HomeMy WebLinkAboutNORTHFIELD COMMONS - MJA210001 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
FOR
Northfield Commons
Prepared by:
Highland Development Services
6355 Fairgrounds Ave, Suite 100
Windsor, Colorado 80550
Phone: 970.674.7550
Prepared for:
Mercy Housing
1600 Broadway, Suite 200
Denver, CO 80202
Phone: 303.830.3470
April 28, 2021
Job Number 21-1037-00
6355 FAIRGROUNDS AVE, SUITE 100, WINDSOR, COLORADO 80550 | PHONE 970.674.7550
April 28, 2021
Mr. Dan Mogen
Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80522
RE: Preliminary Drainage Report for Northfield Commons
Dear Dan,
We are pleased to submit for your review, the Preliminary Drainage Report for the Northfield
Commons, an amendment to the “Final Drainage Report for Northfield” prepared by Highland
Development Services, dated February 26, 2020. This report describes the drainage design
intent to be in accordance with the criteria in the City of Fort Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely,
Jason T. Claeys, P.E., LEED AP Dan T. Egger, EI
Highland Development Services
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. i
Engineer’s Certification Block ..........................................................................................................ii
General Description and Location .................................................................................................. 1
Site Description and Location ...................................................................................................... 1
Site Soils ....................................................................................................................................... 1
Previous Studies .......................................................................................................................... 2
Storm Drainage Criteria .................................................................................................................. 3
Hydrologic Criteria ....................................................................................................................... 3
Hydraulic Criteria ......................................................................................................................... 3
Drainage Basins ............................................................................................................................... 4
Drainage Facility Design .................................................................................................................. 5
Drainage Conveyance Design ...................................................................................................... 5
Detention/Water Quality Pond Design ....................................................................................... 5
Low Impact Development ............................................................................................................... 6
Stormwater Pollution Prevention ................................................................................................... 8
Conclusions ..................................................................................................................................... 9
References .................................................................................................................................... 10
Appendix ....................................................................................................................................... 11
Appendix A – Site Descriptions, Characteristics, & References .................................................. A
Appendix B – Rational Calculations ............................................................................................. B
Appendix C – Low Impact Development Calculations ................................................................. C
Page ii
ENGINEER’S CERTIFICATION BLOCK
I hereby certify that this Preliminary Drainage Report for Northfield Commons was prepared by
me (or under my direct supervision) for the owners thereof and meets or exceeds the criteria of
the City of Fort Collins Stormwater Design Standards.
________________________________________
Jason T. Claeys, PE
Registered Professional Engineer
State of Colorado No. 42122
Page 1
GENERAL DESCRIPTION AND LOCATION
SITE DESCRIPTION AND LOCATION
Northfield Commons (NFC) is located in the Southeast Quarter of Section 1, Township 7 North,
Range 69 West of the Sixth Principal Meridian, City of Fort Collins, County of Larimer, within the
State of Colorado. NFC is located west of the Alta Vista Subdivision, north of the Rocky
Mountain Raptor Center, south of the proposed Suniga Road, and southeast of the Lake Canal
irrigation ditch. More specifically, NFC is located within the replat of Tracts U & V of Northfield,
with the areas of water quality and detention being provided for these proposed improvements
within Northfield Tract W.
The project site is approximately 6.45 acres and is currently undeveloped agricultural land. The
site appears to be vegetated with grasses harvested for livestock feed. The site generally slopes
from the northwest to the southeast at about 0.5% slope. This area is part of the approved
improvements associated with Northfield and the improvements described within are
considered an amendment to the approved plans and reports. The overall Northfield site is
currently under construction though there are no existing surface improvements currently on
the property.
The property is proposed to be replatted into a multi-family development. NFC will consist of 7
apartment buildings and 4 condominium buildings, along with the associated utility and access
infrastructure.
The NFC improvements are located within the FEMA Zone X, area of 0.2% annual chance of
flood hazard as shown on FEMA FIRM map numbers LOMR 19-08-0715P (effective June 15,
2020). The site is located within the Cache la Poudre River 500-yr floodplain. Critical facilities
are prohibited within the 100-yr and/or 500-yr floodplains. Critical facilities include facilities for
at-risk populations (daycares, schools, nursing homes, etc) and emergency service facilities
(urgent care, hospitals, fire stations, police stations, etc).
SITE SOILS
The NFC site consists of Loveland clay loam and Nunn clay loam and are classified as Type C
hydrologic group. According to USDA/Natural Resource Conservation Group, this soil has a slow
infiltration rate when thoroughly wet. These soils consist chiefly of soils having a layer that
impedes the downward movement of water or soils of moderately fine texture or fine texture.
These soils have a slow rate of water transmission.
Page 2
Per the “Preliminary Subsurface Exploration and Groundwater Report – Schlagel Property”,
prepared be Earth Engineering Consultants (EEC), dated August 16, 2017:
Vegetation growth and topsoil was encountered at the surface of each boring. Underlying the
topsoil/vegetation layer was a zone of cohesive subsoils classified lean to fat clay with varying
amounts of sand and clayey sand to approximate depths of 2 to 5-1/2 feet. Underlying the
cohesive subsoils was a granular layer of poorly to well graded sand with silt and gravel
extending to the depths explored at approximately 14 to 21-1/2 feet or to underlying bedrock.
It appears that below the lean to fat clay, there is a granular materials layer that would exhibit
more moderate infiltration rates than the surface materials.
Groundwater was also observed during the subsurface soil exploration:
Groundwater and/or the presence of a piezometric water surface, was generally observed at
depths ranging from approximately 3 to 7 feet below ground surface as indicated on the
enclosed boring logs.
A permanent dewatering system has been installed with the Northfield project and the
groundwater is anticipated to be maintained approximately 9 to 10 feet below the existing
grades.
Supporting figures can be found in Appendix A.
PREVIOUS STUDIES
The Northfield Subdivision originally included the Northfield Commons project site as part of
the drainage design. In the approved Northfield Utility Plans and Final Drainage Report, the NFC
site was broken into sub-basins and analyzed using rational calculations for inlet sizing and EPA
SWMM for pond and conveyance element sizing. These results, along with the LID calculations,
are referenced to provide confirmation that the proposed NFC improvements are within the
previously assumed improvements determined to size the stormwater infrastructure
accordingly. The inlets and storm drains in NFC will be sized to accommodate the proposed
improvements. Detention, water quality, and LID calculations will be updated as necessary.
Page 3
STORM DRAINAGE CRITERIA
This report was prepared to meet or exceed the City of Fort Collins storm water criteria. The
City of Fort Collin’s Stormwater Criteria Manual was referenced as guidelines for this design.
HYDROLOGIC CRITERIA
The rational method was performed to calculate the peak runoff rates for each basin. Percent
imperviousness and runoff coefficients were calculated for each basin using the surface
characteristics of each basin. The time of concentration was calculated using City of Fort Collins
initial time of concentration and the intensity was calculated using the corresponding storm
rainfall depth and the City of Fort Collins’ Intensity-Duration-Frequency Curve.
HYDRAULIC CRITERIA
The NFC storm drainage system has been analyzed to verify conformance with the drainage
system design of Northfield. The NFC system is to be designed to convey the minor and major
storm events through the combination of private drives, inlets, storm sewer pipes, and pans.
The NFC peak basin runoff flows from the rational calculations will be used to size area inlets
and confirm private drive capacities. For the purposes of this preliminary study, the rational and
attenuated rational calculations have been prepared to confirm the proposed improvements
are within, and not exceeding, the original assumptions of the Northfield Final Drainage Report.
