PACIFIC COAST SUPPLY
A TRACT OF LAND LOCATED IN THE SOUTHWEST QUARTER OF SECTION 3,
TOWNSHIP 7 NORTH, RANGE 68 WEST OF THE 6TH P.M.,
CITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADO
ZP#: Z19-050
September 2, 2020
Prepared for: Pacific Coast
12860 W. Cedar Dr.
lakewood, CO 80228
Contact: Stuart Nielson
303-659-2313
Prepared by: ZP Architects Engineers, Inc.
2727 Bryant Street, Suite 610
Denver, CO 80211
(303) 455-3322
William J. Logan, P.E.
Project Engineer
i
Engineers Certification Statement
“I hereby attest that this report for the final drainage design for the Pacific Coast Supply
was prepared by me or under my direct supervision, in accordance with the provisions
of the Fort Collins Stormwater Criteria Manual. I understand that the City of Fort Collins
does not and will not assume liability for drainage facilities designed by others.”
Registered Professional Engineer Date
State of Colorado No.31705
ii
TABLE OF CONTENTS
PHASE II DRAINAGE REPORT
I. GENERAL LOCATION AND DESCRIPTION
A. Location ................................................................................................................. 1
B. Description of Property .......................................................................................... 2
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description ......................................................................................... 2
B. Sub-Basin Description ........................................................................................... 2
III. DRAINAGE DESIGN CRITERIA
A. Regulations............................................................................................................ 3
B. Development Criteria Reference and Constraints ................................................. 3
C. Hydrological Criteria .............................................................................................. 3
D. Hydraulic Criteria ................................................................................................... 3
E. Waivers from the Criteria ....................................................................................... 4
IV. DRAINAGE FACILITY DESIGN
A. General Concept ................................................................................................... 5
B. Specific Details ...................................................................................................... 6
V. EROSION and SEDIMENT CONTROL…………………………………………………...6
VI. CONCLUSIONS
A. Compliance with Standards ................................................................................... 7
B. Drainage Concept .................................................................................................. 7
VI. LIST OF REFERENCES ............................................................................................ 8
APPENDIX A ................................................................................................................... 9
Hydrologic & Hydraulic Computations
APPENDIX B ................................................................................................................. 24
Charts and Tables
APPENDIX C ................................................................................................................ 33
FIRM Map, Drainage Plan
iii
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The proposed Pacific Coast Supply building is located in a Tract of land located
in the Southwest Quarter of Section 3, Township 7 North, Range 68 West of the
6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado.
The site is specifically located at 1012 NE I-25 Frontage Road.
Vicinity Map
A new structure is to be located north of the existing Pacific Coast Supply
buildings. Site access is off Northeast I-25 Frontage Road to the west. To the
north and east is cultivated land with further development beyond the boundary
of the proposed site. To the south the property is separated from the cultivated
property by an existing 30-feet public access right-of-way. A private irrigation
ditch lies along the easterly boundary. The Larimer and Weld Canal also lies to
the north and east of the property, (Reference 4).
A number of easements exist within the proposed property improvements. The
easements consist of a 20’ water line easement, and two 15’ and 10’ easements
per the plate from the K-2 Industrial Park; no description of the last two is given.
1
B. Description of Property
The site consists of two tracts for an approximate area of 4.263 acres. The
existing southern tract is currently developed, and includes the three buildings
used by Pacific Coast Supply. The recently obtained north tract is undeveloped
and will contain most of the new improvements. The plan is to construct a new
20,000 square-foot metal building with approximately 42,955 square-feet of hard
surfaces on both tracts. The proposed development will provide additional
storage space for the Pacific Coast Supply operations.
The existing topography of the site slopes over a combination of native and
gravel yards from the east to the west at an average slope of 1.2%. New
detention and access easements for detention, maintenance and fire access are
proposed.
The web soil survey describes the site soils primarily as Longmont Clay and
Nunn Clay Loam to Satanta Loam with a Hydrologic Soil Group C and D. Group
C/D soils have a slow infiltration rate when thoroughly wet, and consist chiefly of
layers that impedes the downward movement of water or soils of moderately fine
to fine texture (Reference appendix B for Soil Survey Map Information). The site
also has a high water table per the Geotechnical Evaluation Report by American
Geoservices (Reference 6).
The Larimer and Weld Canal to the east and north flows easterly under I-25 to
the west. An irrigation ditch lies along the easterly most boundary and will not be
affected by the proposed improvements.
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
The site is located within the Cooper Slough/Box Elder Basin Master Drainage
Study. (Reference 3 and hereafter called Master).
This site is located within a 100-year floodplain as defined by the Federal
Emergency Management Agency Community Panel numbers 08069C1001F,
(Reference 4) and 08069C0982F, (Reference 5), both dated December 19, 2006.
B. Sub-Basin Description
Both tracts currently surface drain to the west into the ditch along NE I-25
Frontage Road. Runoff into the ditch drains south and crosses under I-25
through a culvert leading to the west. Offsite runoff to the site is limited from the
east basins labeled OS1 and OS2.
2
The proposed site improvements will collect and surface drain the majority of the
site to a water quality Bioretention pond in the middle of the site. Stormwater,
along with most of the site’s proposed improvements will be directed to the
detention pond located at the northwest corner of the property. The runoff
collected in the pond will be directed to the west into the frontage ditch.
