HomeMy WebLinkAboutMAGNOLIA DWELLINGS - PDP200018 - - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
FOR
335 East Magnolia Street
Prepared by:
Highland Development Services
6355 Fairgrounds Ave, Suite 100
Windsor, Colorado 80550
Phone: 970.674.7550
Prepared for:
Forge + Bow Dwellings
116 N. College Ave
Fort Collins, CO 80524
February 19, 2021
Job Number 20-1021-00
Highland Development Services, Inc.
6355 Fairgrounds Avenue, Suite 100 | Windsor, CO 80550 | 970.674.7550
February 19, 2021
Mr. Dan Mogen
Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80522
RE: Preliminary Drainage Report for 335 East Magnolia Street
Dear Dan,
We are pleased to submit for your review, the Preliminary Drainage Report for the 335 East
Magnolia multi-family redevelopment project. This report describes the drainage design intent
to be in accordance with the City of Fort Collins Stormwater Criteria Manual.
We appreciate your time and consideration in reviewing this submittal. Please call if you have
any questions.
Sincerely,
Highland Development Services
Dan T. Egger, EI Jason T. Claeys, P.E., LEED AP
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. i
Engineer Certification ......................................................................................................................ii
General Description and Location .................................................................................................. 1
Site Description and Location ...................................................................................................... 1
Site Soils ....................................................................................................................................... 1
Storm Drainage Criteria .................................................................................................................. 3
Hydrologic Criteria ....................................................................................................................... 3
Hydraulic Criteria ......................................................................................................................... 3
Drainage Basins ............................................................................................................................... 4
Drainage Facility Design .................................................................................................................. 5
Drainage Conveyance 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 CERTIFICATION
I hereby certify that this report (plan) for the preliminary drainage design of 335 East Magnolia
Street was prepared by me (or under my direct supervision) in accordance with the provisions
of the City of Fort Collins Stormwater Criteria Manual and Construction of Public and Private
Improvements for the Responsible Parties thereof. I understand that the City of Fort Collins
does not and shall not assume liability for drainage facilities designed by others.
________________________________________
Jason T. Claeys, PE
Registered Professional Engineer
State of Colorado No. 42122
Page 1
GENERAL DESCRIPTION AND LOCATION
SITE DESCRIPTION AND LOCATION
335 E. Magnolia Street is located in the Southeast Quarter and Southwest Quarter of Section
12, Township 7 North, Range 69 West of the Sixth Principal Meridian, City of Fort Collins,
County of Larimer, within the State of Colorado. The property is the west half of Lot 1, Block
144 of the original Fort Collins plat, dated January 16, 1873. The site is bounded by private
residential lots to the west and east, the alleyway to the south, and Magnolia Street to the
north.
The project site totals approximately 0.22 acres and is currently a single-family residential lot.
The existing structures include a single-family residential home and a garden shed. The site is
located within the Old Town Drainage Basin, which provides standard water quality for the site.
The site generally slopes from the southwest to the northeast. A 2 ft tall retaining wall lies
approximately 50 ft north of the alley right-of-way and steps down from south to north. The
site grade south of the wall is approximately 3.5% and is approximately 2.0% north of the wall.
Storm runoff via overland flow is conveyed through the site to Magnolia Street. The existing site
is approximately 24.1% impervious. No wetlands are located within the area of proposed
development.
Offsite drainage is also conveyed through the existing site. Approximately 0.58 acres of offsite
drainage area is conveyed along the western property line. It is assumed that this offsite basin
is 25.3% impervious. It is anticipated that the proposed improvements will adequately convey
the offsite runoff to Magnolia Street as it has historically.
The project site is located within FEMA Zone X, Area of minimal flood hazard, per FEMA Flood
Insurance Rate Panel 08069C0979H, effective 5/2/2012. FEMA Firmette is included in Appendix
A.
The existing single-family building is proposed to be removed and the site redeveloped with a
four-unit, multi-family residential building. The proposed redevelopment also includes alley
improvements, a parking area with access from the alley, and associated pedestrian walkways.
Low impact development techniques are proposed to provide the stormwater quality
enhancement requirements.
SITE SOILS
The 335 E. Magnolia Street site consists primarily of Fort Collins loam and Satanta loam and are
classified as Type C hydrologic group, respectively. According to USDA/Natural Resource
Page 2
Conservation Group, Type C soils a have 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 also have a slow rate of water transmission.