The Northfield drainage design utilized EPA SWMM to model the captured flows and size
conveyance elements and detention ponds. It is assumed that the inlets are free of clogging
debris and capturing the maximum amount of runoff. The program accounts for head losses
within manholes and bends and head losses associated with pipe friction. The SWMM model
will be updated for the final report.
All pipe outlets are protected with buried riprap or suitable erosion protection methods. Storm
sewer pipe outlets are protected using the requirements set by the USDCM for the protection
downstream of culverts.
All supporting calculations for runoff rates, street sections, and inlets are located in the
Appendix.
Page 4
DRAINAGE BASINS
The Northfield Commons (NFC) project site is located within Northfield Drainage System D.
Drainage System D outfalls into the existing Northeast College Corridor Outfall (NECCO) storm
system. The descriptions within are an amendment to Northfield’s Drainage System D and
described below:
Drainage System D:
Drainage System D consists of 9.18 acres of improvements within the area south of Suniga
Road. Runoff from basins in the D system drain to an extended detention basin, Pond D.
Sub-basin D1 consist of 3.05 acres of apartment buildings, private drives, and open space.
Runoff is conveyed via roof downspouts, roadways, and concrete pans, and is captured by a
Type 13 and a Type C inlet, ultimately discharged to detention Pond D and treated for
standard water quality.
Sub-basins D2 thru D3 consist of 0.15 acres of public roadway. This basin includes portions
of Steeley Drive. Runoff from these basins is conveyed along roadways and is captured by
two on-grade 5’ Type R curb inlets, ultimately discharging to detention Pond D and treated
for standard water quality.
Sub-basin D4 consist of 0.24 acres of open space and concrete sidewalk. Runoff is conveyed
via sheet flow to area inlets and is ultimately discharged to detention Pond D and treated
for standard water quality.
Sub-basins D5 thru D8 consist of 3.15 acres of apartment buildings, condominiums, private
drives, and open space. Runoff from these basins is conveyed via roof downspouts,
roadways, concrete pans and storm pipes, ultimately discharging to LID facility, Rain Garden
D1.
Sub-basin D9 consists of 2.50 acres of open space encompassing detention Pond D. This
basin’s detention requirements allows a release rate equal to the current/historic runoff
rates and is accounted for in the Pond D detention volume calculations. An outlet structure
in Pond D has been designed as part of the Northfield subdivision to limit discharge into the
NECCO storm system as well as treat for standard water quality enhancement.
Page 5
DRAINAGE FACILITY DESIGN
DRAINAGE CONVEYANCE DESIGN
Storm infrastructure to convey runoff will include concrete trickle pans, inlets, storm sewer and
culverts. Stormwater detention and water quality enhancement will be achieved through the
use of Northfield Pond D and Northfield Rain Garden D1. Storm inlets, storm sewers and the
roadway culverts have been appropriately sized to convey the minor and major storms.
DETENTION/WATER QUALITY POND DESIGN
Below is an excerpt of the detention and water quality design from the “Final Drainage Report
for Northfield” prepared by Highland Development Services as it pertains to the amended
Northfield Commons development:
EPA SWMM 5.0 has been utilized for the final drainage design. UDFCD is referenced for the
standard water quality capture volume (WQCV) with a 40-hr drain time and the LID rain
gardens and infiltration galleries WQCV with a 12-hr drain time. Below is a brief summary of
the proposed design for each pond:
Pond D:
Extended detention basin for all area south of Suniga Road, with LID rain garden and
standard water quality treatment via the outlet structure located at the north center of the
pond. An 4-3/4” 100-yr orifice plate maximizes volume in the pond and restricts release
rate into the NECCO system. The rain garden includes a concrete forebay sized for 1% of
the surface area for WQCV with a rock embankment to dissipate flows before entering the
media material. Large storm events in excess of the rain garden capacity will spill over a
turf mat reinforced berm and down into Pond D. The 100-yr water surface elevation is
4949.54 feet, with a maximum depth in the pond of 3.92 feet, with another 1.46 feet of
additional volume available. Should the pond outlet become clogged, overtopping will occur
along the east side near design point D15, spilling over the sidewalk across a length of 120
feet at a depth of 0.32 feet (spill elevation = 4951.75), into Lemay Ave public ROW.
As stated, the ultimate outfall for the Northfield site is the existing NECCO storm drain
system. A portion of the area south of Suniga Road (delineated as sub-basins D13-D15) is
allowed to release at a rate equal to current undeveloped/historic rates with the remaining
area (delineated as sub-basins D1-D12) restricted to the 0.2 cfs/acre rate.
Page 6
LOW IMPACT DEVELOPMENT
The City of Fort Collins updated the Low Impact Development ordinance in 2016 (Ordinance No.
007, 2016) to require:
· Treat at least 75% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques, or
· Treat at least 50% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques when 25% of private driveable surfaces are permeable.
To satisfy the required implementation of Low Impact Development (LID) techniques,
Northfield Commons will utilize bioretention ponds/Rain Garden D1 that was previously
designed as part of the Northfield subdivision.
Impervious calculations for the tributary areas to the rain garden and standard water quality
facility have been updated for the amended site layout. LID treatment requirements for the
entire Northfield subdivision are still exceeded, achieving approximately 104% of the required
impervious area treatment in the rain gardens and infiltration galleries. The water quality
capture volumes for both the rain garden and pond are less than the Northfield design and
therefore will not require redesign.
Below is a description of the 4-step process for selecting structural BMPs:
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for
receiving water protection that focuses on reducing runoff volumes, treating the water quality
capture volume (WQCV), stabilizing drainageways and implementing long-term source controls.
The Four Step Process applies to the management of smaller, frequently occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low
Impact Development (LID) strategies, including Minimizing Directly Connected Impervious
Areas (MDCIA).
Captured runoff from strategic areas are routed through below grade infiltration galleries and
bioretention pond/rain gardens. Infiltration galleries and rain gardens will slow runoff, promote
infiltration, and filter runoff prior to being released into the adjacent storm drain system.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release
Page 7
The infiltration galleries and rain gardens are designed to provide water quality capture volume
per Urban Drainage’s recommendations and calculations. The captured runoff is designed for a
12-hr drain time.
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site will
drain to an existing storm system, bank stabilization is unnecessary with this project. Riprap
and turf reinforcement mats are utilized throughout for onsite permanent stabilization.
Step 4: Implement Site Specific and Other Source Control BMPs
The proposed project will improve upon site specific source controls compared to historic
conditions by providing localized trash enclosures within the development for disposal of solid
waste; Snouts, infiltration galleries, and rain gardens for water treatment prior to flows
entering storm systems; and additional water quality measures to protect and prolong the
design life of BMPS delineated in Step 1.
Page 8
STORMWATER POLLUTION PREVENTION
Erosion and sedimentation will be controlled on-site by use of sediment control logs, silt
fencing, inlet protection, gravel construction entrances, temporary sediment basins, seeding,
mulch, and turf. The measures are designed to limit the overall sediment yield increase due to
construction as required by the City of Fort Collins. During overlot and final grading the soil will
be roughened and furrowed perpendicular to the prevailing winds.
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the
contractor shall furnish all labor, equipment, materials, and means required. The Contractor
shall carry out proper efficient measures wherever and as necessary to reduce dust nuisance,
and to prevent dust nuisance that has originated from his operations from damaging crops,
orchards, cultivated fields, and dwellings, or causing naissance to persons. The Contractor will
be held liable for any damage resulting from dust originating from his operations under these
specifications on right-of-way or elsewhere.