An existing sump condition exists along the frontage ditch near the northwest
corner of the property. The low spot has been identified and corrected in the
proposed plans. In order to correct the low spot, some minor over lot grading is
needed at the northern neighbor’s southwest corner.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
The primary criteria for this development is the “Fort Collins Stormwater Criteria
Manual”, (Reference 1 and hereafter called Criteria), and the Urban Drainage
Flood Control District’s Urban Storm Drainage Criteria Manuals (Reference 2 and
hereafter called Manual).
B. Development Criteria References and Constraints
The subject area is identified within the Master drainage study. In addition to the
Criteria, additional physical site restraints are realized due to this property being
partially developed with three buildings already on site. See waivers below.
C. Hydrological Criteria
The design rainfall for the runoff generated on-site was based on the Rational
Method for the 2 and 100-year rainfall events for developed conditions as
established in the Criteria and Manual. The runoff results are summarized on the
Drainage Plan and in Appendix A. Rainfall intensities were determined from the
Criteria by using the 1-hour point rainfall values of 0.82 in/hr for the 2-year storm
event and 2.86 in/hr for the 100-year storm event.
The detention and discharge limits are based on the 2-year historic runoff.
D. Hydraulic Criteria
The capacity of the detention facility is based on the FAA method outlined in the
Criteria. The proposed Bioretention pond and Extended Drainage Basin water
quality volumes are per the Manual.
3
E. Waivers from the Criteria
The site contains unique conditions that make development per the Criteria with
LID features extremely difficult. Within the proposed site, three existing buildings
exist with floor elevations surveyed at 4973.00 feet, establishing an upper limit to
design. At the other end, the need to eliminate the existing sump condition and
still drain to the ditch establishes the lower design elevation at 4968.40 feet. The
combination of full detention, an Extended Detention Basin, a Bioretention pond,
an emergency overflow, and a free board forces the drainage facility within a
vertical design limit of 4.6 feet. This is further reduced to 3.0 feet once a
connection to the ditch is made and a freeboard is established. Due to the
existing site limitations, five (5) variances are requested from the Criteria and
Manual.
1. Section 3.1: “Minimum freeboard of 12” above 100-yr WSEL.”
Variance: 9” of freeboard above 100-year water surface elevation will allow
the Bioretention pond to drain directly to the detention pond in the event of
flooding.
2. Section 3.1: “…maximum side slopes of four feet horizontal to one foot
vertical (4:1) and stabilized…”
Variance: The detention pond slopes are set at 3.5:1, interior only. This is in
part due to the proposed building and its location to the existing water line
easement on the east, and the requirements for landscaping along the
frontage road.
3. Section 3.1: “…Detention basin bottoms shall have a minimum cross-slope
… of two percent (2%) for vegetated surfaces …”
Variance: The bottom of the pond is reduced to 1.60% slope to
accommodate the required detention volumes.
4. Ground Cover of drainage pipe:
Variance: Due to insufficient ground cover across the drive lane, a structural
concrete box culvert is proposed to accommodate drainage between the
Bioretention too the detention pond.
5. Section 2.3.7: “75% of all newly added or modified impervious area must be
treated by LID techniques.”
Variance: 72.6% of the new hard surfaces are directed to the Bioretention
pond. Other new hard surfaces cannot be directed to the Bioretention pond
4
due to the vertical site constraints, and the inability to drain the southern side
of the property around the existing buildings to the north.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
Currently the surface drains primarily over native vegetation and existing gravel
from the east to west onto the frontage drainage ditch. The proposed
improvements will maintain the same drainage patterns by collecting the majority
of the improvements into the detention pond along the frontage road. Minor offsite
runoff will contribute to the detention pond from basin OS1.
Appendix B contains the tables and charts from the Criteria and the Manual.
Rainfall is based on the rational method and the City’s rainfall intensities with the
site grading divided into seven onsite drainage basins. Basins A through C and
OS1 define the areas directly tributary to the detention pond. Basins of direct
runoff are designated DRS, DRE, DRN, DRW and OS2 are limited to the perimeter
areas about the site.
Basin A:
Basin A comprises of the center of the property and the east storage yard area.
Water collected along with basin OS1 will drain first to the Bioretention pond before
transferring to the detention pond.
Basin B:
Basin B consists of the north roof of the building. Water off the north roof is
collected in underground drain lines and discharged in the detention near the
northeast corner of the building.
Basin C:
Basin C contains the detention pond area. Water collected in basin C is combined
with basins A, B and OS1 for design point DET, the emergency overflow weir.
Basin DRS:
The area of Direct Runoff South (DRS) represents the existing surfaces on the
south side of the property. This runoff is existing and is not changed due to the
proposed improvements.
Basin DRE:
Direct Runoff East (DRE) represents the small area of runoff intercepted by the
existing irrigation ditch. The proposed improvements due not change the ditch are
the surrounding banks along the easterly property line.
5
Basin DRN:
The area of Direct Runoff North (DRN) represents the surface behind the building.
The surface runoff to the north is over native vegetation and is insignificant.
Basin DRW:
The area of Direct Runoff West (DRW) represents the surface tributary to the
frontage road. This are is the result of the berm created for the detention pond and
the existing landscaped are south of the access drive lane.
