HomeMy WebLinkAboutTHE STANDARD AT FORT COLLINS - FDP - FDP170023 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTFINAL DRAINAGE REPORT
The Standard at Fort Collins
Fort Collins, Colorado
September 20, 2017
Prepared for:
Landmark Properties
4455 Epps Bridge Parkway, Suite 20
Athens, GA 30606
Prepared by:
301 North Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 1290-001
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
September 20, 2017
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
The Standard @ Fort Collins
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the Preliminary Development Review submittal for the
proposed The Standard @ Fort Collins. Comments from the Preliminary Development Plans Letter
dated August 8, 2017 have been addressed. Written responses thereto can be found in the
comprehensive response to comments letter on file with Current Planning.
This report has been prepared in accordance to the Fort Collins Stormwater Criteria Manual
(FCSCM), and serves to document the stormwater impacts associated with the proposed The
Standard @ Fort Collins project. We understand that review by the City is to assure general
compliance with standardized criteria contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Nicholas W. Haws, PE Cody Snowdon
Project Manager Project Engineer
The Standard @ Fort Collins
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain.......................................................................................................................................... 3
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 5
A. Major Basin Description .................................................................................................................... 5
B. Sub-Basin Description ....................................................................................................................... 5
III. DRAINAGE DESIGN CRITERIA ................................................................................... 5
A. Regulations........................................................................................................................................ 5
B. Four Step Process .............................................................................................................................. 5
C. Development Criteria Reference and Constraints ............................................................................ 6
D. Hydrological Criteria ......................................................................................................................... 7
E. Hydraulic Criteria .............................................................................................................................. 7
F. Floodplain Regulations Compliance .................................................................................................. 7
G. Modifications of Criteria ................................................................................................................... 7
IV. DRAINAGE FACILITY DESIGN .................................................................................... 8
A. General Concept ............................................................................................................................... 8
B. Specific Details ................................................................................................................................ 10
V. CONCLUSIONS ...................................................................................................... 13
A. Compliance with Standards ............................................................................................................ 13
B. Drainage Concept ............................................................................................................................ 13
References ....................................................................................................................... 14
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (For Future Use)
B.2 – Inlets (For Future Use)
B.3 – Detention Facilities (For Future Use)
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
The Standard @ Fort Collins
Final Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2 – Proposed Site Plan ............................................................................................... 3
Figure 3 – Existing FEMA Floodplains .................................................................................... 4
Figure 4 – Existing City Floodplains ....................................................................................... 4
MAP POCKET:
C8.00 - Drainage Exhibit
The Standard @ Fort Collins
Final Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The Standard @ Fort Collins project is located in the southwest quarter of Section 14,
Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins,
County of Larimer, State of Colorado.
3. The project site is located south of Lake Street and expands all the way to West
Prospect Road. It encompasses Blue Ridge Apartments (775 West Lake Street) and
four single family residences (900, 836 832, and 820 West Prospect Road).
4. Currently the existing lots do not have any stormwater or water quality facilities. The
northern property consists of Blue Ridge Apartments, which includes an existing
building, two parking lots and associated sidewalks. The southern properties consist
of single family residences, which includes, multiple buildings, gravel drives, and
associated sidewalks. The northern project site is composed of 81 percent
imperviousness, while the southern portion of the project is composed of only 20
percent imperviousness, resulting in an overall imperviousness of 49 percent. The
existing site all drains to both West Lake Street and West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 2
5. The project is currently bordered to the south by West Prospect Road, west by
Plymouth Congregational Church, north by West Lake Street and east by Farmhouse
Fraternity.
B. Description of Property
1. The Standard @ Fort Collins is approximately 4.23 net acres.
Figure 1 – Aerial Photograph
2. The Standard @ Fort Collins consists of five properties with five existing structures
and multiple out buildings. The northern lot consist of Blue Ridge Apartments with
two parking lots and associated sidewalks. The southern lot consists of four single
family residences with associated gravel driveways, multiple accessory buildings and
associated sidewalks. There is no off-site drainage entering the existing properties.
All runoff generated from the project drains either south to West Prospect Road or
north to West Lake Street.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey, 100 percent of the site consists of Altvan-
Satanta loam, which falls into Hydrologic Soil Groups B.
4. The proposed development will include the demolition of the existing structures,
parking lots, gravel drives and associated sidewalks. The proposed project will include
two large multi-family buildings, an internal parking structure and a central drive aisle
acting as a pedestrian spine between West Prospect Road and West Lake Street. The
central drive aisle and courtyards are planned to be composed of StormTech
chambers underneath the surface. These areas will act as a portion of the project’s
water quality and detention facility. Internal to Building B, a concrete vault is
proposed to treat stormwater through the use of a sand filter, as well as detaining the
major storm event. The surrounding green space will act as the remaining water
quality.
The Standard @ Fort Collins
Final Drainage Report 3
Figure 2– Proposed Site Plan
5. No irrigation facilities or major drainageways are within the property limits.
6. The project site is within the High Density Mixed-Use Neighborhood District (H-M-N)
Zoning District. The proposed use is permitted within the zone district.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
2. The FEMA Panel 0801010979H illustrates the proximity of the project site to the
nearest FEMA delineated regulatory floodplain. It is noted that the vertical datum
utilized for site survey work is the City of Fort Collins Benchmark #29-92
Elevation = 5025.67 (NAVD 88)
The Standard @ Fort Collins
Final Drainage Report 4
Figure 3 – Existing FEMA Floodplains
Figure 4 – Existing City Floodplains
The Standard @ Fort Collins
Final Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The Standard @ Fort Collins is located within the Old Town Basin, which is located
primarily in Old Town Fort Collins.
B. Sub-Basin Description
1. The property historically drains from the southeast corner of the southern lots and to
the northeast corner of the northern lot. Stormwater is routed via overland flow across
the existing lots. The project only consists of two basins; Basin HN1 and HS1
representing the historic basin draining to the north and the historic basin draining to
the south, respectively. The stormwater within Historic Basin HN1, historically
discharges directly into West Lake Street at a rate of 4.11 cfs and 20.03 cfs for the
2-year and 100-year storm event, respectively. The stormwater within Historic Basin
HS1, historically discharges directly into West Prospect Road at a rate of 1.36 cfs and
6.21 cfs for the 2-year and 100-year storm event, respectively. See Section IV.A.4.
below, for a more detailed description of the projects proposed drainage patterns.
2. No drainage is routed onto the property from the surrounding properties.
A full-size copy of the Proposed Drainage Exhibit can be found in the Map Pocket at
the end of this report.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with The Standard @
Fort Collins project.
B. Four Step Process
The overall stormwater management strategy employed with The Standard @ Fort Collins
project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on
receiving waters. The following is a description of how the proposed development has
incorporated each step.
Step 1 – Employ Runoff Reduction Practices
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low-Impact Development (LID) strategies including:
Selecting a site that has been previously developed and currently consist of Blue
Ridged Apartments and single family residences, two asphalt parking lots, multiple
gravel access drives and associated sidewalks.
Providing vegetated open areas along the north, south, east and west portion of the
site to reduce the overall impervious area and to minimize directly connected
impervious areas (MDCIA).
Routing flows, to the extent feasible, through drain rock both within the underground
detention section to increase time of concentration, promote infiltration and provide
initial water quality.
The Standard @ Fort Collins
Final Drainage Report 6
Routing runoff through the drain rock within the underground detention area to
increase time of concentration, promote infiltration and provide water quality.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, this
development will still generate stormwater runoff that will require additional BMPs and
water quality. The stormwater generated from Building B will be routed internally and
discharge into a pond/sand filter located in the garage. The water quality event will be
filtered through the sand layer and discharge into West Lake Street. Stormwater generated
from the northern portion of the central drive will be either treated through the use of
StormTech Chambers or permeable pavers. Stormwater generated from the southern
portion of the central drive will be treated through the use of pavers. Stormwater
generated from Building A will be routed internal and discharge into StormTech Chambers
located around the building where it will be treated through the drain rock section. The
areas running off-site to the west and the east only consist of landscape area and will be
routed across landscape before leaving the site.
Step 3 – Stabilize Drainageways
As stated in Section I.B.5, above, there are no major drainageways in or near the subject
site. While this step may not seem applicable to The Standard @ Fort Collins, the
proposed project indirectly helps achieve stabilized drainageways nonetheless. Once again,
site selection has a positive effect on stream stabilization. By repurposing an already
developed, under-utilized site with existing stormwater infrastructure, combined with LID,
the likelihood of bed and bank erosion is greatly reduced. Furthermore, this project will
pay one-time stormwater development fees, as well as ongoing monthly stormwater utility
fees, both of which help achieve Citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs.
This step typically applies to industrial and commercial developments and is not
applicable for this project.
C. Development Criteria Reference and Constraints
1. There are no known drainage studies for the existing properties.
2. There are drainage studies for both the Stadium Apartments to the north and The Slab
Project east, but those projects will not have any effect on The Standard @ Fort
Collins project.
3. The subject property is essentially an "in-fill" development project as the property is
surrounded by currently developed properties. As such, several constraints have been
identified during the course of this analysis that will impact the proposed drainage
system including:
Existing elevations along the north property lines adjacent to West Lake Street will
be maintained. Existing elevations along the south property lines adjacent to the
West Prospect Road will be maintained. Existing elevations along the west will
also be maintained. Areas along the southern property line of Building B and east
of the southern half of the alley will be raised through use of a landscape wall.
As previously mentioned, overall drainage patterns within the Master Drainage
Basin will be maintained. To alleviate the current drainage problem within West
Lake Street, the majority of the drainage will be routed to West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 7
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations
associated with this development. Tabulated data contained in Table RA-7 has been
utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. The Rational Formula-based Modified Federal Aviation Administration (FAA)
procedure has been utilized for detention storage calculations.
4. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 80th percentile rain event, which has been
employed to design the project’s water quality features. The second event analyzed is
the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third
event considered is the “Major Storm,” which has a 100-year recurrence interval.
The fourth storm computed, for comparison purposes only, is the 10-year event.
5. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
1. As previously noted, the subject property historically drains into both West Lake Street
and West Prospect Road. The majority of the site drains stormwater via overland
flow.
2. All drainage facilities proposed with The Standard @ Fort Collins project are designed
in accordance with criteria outlined in the FCSCM and/or the Urban Drainage and
Flood Control District’s (UDFCD) Urban Storm Drainage Criteria Manual.