It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights-of-
way. Wherever construction vehicles access routes or intersect paved public roads, previsions
must be made to minimize the transport of sediment by runoff or vehicles tracking onto the
paved surface. Stabilized construction entrances are required with base material consisting of
6” coarse aggregate. The contractor will be responsible for clearing mud tracked onto city
streets on a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Silt fence and
sediment control logs will require periodic replacement. Maintenance is the responsibility of
the contractor.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation
shall not be considered established until a ground cover is achieved which is demonstrated to
be mature enough to control soil erosion to the satisfaction of the City Inspector and to survive
severe weather condition.
Page 9
CONCLUSIONS
This Preliminary Drainage Report for Northfield Commons has been prepared to comply with
the stormwater criteria set by the City of Fort Collins. The proposed drainage system presented
in this report adheres to the overall Northfield subdivision design. The system conveys the
developed peak storm water runoff through the site to the existing storm drain system and to
the development’s LID features, detention and water quality facilities. The peak flows for the
amended design are less than the original design (Exhibit B02) and therefore no updated design
is required for the street capacities and inlet sizing. This drainage report anticipates the
implementation of best management practices for erosion control, temporary and permanent,
and on-site construction facilities.
It can therefore be concluded that development of Northfield Commons complies with the
storm water jurisdictional criteria and will not adversely affect the adjacent properties, streets,
storm drain system and/or detention/water quality facilities. Controlling the developed runoff
from these improvements will improve the situations currently existing on the site.
Page 10
REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, June 2001, Revised January 2016.
2. Fort Collins Stormwater Criteria Manual, Fort Collins Utilities, City of Fort Collins,
Colorado, Dated December 2018, Adopted January 2019.
3. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural Resources
Conservation Service, National Cooperative Soil Survey. Web Soil Survey URL:
http://websoilsurvey.nrcs.usda.gov. [12/06/2017]
4. “Preliminary Subsurface Exploration and Groundwater Report – Schlagel Property”,
prepared by Earth Engineering Consultants, LLC, Dated August 16, 2017
5. “Flood Insurance Rate Map, Larimer County, Colorado – LOMR 19-08-0751P”, Federal
Emergency Management Agency, Map Revised June 15, 2020.
6. “Final Drainage Report for Northfield”, prepared by Highland Development Services,
Dated February 26, 2020.
Page 11
APPENDIX
Appendix A – Site Descriptions, Characteristics, & References
Appendix B – Rational Calculations
Appendix C – Low Impact Development Calculations
Appendix A
APPENDIX A – SITE DESCRIPTIONS, CHARACTERISTICS, & REFERENCES
SITE
Vicinity Map
Scale: 1" = 1000'
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK #43-97
ON THE SOUTH END OF THE WEST HEADWALL OF THE LAKE CANAL BRIDGE AT NORTH LEMAY AVENUE, 200 FEET SOUTH OF
THE INTERSECTION OF LEMAY AVENUE AND CONIFER STREET
ELEV= 4960.11
CITY OF FORT COLLINS BENCHMARK #12-07
SOUTH SIDE OF VINE DRIVE ON THE SOUTH HEADWALL OF THE BRIDGE OVER DRY CREEK BASIN 0.4 MILES EAST OF NORTH
LEMAY AVENUE
ELEV= 4947.86
BASIS OF BEARINGS:
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS HAVE USED
NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) FOR THEIR VERTICAL DATUMS.
IF NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) IS REQUIRED FOR ANY PURPOSE,
THE FOLLOWING EQUATIONS SHOULD BE USED:
NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) = 4960.11 (NAVD88 DATUM) - 3.17'
NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) = 4947.86 (NAVD88 DATUM) - 3.18'
N
W E
S
NORTHFIELD COMMONS
Hydrologic Soil Group—Larimer County Area, Colorado
(NorthField)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
12/6/2017
Page 1 of 444941304494220449431044944004494490449458044946704494130449422044943104494400449449044945804494670494350494440494530494620494710494800494890494980495070495160
494350 494440 494530 494620 494710 494800 494890 494980 495070 495160
40° 36' 11'' N 105° 4' 2'' W40° 36' 11'' N105° 3' 23'' W40° 35' 52'' N
105° 4' 2'' W40° 35' 52'' N
105° 3' 23'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 200 400 800 1200
Feet
0 50 100 200 300
Meters
Map Scale: 1:4,140 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 12, Oct 10, 2017
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Mar 20, 2015—Oct
15, 2016
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(NorthField)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
12/6/2017
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
64 Loveland clay loam, 0 to
1 percent slopes
C 11.9 20.9%
73 Nunn clay loam, 0 to 1
percent slopes
C 16.6 29.2%
76 Nunn clay loam, wet, 1
to 3 percent slopes
C 28.3 49.9%
Totals for Area of Interest 56.7 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Hydrologic Soil Group—Larimer County Area, Colorado NorthField
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
12/6/2017
Page 3 of 4
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado NorthField
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
12/6/2017
Page 4 of 4
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 4/23/2021 at 10:39 AM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
105°4'9"W 40°36'2"N
105°3'32"W 40°35'35"N
Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
3.0 Rational Method
3.4 Intensity-Duration-Frequency Curves for Rational Method
Page 8
Table 3.4-1. IDF Table for Rational Method
Duration
(min)
Intensity
2-year
(in/hr)
Intensity
10-year
(in/hr)
Intensity
100-year
(in/hr)
Duration
(min)
Intensity
2-year
(in/hr)
Intensity
10-year
(in/hr)
Intensity
100-year
(in/hr)
5 2.85 4.87 9.95
39 1.09 1.86 3.8
6 2.67 4.56 9.31
40 1.07 1.83 3.74
7 2.52 4.31 8.80
41 1.05 1.80 3.68
8 2.40 4.10 8.38
42 1.04 1.77 3.62
9 2.30 3.93 8.03
43 1.02 1.74 3.56
10 2.21 3.78 7.72
44 1.01 1.72 3.51
11 2.13 3.63 7.42
45 0.99 1.69 3.46
12 2.05 3.50 7.16
46 0.98 1.67 3.41
13 1.98 3.39 6.92
47 0.96 1.64 3.36
14 1.92 3.29 6.71
48 0.95 1.62 3.31
15 1.87 3.19 6.52
49 0.94 1.6 3.27
16 1.81 3.08 6.30
50 0.92 1.58 3.23
17 1.75 2.99 6.10
51 0.91 1.56 3.18
18 1.70 2.90 5.92
52 0.9 1.54 3.14
19 1.65 2.82 5.75
53 0.89 1.52 3.10
20 1.61 2.74 5.60
54 0.88 1.50 3.07
21 1.56 2.67 5.46
55 0.87 1.48 3.03
22 1.53 2.61 5.32
56 0.86 1.47 2.99
23 1.49 2.55 5.20
57 0.85 1.45 2.96
24 1.46 2.49 5.09
58 0.84 1.43 2.92
25 1.43 2.44 4.98
59 0.83 1.42 2.89
26 1.4 2.39 4.87
60 0.82 1.4 2.86
27 1.37 2.34 4.78
65 0.78 1.32 2.71
28 1.34 2.29 4.69
70 0.73 1.25 2.59
29 1.32 2.25 4.60
75 0.70 1.19 2.48
30 1.30 2.21 4.52
80 0.66 1.14 2.38
31 1.27 2.16 4.42
85 0.64 1.09 2.29
32 1.24 2.12 4.33
90 0.61 1.05 2.21
33 1.22 2.08 4.24
95 0.58 1.01 2.13
34 1.19 2.04 4.16
100 0.56 0.97 2.06
35 1.17 2.00 4.08
105 0.54 0.94 2.00
36 1.15 1.96 4.01
110 0.52 0.91 1.94
37 1.16 1.93 3.93
115 0.51 0.88 1.88
38 1.11 1.89 3.87
120 0.49 0.86 1.84
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
3.0 Rational Method
3.4 Intensity-Duration-Frequency Curves for Rational Method
Page 9
Figure 3.4-1. Rainfall IDF Curve – Fort Collins
Figure 2. Depth to groundwater over time at Northfield monitoring points (in feet).