The detention facility is made up of four volumes. Two water quality volumes, and
the 2-year and 100-year detention volumes. As part of the LID criteria, a
Bioretention pond is proposed in the middle of basin A. 72.6% of the new hard
surfaces are collected in the Bioretention pond. Water through the Bioretention
pond is directed through a discharge box into a structural box culvert that leads to
the detention pond. The detention pond consists of an Extended Detention Basin
volume and the 2-year and 100-year detention volumes. The Extended Detention
Basin is reduced by the Bioretention volume. A Forebay is established at the
entrance to the Bioretention pond, and is based on the total detention area
tributary to the detention pond. Specific volumes and elevations are tabulated in
appendix A and on the drainage plan.
The detention ponds outlet box uses a water quality plate to restrict runoff to a 40-
hour discharge limit. The 2-year stormwater volume is in turn discharged through
the water quality plate for a significant reduction in discharge. The 100-year
volume is then controlled by a 5.625” inside diameter pipe at the bottom of the
drainage box. Both storm release rates are based on the Criteria’s limit that the site
shall not be drained faster than the 2-year historic limit. In the event the outlet box
is blocked by debris, an emergency overflow weir is set at the 100-year water
elevation of 4972.00 feet. This weir is designed to discharge the 100-year runoff
(15.85 cfs) to the ditch along the frontage road. In addition, flood control from the
Bioretention pond is managed both through the concrete box culvert, and over and
through the drainage swale set across the drive lane.
B. Specific Details
Access and maintenance to the outlet structures and to the detention features is
obtained from an access and drainage easement located off the frontage road.
The area of access and detention is contained in the designated easement.
V. EROSION and SEDIMENT CONTROL
An erosion and sediment control plan has been provided in the final construction
set. The plan addresses both temporary measures during construction during
construction, as well as permanent erosion control protection. Best Management
Practices (BMPs) from the UDFCD and the City Criteria have been utilized. The
6
following erosion control devices have been implemented for the project site: silt
fencing along downstream perimeters, wattle protection along drainage ditch
culverts, and at the outlet from the pond, a vehicle tracking control pad at the
construction entrance, and a concrete washout location. Permanent erosion control
is established with rip-rap at outfall points into and from the detention, and with the
establishment of erosion control.
VI. CONCLUSIONS
A. Compliance with Standards
The runoff calculations are based on the Criteria and Manual for the 2-year and
100-year storm recurrences. In addition, water quality volumes are provided in the
form of a Bioretention pond and an Extended Detention Basin per the Manual. The
storm detention volumes are based on the Modified FAA method for the 2-year and
100-year storm events. The emergency overflow and storm outlet pipe drain to the
right-of-way and are sized for the 100-year storm event.
B. Drainage Concept
The drainage system has been designed to convey the developed runoff to the
designated detention pond in a safe and effective manner. In addition, all on site
flows as well as the detention pond and its components have been sized to
transfer stormwater to the drainage ditch. The proposed release rates from the
detention pond will reduce the peak runoff to the 2-year historic limit. In its current
condition, runoff from the site runs un-detained. The improvements being made will
detain a large amount of stormwater and reduce runoff from the site so that the
100-year storm event can be conveyed safely downstream. As a result, no
negative impacts are anticipated to any downstream stormwater facilities.
7
VI. REFERENCES
1. “Fort Collins Stormwater Criteria Manual”, dated revised November 2017.
2. "Urban Storm Drainage Criteria Manual", by Urban Drainage and Flood Control
District, Vol. 1 and 2 dated January 2016, and Vol. 3 dated November 2010.
3. “Cooper Slough/Box Elder Basin Master Drainage Study”
4. Federal Emergency Management Agency Community Panel Number
08069C1001F, dated December 19, 2006.
5. Federal Emergency Management Agency Community Panel Number
08069C0982F, dated December 19, 2006.