Per the “Geotechnical Subsurface Exploration, Proposed Multi-Family Residence”, prepared by
Earth Engineering Company, Inc. dated May 19, 2020:
“Brown to reddish brown sandy lean clay soils were encountered at the surface at the boring
locations. The sandy lean clay soils encountered in the borings were medium stiff to very stiff in
consistency and exhibited a low potential for swelling with variation in moisture content at
current moisture/density conditions. The moderately plastic sandy lean clay soils were
underlain by brown sand and gravel materials at a depth of approximately 12 and 16 feet below
present site grades at borings B-1 and B-2, respectively. The essentially granular materials were
very dense in consistency, contained cobbles and extended to the bottom of the borings at a
depth of approximately 20 and 25½ feet below present site grades.”
Groundwater was also observed during the subsurface soil exploration:
“At the time of drilling, free water was observed at a depth of approximately 16 and 19 feet
below present site grades in the borings completed on this property. Approximately 48 hours
after drilling, free water was observed at a depth of approximately 14½ and 18 feet below
present site grades at borings B-1 and B-2, respectively.”
Page 3
STORM DRAINAGE CRITERIA
This final drainage report was prepared to meet or exceed the City of Fort Collins Stormwater
Criteria Manual. The Criteria Manual and amendments to the Urban Drainage Flood Control
District’s (UDFCD) Drainage Criteria Manual (USDCM) Volumes 1, 2 and 3 were 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 final storm drainage system will be designed to convey the minor and major storm events
through the combination of storm sewer pipes and drain pans/channels. The Autodesk
Hydraflow will be used to analyze the drainage system on the site.
Page 4
DRAINAGE BASINS
The 335 East Magnolia Street developed drainage basins are delineated by areas draining
through the site. The site is broken into 3 main drainage systems:
Drainage Basin D1:
Drainage Basin D1 pertains to the improvements on the site, which has an approximate area of
0.18 acres and is approximately 69.9% impervious. The improvements include the entire
condominium building and the sidewalk on the east side of the building, as well as the parking
lot and bike shed.
Drainage Basin D2:
Drainage Basin D2 pertains to the improvements on the site, which has an approximate area of
0.04 acres and is approximately 28.9% impervious. This area consists of the landscaping and
sidewalk on the west side of the proposed building that drains to the proposed channel on the
west property line.
Drainage Basin OS1:
Drainage Basin OS1 pertains to the existing drainage that flows through the site from the lot to
the west and the lots to the south that currently drain across the alleyway and onto the site.
This drainage system has an approximate area of 0.58 acres and is approximately 25.3%
impervious.
Page 5
DRAINAGE FACILITY DESIGN
DRAINAGE CONVEYANCE DESIGN
Storm infrastructure to convey runoff will include drain pans/channels and storm sewer pipes.
Stormwater detention is not required for the site because the increase to impervious area on
the site is less than 5,000 square feet. Water quality treatment for 50% of the site is provided
by the Udall Natural Area water treatment facility. The remaining treatment must be provided
by Low Impact Development (LID) methods.
Drainage Basin D1:
Drainage Basin D1 pertains to the improvements on the site, which has an approximate area of
0.18 acres. The proposed improvements will utilize a system of roof drains, area inlets, and
storm drains to convey drainage to the proposed LID facility and then outlet to an existing 12”
clay storm pipe in Magnolia Street.
Drainage Basin D2:
Drainage Basin D2 pertains to the improvements on the site, which has an approximate area of
0.04 acres. This system will intercept drainage from the western portion of the proposed lot.
The area consists of landscaping and a sidewalk and is not able to be conveyed to the
Stormtech chambers. Instead, drainage will sheet flow to the proposed concrete channel that
runs the entire length of the western property line and drains into Magnolia Street.
Drainage Basin OS1:
Drainage Basin OS1 pertains to the existing drainage that flows through the site. This system
will intercept drainage from the lot to the west and the lots to the south that currently drain
across the alleyway and onto the site. The proposed improvements will include a concrete
channel that runs the entire length of the western property line and drains into Magnolia
Street.
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, below
grade filtration chambers (such as ADS StormTech chamber system) are proposed to be utilized.
The chambers will treat approximately 82.5% of the total site area. For the purposes of water
quality, all chambers will be isolator rows with filter fabric placed along the bottom of all the
chambers. Other LID techniques were explored, but due to the limited space available on-site
filtration chambers were the most feasible means for additional water quality enhancement.
Pavers within the parking area did not treat enough contributing area to justify their use. It is
anticipated that the filtration chambers will include an impermeable liner due to the proximity
to the proposed and neighboring structures. Sediment will be captured within the chambers
prior to the runoff being released. The chambers will be accessible to remove sediments.
Standard water quality is provided regionally off site. A Standard Operations Procedure will be
provided at final design to assist in ensuring that these BMPs will adequately perform over
time.
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).
Page 7
Captured runoff from strategic areas are routed through below grade filtration chambers.
Filtration chambers will slow 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
The filtration chambers 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.