3. As stated in Section I.C.1, above, the subject property is not located within any
regulatory floodplain.
4. The Standard @ Fort Collins project does not propose to modify any natural
drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, all structures are located outside of any FEMA 100-year or
City floodplain, and thus are not subject to any floodplain regulations.
G. Modifications of Criteria
1. The proposed The Standard @ Fort Collins development is not requesting any
modification at this time.
The Standard @ Fort Collins
Final Drainage Report 8
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of The Standard @ Fort Collins drainage design are to maintain
existing drainage patterns, minimize the amount of drainage routed to West Lake
Street and ensure no adverse impacts to any adjacent properties.
2. As previously mentioned, there are no off-site flows draining onto the existing
property.
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within the
sections to which the content best applies.
4. The Standard @ Fort Collins project is composed of four major drainage basins,
designated as Basins N, S, ON, and OS. The drainage patterns for each major basin
are further described below.
Basin N
Basin N is further subdivided into four (4) sub-basins, designated as Basins N1, N2,
N3 and N4. Sub-basin N1 is composed primarily of the drive located west of Building
B and the fire turnaround located north of Building A with minor roof contribution from
Building A. It consists of some landscape surfacing, but predominantly hardscape.
Stormwater generated from this sub-basin is routed via overland and gutter flow and
discharges into underground StormTech Chambers during the water quality event, and
detained within the same chambers during the 100-year event. Sub-basin N2 is
composed primarily of the drive located west of Building B and consists of some
landscape surfacing, but predominantly hardscape. Stormwater generated from this
sub-basin is routed via overland flow and gutter flow and is treated through use of a
paver section. During the major storm event, runoff from both Basin N2 will be
discharged undetained into West Lake Street. Sub-basin N3 is composed entirely of
Building B. Stormwater generated from this sub-basin is routed internal to the
building and discharges into a detention structure within the parking garage. The
structure has three components incorporated within the design. The lower section of
the structure will include a sand bed and treat the stormwater before releasing the
Water Quality event into West Lake Street. The middle portion will consist of the 2-
year rain event and will release at a rate less than the 2-year event into Lake Street.
The upper section will detain for the events larger than the 2-year event and restrict
flow out to Prospect Road. The overall release from this vault will not exceed the
historic runoff allowed. The stormwater within this section will be routed to West
Prospect Road by use of a siphoned storm drain. Sub-Basin N4 is composed entirely
of the internal courtyards within Building B. Stormwater generated from this sub-
basin is routed internal to the building and discharges in to Storm Line C. This
stormwater is routed through Storm Line C and discharged undetained into West Lake
Street.
Basin S
Basin S is further subdivided into six (6) sub-basins, designated as Basins S1-S6.
Sub-basin S1 is composed of the area to the west Building A, as well as a portion of
the roof from Building A. Stormwater generated from this sub-basin will be routed
external to the building and discharges directly into Detention Pond S1. Pond S1 was
The Standard @ Fort Collins
Final Drainage Report 9
designed with isolator rows to treat the Water Quality Event and sized to detain the
100-year event. Sub-basin S2 is composed of the western courtyard, as well as a
portion of the roof from Building A. Stormwater generated from this sub-basin will be
routed both internal and external to the building and discharges directly into Detention
Pond S2. Pond S2 was designed with isolator rows to treat the Water Quality Event
and sized to detain the 100-year event. Sub-basin S3 is composed of the central
courtyard, as well as a portion of the roof from Building A. Stormwater generated from
this sub-basin will be routed both internal and external to the building and discharges
directly into Detention Pond S3. Pond S3 was designed with isolator rows to treat the
Water Quality Event and sized to detain the 100-year event. Sub-basin S4 is
composed of the eastern courtyard, as well as a portion of the roof from Building A.
Stormwater generated from this sub-basin will be routed both internal and external to
the building and discharges directly into Detention Pond S4. Pond S4 was designed
with isolator rows to treat the Water Quality Event and sized to detain the 100-year
event. Sub-basin S5 is composed of a portion of the roof from Building A.
Stormwater generated from this sub-basin will be routed internal to the building and
discharges directly into Detention Pond S5. Pond S5 was designed with isolator rows
to treat the Water Quality Event and sized to detain the 100-year event. Sub-basin S6
is composed primarily of the drive located east of Building A and consists of some
landscape surfacing, but predominantly hardscape. Stormwater generated from this
sub-basin is routed via overland flow and gutter flow and is treated through use of a
paver section. During the major storm event, runoff from Sub-basin S6 will be
discharged undetained into West Prospect Road.
Basin ON
Basin ON is further subdivided into two (2) sub-basins, designated as Basins ON1 and
ON2. Sub-basin ON1 is composed primarily of the area located north of the Building
B, and consists of landscape and public sidewalk. Stormwater generated from this
sub-basin is routed via overland flow and discharges undetained into West Lake
Street. Sub-basin ON2 is composed of a small area located east and south of Building
B and consists entirely of landscaping. Stormwater generated from this sub-basin is
routed via overland flow and discharges undetained into the bio-swale designed by the
Slab project.
Basin OS
Basin OS is further subdivided into two (2) sub-basins, designated as Basins OS1 and
OS2. Sub-basin OS1 is composed primarily of the area located south of the Building
A, and consists of landscape sand public sidewalk. Stormwater generated from this
sub-basin is routed via overland flow and discharges undetained into West Prospect
Road. Sub-basin OS2 is composed of a small area located north of Building A and
consists entirely of landscaping. Stormwater generated from this sub-basin is routed
via overland flow and discharges undetained to the north.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
The Standard @ Fort Collins
Final Drainage Report 10
B. Specific Details
1. The main drainage problem associated with this project site is the deficiency of water
quality present within the existing site. The northern portion of the site (Blue Ridge
Apartments) drains overland and discharges directly into the West Lake Street without
water quality. The southern portion of the site (single family residences) drains
overland flow and discharges directly into the West Prospect Road without water
quality. The proposed site will mitigate this issue by instituting the following water
quality devices:
All of the runoff generated from the proposed roof of Building A (Sub-basin N3)
will be routed through a sand filter before discharging into West Lake Street.
All of the runoff generated from the proposed roof of Building A (Sub-basins S1-
S6) will be routed to StormTech Chambers and filter through the drain rock
surrounding the chambers before discharging in to West Prospect Road.
All of the runoff generated to the west of Building A (Sub-basin S1) will be treated
by a paver section, as well as the StormTech Chambers within the drive aisle.
The runoff generated from the central drive corridor will be treated through a
combination of the paver section and StormTech Chambers.
The landscape areas surrounding the project (Sub-basin ON1, ON2, OS1, and
OS2) will be treated by use of a grass buffer, as the run on area is less that 1:1.
2. The release rate for the undeveloped land (pre-development) was established by
calculating the 2-year peak runoff rate of the existing pervious area and the 100-year
peak runoff rate of the existing impervious area located within the project area,
resulting in an overall release of 23.68 cfs. In excluding all portions of the proposed
project that releases undetained (Sub-basins N1, N2, N4, S6, OS1, OS2, ON1, and
ON2), the overall allowable peak runoff rate for the remaining site was calculated at
14.50 cfs. This remaining release rate was divided among Sub-Basins N3, S1, S2,
S3, S4 and S5. These release rates were utilized in the FAA method for design of
Ponds S1-S5 and N3. (Refer to Appendix B for these calculations).
3. Detention Pond Calculations
Pond N1
Calculations for Pond N1, based on the characteristics of Sub-basin N1 and an
adjusted release rate of 2.45 cfs, indicate a detention volume of 283 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (252 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond N3
Calculations for Pond N3, based on the characteristics of Sub-basin N3 and an
adjusted release rate of 6.18 cfs, indicate a detention volume of 2,804 cu. ft. This
does not included the Water Quality Capture Volume (WQCV) of 1,291cu. ft.,
resulting in an overall detention volume of 4,095 cu. ft. Water quality will be treated
through the use of a sand filter and discharge into West Lake Street, while overall
quantity detention will be released into West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 11
Pond S1
Calculations for Pond S1, based on the characteristics of Sub-basin S1 and an
adjusted release rate of 1.00 cfs, indicate a detention volume of 1,254 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (229 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S2
Calculations for Pond S2, based on the characteristics of Sub-basin S2 and an
adjusted release rate of 1.08 cfs, indicate a detention volume of 1,225 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (248 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S3
Calculations for Pond S3, based on the characteristics of Sub-basin S3 and an
adjusted release rate of 0.56 cfs, indicate a detention volume of 1,480 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (207 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S4
Calculations for Pond S4, based on the characteristics of Sub-basin S4 and an
adjusted release rate of 1.06cfs, indicate a detention volume of 1,412 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (275 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
Pond S5
Calculations for Pond S5, based on the characteristics of Sub-basin S5 and an
adjusted release rate of 0.42 cfs, indicate a detention volume of 340 cu. ft. This
volume includes the 12-hour release WQCV calculated for this basin (112 cu. ft.).
During a Water Quality storm event, the WQCV will be routed directly into an isolator
row. The isolator rows were sized to capture either the 12-hour release WQCV within
the chambers and the surrounding aggregate or the volume required to detain the
Water Quality storm event only within the chambers, whichever is greater.
4. Detention Pond Results
Pond N1
The storage volume available within StormTech Vault Structure within Pond N1 is
536 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 18 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
The Standard @ Fort Collins
Final Drainage Report 12
isolator rows (aggregate included) is 287 cu. ft., while the volume achieved within
only the chambers of the isolator row is 123 cu. ft. In the case that the area inlet
within Sub-basin S1 should clog or backwatering should occur, stormwater would
overtop the inlet and discharge directly into Lake Street.
Pond N3
The total storage available within Pond N3 is 4,484 cu. ft at a High Water Surface
Elevation (HWSE) of 5031.0 feet. The top of the structure will provide more 12-
inches of freeboard. The WQCV is achieved at a water surface elevation of 5028.36
feet, while the 100-year detention volume is achieved at a water surface elevation of
5031.0 feet. There are two outlet pipes proposed with the vault; one discharging
less than the 2-year event (2.35 cfs) to Lake Street and the other discharging the
100-year event to Prospect Road and a restricted rate (3.83 cfs). The overall
combined flow being released from the vault is 6.18 cfs. In the case that the outlet
structure within Pond N1 were to clog, stormwater will exit the pond structure
through vents within the exterior wall and discharge into the drainage swale to the
east that was designed for The Slab. Once within this swale, the emergency flow will
discharge directly into West Lake Street.