Date MW-1 MW-2 PZ-1 PZ-2 PZ-3 PZ-4 PZ-5 PZ-6 PZ-7
7/27/2017 3.8 5.3 4.7 4.6 5.1 5.0 6.0 6.8 7.2
9/19/2017 4.0 5.7 5.2 4.7 5.8 5.3 7.0 6.7 7.3
10/19/2017 4.0 5.6 5.0 4.6 5.9 5.1 7.1 6.6 7.3
2/12/2018 5.7 7.0 6.8 6.2 7.5 6.5 8.8 8.0 8.9
6/7/2018 3.7 5.2 4.4 4.6 4.4 5.3 5.1 7.2 7.0
2/15/2019 6.5 7.4 7.6 7.3 9.7
6/6/2019 3.8 5.5 4.5 4.4 5.3 6.9 7.5
0
1
2
3
4
5
6
7
8
9
10
6/1/2017 8/31/2017 11/30/2017 3/1/2018 6/1/2018 8/31/2018 11/30/2018 3/2/2019 6/1/2019 8/31/2019 Depth to Water (feet) Date
MW-1
MW-2
PZ-1
PZ-2
PZ-3
PZ-4
PZ-5
PZ-6
PZ-7
6/25/2019 Miller Groundwater Engineering, LLC
C2-10C100tc2 yr (min)tc100-yr (min)I2(in/hr)I100(in/hr)Q2(cfs)Q100(cfs)DESIGN POINTRunoff CoefficientTime of ConcentrationRainfaill IntensityAREA (acres)TRIBUTARY SUB-BASINPeak RunoffB7B7 0.27 0.81 1.00 5.00 5.00 2.85 9.95 0.62 2.64B8B8 0.40 0.78 0.98 5.27 5.00 2.74 9.95 0.86 3.90B9B9 2.29 0.81 1.00 5.00 13.07 1.87 6.90 1.93 8.89B10B10 0.48 0.66 0.82 5.00 5.00 2.85 9.95 0.90 3.91B11B11 2.47 0.73 0.91 11.21 8.85 2.11 8.09 3.82 18.29B12B12 0.41 0.26 0.33 6.00 5.57 2.64 9.40 0.28 1.27B13B13 0.38 0.87 1.00 5.00 5.00 2.85 9.95 0.95 3.81B14B14 0.36 0.86 1.00 5.00 5.00 2.85 9.95 0.88 3.59B15B15 0.89 0.80 1.00 6.29 5.67 2.60 9.36 1.86 8.31B16B16 0.54 0.91 1.00 5.00 5.00 2.85 9.95 1.41 5.38B17B17 0.35 0.79 0.99 5.40 5.00 2.72 9.95 0.76 3.48B18B18 0.43 0.67 0.84 8.49 6.56 2.36 8.96 0.68 3.24B19B19 0.43 0.69 0.87 8.25 6.26 2.38 9.09 0.71 3.38B20B20 2.94 0.34 0.43 21.24 19.62 1.56 5.67 1.57 7.12B Total 19.4828.44 126.55C1C1 1.30 0.45 0.56 14.81 10.70 2.05 7.52 1.41 6.48C2C2 0.14 0.53 0.67 12.07 5.00 2.85 9.95 0.10 0.42C3C3 0.83 0.25 0.31 5.00 6.12 2.38 9.15 1.39 6.66C4C4 0.22 0.70 0.88 8.23 5.00 2.85 9.95 0.47 2.07C5C5 1.20 0.77 0.96 5.00 10.27 2.11 7.64 1.05 4.74C Total 3.684.42 20.37D1AD1A 0.70 0.57 0.71 7.86 6.93 2.41 8.80 0.70 3.18D1D1 0.73 0.42 0.52 6.39 5.00 2.59 9.95 1.40 6.75D2D2 0.65 0.42 0.52 7.94 5.00 2.77 9.95 1.57 6.50D3D3 0.45 0.25 0.31 5.00 6.81 2.42 8.85 0.61 2.81D4D4 0.16 0.61 0.76 8.39 5.00 2.85 9.95 0.33 1.42D5D5 0.43 0.87 1.00 5.07 6.88 2.36 8.82 0.61 2.85D6D6 0.10 0.70 0.87 5.00 5.00 2.59 9.95 0.20 0.94D7D7 0.09 0.73 0.92 6.38 5.00 2.85 9.95 0.21 0.87D8D8 0.72 0.63 0.78 11.58 5.00 2.69 9.95 1.67 7.15D9D9 0.61 0.83 1.00 5.00 9.99 2.09 7.72 0.79 3.67D10D10 0.16 0.65 0.81 11.91 5.00 2.68 9.95 0.28 1.30D11D11 0.88 0.89 1.00 5.83 10.39 2.06 7.61 1.17 5.42D12D12 0.76 0.86 1.00 5.61 5.04 2.66 9.67 1.80 7.3718-1000-00 Rational Calcs (FC).xlsx Page 18 of 19Highland Development ServicesAREA MATCHESPROPOSED BASIN D1AREA MATCHESPROPOSED BASIN D2-D3AREA MATCHESPROPOSED BASIN D5-D7NORTHFIELD RATIONAL CALCS SUMMARY SHEET
C2-10C100tc2 yr (min)tc100-yr (min)I2(in/hr)I100(in/hr)Q2(cfs)Q100(cfs)DESIGN POINTRunoff CoefficientTime of ConcentrationRainfaill IntensityAREA (acres)TRIBUTARY SUB-BASINPeak RunoffD13D13 0.28 0.67 0.83 5.72 5.00 2.85 9.95 0.24 1.06D14D14 2.50 0.31 0.39 5.00 13.75 1.89 6.75 1.33 5.90D15D15 0.44 0.72 0.89 14.39 5.53 2.61 9.42 0.84 3.80D Total 9.6513.75 60.99E1E1 0.48 0.28 0.35 14.39 5.11 2.56 9.63 1.01 4.62E2E2 0.66 0.82 1.00 6.61 5.33 2.53 9.52 1.43 6.32E3E3 1.55 0.85 1.00 6.88 13.92 1.92 6.71 2.50 10.42E4E4 1.95 0.84 1.00 13.92 15.22 1.75 6.43 2.50 11.50E5E5 0.58 0.73 0.91 17.04 6.38 2.40 9.03 1.16 5.28E6E6 0.56 0.83 1.00 8.05 6.18 2.42 9.12 1.13 5.15E7E7 0.75 0.83 1.00 7.87 6.94 2.34 8.80 1.31 6.19E8E8 0.60 0.75 0.93 8.67 7.42 2.28 8.61 0.97 4.58E9E9 0.39 0.71 0.89 9.31 5.15 2.85 9.95 0.91 3.58E10E10 0.24 0.81 1.00 5.00 5.00 3.82 13.32 0.80 3.24E Total 7.7913.74 60.88Overall 58.7087.03 387.81*NOTE - Flows represented above are to the design point and do not account for any excess flow from another basin. Please refer to the Inlet Summary Sheet for overflow.18-1000-00 Rational Calcs (FC).xlsx Page 19 of 19Highland Development ServicesAREA MATCHESPROPOSED BASIN D8AREA MATCHESPROPOSED BASIN D9