Step 4: Implement Site Specific and Other Source Control BMPs
Proactively controlling pollutants at their source by preventing pollution rather than removing
contaminants once they have entered the stormwater system or receiving waters is important
when protecting storm systems and receiving waters. This can be accomplished through site
specific needs such as construction site runoff control, post-construction runoff control and
pollution prevention / good housekeeping. It will be the responsibility of the contractor to
develop a procedural best management practice for the site.
All calculations are attached for reference.
Page 8
STORMWATER POLLUTION PREVENTION
Erosion and sedimentation will be controlled on-site by use of sediment control logs, inlet
protection, and a gravel construction entrance. 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 nuisance 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 public 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 public 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. 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 Town Inspector and to
survive severe weather condition.
Page 9
CONCLUSIONS
This Preliminary Drainage Report for 335 East Magnolia Street has been prepared to comply
with the stormwater criteria set by the City of Fort Collins. The proposed drainage system will
be designed to convey the developed peak storm water runoff through the site to the existing
storm system. Drainage conveyance systems will be designed to convey drainage to existing
roadways and collect onsite drainage and treat it in accordance with LID before discharging it
into the existing storm drain system. Additionally, the drainage system will improve existing
offsite conditions and protect the proposed building and neighboring lots by establishing
conveyance to Magnolia Street and Peterson Street. This preliminary 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 335 East Magnolia Street will comply with
the storm water jurisdictional criteria and the approved City of Fort Collins Stormwater Criteria
Manual and will not adversely affect the adjacent properties, streets, storm drain system
and/or detention/water quality facilities.
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. [9/28/2020]
4. “Geotechnical Subsurface Exploration, Proposed Multi-Family Residence 335 East
Magnolia Street”, prepared by Earth Engineering Consultants, LLC, Dated May 19, 2020
5. “Flood Insurance Rate Map, Larimer County, Colorado – Map Number 08069C0979H”,
Federal Emergency Management Agency, Map Revised May 2, 2012.
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
PROJECT SITE
PETERSON STREETE. MAGNOLIA STREET
E. MULBERRY STREET WHEDBEE STREETMATHEWS STREETREMINGTON STREETOLIVE STREET
Vicinity Map
Scale: 1" = 250'
PROJECT DATUM: NAVD 88
CITY OF FORT COLLINS BENCHMARK NO. 29-97:
NORTHEAST CORNER OF MULBERRY ST. AND WHEDBEE ST., ON A CONCRETE TRAFFIC SIGNAL BASE
ELEV = 4978.01
CITY OF FORT COLLINS BENCHMARK NO. 6-00:
ON A CATCH BASIN AT THE NORTHWEST CORNER OF MULBERRY ST. AND COLLEGE AVE.
ELEV = 4993.85
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS HAVE USED
NGVD29 UNADJUSTED DATUM (PRIOR TO CITY OF FORT COLLINS DATUM) FOR THEIR VERTICAL DATUMS.
IF NGVD 29 UNADJUSTED (PRIOR TO CITY OF FORT COLLINS DATUM) IS REQUIRED FOR ANY PURPOSE, THE FOLLOWING
EQUATIONS SHOULD BE USED:
NGVD29 UNADJUSTED (PRIOR TO CITY OF FORT COLLINS DATUM) = 4978.01 (NAVD88 DATUM) - 3.18
NGVD29 UNADJUSTED (PRIOR TO CITY OF FORT COLLINS DATUM) = 4993.85 (NAVD88 DATUM) - 3.17
N
W E
S
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/28/2020
Page 1 of 44492380449239044924004492410449242044924304492440449245044923804492390449240044924104492420449243044924404492450493850493860493870493880493890493900
493850 493860 493870 493880 493890 493900
40° 34' 58'' N 105° 4' 21'' W40° 34' 58'' N105° 4' 19'' W40° 34' 55'' N
105° 4' 21'' W40° 34' 55'' N
105° 4' 19'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 15 30 60 90
Feet
0 5 10 20 30
Meters
Map Scale: 1:390 if printed on A portrait (8.5" x 11") 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 15, Jun 9, 2020
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 11, 2018—Aug
12, 2018
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/28/2020
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
35 Fort Collins loam, 0 to 3
percent slopes
C 0.2 74.9%
94 Satanta loam, 0 to 1
percent slopes
C 0.1 25.1%
Totals for Area of Interest 0.2 100.0%
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.