Pond S1
The storage volume available within StormTech Vault Structure within Pond S1 is
1,491 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 18 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 287 cu. ft., while the volume achieved within
only the chambers of the isolator row is 123 cu. ft. In the case that the area inlet
within Sub-basin S1 should clog or backwatering should occur, stormwater would
overtop the inlet and discharge directly into West Prospect Road.
Pond S2
The storage volume available within StormTech Vault Structure within Pond S2 is
1,532 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 4 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 300 cu. ft., while the volume achieved within
only the chambers of the isolator row is 184 cu. ft. In the case that the outlet
structure within Sub-basin S2 should clog or backwatering should occur, stormwater
will bubble up from the outlet structure and overtop the wall located at the south end
of the courtyard and discharge directly into West Prospect Road.
Pond S3
The storage volume available within StormTech Vault Structure within Pond S3 is
1,697 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 5 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 375 cu. ft., while the volume achieved within
only the chambers of the isolator row is 230 cu. ft. In the case that the outlet
structure within Sub-basin S3 should clog or backwatering should occur, stormwater
will bubble up from the outlet structure and overtop the wall located at the south end
of the courtyard and discharge directly into West Prospect Road.
The Standard @ Fort Collins
Final Drainage Report 13
Pond S4
The storage volume available within StormTech Vault Structure within Pond S4 is
1,697 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 5 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 375 cu. ft., while the volume achieved within
only the chambers of the isolator row is 230 cu. ft. In the case that the outlet
structure within Sub-basin S4 should clog or backwatering should occur, stormwater
will bubble up from the outlet structure and overtop the wall located at the south end
of the courtyard and discharge directly into West Prospect Road.
Pond S5
The storage volume available within StormTech Vault Structure within Pond S5 is
453 cu. ft. This includes the volume stored in the aggregate surrounding the
chambers. To achieve water quality, a total of 3 chambers are proposed to be
wrapped and installed as isolator rows. The water quality volume achieved within
isolator rows (aggregate included) is 117 cu. ft., while the volume achieved within
only the chambers of the isolator row is 44 cu. ft. In the case that the outlet
structure within Sub-basin S2 should clog or backwatering should occur, stormwater
bubble up from the outlet structure and overtop into the central drive aisle, where it
will be routed directly into West Prospect Road.
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with The Standard @ Fort Collins project complies with
the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with The Standard @ Fort Collins project complies with
the City of Fort Collins’ Master Drainage Plan for the Old Town Basin.
3. There are no regulatory floodplains associated with The Standard @ Fort Collins
development.
4. The drainage plan and stormwater management measures proposed with The
Standard @ Fort Collins development are compliant with all applicable State and
Federal regulations governing stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit potential damage
associated with its stormwater runoff. The Standard @ Fort Collins will detain for the
pervious area converted to impervious areas by releasing at the 2-year existing rate
during the developed100-year storm.
2. The proposed The Standard @ Fort Collins development will not impact the Master
Drainage Plan recommendations for the Old Town major drainage basin.
The Standard @ Fort Collins
Final Drainage Report 14
References
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Standard @ Fort Collins
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: C. Snowdon
Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….. 0.50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C
f = 1.00 100-year C
f = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
HN1 87709 2.01 0.84 0.27 0.61 0.00 0.30 0.83 0.83 1.00 81%
HS1 96447 2.21 0.00 0.14 0.25 0.24 1.58 0.33 0.33 0.41 20%
Total 184156 4.23 0.84 0.41 0.86 0.24 1.88 0.57 0.57 0.71 49%
HN1 (Impervious) 74619 1.71 0.84 0.27 0.61 0.00 0.00 0.95 0.95 1.00 95%
HN1 (Pervious) 13090 0.30 0.00 0.00 0.00 0.00 0.30 0.15 0.15 0.19 0%
HS2 (Impervious) 27620 0.63 0.00 0.14 0.25 0.24 0.00 0.78 0.78 0.97 71%
HS2 (Pervious) 68827 1.58 0.00 0.00 0.00 0.00 1.58 0.15 0.15 0.19 0%
Existing Impervious Area Breakdown
HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Overland Flow, Time of Concentration:
Project: Standard @ Fort Collins
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
Rational Method Equation: Project: Standard @ Fort Collins
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
hn1 HN1 2.01 8 8 5 0.83 0.83 1.00 2.46 4.21 9.95 4.11 7.03 20.03
hs1 HS1 2.21 15 15 14 0.33 0.33 0.41 1.87 3.19 6.82 1.36 2.33 6.21
N/A HN1 (Impervious) 1.71 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 4.64 7.93 17.04
N/A HN1 (Pervious) 0.30 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.13 0.22 0.56
N/A HS2 (Impervious) 0.63 6 6 5 0.78 0.78 0.97 2.67 4.56 9.95 1.31 2.25 6.12
N/A HS2 (Pervious) 1.58 20 20 19 0.15 0.15 0.19 1.61 2.74 5.75 0.38 0.65 1.70
C2
Total allowable release from Basin Hs1
= 6.51
Total allowable release from Basin HN1
= 17.17
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C10
C100
Total Release = 23.68
HISTORIC RUNOFF COMPUTATIONS
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
C. Snowdon
September 20, 2017
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Q = C f ( C )( i )( A )
Page 3 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Hist-Direct-Runoff
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Standard @ Fort Collins
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….0.. 50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C
f = 1.00 100-year C
f = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
N1 13294 0.305 0.000 0.166 0.079 0.000 0.020 0.040 0.81 0.81 1.00 72%
N2 9915 0.228 0.000 0.087 0.078 0.000 0.042 0.020 0.78 0.78 0.97 65%
N3 48231 1.107 0.000 0.000 1.107 0.000 0.000 0.000 0.95 0.95 1.00 90%
N4 3856 0.089 0.000 0.066 0.000 0.000 0.000 0.022 0.75 0.75 0.94 68%
S1 12706 0.292 0.000 0.073 0.151 0.000 0.017 0.051 0.78 0.78 0.97 69%
S2 12648 0.290 0.000 0.024 0.214 0.000 0.000 0.052 0.81 0.81 1.00 74%
Overland Flow, Time of Concentration:
Project: Standard @ Fort Collins
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt
= L / 60V
Tc
= Ti
+ Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf
=1.00)
C*Cf
(10-yr
Cf
=1.00)
C*Cf
(100-yr
Cf
=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
Rational Method Equation: Project: Standard @ Fort Collins
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
n1 N1 0.31 5 5 5 0.81 0.81 1.00 2.85 4.87 9.95 0.70 1.20 3.04 2.45
n2 N2 0.23 5 5 5 0.78 0.78 0.97 2.85 4.87 9.95 0.50 0.86 2.20 2.20
n3 N3 1.11 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 3.00 5.12 11.02 6.18
n4 N4 0.09 5 5 5 0.75 0.75 0.94 2.85 4.87 9.95 0.19 0.32 0.83 0.83
s1 S1 0.29 5 5 5 0.78 0.78 0.97 2.85 4.87 9.95 0.65 1.11 2.83 1.00
s2 S2 0.29 5 5 5 0.81 0.81 1.00 2.85 4.87 9.95 0.67 1.14 2.89 1.08
s3 S3 0.25 5 5 5 0.78 0.78 0.97 2.85 4.87 9.95 0.56 0.96 2.46 0.56
s4 S4 0.31 5 5 5 0.83 0.83 1.00 2.85 4.87 9.95 0.73 1.25 3.09 1.06
s5 S5 0.10 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.26 0.44 0.96 0.42
s6 S6 0.24 8 8 6 0.61 0.61 0.76 2.46 4.21 9.63 0.36 0.61 1.75 1.74
on1 ON1 0.27 5 5 5 0.70 0.70 0.87 2.85 4.87 9.95 0.54 0.92 2.34 2.34
on2 ON2 0.21 5 5 5 0.30 0.30 0.37 2.85 4.87 9.95 0.18 0.31 0.79 0.79
os1 OS1 0.43 5 5 5 0.53 0.53 0.66 2.85 4.87 9.95 0.64 1.10 2.81 2.81
os2 OS2 0.11 5 5 5 0.16 0.16 0.21 2.85 4.87 9.95 0.05 0.09 0.22 0.22
Total 23.68
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
100-year Release
Rate
DEVELOPED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
C. Snowdon
September 20, 2017
Intensity,
i10
(in/hr)
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
Designed
Release
(cfs)
n1 N1 0.305 0.81 1.00 5.0 5.0 0.70 3.04 2.45
n2 N2 0.228 0.78 0.97 5.0 5.0 0.50 2.20 2.20
n3 N3 1.107 0.95 1.00 5.0 5.0 3.00 11.02 6.18
n4 N4 0.089 0.75 0.94 5.0 5.0 0.19 0.83 0.83
s1 S1 0.292 0.78 0.97 5.0 5.0 0.65 2.83 1.00
s2 S2 0.290 0.81 1.00 5.0 5.0 0.67 2.89 1.08
s3 S3 0.255 0.78 0.97 5.0 5.0 0.56 2.46 0.56
s4 S4 0.310 0.83 1.00 5.0 5.0 0.73 3.09 1.06
s5 S5 0.096 0.95 1.00 5.0 5.0 0.26 0.96 0.42
s6 S6 0.240 0.61 0.76 7.9 5.8 0.36 1.75 1.74
on1 ON1 0.269 0.70 0.87 5.0 5.0 0.54 2.34 2.34
on2 ON2 0.214 0.30 0.37 5.0 5.0 0.18 0.79 0.79
os1 OS1 0.428 0.53 0.66 5.0 5.0 0.64 2.81 2.81
os2 OS2 0.106 0.16 0.21 5.0 5.0 0.05 0.22 0.22
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
hn1 HN1 2.014 0.83 1.00 7.7 5.0 4.11 20.03
hs1 HS1 2.214 0.33 0.41 15.1 13.8 1.36 6.21
Page 7 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\SUMMARY-TABLE
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers
B.2 – Inlets
B.3 – Detention Facilities
APPENDIX B.1
STORM SEWERS (FOR FUTURE USE)
POROUS PAVERS
APPENDIX B.2
INLETS (FOR FUTURE USE)
APPENDIX B.3
DETENTION FACILITIES
Pond No :
n1
100-yr
0.98
5.00 min 283 ft3
0.31 acres 0.007 ac-ft
Max Release Rate = 2.45 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 892 1.00 2.45 735 157
10 7.720 1385 0.75 1.84 1103 282
15 6.520 1754 0.67 1.63 1471 283
20 5.600 2009 0.63 1.53 1838 170
25 4.980 2233 0.60 1.47 2206 27
30 4.520 2432 0.58 1.43 2574 -142
35 4.080 2561 0.57 1.40 2941 -380
40 3.740 2683 0.56 1.38 3309 -626
45 3.460 2792 0.56 1.36 3677 -884
50 3.230 2896 0.55 1.35 4044 -1148
55 3.030 2989 0.55 1.34 4412 -1423
60 2.860 3077 0.54 1.33 4779 -1702
65 2.720 3171 0.54 1.32 5147 -1976
70 2.590 3251 0.54 1.31 5515 -2263
75 2.480 3336 0.53 1.31 5882 -2547
80 2.380 3415 0.53 1.30 6250 -2835
85 2.290 3491 0.53 1.30 6618 -3127
90 2.210 3567 0.53 1.29 6985 -3418
95 2.130 3629 0.53 1.29 7353 -3724
100 2.060 3694 0.53 1.29 7721 -4026
105 2.000 3766 0.52 1.28 8088 -4322
110 1.940 3827 0.52 1.28 8456 -4629
115 1.890 3898 0.52 1.28 8824 -4926
120 1.840 3960 0.52 1.28 9191 -5231
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond N1
A =
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 2.45 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 28.56 ft
g = Gravity (32.2 ft/s2) Ei = 25.11 ft
Eh = High Water Surface Elevation (ft) Ec = 25.39 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 25.36 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.252871711 ft2
36.413526 in2
Orifice Size (in.) 6 - 3/4 in. Orifice Height (in.) 6 in.