A11A12A14A15A18A3A4A6A9B1B10B11B12B17B18B19B2B20B3B4B6B8B9C1C2C3C4C5D13D14D3D4D5D6D7D1AD1OPA1OPA3OPA4OPB1OPB2OPB3OP-MHA4OP-MHA6OP-MHA7OP-MHB2OP-MHB5PA1PA10PA11PA12PA13PA14PA15PA16PA17PA2PA3PA4PA5PA6PA7PA8PB1PB10PB11PB12PB13PB14PB15PB16PB17PB18PB19PB2PB20PB3PB4PB5PB6PB7PB8PB9PC1PC2PC3PC4PC5PC6PC7PD5PD6PD7PD8PD11PD12PD13PE1PE2PA9PD9PD10PD1PD2PD3PD4OutB2OutA4OutA3OutB3OutB1OutD1OutC1OutA1IA1IA2IA3IA4IA5IA6IB1IB10IB11IB2IB3IB4IB5IB6IB7IB8IB9IC1IC2IC3IC4ID3ID4ID5ID6IE1IE2MHA1MHA2MHA3MHA5MHB1MHB3MHB4MHB6MHC1MHC2MHD2MHD4MHD5OA2OA3-Stage1OA3-Stage2OA4-Stage1OA4-Stage2OB1-Stage1OB1-Stage2OB2-Stage1OB2-Stage2OB3-Stage1OB3-Stage2OC1OD1MHD3ID1AID1ID2MHD1OA1-Stage1OA1-Stage2Out2Out1Out3MHB2MHA4MHB5MHA7MHA6VB3VB2VB1VA2VA1VC1VD1CoFC_100-yr03/11/2019 00:05:00SWMM 5.1Page 1A11A12A14A15A18A3A4A6A9B1B10B11B12B17B18B19B2B20B3B4B6B8B9C1C2C3C4C5D13D14D3D4D5D6D7D1AD1OPA1OPA3OPA4OPB1OPB2OPB3OP-MHA4OP-MHA6OP-MHA7OP-MHB2OP-MHB5PA1PA10PA11PA12PA13PA14PA15PA16PA17PA2PA3PA4PA5PA6PA7PA8PB1PB10PB11PB12PB13PB14PB15PB16PB17PB18PB19PB2PB20PB3PB4PB5PB6PB7PB8PB9PC1PC2PC3PC4PC5PC6PC7PD5PD6PD7PD8PD11PD12PD13PE1PE2PA9PD9PD10PD1PD2PD3PD4OutB2OutA4OutA3OutB3OutB1OutD1OutC1OutA1IA1IA2IA3IA4IA5IA6IB1IB10IB11IB2IB3IB4IB5IB6IB7IB8IB9IC1IC2IC3IC4ID3ID4ID5ID6IE1IE2MHA1MHA2MHA3MHA5MHB1MHB3MHB4MHB6MHC1MHC2MHD2MHD4MHD5OA2OA3-Stage1OA3-Stage2OA4-Stage1OA4-Stage2OB1-Stage1OB1-Stage2OB2-Stage1OB2-Stage2OB3-Stage1OB3-Stage2OC1OD1MHD3ID1AID1ID2MHD1OA1-Stage1OA1-Stage2Out2Out1Out3MHB2MHA4MHB5MHA7MHA6VB3VB2VB1VA2VA1VC1VD1CoFC_100-yrA11A14A15A18A3A4A6A9B1B10B11B12B17B18B19B2B20B3B4B6B8B9C1C2C3C4C5D14D3D4D5D6D7D1AD1A12D9D10D12E6E8OPA4OPA2OPA1OPB3OPB2OPB1OP-MHA4OP-IA03OP-IA01OP-MHB05OP-MHB01PA14PA07PA06PA05PA17PA03PA02PA01PA04PA13PA12PA15PA11PA10PA16PA09PB11PB15PB14PB13PB12PB04PB03PB02PB20PB18PB19PB10PB01PB109PB08PB07PB06PB16PB17PB05PC1PC2PC3PC4PC5PC6PC7PD5PD6PD7PD8PD11PD12PD13PE1PE2PA08PD9PD10PD1PD2PD3PD4PD14PD15PD16PD17OutB2OutA1OutA2OutB1OutD1OutC1OutA4OutB3IA07IA06IA08IA09IA04IA02IB06IB11IB12IB05IB04IB03IB09IB10IB08IB07IB13FESC01IC01IC03IC02ID04ID03ID02ID01IE02IE01MHA04MHA03MHA02MHA01MHB06MHB03MHB02MHB04FESC02MHC02MHD04MHD02MHD01OA3OA2-Stage1OA2-Stage2OA1-Stage1OA1-Stage2OB3-Stage1OB3-Stage2OB2-Stage1OB2-Stage2OB1-Stage1OB1-Stage2OC1OD1MHD03ID09ID08ID05MHD05OA4-Stage1OA4-Stage2IA05IA03IA01IB01IB02FESD06ID06FESD05MHD01AOut2Out1Out3VB3VB2VB1VA2VA1VC1VD1CoFC_100-yrPROPOSEDNORTHFIELDCOMMONS SITE
Northfield SWMM Output_2019-10-15.rpt FESD06 JUNCTION 9.23 9.23 0 00:40 0.107 0.107 -0.016 ID06 JUNCTION 1.21 10.28 0 00:40 0.0119 0.119 0.024 FESD05 JUNCTION 11.14 11.14 0 00:40 0.132 0.132 0.005 MHD01A JUNCTION 0.00 20.23 0 00:40 0 0.25 -0.004 Out2 OUTFALL 0.00 7.49 0 05:08 0 1.08 0.000 Out1 OUTFALL 0.00 4.55 0 00:31 0 0.613 0.000 Out3 OUTFALL 0.00 19.63 0 00:40 0 0.365 0.000 VB3 STORAGE 11.44 57.73 0 00:40 0.162 0.65 0.910 VB2 STORAGE 2.26 18.07 0 00:40 0.0223 0.11 0.015 VB1 STORAGE 6.57 48.96 0 00:36 0.146 1.24 0.240 VA2 STORAGE 19.99 49.73 0 00:40 0.238 0.52 0.082 VA1 STORAGE 8.84 49.86 0 00:40 0.162 1.15 4.181 VC1 STORAGE 5.30 20.73 0 00:40 0.0728 0.25 0.252 VD1 STORAGE 4.91 44.51 0 00:42 0.128 0.619 0.250 ********************** Node Surcharge Summary ********************** Surcharging occurs when water rises above the top of the highest conduit. --------------------------------------------------------------------- Max. Height Min. Depth Hours Above Crown Below Rim Node Type Surcharged Feet Feet --------------------------------------------------------------------- IA07 JUNCTION 1.17 3.186 0.374 IA06 JUNCTION 1.92 3.743 0.417 IA08 JUNCTION 1.09 4.173 0.027 IA09 JUNCTION 5.48 3.104 0.186 IA04 JUNCTION 5.53 3.299 4.381 IA02 JUNCTION 5.45 4.904 0.206 IB06 JUNCTION 5.47 3.325 0.345 IB11 JUNCTION 5.33 1.830 1.470 IB12 JUNCTION 5.25 1.498 1.152 