6. Geotechnical Evaluation Report, Project No. 0281-D20, by American
Geoservices, dated June 30, 2020
8
APPENDIX A
Hydrologic & Hydraulic Computations
9
Fort Collins Stormwater Rational Method
Project Name: Pacific Coast Supply
Coefficent Impervious
Basin Surface Types C (%)
Hard Surfaces
Asphalt, Conc 0.95 100
Rooftops 0.95 90
Recycled Asphalt 0.80 80
Gravel or Pavers 0.50 40
Landscape (Lawns)
Playgrounds 25
Lawns, Sandy Soil, Flat Slope < 2% 0.10 2
Lawns, Sandy Soil, Avg Slope 2-7% 0.15 2
Lawns, Sandy Soil, Steep Slope > 7% 0.20 2
Lawns, Clayey Soil, Flat Slope < 2% 0.20 2
Lawns, Clayey Soil, Avg Slope 2-7% 0.25 2
Lawns, Clayey Soil, Steep Slope >7% 0.35 2
Dominant Predevelopement NRCS Soils Group: C/D
Asphalt Recycled Gravel or Lawns, Sandy Lawns, Clayey Area Area
Total & Conc. Rooftops Asphalt Pavers Playgrnds Flat Average Steep Flat Average Steep Average Average Total
Area Area Areas Areas Area Area Area Area Area Area Area Area Area Coeff. 1.00 1.00 1.00 1.10 1.20 1.25 Impervs Area
Basin Description (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (sq.ft.) (C) C
2 C
5 C
10 C
25 C
50 C
100 (%) (acre) Basin
A Center/Storage 86902 34883 16285 0 26657 0 0 0 0 9077 0 0 0.73 0.73 0.73 0.73 0.81 0.88 0.91 69.5 1.995 A
B North Roof 10000 0 10000 0 0 0 0 0 0 0 0 0 0.95 0.95 0.95 0.95 1.00 1.00 1.00 90.0 0.230 B
C West Front Area 21377 4415 0 0 0 0 0 0 0 16962 0 0 0.35 0.35 0.35 0.35 0.39 0.43 0.44 22.2 0.491 C
DRS Direct Runoff South 39853 5773 4915 0 20108 0 0 0 0 9057 0 0 0.55 0.55 0.55 0.55 0.61 0.66 0.69 46.2 0.915 DRS
DRE Direct Runoff East 2302 0 0 0 391 0 0 0 0 1911 0 0 0.25 0.25 0.25 0.25 0.28 0.30 0.31 8.5 0.053 DRE
DRN Direct Runoff North 16484 0 0 0 11200 0 0 0 0 5284 0 0 0.40 0.40 0.40 0.40 0.44 0.48 0.50 27.8 0.378 DRN
DRW Direct Runoff West 8757 697 0 0 0 0 0 0 0 8060 0 0 0.26 0.26 0.26 0.26 0.29 0.31 0.32 9.8 0.201 DRW
OS1 Offsite 1 5329 0 0 0 0 0 0 0 0 5329 0 0 0.20 0.20 0.20 0.20 0.22 0.24 0.25 2.0 0.122 OS1
OS2 Offsite 2 15754 0 0 0 0 0 0 0 0 15754 0 0 0.20 0.20 0.20 0.20 0.22 0.24 0.25 2.0 0.362 OS2
Det Detention+EDB 118279 39298 26285 0 26657 0 0 0 0 26039 0 0 0.68 0.68 0.68 0.68 0.75 0.82 0.85 62.7 2.715 Det
RG A+OS1 Rain Garden 92231 34883 16285 0 26657 0 0 0 0 14406 0 0 0.70 0.70 0.70 0.70 0.77 0.84 0.87 65.6 2.117 RG
H Trib Historic 151151 0 0 0 0 0 0 0 0 151151 0 0 0.20 0.20 0.20 0.20 0.22 0.24 0.25 2.0 3.470 H Trib
Sec. 6.0 Low Impact Development (LID) Option 2 Impervious Surfaces
Pavement Roof Pavement Roof
A Center/Storage 34883 13000 34883 13000
B North Roof 0 10000 0 0
C West Front Area 4415 0 0 0
DRS Direct Runoff South 2960 0 0 0
DRE Direct Runoff East 0 0 0 0
DRN Direct Runoff North 0 0 0 0
DRW Direct Runoff West 697 0 0 0
Sub-Totals = 42955 23000 34883 13000
Total New = 65955 sq.ft. Total Captured = 47883 sq.ft.
Percent of New Hard Surfaces Tributary to RG = 72.6%
Runoff Coefficients
Frequency Adjustment Factor Cf
Total New Hardsurfaces RG Cature Area
10
TIME OF CONCENTRATION
Project Name: Pacific Coast Supply
Calculated By: WJL DATE: 8/26/2020
SUB-BASIN INITIAL/OVERLAND INITIAL FINAL
DATA TIME (t i ) TIME tc
TOTAL t c ;t i +t t
DESIGN C*Cf = AREA LENGTH SLOPE t i LENGTH SLOPE CHANNEL VEL. t t t i +t t LENGTH t c =(L/180)+10 minimum
C5 (Ac) (ft) (ft/ft) (min) (ft) (ft/ft) CONSTANT (fps) (min) (min) (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (12) (13) (14)