Area (in2) 36.41 sq-in Orifice Width (in.) 6 in.
Q 2.35 cfs Area (in2) 36.41 sq-in
Q 2.36 cfs
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
100-Year Orifice - Pond N1
Pond No :
n3
2-yr
0.95
5.00 min 365 ft3
1.11 acres 0.008 ac-ft
Max Release Rate = 2.35 cfs
Time (min)
Ft Collins 2-
yr Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 2.85 902 1.00 2.35 705 197
10 2.21 1398 0.75 1.76 1058 341
15 1.87 1775 0.67 1.57 1410 365
20 1.61 2037 0.63 1.47 1763 275
25 1.43 2262 0.60 1.41 2115 147
30 1.30 2468 0.58 1.37 2468 0
35 1.17 2591 0.57 1.34 2820 -229
40 1.07 2708 0.56 1.32 3173 -465
45 0.99 2819 0.56 1.31 3525 -706
50 0.92 2910 0.55 1.29 3878 -967
55 0.87 3027 0.55 1.28 4230 -1203
60 0.82 3113 0.54 1.27 4583 -1470
65 0.77 3167 0.54 1.27 4935 -1768
70 0.73 3233 0.54 1.26 5288 -2054
75 0.69 3274 0.53 1.25 5640 -2366
80 0.66 3341 0.53 1.25 5993 -2652
85 0.63 3388 0.53 1.24 6345 -2957
90 0.61 3474 0.53 1.24 6698 -3224
95 0.58 3486 0.53 1.24 7050 -3564
100 0.56 3543 0.53 1.23 7403 -3859
105 0.54 3587 0.52 1.23 7755 -4168
110 0.52 3619 0.52 1.23 8108 -4488
115 0.51 3711 0.52 1.23 8460 -4749
120 0.49 3720 0.52 1.22 8813 -5092
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
Pond No :
N3
100-yr
1.00
5.00 min 2804 ft3
1.11 acres 0.064 ac-ft
Max Release Rate = 6.18 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 3304 1.00 6.18 1854 1450
10 7.720 5128 0.75 4.64 2781 2347
15 6.520 6496 0.67 4.12 3708 2788
20 5.600 7439 0.63 3.86 4635 2804
25 4.980 8269 0.60 3.71 5562 2707
30 4.520 9007 0.58 3.61 6489 2518
35 4.080 9485 0.57 3.53 7416 2069
40 3.740 9936 0.56 3.48 8343 1593
45 3.460 10342 0.56 3.43 9270 1072
50 3.230 10727 0.55 3.40 10197 530
55 3.030 11069 0.55 3.37 11124 -55
60 2.860 11398 0.54 3.35 12051 -653
65 2.720 11743 0.54 3.33 12978 -1235
70 2.590 12042 0.54 3.31 13905 -1863
75 2.480 12354 0.53 3.30 14832 -2478
80 2.380 12646 0.53 3.28 15759 -3113
85 2.290 12929 0.53 3.27 16686 -3757
90 2.210 13211 0.53 3.26 17613 -4402
95 2.130 13440 0.53 3.25 18540 -5100
100 2.060 13683 0.53 3.24 19467 -5784
105 2.000 13948 0.52 3.24 20394 -6446
110 1.940 14174 0.52 3.23 21321 -7147
115 1.890 14436 0.52 3.22 22248 -7812
120 1.840 14666 0.52 3.22 23175 -8509
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond N3
A =
100-YEAR OUTLET PIPE
RELEASE TO PROSPECT ROAD
WQCV & 10-YEAR OUTLET PIPE
A DETENTION STRUCTURE A RELEASE TO LAKE STREET
WITHIN GARAGE
CONCRETE FLOOR
1.5' WATER QUALITY VOLUME 1.5' WATER QUALITY VOLUME
2.35' DETENTION VOLUME
6" UNDERDRAIN
WATER QUALITY
RELEASE TO
LAKE STREET
INVERT EL: 5025.50
0.5% MIN. 0.5% MIN.
INVERT EL: 5026.0'
12" SAND FILTER 12" SAND FILTER
2.35' DETENTION VOLUME
100-YEAR
OUTLET PIPE
RELEASE TO
PROSPECT ROAD
INVERT EL: 5028.5
WQ EL: 4928.5'
HWSE: 4930.85'
SPILLWAY VENTS SPILLWAY VENTS
TOP OF POND: 4931.85'
INVERTED SIPHON
10-YEAR
OUTLET PIPE
RELEASE TO
LAKE STREET
INVERT 5025.5'
10-YEAR ORIFICE PLATE
RESTRICTED FLOW RATE 5.12 CFS
INVERT = 5028.5'
100-YEAR ORIFICE PLATE
RESTRICTED FLOW RATE 1.06 CFS
INVERT = 5030.0'
E NGINEER ING
N O R T H E RN FIGURE 1
Drainage Structure with Sand Filter
August 9, 2017 the standard @ ft.collins
( IN FEET )
0
1 INCH = 20 FEET
20 20
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 2.35 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 28.56 ft
g = Gravity (32.2 ft/s2) Ei = 25.10 ft
Eh = High Water Surface Elevation (ft) Ec = 25.38 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 25.34 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.242199656 ft2
34.876751 in2
Orifice Size (in.) 6 -11/16 in. Orifice Height (in.) 5 - 3/4 in.
Area (in2) 34.88 sq-in Orifice Width (in.) 6 in.
Q 2.25 cfs Area (in2) 34.88 sq-in
Q 2.27 cfs
100-Year Orifice
The Standard @ Fort Collins
100-Year Orifice
August 9, 2017
1290-001 C. Snowdon
2-Year Orifice - N3
Aa =
Circular Orifice Rectangular Orifice
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 3.83 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 31.00 ft
g = Gravity (32.2 ft/s2) Ei = 28.56 ft
Eh = High Water Surface Elevation (ft) Ec = 28.95 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 29.03 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.470053803 ft2
67.687748 in2
Orifice Size (in.) 9 - 1/4 in. Orifice Height (in.) 11 - 1/4 in.
Area (in2) 67.69 sq-in Orifice Width (in.) 6 in.
Q 3.51 cfs Area (in2) 67.69 sq-in
Q 3.44 cfs
100-Year Orifice - N3
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
Pond No :
s1
100-yr
0.97
5.00 min 1254 ft3
0.29 acres 0.029 ac-ft
Max Release Rate = 1.00 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 845 1.00 1.00 300 545
10 7.720 1312 0.75 0.75 450 862
15 6.520 1662 0.67 0.67 600 1062
20 5.600 1903 0.63 0.63 750 1153
25 4.980 2116 0.60 0.60 900 1216
30 4.520 2304 0.58 0.58 1050 1254
35 4.080 2427 0.57 0.57 1200 1227
40 3.740 2542 0.56 0.56 1350 1192
45 3.460 2646 0.56 0.56 1500 1146
50 3.230 2745 0.55 0.55 1650 1095
55 3.030 2832 0.55 0.55 1800 1032
60 2.860 2916 0.54 0.54 1950 966
65 2.720 3005 0.54 0.54 2100 905
70 2.590 3081 0.54 0.54 2250 831
75 2.480 3161 0.53 0.53 2400 761
80 2.380 3236 0.53 0.53 2550 686
85 2.290 3308 0.53 0.53 2700 608
90 2.210 3380 0.53 0.53 2850 530
95 2.130 3439 0.53 0.53 3000 439
100 2.060 3501 0.53 0.53 3150 351
105 2.000 3569 0.52 0.52 3300 269
110 1.940 3627 0.52 0.52 3450 177
115 1.890 3694 0.52 0.52 3600 94
120 1.840 3752 0.52 0.52 3750 2
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 1.00 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 32.55 ft
g = Gravity (32.2 ft/s2) Ei = 28.58 ft
Eh = High Water Surface Elevation (ft) Ec = 28.76 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 28.77 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.096216257 ft2
13.855141 in2
Orifice Size (in.) 4 - 1/4 in. Orifice Height (in.) 4 - 1/2 in.
Area (in2) 13.86 sq-in Orifice Width (in.) 3 in.