IB05 JUNCTION 5.48 3.945 1.105 IB04 JUNCTION 5.48 3.411 1.229 IB03 JUNCTION 5.48 3.615 1.785 IB09 JUNCTION 5.47 3.462 0.048 IB10 JUNCTION 2.74 0.352 2.848 IB08 JUNCTION 3.90 4.295 0.695 IB07 JUNCTION 3.11 3.974 0.696 IC01 JUNCTION 1.17 0.131 2.669 IC02 JUNCTION 1.57 0.200 3.300 IE02 JUNCTION 0.12 0.241 3.459 IE01 JUNCTION 0.60 0.398 3.502 MHA04 JUNCTION 1.25 3.277 0.713 MHA03 JUNCTION 1.24 3.156 1.294 MHA02 JUNCTION 5.48 3.828 1.892 MHA01 JUNCTION 5.54 3.737 4.923 MHB06 JUNCTION 5.48 3.824 2.476 MHB03 JUNCTION 5.55 4.237 5.163 MHB02 JUNCTION 5.57 4.972 2.448 MHB04 JUNCTION 5.38 2.319 4.481 FESC02 JUNCTION 2.61 0.420 2.380Page 7PEAK FLOW FOR NORTHFIELDSUB-BASINS D1-D14NORTHFIELD EPA SWMM OUTPUT
REDWOOD STREETDRY CREEKLA
K
E
CA
NA
L
D
I
TC
H
FUTURE LEMAY AVENUEN. LEMAY AVENUECOLLAMER DRIVEPIONEER TRAIL ROADSTEELEY DRIVELANDMARK WAY
N. LEMAY AVENUE RAINGARDEND1SC
H
LAG
E
L
S
T
R
E
E
T
FUTURESUNIGAROADPOND B3POND A2POND A1POND B2POND CPOND B1POND DRAIN GARDEN B1E. SUNIGA ROADSUNIGA ROAD AREADETENTION / LANDSCAPE AREAPROPOSED SINGLE FAMILY AREAPROPOSED MULTI-FAMILY AREAAREA CONTRIBUTING TO LID TREATMENTLEGEND0100'20010050100SCALE: 1" = REVISIONNO.BY DATE
HIGHLAND
DEVELOPMENT SERVICES
6355 FAIRGROUNDS AVENUE, SUITE 100 | WINDSOR, CO 80550
PHONE: 970.674.7550 | FAX: 970.674.7568 | www.Highland-DS.comPREPARED BY OR UNDER THEDIRECT SUPERVISION OF:FOR AND ON BEHALF OF HIGHLANDDEVELOPMENT SERVICESREVIEW SETNOT FORCONSTRUCTIONOFSHEETDRAWN BYCHECKED BYDATESCALE (H)HDS PROJECT #SCALE (V)NORTHFIELD
LID & WQ TREATMENT AREAS EXHIBIT10/15/191" = 100'N/AKRBJTC18-1000-00----11NWESPROPOSED COMMERCIAL AREAAREA CONTRIBUTING TO EXTENDEDDETENTION BASIN WATER QUALITY TREATMENTAREA CONTRIBUTING TO SNOUT HOODWATER QUALITY TREATMENT
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Low Impact Development Summary
Sq-Ft Acres
Impervious Area
(sq-ft)
% of Impervious
Area Requiring
Treatment
Impervious Area
Requiring
Treatment
537,816 12.35 330,931 50% 165,465
1,189,400 27.30 794,336 75% 595,752
40,986 0.94 20,720 75% 15,540
304,148 6.98 248,720 0% N/A
445,251 10.22 0 0% N/A
2,517,600 57.80 1,394,707 - 776,757
LID
Facility
Contributing
Basins
Area Drainage
to LID
(sq-ft)
% Impervious
Impervious
Area Treated
(sq-ft)
WQCV12-hr
(watershed inches)
WQCV12-hr
(cu-ft)
Treatment
Method
A2 A1+…+A12 427,599 66.5% 302,122 0.21 7,414 Infiltration Gallery
B1 B13+…B17 110,074 79.3% 93,219 0.26 2,378 Rain Garden
B2 B10+…+B12 146,450 55.7% 86,485 0.18 2,173 Infiltration Gallery
B3 B1+…+B9 426,521 54.7% 251,577 0.18 6,243 Infiltration Gallery
D1 D8+…+D13 148,227 61.5% 98,626 0.19 2,384 Rain Garden
EDB Pond Contributing
Basins
Drainage Area
(sq-ft)
Drainage Area
(sq-ft)% Impervious WQCV40-hr
(watershed inches)
WQCV40-hr
(ac-ft)
Pond A A18 131,657 3.022 12.5% 0.08 0.024
Pond B B18+…+B20 165,673 3.803 22.5% 0.13 0.048
Pond C C1+…+C5 160,137 3.676 38.2% 0.18 0.064
Pond D D1+…+D7+D14 253,037 5.809 32.5% 0.16 0.092
776,757
832,029
107.1%
Area (sq-ft) Area (acres) Treatment Ratio
1,258,871 28.90 50.0%
710,504 16.31 28.2%
322,629 7.41 12.8%
126,940 2.91 5.0%
2,418,944 55.53 96.1%
98,790 2.27 3.9%
2,517,734 57.80
Total Area unable to be Treated
(Basins A13, A14, portion of A16, & A17)
Total Treated Area
Total Improvement Area
Water Quality Area Treatment Summary
Description
Total Area Treated by Snout (Lemay - Basins A15 & D15)
Standard Water Quality Areas
Total Area Treated by LID
Total Area Treated by EDB
Total Area Treated by Snout (Suniga)
Description
Single Family Area
Multifamily Area
Commercial Area
Suniga Road (no LID treatment)
Northfield
Low Impact Development
Total % Treatment
Development Area Breakdown
City of Fort Collins - Ordinance No. 007, 2016
- Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or
- Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are
permeable.