A 0.73 1.99 204 0.014 40.51 143 0.007 20 1.69 1.41 41.93 347 11.93 11.93
B 0.95 0.23 50 0.020 7.31 7.31 50 10.28 7.31
C 0.35 0.49 183 0.029 61.57 61.57 183 11.02 11.02
DRS 0.55 0.91 198 0.015 58.22 58.22 198 11.10 11.10
DRE 0.25 0.05 25 0.060 20.28 20.28 25 10.14 10.14
DRN 0.40 0.38 55 0.073 23.13 23.13 55 10.31 10.31
DRW 0.26 0.20 27 0.040 23.87 23.87 27 10.15 10.15
OS1 0.20 0.12 183 0.011 102.59 102.59 183 11.02 11.02
OS2 0.20 0.36 102 0.010 79.42 79.42 102 10.57 10.57
Det 0.68 2.72 204 0.014 46.06 367 0.005 20 1.41 4.33 50.38 571 13.17 13.17
RG 0.70 2.12 204 0.014 43.92 142 0.006 20 1.55 1.53 45.45 346 11.92 11.92
H Trib 0.20 4.26 300 0.012 126.25 228 0.012 10 1.11 3.42 129.67 528 12.93 12.93
t i =1.87(1.1-CxCf)(L^0.5)/S^1/3 t t =L/(60V)
t c CHECK
(URBANIZED BASINS)
TRAVEL TIME
(t t )
11
STANDARD FORM SF-3
Calculated By: WJL JOB NO: Z19-050
DATE: STORM DRAINAGE SYSTEM DESIGN PROJECT : Name
CHECKED BY:______________ (RATIONAL METHOD PROCEDURE) DESIGN STORM: 2 Year
AREA
DESIGN
AREA
(AC)
RUNOFF
COEFF
tc
(MIN)
C*A
(AC)
I
(IN/HR)
Q
(CFS)
tc
(MIN)
SUM(C*A)
(AC)
I
(IN/HR)
Q
(CFS)
SLOPE
(%)
STREET
FLOW(CFS)
DESIGN
FLOW (CFS)
SLOPE
(%)
PIPE SIZE
(IN)
LENGTH
(FT)
VELOCITY
(FPS)
tt
(MIN)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
1 AAA 1.99 0.73 11.9 1.46 2.05 3.01 11.0 1.49 2.12 3.16
2 BBB 0.23 0.95 7.3 0.22 2.48 0.54
3 CCC 0.49 0.35 11.0 0.17 2.12 0.37
4
5 DRS DRS DRS 0.91 0.55 11.1 0.51 2.12 1.07
6 DRE DRE DRE 0.05 0.25 10.1 0.01 2.20 0.03
7 DRN DRN DRN 0.38 0.40 10.3 0.15 2.18 0.33
8 DRW DRW DRW 0.20 0.26 10.2 0.05 2.20 0.11
9 OS1 OS1 OS1 0.12 0.20 11.0 0.02 2.12 0.05
10 OS2 OS2 OS2 0.36 0.20 10.6 0.07 2.16 0.16
11 Det Det Det 2.72 0.68 13.2 1.86 1.97 3.65
12 RG RG RG 2.12 0.70 11.9 1.49 2.06 3.06
13
14 H Trib H Trib H Trib 3.47 0.20 12.9 0.69 1.98 1.38
STREET
DESIGN
POINT
STANDARD FORM SF-3
Calculated By: WJL JOB NO: Z19-050
DATE: STORM DRAINAGE SYSTEM DESIGN PROJECT : Name
CHECKED BY:______________ (RATIONAL METHOD PROCEDURE) DESIGN STORM: 100 Year
AREA
DESIGN
AREA
(AC)
RUNOFF
COEFF
tc
(MIN)
C*A
(AC)
I
(IN/HR)
Q
(CFS)
tc
(MIN)
SUM(C*A)
(AC)
I
(IN/HR)
Q
(CFS)
SLOPE
(%)
STREET
FLOW(CFS)
DESIGN
FLOW (CFS)
SLOPE
(%)
PIPE SIZE
(IN)
LENGTH
(FT)
VELOCITY
(FPS)
tt
(MIN)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
1 AAA 1.99 0.91 11.9 1.82 7.17 13.1 11.9 1.85 7.17 13.3
2 BBB 0.23 1.00 7.3 0.23 8.63 2.0
3 CCC 0.49 0.44 11.0 0.22 7.41 1.6
4
5 DRS DRS DRS 0.91 0.69 11.1 0.63 7.39 4.6
6 DRE DRE DRE 0.05 0.31 10.1 0.02 7.66 0.1
7 DRN DRN DRN 0.38 0.50 10.3 0.19 7.61 1.4
8 DRW DRW DRW 0.20 0.32 10.2 0.06 7.66 0.5
9 OS1 OS1 OS1 0.12 0.25 11.0 0.03 7.41 0.2
10 OS2 OS2 OS2 0.36 0.25 10.6 0.09 7.54 0.7
11 Det Det Det 2.72 0.85 13.2 2.31 6.86 15.9
12 RG RG RG 2.12 0.87 11.9 1.85 7.17 13.3
13
12 H Trib H Trib H Trib 3.47 0.25 12.9 0.86 6.92 6.0
STREET PIPE TRAVEL TIME
STREET REMARKS
DESIGN
Fort Collins Modified FAA Detention
Project Name: Pacific Coast Supply
Design Informtion (Input):
Tributary Area: 2.72 sq.ft.
Imperviousness: 62.68 %
Tc: 1.38 min.
Allowable Release Rate Qout: 1.38 cfs (2-year Historic) Allowable Release Rate Qout: 1.38 cfs (2-year Historic)
2-Year Minor Detention 100-Year Major Detention
Runoff Coefficient C2: 0.68 Runoff Coefficient C100: 0.85
Inflow Peak Runoff Qin: 3.65 cfs Inflow Peak Runoff Qin: 15.85
Duration Duration
Results: (cu.ft.) (acre-ft) (min.) Results: (cu.ft.) (acre-ft) (min.)