Q 0.98 cfs Area (in2) 13.86 sq-in
Q 0.98 cfs
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
100-Year Orifice - S1
Pond No :
s2
100-yr
1.00
5.00 min 1225 ft3
0.29 acres 0.028 ac-ft
Max Release Rate = 1.08 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 866 1.00 1.08 324 542
10 7.720 1343 0.75 0.81 486 857
15 6.520 1702 0.67 0.72 648 1054
20 5.600 1949 0.63 0.68 810 1139
25 4.980 2166 0.60 0.65 972 1194
30 4.520 2359 0.58 0.63 1134 1225
35 4.080 2485 0.57 0.62 1296 1189
40 3.740 2603 0.56 0.61 1458 1145
45 3.460 2709 0.56 0.60 1620 1089
50 3.230 2810 0.55 0.59 1782 1028
55 3.030 2900 0.55 0.59 1944 956
60 2.860 2986 0.54 0.59 2106 880
65 2.720 3076 0.54 0.58 2268 808
70 2.590 3155 0.54 0.58 2430 725
75 2.480 3236 0.53 0.58 2592 644
80 2.380 3313 0.53 0.57 2754 559
85 2.290 3387 0.53 0.57 2916 471
90 2.210 3461 0.53 0.57 3078 383
95 2.130 3521 0.53 0.57 3240 281
100 2.060 3584 0.53 0.57 3402 182
105 2.000 3654 0.52 0.57 3564 90
110 1.940 3713 0.52 0.56 3726 -13
115 1.890 3782 0.52 0.56 3888 -106
120 1.840 3842 0.52 0.56 4050 -208
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S2
A =
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 1.08 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 32.56 ft
g = Gravity (32.2 ft/s2) Ei = 28.42 ft
Eh = High Water Surface Elevation (ft) Ec = 28.60 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 28.57 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.101757703 ft2
14.653109 in2
Orifice Size (in.) 4 - 3/8 in. Orifice Height (in.) 3 - 3/4 in.
Area (in2) 14.65 sq-in Orifice Width (in.) 4 in.
Q 1.06 cfs Area (in2) 14.65 sq-in
Q 1.06 cfs
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
100-Year Orifice - S2
Pond No :
s3
100-yr
0.97
5.00 min 1473 ft3
0.26 acres 0.034 ac-ft
Max Release Rate = 0.56 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 738 1.00 0.56 168 570
10 7.720 1146 0.75 0.42 252 894
15 6.520 1451 0.67 0.37 336 1115
20 5.600 1662 0.63 0.35 420 1242
25 4.980 1848 0.60 0.34 504 1344
30 4.520 2012 0.58 0.33 588 1424
35 4.080 2119 0.57 0.32 672 1447
40 3.740 2220 0.56 0.32 756 1464
45 3.460 2311 0.56 0.31 840 1471
50 3.230 2397 0.55 0.31 924 1473
55 3.030 2473 0.55 0.31 1008 1465
60 2.860 2547 0.54 0.30 1092 1455
65 2.720 2624 0.54 0.30 1176 1448
70 2.590 2691 0.54 0.30 1260 1431
75 2.480 2760 0.53 0.30 1344 1416
80 2.380 2826 0.53 0.30 1428 1398
85 2.290 2889 0.53 0.30 1512 1377
90 2.210 2952 0.53 0.30 1596 1356
95 2.130 3003 0.53 0.29 1680 1323
100 2.060 3057 0.53 0.29 1764 1293
105 2.000 3117 0.52 0.29 1848 1269
110 1.940 3167 0.52 0.29 1932 1235
115 1.890 3226 0.52 0.29 2016 1210
120 1.840 3277 0.52 0.29 2100 1177
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S3
A =
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 0.56 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 32.78 ft
g = Gravity (32.2 ft/s2) Ei = 28.22 ft
Eh = High Water Surface Elevation (ft) Ec = 28.35 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 28.32 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.05027468 ft2
7.239554 in2
Orifice Size (in.) 3 in. Orifice Height (in.) 2 - 1/2 in.
Area (in2) 7.24 sq-in Orifice Width (in.) 3 in.
Q 0.55 cfs Area (in2) 7.24 sq-in
Q 0.55 cfs
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
100-Year Orifice - S3
Pond No :
s4
100-yr
1.00
5.00 min 1409 ft3
0.31 acres 0.032 ac-ft
Max Release Rate = 1.06 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 925 1.00 1.06 318 607
10 7.720 1436 0.75 0.80 477 959
15 6.520 1819 0.67 0.71 636 1183
20 5.600 2083 0.63 0.66 795 1288
25 4.980 2316 0.60 0.64 954 1362
30 4.520 2522 0.58 0.62 1113 1409
35 4.080 2656 0.57 0.61 1272 1384
40 3.740 2783 0.56 0.60 1431 1352
45 3.460 2896 0.56 0.59 1590 1306
50 3.230 3004 0.55 0.58 1749 1255
55 3.030 3100 0.55 0.58 1908 1192
60 2.860 3192 0.54 0.57 2067 1125
65 2.720 3288 0.54 0.57 2226 1062
70 2.590 3372 0.54 0.57 2385 987
75 2.480 3460 0.53 0.57 2544 916
80 2.380 3541 0.53 0.56 2703 838
85 2.290 3620 0.53 0.56 2862 758
90 2.210 3700 0.53 0.56 3021 679
95 2.130 3764 0.53 0.56 3180 584
100 2.060 3832 0.53 0.56 3339 493
105 2.000 3906 0.52 0.56 3498 408
110 1.940 3969 0.52 0.55 3657 312
115 1.890 4043 0.52 0.55 3816 227
120 1.840 4107 0.52 0.55 3975 132
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S4
A =
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 1.06 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 32.53 ft
g = Gravity (32.2 ft/s2) Ei = 28.02 ft
Eh = High Water Surface Elevation (ft) Ec = 28.19 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 28.21 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.095688843 ft2
13.779193 in2
Orifice Size (in.) 4 - 1/4 in. Orifice Height (in.) 4 - 1/2 in.
Area (in2) 13.78 sq-in Orifice Width (in.) 3 in.
Q 1.04 cfs Area (in2) 13.78 sq-in
Q 1.04 cfs
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
100-Year Orifice - S4
Pond No :
s5
100-yr
1.00
5.00 min 340 ft3
0.10 acres 0.008 ac-ft
Max Release Rate = 0.42 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 287 1.00 0.42 126 161
10 7.720 445 0.75 0.32 189 256
15 6.520 563 0.67 0.28 252 311
20 5.600 645 0.63 0.26 315 330
25 4.980 717 0.60 0.25 378 339
30 4.520 781 0.58 0.25 441 340
35 4.080 823 0.57 0.24 504 318
40 3.740 862 0.56 0.24 567 295
45 3.460 897 0.56 0.23 630 267
50 3.230 930 0.55 0.23 693 237
55 3.030 960 0.55 0.23 756 204
60 2.860 988 0.54 0.23 819 169
65 2.720 1018 0.54 0.23 882 136
70 2.590 1044 0.54 0.23 945 99
75 2.480 1071 0.53 0.22 1008 63
80 2.380 1097 0.53 0.22 1071 26
85 2.290 1121 0.53 0.22 1134 -13
90 2.210 1146 0.53 0.22 1197 -51
95 2.130 1166 0.53 0.22 1260 -95
100 2.060 1187 0.53 0.22 1323 -137
105 2.000 1210 0.52 0.22 1386 -177
110 1.940 1229 0.52 0.22 1449 -220
115 1.890 1252 0.52 0.22 1512 -260
120 1.840 1272 0.52 0.22 1575 -303
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Project Title Date:
Project Number Calcs By:
Client
Pond Designation
Q = Release Rate (cfs) Q = 0.42 cfs
C = Discharge Coefficients (unitless) C = 0.65
Aa = Area Allowed of Opening (ft2) Eh = 32.96 ft
g = Gravity (32.2 ft/s2) Ei = 28.77 ft
Eh = High Water Surface Elevation (ft) Ec = 28.88 ft Circular
Ei = Elevation of Outlet Invert (ft) Ec = 28.85 ft Rectangular
Ec = Elevation of Outlet Centroid (ft)
0.039335619 ft2
5.664329 in2
Orifice Size (in.) 2 - 5/8 in. Orifice Height (in.) 2 in.
Area (in2) 5.66 sq-in Orifice Width (in.) 3 in.
Q 0.41 cfs Area (in2) 5.66 sq-in
Q 0.42 cfs
Aa =
Circular Orifice Rectangular Orifice
100-Year Orifice 100-Year Orifice
The Standard @ Fort Collins August 9, 2017
1290-001 C. Snowdon
100-Year Orifice - S5
Pond ID
Restricted
Flow Rate
(cfs)
Required
WQ Volume
(cf)
Required
Detention
Volume
(cf)
Total Required
Volume
(cf)
Detention Type
N1 2.45 252 283 535 Stormtech Chambers
N3 6.18 1119 2804 3923 Internal Vault
S1 1.00 229 1254 1483 Stormtech Chambers
S2 1.08 248 1225 1473 Stormtech Chambers
S3 0.56 207 1480 1687 Stormtech Chambers
S4 1.06 275 1412 1687 Stormtech Chambers
S5 0.42 112 340 452 Stormtech Chambers
Total 12.75
Detention Pond Summary
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia Ia = 50.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.500
C) Tributary Watershed Area ATotal = 6,789 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS = 1,843 sq ft
(Minimum recommended permeable pavement area = 1358 sq ft)
E) Impervious Tributary Ratio RT = 1.3
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 93 cu ft
(WQCV = (0.8 * (0.91 * i3 - 1.19 * i2 + 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal = cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin = 16.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 691 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (Dmin - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells =
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
The Standard @ Fort Collins - Basin N2
Fort Collins, CO
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
August 9, 2017
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = 2.0 ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV = 2.03 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice = inches
(Use a minimum orifice diameter of 3/8-inches)
Notes:
Fort Collins, CO
The Standard @ Fort Collins - Basin N2
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
August 9, 2017
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
WQ - Basin N2 - UD-BMP_v3.03.xlsm, PPS 8/9/2017, 9:01 AM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 90.0 %
(100% if all paved and roofed areas upstream of sand filter)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.900
C) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 0.32 watershed inches
WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including sand filter area) Area = 48,231 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 1,291 cu ft
VWQCV = 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 DWQCV = 1.33 ft
B) Sand Filter Side Slopes (Horizontal distance per unit vertical, Z = 0.00 ft / ft
4:1 or flatter preferred). Use "0" if sand filter has vertical walls.