Total Impervious Area Treated (sq-ft)
Total Impervious Area Required for LID Treatment (sq-ft)
LID Treatment Summary
LID Treatment Areas
Detention / Landscape Areas (no LID treatment)
J.Claeys
Highland Development Services
18-1000-00
October 15, 2019
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Totals
Appendix B
APPENDIX B – RATIONAL CALCULATIONS
Design Engineer:Design Firm:Project Number:Date:POND D SUMMARY TABLENF Approved (D1-D14)NFC Proposed (D1-D9)NF ApprovedNFC ProposedNF ApprovedNFC ProposedPOND D 9.21 9.18 41.3% 37.9% 44.51 28.94Notes: 1. Northfield sub-basins D1-D14 correlate to Northfield Commons sub-basins D1-D9.2. Northfield Approved area and % Impervious taken from Northfield Rational Calcs, dated October 15, 2019. 3. Northfield Peak Runoff was obtained from the EPA SWMM model output in the "Final Drainage Report for Northfield" dated February 26, 2020.4. Northfield Commons Peak Runoff was obtained from Attenuated Flows spreadsheet included in this report.Northfield CommonsDEVELOPED PEAK RUNOFFArea (acres) % ImperviousD. EggerHighland Development Services21-1037-00April 21, 2021Peak Runoff (cfs)21-1037-00 Rational Calcs (FC).xlsx Page 5 of 6Highland Development Services
Design Engineer:Design Firm:Project Number:Date:%ImperviousRunoff Coefficient CReturn PeriodFrequency Adjustment Factor (Cf)100% 0.952-year to 10-year1.0090% 0.95 100-year 1.2590% 0.9540% 0.500% 0.25C2 to C10C100D1 137,252 3.151 30,572 29,347 8,661 0 68,67147.2% 0.60 0.75D2 3,228 0.074 3,228 0 0 0 0100.0% 0.95 1.00D3 3,219 0.074 3,219 0 0 0 0100.0% 0.95 1.00D4 10,255 0.235 0 0 2,007 0 8,24817.6% 0.39 0.48D5 35,323 0.811 959 13,174 1,044 0 20,14538.9% 0.55 0.69D6 6,832 0.157 517 2,669 0 0 3,64642.7% 0.58 0.72D7 83,097 1.908 40,019 17,887 762 0 24,42968.4% 0.74 0.93D8 11,992 0.275 0 0 1,007 0 10,9857.6% 0.31 0.39D9 108,741 2.496 0 0 4,743 0 103,9983.9% 0.28 0.35Overall 399,938 9.181 78,514 63,077 18,224 0 240,12337.9% 0.53 0.66Northfield CommonsDEVELOPED IMPERVIOUS AREA CALCULATIONDESIGN CRITERIA:Fort Collins Stormwater Criteria ManualBASINS:Highland Development ServicesD. Egger21-1037-00April 21, 2021Land UsePavedRoofWalksGravel/PaversLawns(Heavy, 2-7% Slope)Sub-basinDesignationAtotal(sq feet)Atotal(acres)Weighted % ImperviousCOMPOSITEApaved(sq feet)Aroof(sq feet)Awalk(sq feet)Agravel/pavers(sq feet)Alawn(sq feet)21-1037-00 Rational Calcs (FC).xlsxPage 1 of 6Highland Development Services
Design Engineer:Design Firm:Project Number:Date:City of Fort Collins Stormwater Criteria ManualOverland Flow Equations for City of Fort Collins Stormwater Criteria ManualEQUATIONS:-Equation 5-3-Equation 5-4-Urbanized Check Equation 3.3-5- CoFC Overland FlowCONSTRAINTS:300ft - Overland flow shall not exceed for developed condition500ft - Overland flow shall not exceed for undeveloped conditionFinal tc = minimum of ti + tt and urbanized basin checkrecommended minimum tc = 5 min for urbanized basinsTime of Concentration (2-yr to 10-yr) D1 D1 47.2% 0.60 3.151 101 0.0485 5.55 480 0.0064 0.10 0.016 1.61 4.98 10.54 581 13.2310.54D2 D2 100.0% 0.95 0.074 24 0.0195 1.10 89 0.0177 0.10 0.016 2.67 0.56 5.00 113 10.635.00D3 D3 100.0% 0.95 0.074 24 0.0208 1.08 89 0.0174 0.10 0.016 2.65 0.56 5.00 113 10.635.00D4 D4 17.6% 0.39 0.235 43 0.0418 5.43 263 0.0050 0.10 0.016 1.42 3.09 8.52 306 11.708.52D5 D5 38.9% 0.55 0.811 19 0.1021 2.06 575 0.0050 0.10 0.016 1.42 6.76 8.82 594 13.308.82D6 D6 42.7% 0.58 0.157 40 0.0200 4.92 132 0.0156 0.10 0.016 2.51 0.88 5.79 172 10.965.79D7 D7 68.4% 0.74 1.908 40 0.0248 3.11 735 0.0069 0.10 0.016 1.67 7.35 10.46 775 14.3110.46D8 D8 7.6% 0.31 0.275 15 0.0200 4.55 29 0.0050 0.10 0.016 1.42 0.34 5.00 44 10.245.00D9 D9 3.9% 0.28 2.496 37 0.0200 7.40 593 0.0050 0.10 0.016 1.426.97 14.36 630 13.5013.50April 21, 2021Northfield CommonsDEVELOPED TIME OF CONCENTRATIOND. Egger21-1037-00Highland Development ServicesLENGTH(ft)DESIGN CRITERIA:SUB-BASIN DATAINITIAL/OVERLAND TIME (ti)TRAVEL TIME (tt)tc=ti+tt(min)Urban CheckFinaltc(min)DESIGN POINTSub-basin%ImperviousC2-10AREA (acres)tt(min)OVERALL LENGTH(ft/ft)tc(min)SLOPE(ft/ft)ti(min)LENGTH(ft)SLOPE(ft/ft)VELOCITY(ft/s)HYDRAULIC RADIUS(ft)ROUGHNESS COEFFICIENTticttt+=VLtt60=1.871.1 10180+=LtcV.R2/3S 1/221-1037-00 Rational Calcs (FC).xlsxPage 2 of 6Highland Development Services
Design Engineer:Design Firm:Project Number:Date:City of Fort Collins Stormwater Criteria ManualOverland Flow Equations for City of Fort Collins Stormwater Criteria ManualEQUATIONS:-Equation 5-3-Equation 5-4-Urbanized Check Equation 3.3-5- CoFC Overland FlowCONSTRAINTS:300ft - Overland flow shall not exceed for developed condition500ft - Overland flow shall not exceed for undeveloped conditionFinal tc = minimum of ti + tt and urbanized basin checkrecommended minimum tc = 5 min for urbanized basinsTime of Concentration (100-yr) D1 D1 47.2% 0.75 3.151 101 0.0485 3.89 480 0.0064 0.10 0.016 1.61 4.98 8.87 581 13.238.87D2 D2 100.0% 1.00 0.074 24 0.0195 0.73 89 0.0177 0.10 0.016 2.67 0.56 5.00 113 10.635.00D3 D3 100.0% 1.00 0.074 24 0.0208 0.72 89 0.0174 0.10 0.016 2.65 0.56 5.00 113 10.635.00D4 D4 17.6% 0.48 0.235 43 0.0418 4.69 263 0.0050 0.10 0.016 1.42 3.09 7.78 306 11.707.78D5 D5 38.9% 0.69 0.811 19 0.1021 1.55 575 0.0050 0.10 0.016 1.42 6.76 8.30 594 13.308.30D6 D6 42.7% 0.72 0.157 40 0.0200 3.56 132 0.0156 0.10 0.016 2.51 0.88 5.00 172 10.965.00D7 D7 68.4% 0.93 1.908 40 0.0248 1.48 735 0.0069 0.10 0.016 1.67 7.35 8.83 775 14.318.83D8 D8 7.6% 0.39 0.275 15 0.0200 4.10 29 0.0050 0.10 0.016 1.42 0.34 5.00 44 10.245.00D9 D9 3.9% 0.35 2.496 37 0.0200 6.77 593 0.0050 0.10 0.016 1.426.97 13.73 630 13.5013.50April 21, 2021Northfield CommonsDEVELOPED TIME OF CONCENTRATIOND. Egger21-1037-00Highland Development ServicesLENGTH(ft)DESIGN CRITERIA:SUB-BASIN DATAINITIAL/OVERLAND TIME (ti)TRAVEL TIME (tt)tc=ti+tt(min)Urban CheckFinaltc(min)DESIGN POINTSub-basin%ImperviousC2-10AREA (acres)tt(min)OVERALL LENGTH(ft/ft)tc(min)SLOPE(ft/ft)ti(min)LENGTH(ft)SLOPE(ft/ft)VELOCITY(ft/s)HYDRAULIC RADIUS(ft)ROUGHNESS COEFFICIENTticttt+=VLtt60=1.871.1 VLtt60=10180+=LtcV.R2/3S 1/221-1037-00 Rational Calcs (FC).xlsxPage 3 of 6Highland Development Services