Max. Minor Storage Vol: 1934 0.044 20 Max. Major Storage Vol: 21505 0.494 180
WQCV (EDB): 748 0.017 WQCV (EDB): 748 0.017
Total Minor Storm Vol: 2682 0.062 Total Major Storm Vol: 22253 0.511
1 (min) Duration Interval 5 (min) Duration Interval
Rainfall Rainfall Inflow Outflow Storage Storage Rainfall Rainfall Inflow Outflow Storage Storage
Duration Intensity Volume Volume Volume Volume Duration Intensity Volume Volume Volume Volume
minutes inches / hr cubic feet cubic feet cubic feet acre feet minutes inches / hr cubic feet cubic feet cubic feet acre feet
(input) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output)
5 2.85 1587 413 1174 0.0269 5 9.95 6897 413 6484 0.1489
6 2.67 1784 496 1288 0.0296 10 7.72 10702 826 9876 0.2267
7 2.52 1964 578 1386 0.0318 15 6.52 13558 1239 12319 0.2828
8 2.40 2138 661 1477 0.0339 20 5.60 15527 1652 13875 0.3185
9 2.30 2305 743 1562 0.0359 25 4.98 17260 2065 15195 0.3488
10 2.21 2461 826 1635 0.0375 30 4.52 18798 2478 16321 0.3747
11 2.13 2609 908 1700 0.0390 35 4.08 19796 2891 16906 0.3881
12 2.05 2739 991 1748 0.0401 40 3.74 20739 3304 17436 0.4003
13 1.98 2866 1074 1792 0.0411 45 3.46 21585 3717 17868 0.4102
14 1.92 2993 1156 1837 0.0422 50 3.23 22389 4130 18259 0.4192
15 1.87 3123 1239 1885 0.0433 55 3.03 23103 4542 18560 0.4261
16 1.81 3225 1321 1903 0.0437 60 2.86 23789 4955 18834 0.4324
17 1.75 3313 1404 1909 0.0438 65 2.71 24420 5368 19051 0.4374
18 1.70 3407 1487 1921 0.0441 70 2.59 25134 5781 19352 0.4443
19 1.65 3491 1569 1922 0.0441 75 2.48 25785 6194 19591 0.4497
20 1.61 3585 1652 1934 0.0444 80 2.38 26395 6607 19788 0.4543
21 1.56 3648 1734 1913 0.0439 85 2.29 26984 7020 19964 0.4583
22 1.53 3748 1817 1931 0.0443 90 2.21 27574 7433 20141 0.4624
23 1.49 3816 1900 1916 0.0440 95 2.13 28052 7846 20206 0.4639
24 1.46 3902 1982 1920 0.0441 100 2.06 28558 8259 20299 0.4660
25 1.43 3981 2065 1916 0.0440 105 2.00 29112 8672 20440 0.4692
26 1.40 4053 2147 1906 0.0438 110 1.94 29584 9085 20499 0.4706
27 1.37 4119 2230 1889 0.0434 115 1.88 29972 9498 20474 0.4700
28 1.34 4178 2313 1865 0.0428 120 1.84 30610 9911 20699 0.4752
29 1.32 4262 2395 1867 0.0429 125 1.79 30969 10324 20645 0.4739
30 1.30 4343 2478 1865 0.0428 130 1.75 31452 10737 20715 0.4756
31 1.27 4384 2560 1824 0.0419 135 1.71 31935 11150 20786 0.4772
32 1.24 4418 2643 1775 0.0408 140 1.67 32420 11563 20857 0.4788
33 1.22 4483 2725 1757 0.0403 145 1.64 32905 11976 20930 0.4805
34 1.19 4505 2808 1697 0.0390 150 1.61 33393 12389 21004 0.4822
35 1.17 4560 2891 1669 0.0383 155 1.58 33882 12802 21081 0.4840
36 1.15 4610 2973 1637 0.0376 160 1.55 34375 13215 21160 0.4858
37 1.13 4656 3056 1600 0.0367 165 1.52 34869 13627 21242 0.4876
38 1.11 4697 3138 1558 0.0358 170 1.50 35367 14040 21326 0.4896
39 1.09 4733 3221 1512 0.0347 175 1.48 35867 14453 21414 0.4916
40 1.07 4766 3304 1462 0.0336 180 1.46 36371 14866 21505 0.4937
41 1.05 4794 3386 1407 0.0323
42 1.04 4864 3469 1395 0.0320
43 1.02 4884 3551 1332 0.0306
44 1.01 4948 3634 1314 0.0302
0
1000
2000
3000
4000
5000
6000
5 10 15 20 25 30 35 40 45 50 55 60
Volume (Cubic Feet)
Duration (Minutes)
2-Year Modified FAA Storm Detention
2-Vol
2-Inflow
2-Outflow
15
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155 165 175
Volume (Cubic Feet)
Duration (Minutes)
100-Year Modified FAA Stom Detention
100-Vol
100-Inflow
100-Outflow
16
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 65.6 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.656
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.21 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 92,231 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 1,577 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 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 = 6.00 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 1210 sq ft
D) Actual Flat Surface Area AActual = 3344 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 3344 sq ft
F) Rain Garden Total Volume VT= 1,672 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
88 88.00 0.00
38 38.00 0.00
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 = 0.948 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = 1,577 cu ft
iii) Orifice Diameter, 3/8" Minimum DO = 1 1/16 in
Design Procedure Form: Rain Garden (RG)
W. Logan
ZP Architects Engineers
September 8, 2020
Pacific Coast Supply
Fort Collins Bioretention
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.07.xlsm, RG 17 9/8/2020, 8:40 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?