C) Minimum Filter Area (Flat Surface Area) AMin = 543 sq ft
D) Actual Filter Area AActual = 970 sq ft
E) Volume Provided VT = 1293 cu ft
3. Filter Material
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = 1.8 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = 1,291 cu ft
iii) Orifice Diameter, 3/8" Minimum DO = 13 / 16 in
The Standard
Fort Collins
Design Procedure Form: Sand Filter (SF)
Cody Snowdon
Northern Engineering
September 20, 2017
UD-BMP (Version 3.06, November 2016)
Choose One
Choose One
18" CDOT Class B or C Filter Material
Other (Explain):
YES
NO
WQ - Basin N3 - UD-BMP_v3.03.xlsm, SF 9/20/2017, 8:37 AM
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?
6-7. Inlet / Outlet Works
A) Describe the type of energy dissipation at inlet points and means of
conveying flows in excess of the WQCV through the outlet
Notes:
Design Procedure Form: Sand Filter (SF)
Cody Snowdon
Northern Engineering
September 20, 2017
The Standard
Fort Collins
Choose One
YES NO
WQ - Basin N3 - UD-BMP_v3.03.xlsm, SF 9/20/2017, 8:37 AM
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 69.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.216 in
A = 0.29 ac
V = 0.0053 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
229 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins September 8, 2017
1290-001 C. Snowdon
Landmark
S1
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
s1
WQ
0.97
5.00 min 119 ft3
0.29 acres 0.00 ac-ft
Max Release Rate = 0.21 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 121 1.00 0.21 62 59
10 1.105 188 1.00 0.21 123 64
15 0.935 238 0.67 0.14 123 115
20 0.805 274 0.63 0.13 154 119
25 0.715 304 0.60 0.12 185 119
30 0.650 331 0.58 0.12 216 115
35 0.585 348 0.57 0.12 247 101
40 0.535 364 0.56 0.12 278 86
45 0.495 379 0.56 0.11 309 70
50 0.460 391 0.55 0.11 339 52
55 0.435 407 0.55 0.11 370 36
60 0.410 418 0.54 0.11 401 17
65 0.385 425 0.54 0.11 432 -7
70 0.365 434 0.54 0.11 463 -29
75 0.345 440 0.53 0.11 494 -54
80 0.330 449 0.53 0.11 524 -76
85 0.315 455 0.53 0.11 555 -100
90 0.305 466 0.53 0.11 586 -120
95 0.290 468 0.53 0.11 617 -149
100 0.280 476 0.53 0.11 648 -172
105 0.270 482 0.52 0.11 679 -197
110 0.260 486 0.52 0.11 710 -224
115 0.255 498 0.52 0.11 740 -242
120 0.245 500 0.52 0.11 771 -272
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Client :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 74.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.235 in
A = 0.29 ac
V = 0.0057 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
248 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins September 8, 2017
1290-001 C. Snowdon
Landmark
S2
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
s2
WQ
0.79
5.00 min 169 ft3
0.29 acres 0.00 ac-ft
Max Release Rate = 0.09 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 98 1.00 0.09 28 70
10 1.105 152 1.00 0.09 57 95
15 0.935 193 0.67 0.06 57 136
20 0.805 221 0.63 0.06 71 151
25 0.715 246 0.60 0.06 85 161
30 0.650 268 0.58 0.06 99 169
35 0.585 281 0.57 0.05 113 168
40 0.535 294 0.56 0.05 127 167
45 0.495 306 0.56 0.05 142 165
50 0.460 316 0.55 0.05 156 160
55 0.435 329 0.55 0.05 170 159
60 0.410 338 0.54 0.05 184 154
65 0.385 344 0.54 0.05 198 146
70 0.365 351 0.54 0.05 212 139
75 0.345 356 0.53 0.05 226 129
80 0.330 363 0.53 0.05 241 122
85 0.315 368 0.53 0.05 255 113
90 0.305 377 0.53 0.05 269 108
95 0.290 379 0.53 0.05 283 96
100 0.280 385 0.53 0.05 297 88
105 0.270 390 0.52 0.05 311 78
110 0.260 393 0.52 0.05 325 68
115 0.255 403 0.52 0.05 340 63
120 0.245 404 0.52 0.05 354 50
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S2
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 71.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.224 in
A = 0.26 ac
V = 0.0048 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
207 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins September 8, 2017
1290-001 C. Snowdon
Landmark
S3
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
s3
WQ
0.97
5.00 min 191 ft3
0.26 acres 0.00 ac-ft
Max Release Rate = 0.09 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 106 1.00 0.09 28 77
10 1.105 164 1.00 0.09 57 107
15 0.935 208 0.67 0.06 57 152
20 0.805 239 0.63 0.06 71 168
25 0.715 265 0.60 0.06 85 180
30 0.650 289 0.58 0.06 99 190
35 0.585 304 0.57 0.05 113 191
40 0.535 318 0.56 0.05 127 190
45 0.495 331 0.56 0.05 142 189
50 0.460 341 0.55 0.05 156 186
55 0.435 355 0.55 0.05 170 185
60 0.410 365 0.54 0.05 184 181
65 0.385 371 0.54 0.05 198 173
70 0.365 379 0.54 0.05 212 167
75 0.345 384 0.53 0.05 226 158
80 0.330 392 0.53 0.05 241 151
85 0.315 397 0.53 0.05 255 143
90 0.305 407 0.53 0.05 269 139
95 0.290 409 0.53 0.05 283 126
100 0.280 416 0.53 0.05 297 118
105 0.270 421 0.52 0.05 311 109
110 0.260 424 0.52 0.05 325 99
115 0.255 435 0.52 0.05 340 96
120 0.245 436 0.52 0.05 354 83
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S3
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 76.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.244 in
A = 0.31 ac
V = 0.0063 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
275 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins September 8, 2017
1290-001 C. Snowdon
Landmark
S4
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
s4
WQ
1.00
5.00 min 214 ft3
0.31 acres 0.00 ac-ft
Max Release Rate = 0.14 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 133 1.00 0.14 42 90
10 1.105 206 1.00 0.14 85 121
15 0.935 261 0.67 0.09 85 176
20 0.805 299 0.63 0.09 106 193
25 0.715 332 0.60 0.08 127 205
30 0.650 363 0.58 0.08 149 214
35 0.585 381 0.57 0.08 170 211
40 0.535 398 0.56 0.08 191 207
45 0.495 414 0.56 0.08 212 202
50 0.460 428 0.55 0.08 233 194
55 0.435 445 0.55 0.08 255 190
60 0.410 458 0.54 0.08 276 182
65 0.385 465 0.54 0.08 297 168
70 0.365 475 0.54 0.08 318 157
75 0.345 481 0.53 0.08 340 142
80 0.330 491 0.53 0.08 361 130
85 0.315 498 0.53 0.07 382 116
90 0.305 511 0.53 0.07 403 107
95 0.290 512 0.53 0.07 425 88
100 0.280 521 0.53 0.07 446 75
105 0.270 527 0.52 0.07 467 60
110 0.260 532 0.52 0.07 488 44
115 0.255 545 0.52 0.07 509 36
120 0.245 547 0.52 0.07 531 16
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S4
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 90.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.321 in
A = 0.10 ac
V = 0.0026 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
112 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins September 8, 2017
1290-001 C. Snowdon
Landmark
S5
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
s5
WQ
0.94
5.00 min 40 ft3
0.10 acres 0.00 ac-ft
Max Release Rate = 0.06 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 39 1.00 0.06 19 20
10 1.105 60 1.00 0.06 38 22
15 0.935 76 0.67 0.04 38 38
20 0.805 87 0.63 0.04 47 40
25 0.715 97 0.60 0.04 57 40
30 0.650 106 0.58 0.04 66 40
35 0.585 111 0.57 0.04 75 35
40 0.535 116 0.56 0.04 85 31
45 0.495 121 0.56 0.03 94 26
50 0.460 125 0.55 0.03 104 21
55 0.435 130 0.55 0.03 113 16
60 0.410 133 0.54 0.03 123 11
65 0.385 135 0.54 0.03 132 3
70 0.365 138 0.54 0.03 142 -3
75 0.345 140 0.53 0.03 151 -11
80 0.330 143 0.53 0.03 160 -17
85 0.315 145 0.53 0.03 170 -25
90 0.305 149 0.53 0.03 179 -31
95 0.290 149 0.53 0.03 189 -40
100 0.280 152 0.53 0.03 198 -47
105 0.270 153 0.52 0.03 208 -54
110 0.260 155 0.52 0.03 217 -62
115 0.255 159 0.52 0.03 226 -68
120 0.245 159 0.52 0.03 236 -77
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
S5
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 72.00%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.227 in
A = 0.31 ac
V = 0.0058 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Standard @ Fort Collins September 8, 2017
1290-001 C. Snowdon
Landmark
N1
252 cu. ft.
Drain Time
a =
i =
WQCV =
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
n1
WQ
1.00
5.00 min 123 ft3
0.31 acres 0.00 ac-ft
Max Release Rate = 0.23 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 130 1.00 0.23 69 62
10 1.105 202 1.00 0.23 137 65
15 0.935 257 0.67 0.15 137 120
20 0.805 295 0.63 0.14 171 123
25 0.715 327 0.60 0.14 206 121
30 0.650 357 0.58 0.13 240 117
35 0.585 375 0.57 0.13 274 100
40 0.535 392 0.56 0.13 309 83
45 0.495 408 0.56 0.13 343 65
50 0.460 421 0.55 0.13 377 44
55 0.435 438 0.55 0.12 411 26
60 0.410 450 0.54 0.12 446 5
65 0.385 458 0.54 0.12 480 -22
70 0.365 468 0.54 0.12 514 -47
75 0.345 474 0.53 0.12 548 -75
80 0.330 483 0.53 0.12 583 -100
85 0.315 490 0.53 0.12 617 -127
90 0.305 502 0.53 0.12 651 -149
95 0.290 504 0.53 0.12 686 -181
100 0.280 512 0.53 0.12 720 -207
105 0.270 519 0.52 0.12 754 -235
110 0.260 523 0.52 0.12 788 -265
115 0.255 537 0.52 0.12 823 -286
120 0.245 538 0.52 0.12 857 -319
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
Client : Landmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
C =
Tc =
A =
N1
Input Variables Results
Vault ID
Total
Required
WQ Volume
(cf)
Flow,
WQ
(cfs)
Chamber
Type
Chamber Release
Ratea
(cfs)
Chamber
Volumeb
(cf)
Installed Camber
w/ Aggregatec
(cf)
Mimimum
No. of
Chambersd
Total Release
Ratee
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Mimimum
No. of
Chambersf
Storage
Provided
within the
Chambersg
(cf)
Total
Installed
System
Volumeh
(cf)
S1 229 0.46 SC-160 0.011 6.85 15.97 15 0.17 119 18 123 287
S2 248 0.31 SC-740 0.024 45.90 74.90 4 0.09 169 4 184 300
S3 207 0.31 SC-740 0.024 45.90 74.90 3 0.07 191 5 230 375
S4 275 0.29 SC-740 0.024 45.90 74.90 4 0.09 214 5 230 375
S5 112 0.28 SC-310 0.016 14.70 29.30 4 0.06 40 3 44 117
N1 252 0.23 SC-160 0.011 6.85 15.97 16 0.18 123 18 123 287
a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.
b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.
c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
d. Number of chambers required to provide full WQCV within total installed system, including aggregate.
e. Release rate per chamber times number of chambers.
f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).
g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.
e. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.