Design Engineer:Design Firm:Project Number:Date:EQUATIONS:Qn = n-yr peak discharge (cfs)Cn = n-yr runoff coefficientIn = n-yr rainfall intensity (in/hr) An = Basin drainage area (ac)tc (min)Runoff Coeff(C2-10)C(A) (acres)Intensity (in/hr)Q (ft3/s)tc (min)Runoff Coeff(C2-10)C(A) (acres)Intensity (in/hr)Q (ft3/s)tc (min)Runoff Coeff. (C100)C(A) (acres)Intensity (in/hr)Q (ft3/s)D1D1 3.151 10.54 0.60 1.89 2.174.1010.54 0.60 1.89 3.707.008.87 0.75 2.36 8.0819.09D2D2 0.074 5.00 0.95 0.07 2.850.205.00 0.95 0.07 4.870.345.00 1.00 0.07 9.950.74D3D3 0.074 5.00 0.95 0.07 2.850.205.00 0.95 0.07 4.870.345.00 1.00 0.07 9.950.74D4D4 0.235 8.52 0.39 0.09 2.350.218.52 0.39 0.09 4.020.377.78 0.48 0.11 8.470.96D5D5 0.811 8.82 0.55 0.45 2.321.048.82 0.55 0.45 3.971.778.30 0.69 0.56 8.284.62D6D6 0.157 5.79 0.58 0.09 2.670.245.79 0.58 0.09 4.550.415.00 0.72 0.11 9.951.12D7D7 1.908 10.46 0.74 1.42 2.173.0910.46 0.74 1.42 3.715.278.83 0.93 1.77 8.1014.37D8D8 0.275 5.00 0.31 0.09 2.850.245.00 0.31 0.09 4.870.415.00 0.39 0.11 9.951.06D9D9 2.496 13.50 0.28 0.70 1.951.3713.50 0.28 0.70 3.332.3313.50 0.35 0.88 6.805.9510-yr Peak Runoff100-yr Peak RunoffNorthfield CommonsDEVELOPED PEAK RUNOFFCity of Fort Collins Stormwater Criteria ManualDESIGN CRITERIA:Design PointSub-basin Area (acres)D. EggerHighland Development Services21-1037-00April 21, 20212-yr Peak RunoffnnnnAICQ=21-1037-00 Rational Calcs (FC).xlsxPage 4 of 6Highland Development Services
Northfield Commons
Attenuated Flows
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
EQUATIONS:
-Equation 5-3 -Equation 5-4
-CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition Final t c = minimum of t i + t t and urbanized basin check
500 ft - Overland flow shall not exceed for undeveloped condition recommended minimum t c = 5 min for urbanized basins
Qn = n -yr peak discharge (cfs)I = rainfall intensity (in/hr)
Cn = n -yr runoff coefficient P1 = one-hour point rainfall depth (in)
In = n -yr rainfall intensity (in/hr) tc = time of concentration (min)
A = drainage area (ac)P1-1/2 2yr =0.41 in.
P1-2yr =0.82 in.
P1-100yr =2.86 in.
BASINS:
DP/Manhole D9
Contributing Basins D1-D9
Contributing Area (acres)9.18
C2 C100
Runoff Coefficients 0.53 0.66
Overland Flow Time
Length (ft)101
Slope (%)4.85
2-yr 100-yr
ti
(min)6.33 4.86
Travel Time
Length (ft) Slope (%)
Hydraulic
Radius (ft)
Roughness
Coefficient Velocity (ft/s)tt (min)
480 0.64%0.10 0 1.61 4.98
67 3.80%0.10 0 3.91 0.29 pipe conveyance
799 0.34%0.10 0 1.17 11.38 pipe conveyance
124 0.22%0.10 0 0.94 2.20 pipe conveyance
154 4.25%0.10 0 4.14 0.62 pipe conveyance
227 0.50%0.10 0 1.42 2.67
Total Time 22.14
Final Time of Concentration - tc (min)
2-yr 100-yr
28.47 27.00
Intensities (in/hr)
1/2 2-yr 2-yr 100-yr
0.66 1.32 4.76
Discharge (cfs)
1/2 2-yr 2-yr 100-yr
3.22 6.44 28.94
D. Egger
Highland Development Services
21-1037-00
April 26, 2021
Fort Collins Stormwater Criteria Manual
( )
786.0
1
10
5.28
ct
PI
+
=AICQnnn=
ticttt+=
V
Ltt60
==
1.87 1.1 −
.
V=.R2/3 S 1/2
21-1037-00 Attenuated Flows.xlsx - D1-D9 1 of 1 JVA, Inc.
Appendix C
APPENDIX C – LOW IMPACT DEVELOPMENT CALCULATIONS
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Low Impact Development Summary
Sq-Ft Acres
Impervious Area
(sq-ft)
% of Impervious
Area Requiring
Treatment
Impervious Area
Requiring
Treatment
537,816 12.35 330,931 50% 165,465
1,189,400 27.30 794,336 75% 595,752
40,986 0.94 20,720 75% 15,540
304,148 6.98 248,720 0% N/A
445,251 10.22 0 0% N/A
2,517,600 57.80 1,394,707 - 776,757
LID
Facility
Contributing
Basins
Area Drainage
to LID
(sq-ft)
% Impervious
Impervious
Area Treated
(sq-ft)
WQCV12-hr
(watershed inches)
WQCV12-hr
(cu-ft)
Treatment
Method
A2 A1+…+A12 427,599 66.5% 302,122 0.21 7,414 Infiltration Gallery
B1 B13+…B17 110,074 79.3% 93,219 0.26 2,378 Rain Garden
B2 B10+…+B12 146,450 55.7% 86,485 0.18 2,173 Infiltration Gallery
B3 B1+…+B9 426,521 54.7% 251,577 0.18 6,243 Infiltration Gallery
D1 D5+...+D8 137,244 54.2% 78,037 0.17 1,995 Rain Garden
EDB Pond Contributing
Basins
Drainage Area
(sq-ft)
Drainage Area
(sq-ft)% Impervious WQCV40-hr
(watershed inches)
WQCV40-hr
(ac-ft)
Pond A A18 131,657 3.022 12.5% 0.08 0.024
Pond B B18+…+B20 165,673 3.803 22.5% 0.13 0.048
Pond C C1+…+C5 160,137 3.676 38.2% 0.18 0.064
Pond D D1+…+D4+D9 262,694 6.031 29.4% 0.15 0.090
776,757
811,440
104.5%
Area (sq-ft) Area (acres) Treatment Ratio
1,247,888 28.65 49.6%
720,162 16.53 28.6%
323,951 7.44 12.9%
126,940 2.91 5.0%
2,418,940 55.53 96.1%
98,790 2.27 3.9%
2,517,730 57.80
Northfield Commons
Low Impact Development
Total % Treatment
Development Area Breakdown
City of Fort Collins - Ordinance No. 007, 2016
- Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or
- Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are
permeable.
Total Impervious Area Treated (sq-ft)
Total Impervious Area Required for LID Treatment (sq-ft)
LID Treatment Summary
LID Treatment Areas
Detention / Landscape Areas (no LID treatment)
D. Egger
Highland Development Services
21-1037-00
April 27, 2021
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Totals
Standard Water Quality Areas
Total Area Treated by LID
Total Area Treated by EDB
Total Area Treated by Snout (Suniga)
Description
Single Family Area
Multifamily Area
Commercial Area
Suniga Road (no LID treatment)
Total Area unable to be Treated
(Basins A13, A14, portion of A16, & A17)
Total Treated Area
Total Improvement Area
Water Quality Area Treatment Summary
Description
Total Area Treated by Snout (Lemay - Basins A15 & D15)