PROVIDE A 30 MIL (MIN) PVC LINER WITH CDOT CLASS B
GEOTEXTILE ABOVE IT. USE THE SAME GEOTEXTILE BELOW
THE LINER IF THE SUBGRADE IS ANGULAR
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
W. Logan
ZP Architects Engineers
September 8, 2020
Pacific Coast Supply
Fort Collins Bioretention
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.xlsm, RG 18 9/8/2020, 8:40 PM
Sheet 1 of 3
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 62.7 %
B) Tributary Area's Imperviousness Ratio (i = Ia / 100 ) i = 0.627
C) Contributing Watershed Area Area = 2.715 ac
D) For Watersheds Outside of the Denver Region, Depth of Average d6 = in
Runoff Producing Storm
E) Design Concept
(Select EURV when also designing for flood control) 1
F) Design Volume (WQCV) Based on 40-hour Drain Time VDESIGN= ac-ft
(VDESIGN = (1.0 * (0.91 * i3 - 1.19 * i2 + 0.78 * i) / 12 * Area )
G) For Watersheds Outside of the Denver Region, VDESIGN OTHER= ac-ft
Water Quality Capture Volume (WQCV) Design Volume
(VWQCV OTHER = (d6*(VDESIGN/0.43))
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VDESIGN USER= 0.017 ac-ft
(Only if a different WQCV Design Volume is desired)
I) NRCS Hydrologic Soil Groups of Tributary Watershed
i) Percentage of Watershed consisting of Type A Soils HSG A = %
ii) Percentage of Watershed consisting of Type B Soils HSG B = %
iii) Percentage of Watershed consisting of Type C/D Soils HSG C/D = %
J) Excess Urban Runoff Volume (EURV) Design Volume
For HSG A: EURVA = 1.68 * i1.28 EURVDESIGN = ac-f t
For HSG B: EURVB = 1.36 * i1.08
For HSG C/D: EURVC/D = 1.20 * i1.08
K) User Input of Excess Urban Runoff Volume (EURV) Design Volume EURVDESIGN USER= ac-f t
(Only if a different EURV Design Volume is desired)
2. Basin Shape: Length to Width Ratio L : W = 2.0 : 1
(A basin length to width ratio of at least 2:1 will improve TSS reduction.)
3. Basin Side Slopes
A) Basin Maximum Side Slopes Z = 4.00 ft / ft
(Horizontal distance per unit vertical, 4:1 or flatter preferred)
4. Inlet
A) Describe means of providing energy dissipation at concentrated
inflow locations:
Design Procedure Form: Extended Detention Basin (EDB)
Pacific Coast Supply
ZP Architects Engineers
September 8, 2020
W. Logan
UD-BMP (Version 3.07, March 2018)
Riprap field
Choose One
Excess Urban Runoff Volume (EURV)
Water Quality Capture Volume (WQCV)
UD-BMP_v3.07.xlsm, EDB 19 9/8/2020, 8:48 PM
Use stainless steel well screen #93 Vee w/ 0.139 " wire opening, # 156 VEE
support rods on 3/4" o.c., screen thickness 0.31" w/ 6" wide min. opening.
At 0.29 ft
2
At A
ot 77 e
0.124 D
Aot 0.004 ft
2
Aot
(0.0417 ft )
2
4
D 0.625 in 3
Trashrack Opening Area:
Provide 2 rows at 4" o.c. vertically in face of drainage box with
(1) one 5/8-inch diameter holes per row.
Drain_Time 23.7 hr (approxiomatly)
Drain_Time
WQCV
Qwqcv
1hr
3600sec
Approximate WQCV Drain Time:
Qwqcv 0.00876
ft
3
sec
Qwqcv
d1
2
4
Cd 2g h
1
d1
2
d2
2
4
Cd 2g h
2
d2
2
Q100 1.37
ft
3
sec
Q100
ID
2
4
Cd 2 32.2 H
ID
2
cfs
Actual Discharge
ID 5.625 in ID 0.469 ft
D root D 0.471 ft Use 5 5/8" orfice
d
2
4
Cd 2 32.2 H
d
2
Q2 d
ft
Q2 1.38
ft
3
sec
where Cd 0.60
Q100
D
2
4
Cd 2g H
D
2
Emergency overflow from pond:
Use a retangular contracted weir:
Qof C
w (L 0.2 H ) H
b
where Cw
3.4
b
3
2
H 0.25 ft
Detention Flow Through runoff is: QC
15.85 cfs
Qof Q
C
Qof 15.85
ft
3
sec
Required width of weir for a maximum flow height of 3":
Width root Cw (L 0.2 H ) H
b
Qof L
Width 37.344 ft Use an 40' wide emergency overflow
wier from detention pond.