Chamber Configuration Summary
D:\Projects\1290-001\Drainage\WatQual\1290-001 Chamber Summary.xlsx
Chamber Dimensions SC-160 SC-310 SC-740
Width (in) 25.0 34.0 51.0
Length (in) 84.4 85.4 85.4
Height (in) 12.0 16.0 30.0
Floor Area (sf) 14.7 20.2 30.2
Chamber Volume (cf) 6.9 14.7 45.9
Chamber/Aggregate Volume (cf) 16.0 29.3 74.9
Flow Rate* 0.35 gpm/sf
1 cf = 7.48052 gal
1 gallon = 0.133681 cf
1 GPM = 0.002228 cfs
*Flow rate based on 1/2 of Nov 07 QMAX
in Figure 17 of UNH Testing Report
SC-160 SC-310 SC-740
Flow Rate/chamber (cfs) 0.011426 0.015724 0.023586
StormTech Chamber Data
Chamber Flow Rate
Chamber Flow Rate Conversion (gpm/sf to cfs)
D:\Projects\1290-001\Drainage\WatQual\1290-001 Chamber Summary.xlsx
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia Ia = 48.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 0.480
C) Tributary Watershed Area ATotal = 9,332 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS = 982 sq ft
(Minimum recommended permeable pavement area = 1806 sq ft)
E) Impervious Tributary Ratio RT = 4.1 IMPERVIOUS TRIBUTARY RATIO
(Contributing Imperviuos Area / Permeable Pavement Ratio) EXCEEDS 2.0
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 125 cu ft
(WQCV = (0.8 * (0.91 * i3 - 1.19 * i2 + 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal = cu ft
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin = 16.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.30
D) Slope of the Base Course/Subgrade Interface S = ft / ft
E) Length Between Lateral Flow Barriers L = ft
F) Volume Provided Based on Depth of Base Course V = 368 cu ft
Flat or Stepped: V = P * ((Dmin-1)/12) * Area
Sloped: V = P * [(Dmin - (Dmin - 6*SL-1)) / 12] * Area
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells =
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
The Standard @ Fort Collins - Basin S6
Fort Collins, CO
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
August 9, 2017
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = 2.0 ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV = 5.09 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice = inches
(Use a minimum orifice diameter of 3/8-inches)
Notes:
The Standard @ Fort Collins - Basin S6
Design Procedure Form: Permeable Pavement Systems (PPS)
Cody Snowdon
Northern Engineering
August 9, 2017
Fort Collins, CO
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
WQ - Basin S6 - UD-BMP_v3.03.xlsm, PPS 8/9/2017, 8:59 AM
Design
Point Basin ID Basin Area Treatment Type
LID
System
Area Treated
by LID
System
Percent of Site
Treated by LID
System
Area of
Pavers
Area of
Asphalt
Parking
Percent
Pavers
Run-on Area
for Paver
Section
Run-on Area
Ratio
n1 N1 0.226 ac. StormTech
Chambers Yes 0.226 ac. 5% 0.020 ac. 0.152 ac. 13.16% 0.064 3.2
n2 N2 0.156 ac. Pavers Yes 0.156 ac. 4% 0.042 ac. 0.087 ac. 48.28% 0.087 2.1
n3 N3 1.391 ac. Sand Filter Yes 1.391 ac. 33% 0.000 ac. 0.000 ac. N/A 0 N/A
n4 N4 0.089 ac. No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
s1 S1 0.377 ac. StormTech
Chambers Yes 0.377 ac. 9% 0.024 ac. 0.051 ac. 47.06% 0 N/A
s2 S2 0.270 ac. StormTech
Chambers Yes 0.270 ac. 6% 0.000 ac. 0.038 ac. N/A 0 N/A
s3 S3 0.270 ac. StormTech
Chambers Yes 0.270 ac. 6% 0.000 ac. 0.043 ac. N/A 0 N/A
s4 S4 0.249 ac. StormTech
Chambers Yes 0.249 ac. 6% 0.000 ac. 0.031 ac. N/A 0 N/A
s5 S5 0.207 ac. StormTech
Chambers Yes 0.207 ac. 5% 0.000 ac. 0.000 ac. N/A 0 N/A
s6 S6 0.214 ac. Pavers Yes 0.214 ac. 5% 0.023 ac. 0.113 ac. 20.35% 0.0719 3.1
on1 ON1 0.136 ac. Grass Buffer No N/A 0% 0.000 ac. 0.047 ac. N/A 0 N/A
on2 ON2 0.176 ac. Grass Buffer No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
os1 OS1 0.366 ac. Grass Buffer No N/A 0% 0.000 ac. 0.155 ac. N/A 0 N/A
os2 OS2 0.106 ac. Grass Buffer No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
Total 4.23 ac. 3.360 ac. 79% 0.109 ac. 0.717 ac. 15.20%
APPENDIX D
EROSION CONTROL REPORT
Lake Avenue Apartments
Final Erosion Control Report
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at proposed storm inlets. Vehicle tracking control pads, spill containment and
clean-up procedures, designated concrete washout areas, dumpsters, and job site restrooms shall
also be provided by the Contractor.
Grading and Erosion Control Notes can be found on Sheet CS2 of the Utility Plans. The Utility
Plans at final design will also contain a full-size Erosion Control Plan as well as a separate sheet
dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the
Contractor shall be aware of, and adhere to, the applicable requirements outlined in any existing
Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior
to issuance of the Development Construction Permit. Also, the Site Contractor for this project will
be required to secure a Stormwater Construction General Permit from the Colorado Department of
Public Health and Environment (CDPHE), Water Quality Control Division – Stormwater Program,
before commencing any earth disturbing activities. Prior to securing said permit, the Site Contractor
shall develop a comprehensive StormWater Management Plan (SWMP) pursuant to CDPHE
requirements and guidelines. The SWMP will further describe and document the ongoing activities,
inspections, and maintenance of construction BMPs.
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
UP
D.S.
D.S.
R.D.
D.S.
D.S. D.S.
D.S.
D.S.
D.S.
D.S.
R.D.
D.S.
X
X
X
X X X
X
X X X X
X
X X
X X
X
X
X X X X
X
X
X
UD UD
UD
UD UD
UD
UD
UD
UD
V
AULT
ELEC
VAULT
ELEC
UD
UD UD UD
UD UD UD UD UD
FDC
FDC FDC
MAJOR STORM EVENT
OUTLET FROM INTERNAL
POND STRUCTURE
WATER QUALITY AND 10-YR
EVENT OUTLET FROM INTERNAL
POND STRUCTURE
s1
s1
s1
s1
s1
s2 s3
s4
s4
s5
s6
n3
n3
n2
on1
on2
os2
os1
N3
ON1
S1
OS1
S3
S2
S4
OS2
N2
S5
S6
ON2
POND S4
(SC-740 CHAMBERS)
POND S3
(SC-740 CHAMBERS)
POND S2
(SC-740 CHAMBERS)
POND S1
(SC-160 CHAMBERS)
POND S5
(SC-310 CHAMBERS)
POND N2
(WITH SAND FILTER)
PROSPECT ROAD
(60' PUBLIC ROW)
LAKE STREET
(60' PUBLIC ROW)
THE SLAB
STADIUM APARTMENTS
STORM LINE C2
STORM LINE C
STORM LINE A
UNDERDRAIN
PERMEABLE
PAVERS
PERMEABLE
PAVERS
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
POND OUTLET
STRUCTURE
ROOF
LEADER
ROOF LEADER ROOF LEADER
ROOF
LEADER
ROOF
ROOF LEADER
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
ROOF
LEADER
AREA INLET
SIDEWALK CHASE
STORM LINE C
OUTFALL
AREA INLET W/
WATER QUALITY
PLATE
21 SC-160 CHAMBERS
FOR WATER QUALITY
N1
CURB AND GUTTER
n1
SIDEWALK CHASE
(THE SLAB)
STADIUM APARTMENTS
STORM WATER OUTFALL
INLET
BUILDING A
BUILDING B
STORM LINE A2
DRY WELL
TRENCH DRAIN
INTERNAL PIPE
OUTFALL FOR
BASIN N4
N4 N4
n3
WATER QUALITY
STRUCTURE POND OUTLET
AND WATER QUALITY
STRUCTURE
WATER QUALITY
STRUCTURE
AREA INLET
Sheet
of 31
STANDARD AT FORT COLLINS These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
REVIEW SET
301 North Howes Street, Suite 100
Fort Collins, Colorado 80521
E NGINEER ING
N O R T H E RN
PHONE: 970.221.4158
www.northernengineering.com
C7.00
DRAINAGE EXHIBIT
GRAPHIC SCALE:
LEGEND:
EXISTING INLET GRATE
EXISTING DECID. TREE
EXISTING CONIF. TREE
EXISTING LIGHT POLE
EXISTING STUMP
ST EXISTING STORM SEWER LINE
EXISTING CURB/GUTTER FLOWLINE
EXISTING EDGE OF ASPHALT
4950
4:1
BANK SLOPE
PROPOSED OVERLAND FLOW DIRECTION
CONCENTRATED FLOW DIRECTION
PROPOSED SWALE FLOWLINE
PROPOSED INFLOW CURB/GUTTER FLOWLINE
PROPOSED STORM DRAIN WITH INLET
PROPOSED CONTOUR
EXISTING CONTOUR
PROPOSED OUTFALL CURB/GUTTER FLOWLINE
NORTH
( IN FEET )
0
1 INCH = 20 FEET
20 20 40 60
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
A2
a3
DRAINAGE BASIN AREA
PERMEABLE PAVERS
DRAINAGE BASIN ID
DRAINAGE BASIN MINOR/MAJOR COEFF.
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
NOTES:
30
RUNOFF SUMMARY TABLE:
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
Q2
(cfs)
Q100
(cfs)
N1 0.305 0.81 1.00 0.70 3.04
N2 0.228 0.78 0.97 0.50 2.20
N3 1.107 0.95 1.00 3.00 11.02
N4 0.089 0.75 0.94 0.19 0.83
S1 0.292 0.78 0.97 0.65 2.83
S2 0.290 0.81 1.00 0.67 2.89
S3 0.255 0.78 0.97 0.56 2.46
S4 0.310 0.83 1.00 0.73 3.09
S5 0.096 0.95 1.00 0.26 0.96
S6 0.240 0.61 0.76 0.36 1.75
ON1 0.269 0.70 0.87 0.54 2.34
ON2 0.214 0.30 0.37 0.18 0.79
OS1 0.428 0.53 0.66 0.64 2.81
OS2 0.106 0.16 0.21 0.05 0.22
Design
Point Basin ID Basin Area Treatment Type
LID
System
Area
Treated by
LID System
Percent of Site
Treated by LID
System
Area of
Pavers
Area of
Asphalt
Parking
Percent
Pavers
Run-on Area
for Paver
Section
Run-on Area
Ratio
n1 N1 0.226 ac. StormTech
Chambers Yes 0.226 ac. 5% 0.020 ac. 0.152 ac. 13.16% 0.064 3.2
n2 N2 0.156 ac. Pavers Yes 0.156 ac. 4% 0.042 ac. 0.087 ac. 48.28% 0.087 2.1
n3 N3 1.391 ac. Sand Filter Yes 1.391 ac. 33% 0.000 ac. 0.000 ac. N/A 0 N/A
n4 N4 0.089 ac. No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
s1 S1 0.377 ac. StormTech
Chambers Yes 0.377 ac. 9% 0.024 ac. 0.051 ac. 47.06% 0 N/A
s2 S2 0.270 ac. StormTech
Chambers Yes 0.270 ac. 6% 0.000 ac. 0.038 ac. N/A 0 N/A
s3 S3 0.270 ac. StormTech
Chambers Yes 0.270 ac. 6% 0.000 ac. 0.043 ac. N/A 0 N/A
s4 S4 0.249 ac. StormTech
Chambers Yes 0.249 ac. 6% 0.000 ac. 0.031 ac. N/A 0 N/A
s5 S5 0.207 ac. StormTech
Chambers Yes 0.207 ac. 5% 0.000 ac. 0.000 ac. N/A 0 N/A
s6 S6 0.214 ac. Pavers Yes 0.214 ac. 5% 0.023 ac. 0.113 ac. 20.35% 0.0719 3.1
on1 ON1 0.136 ac. Grass Buffer No N/A 0% 0.000 ac. 0.047 ac. N/A 0 N/A
on2 ON2 0.176 ac. Grass Buffer No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
os1 OS1 0.366 ac. Grass Buffer No N/A 0% 0.000 ac. 0.155 ac. N/A 0 N/A
os2 OS2 0.106 ac. Grass Buffer No N/A 0% 0.000 ac. 0.000 ac. N/A 0 N/A
Total 4.23 ac. 3.360 ac. 79% 0.109 ac. 0.717 ac. 15.20%
LID TABLE:
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
WQ - Basin S6 - UD-BMP_v3.03.xlsm, PPS 8/9/2017, 8:59 AM
Design Point
Design Storm Required Detention Volume
Page 12 of 14
1290-001 Chamber Summary.xlsx
=
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 10 of 14
1290-001 Chamber Summary.xlsx
=
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 8 of 14
1290-001 Chamber Summary.xlsx
=
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 6 of 14
1290-001 Chamber Summary.xlsx
=
12 hr
Project Name : The Standard @ Fort Collins
Project Number : 1290-001
Page 4 of 14
1290-001 Chamber Summary.xlsx
=
12 hr
Landmark
The Standard @ Fort Collins
1290-001
Project Name :
Project Number :
S1
Page 2 of 14
1290-001 Chamber Summary.xlsx
=
12 hr
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
WQ - Basin N2 - UD-BMP_v3.03.xlsm, PPS 8/9/2017, 9:01 AM
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The Standard @ Fort Collins
Project Number :
Project Name :
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1290-001
The Standard @ Fort Collins
Project Number :
Project Name :
Pond S1
Page 1 of 1
1290-001_Pond S1_DetentionVolume_FAAModified Method.xls
Tc =
Project Location :
Design Point
C =
Design Storm
Page 1 of 1
1290-001_Pond N3_DetentionVolume_FAAModified Method.xls
The Standard @ Fort Collins
Project Number :
Project Name :
Pond N3
Page 1 of 1
1290-001_Pond N3-2-yr_DetentionVolume_FAAModified Method.xls
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Page 1 of 1
1290-001_Pond N1_DetentionVolume_FAAModified Method.xls
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Q = C f ( C )( i )( A )
Page 6 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Direct-Runoff
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
n1 N1 No 0.81 0.81 1.00 25 9.40% 1.3 1.3 0.4 174 1.01% 2.01 1.4 0.5 N/A N/A 5 5 5
n2 N2 No 0.78 0.78 0.97 27 3.85% 2.0 2.0 0.8 157 1.70% 2.61 1.0 1.5 N/A N/A 5 5 5
n3 N3 No 0.95 0.95 1.00 N/A N/A N/A N/A 345 2.00% 2.83 2.0 1.5 N/A N/A 5 5 5
n4 N4 No 0.75 0.75 0.94 25 2.00% 2.6 2.6 1.2 50 0.50% 1.41 0.6 2.5 N/A N/A 5 5 5
s1 S1 No 0.78 0.78 0.97 N/A N/A N/A N/A 80 2.00% 2.83 0.5 N/A N/A N/A 5 5 5
s2 S2 No 0.81 0.81 1.00 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s3 S3 No 0.78 0.78 0.97 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s4 S4 No 0.83 0.83 1.00 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s5 S5 No 0.95 0.95 1.00 N/A N/A N/A N/A 100 2.00% 2.83 0.6 N/A N/A N/A 5 5 5
s6 S6 No 0.61 0.61 0.76 100 2.47% 6.8 6.8 4.7 120 0.93% 1.93 1.0 N/A N/A N/A 8 8 6
on1 ON1 No 0.70 0.70 0.87 19 5.05% 1.9 1.9 1.1 N/A N/A N/A N/A N/A N/A 5 5 5
on2 ON2 No 0.30 0.30 0.37 12 16.50% 2.0 2.0 1.9 N/A N/A N/A N/A N/A N/A 5 5 5
os1 OS1 No 0.53 0.53 0.66 41 3.56% 4.5 4.5 3.4 N/A N/A N/A N/A N/A N/A 5 5 5
os2 OS2 No 0.16 0.16 0.21 13 18.38% 2.4 2.4 2.3 N/A N/A N/A N/A N/A N/A 5 5 5
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter/Internal Building Flow Swale Flow
Design
Point
Basin
Overland Flow
C. Snowdon
September 20, 2017
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
= −
Page 5 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr
S3 11093 0.255 0.000 0.021 0.179 0.000 0.000 0.055 0.78 0.78 0.97 71%
S4 13509 0.310 0.000 0.018 0.245 0.000 0.000 0.048 0.83 0.83 1.00 76%
S5 4187 0.096 0.000 0.000 0.096 0.000 0.000 0.000 0.95 0.95 1.00 90%
S6 10439 0.240 0.000 0.128 0.000 0.000 0.027 0.084 0.61 0.61 0.76 48%
ON1 11707 0.269 0.000 0.047 0.137 0.000 0.000 0.084 0.70 0.70 0.87 62%
ON2 9317 0.214 0.000 0.000 0.039 0.000 0.000 0.174 0.30 0.30 0.37 17%
OS1 18633 0.428 0.000 0.148 0.055 0.000 0.000 0.225 0.53 0.53 0.66 43%
OS2 4619 0.106 0.000 0.002 0.000 0.000 0.000 0.104 0.16 0.16 0.21 2%
TOTAL 184154 4.23 0.000 0.778 2.381 0.000 0.106 1.175 0.76 0.76 0.95 67%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf
= 1.00
September 20, 2017
**Soil Classification of site is Sandy Loam**
C. Snowdon
Page 4 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\C-Values
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
hn1 HN1 No 0.83 0.83 1.00 77 0.40% 6.0 6.0 2.2 205 1.01% 2.01 1.7 N/A N/A N/A 8 8 5
hs1 HS1 No 0.33 0.33 0.41 118 1.96% 12.5 12.5 11.2 N/A N/A N/A 113 0.23% 0.72 2.6 15 15 14
N/A HN1 (Impervious) No 0.95 0.95 1.00 77 0.40% 3.3 3.3 2.2 205 1.01% 2.01 1.7 N/A N/A N/A 5 5 5
N/A HN1 (Pervious) No 0.15 0.15 0.19 22 4.23% 5.2 5.2 4.9 N/A N/A N/A N/A N/A N/A 5 5 5
N/A HS2 (Impervious) No 0.78 0.78 0.97 84 2.13% 4.3 4.3 1.7 N/A N/A N/A 130 0.50% 1.06 2.0 6 6 5
N/A HS2 (Pervious) No 0.15 0.15 0.19 80 0.50% 20.0 20.0 19.2 N/A N/A N/A N/A N/A N/A 20 20 19
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
C. Snowdon
September 20, 2017
Design
Point
Basin
Overland Flow Gutter Flow Swale Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
= −
Page 2 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr
Notes
September 20, 2017
10-year Cf
= 1.00
**Soil Classification of site is Sandy Loam**
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Page 1 of 7 D:\Projects\1290-001\Drainage\Hydrology\1290-001_Rational-Calcs.xlsx\Hist-C-Values