22
WQCV Depth: DWQ
ElevWQCV 20.30 ft D
WQ 49.39 ft
K40 0.013 D
WQ
2
0.22 DWQ ft 0.10 ft
2
K40 1.153 ft
2
WQCV 748 ft
3
(0.00706 acre ft )
WQCV 0.0071 acre ft
in
2
Required Area per Row: row
Area
WQCV
K40
Area 268.178 ft
Area
WQCV
K40
in
ft
Area 22.35 ft (1/2-in, dia)
23
APPENDIX B
Charts and Tables
24
Hydrologic Soil Group—Larimer County Area, Colorado
(Pacific Coast Supply)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 1 of 4
4494360 4494380 4494400 4494420 4494440 4494460 4494480 4494500
4494360 4494380 4494400 4494420 4494440 4494460 4494480 4494500
499900 499920 499940 499960 499980 500000 500020 500040 500060 500080 500100 500120
499900 499920 499940 499960 499980 500000 500020 500040 500060 500080 500100 500120
40° 36' 4'' N
105° 0' 4'' W
40° 36' 4'' N
104° 59' 54'' W
40° 35' 59'' N
105° 0' 4'' W
40° 35' 59'' N
104° 59' 54'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 15 30 60 90
Meters
Map Scale: 1:1,070 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
29
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
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
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
53 Kim loam, 1 to 3 percent
slopes
B 0.0 0.1%
63 Longmont clay, 0 to 3
percent slopes
D 1.3 29.3%
74 Nunn clay loam, 1 to 3
percent slopes
C 2.2 51.5%
94 Satanta loam, 0 to 1
percent slopes
C 0.8 19.1%
Totals for Area of Interest 4.3 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Hydrologic Soil Group—Larimer County Area, Colorado Pacific Coast Supply
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 3 of 4
31
Rating Options
Aggregation Method: Dominant Condition
Aggregation is the process by which a set of component attribute values is
reduced to a single value that represents the map unit as a whole.
A map unit is typically composed of one or more "components". A component is
either some type of soil or some nonsoil entity, e.g., rock outcrop. For the
attribute being aggregated, the first step of the aggregation process is to derive
one attribute value for each of a map unit's components. From this set of
component attributes, the next step of the aggregation process derives a single
value that represents the map unit as a whole. Once a single value for each map
unit is derived, a thematic map for soil map units can be rendered. Aggregation
must be done because, on any soil map, map units are delineated but
components are not.
For each of a map unit's components, a corresponding percent composition is
recorded. A percent composition of 60 indicates that the corresponding
component typically makes up approximately 60% of the map unit. Percent
composition is a critical factor in some, but not all, aggregation methods.
The aggregation method "Dominant Condition" first groups like attribute values
for the components in a map unit. For each group, percent composition is set to
the sum of the percent composition of all components participating in that group.
These groups now represent "conditions" rather than components. The attribute
value associated with the group with the highest cumulative percent composition
is returned. If more than one group shares the highest cumulative percent
composition, the corresponding "tie-break" rule determines which value should
be returned. The "tie-break" rule indicates whether the lower or higher group
value should be returned in the case of a percent composition tie. The result
returned by this aggregation method represents the dominant condition
throughout the map unit only when no tie has occurred.
Component Percent Cutoff: None Specified
Components whose percent composition is below the cutoff value will not be
considered. If no cutoff value is specified, all components in the database will be
considered. The data for some contrasting soils of minor extent may not be in the
database, and therefore are not considered.
Tie-break Rule: Higher
The tie-break rule indicates which value should be selected from a set of multiple
candidate values, or which value should be selected in the event of a percent
composition tie.
Hydrologic Soil Group—Larimer County Area, Colorado Pacific Coast Supply
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 4 of 4
32
APPENDIX C
FIRM Map, Drainage Plan and Details
33
34
35
36
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 15, Jun 9, 2020
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 19, 2018—Aug
10, 2018
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.
Hydrologic Soil Group—Larimer County Area, Colorado
(Pacific Coast Supply)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/8/2020
Page 2 of 4
30
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H Elev100 69.00 ft H 2.95 ft
100-year orifice size:
Q2 Q
wqcv 1.36
ft
3
sec
Qwqcv 0.020
ft
3
sec
Qwqcv
d1
2
4
Cd 2g h
1
d1
2
d2
2
4
Cd 2g h
2
d2
2
d h2 0.82917 ft
2 0.052 ft
d h1 1.1625 ft
Additional Discharge from water quality plate: 1 0.052 ft
C Q2 1.38 cfs
d 0.60
H Elev2 Elev H 0.41 ft
Q2 WQCV
D
2
4
Cd 2g H
D
2
where
2-year vertical orifice size:
Detention Outlet Structure:
21
Discharge from water quality plate:
d h2 0.081 ft
2 0.052 ft
Two 1/2" diameter outlets: h
d1 1 0.414 ft
0.052 ft
WQCV 748 ft
3
where Cd 0.60
WQCV Release Plate:
20
45 0.99 4961 3717 1244 0.0286
46 0.98 5020 3799 1220 0.0280
47 0.96 5024 3882 1142 0.0262
48 0.95 5078 3964 1113 0.0256
49 0.94 5129 4047 1082 0.0248
50 0.92 5122 4130 993 0.0228
51 0.91 5168 4212 956 0.0219
52 0.90 5211 4295 916 0.0210
53 0.89 5252 4377 875 0.0201
54 0.88 5291 4460 831 0.0191
55 0.87 5328 4542 786 0.0180
56 0.86 5363 4625 738 0.0169
57 0.85 5395 4708 687 0.0158
58 0.84 5425 4790 635 0.0146
59 0.83 5453 4873 580 0.0133
60 0.82 5478 4955 523 0.0120
65 0.78 5645 5368 277 0.0064
14
POINT
DIRECT RUNOFF TOTAL RUNOFF
8/26/2020
13
DIRECT RUNOFF TOTAL RUNOFF STREET PIPE TRAVEL TIME
REMARKS
8/26/2020
12