Rating Options
Aggregation Method: Dominant Condition
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/28/2020
Page 3 of 4
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/28/2020
Page 4 of 4
USGS The National Map: Orthoimagery. Data refreshed April 2020
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 10/14/2020 at 11:26 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°4'39"W 40°35'11"N
105°4'2"W 40°34'44"N
PROJECT SITE
E. MULBERRY ST.
E. MAGNOLIA ST.PETERSON ST.
Appendix B
APPENDIX B – RATIONAL CALCULATIONS
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year 1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
0% 0.25
C2 to C10 C100
H1 9,492 0.218 0 1,376 321 1,911 5,884 24.1% 0.43 0.53
OS1 25,058 0.575 0 3,350 0 8,333 13,375 25.3% 0.43 0.53
D1 7,827 0.180 2,035 3,113 703 0 1,976 69.9% 0.77 0.97
D2 1,668 0.038 0 535 0 0 1,133 28.9% 0.47 0.59
D total 9,495 0.218 0 3,648 703 0 5,144 41.2% 0.57 0.71
COMPOSITEApaved
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
Agravel/pavers
(sq feet)
Alawn
(sq feet)
Lawns
(Heavy, 2-7% Slope)
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
Weighted %
Impervious
Paved
Roof
Walks
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Gravel/Pavers
% Impervious values from Table 3.2.2 in the Fort Collins Stormwater Criteria Manual
D.Egger
20-1021-00
February 18, 2021
Land Use
335 E. Magnolia Street
DEVELOPED IMPERVIOUS AREA CALCULATION
DESIGN CRITERIA:
Fort Collins Stormwater Criteria Manual
BASINS:
Highland Development Services
20-1021-00 Rational Calcs (2021-02-17).xlsx Page 1 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 5-3 -Equation 5-4 -Urbanized Check Equation 3.3-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (2-yr to 10-yr)
H1 H1 24.1% 0.43 0.218 74 0.0340 7.22 136 0.0200 0.14 0.025 2.27 1.00 8.21 210 11.17 8.21
OS1 OS1 25.3% 0.43 0.575 203 0.0250 13.22 189 0.0320 0.10 0.016 3.59 0.88 14.09 392 12.18 12.18
D1 D1 69.9% 0.77 0.180 58 0.0500 2.72 176 0.0100 0.10 0.016 2.01 1.46 5.00 234 11.30 5.00
D2 D2 28.9% 0.47 0.038 5 0.1000 1.21 121 0.0100 0.10 0.016 2.01 1.01 5.00 126 10.70 5.00
OVERALL LENGTH
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
VELOCITY
(ft/s)
ROUGHNESS
COEFFICIENT
HYDRAULIC
RADIUS
(ft)
LENGTH
(ft)
DESIGN CRITERIA:
City of Fort Collins Stormwater Criteria Manual
Overland Flow Equations for City of Fort Collins Stormwater Criteria Manual
SUB-BASIN DATA INITIAL/OVERLAND TIME
(ti)TRAVEL TIME (tt)
tc=ti+tt
(min)
Urban Check Final
tc
(min)DESIGN
POINT Sub-basin %
Impervious C2-10
AREA
(acres)
tt
(min)
February 19, 2021
335 E. Magnolia Street
DEVELOPED TIME OF CONCENTRATION
D.Egger
20-1021-00
Highland Development Services
ticttt+=
V
Ltt60
=1.871.1
10
180
+=LtcV.R2/3 S 1/2
20-1021-00 Rational Calcs (2021-02-17).xlsx Page 2 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 5-3 -Equation 5-4 -Urbanized Check Equation 3.3-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (100-yr)
H1 H1 24.1% 0.53 0.218 74 0.0340 6.08 136 0.0200 0.14 0.025 2.27 1.00 7.08 210 11.17 7.08
OS1 OS1 25.3% 0.53 0.575 203 0.0250 11.12 189 0.0320 0.10 0.016 3.59 0.88 12.00 392 12.18 12.00
D1 D1 69.9% 0.97 0.180 58 0.0500 1.11 176 0.0100 0.10 0.016 2.01 1.46 5.00 234 11.30 5.00
D2 D2 28.9% 0.59 0.038 5 0.1000 0.98 121 0.0100 0.10 0.016 2.01 1.01 5.00 126 10.70 5.00
OVERALL LENGTH
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
VELOCITY
(ft/s)
HYDRAULIC
RADIUS
(ft)
ROUGHNESS
COEFFICIENT
LENGTH
(ft)
DESIGN CRITERIA:
City of Fort Collins Stormwater Criteria Manual
Overland Flow Equations for City of Fort Collins Stormwater Criteria Manual
SUB-BASIN DATA INITIAL/OVERLAND TIME
(ti)TRAVEL TIME (tt)
tc=ti+tt
(min)
Urban Check Final
tc
(min)DESIGN
POINT Sub-basin %
Impervious C100
AREA
(acres)
tt
(min)
February 19, 2021
335 E. Magnolia Street
DEVELOPED TIME OF CONCENTRATION
D.Egger
20-1021-00
Highland Development Services
ticttt+=
V
Ltt60
=1.871.1
10
180
+=LtcV.R2/3 S 1/2
20-1021-00 Rational Calcs (2021-02-17).xlsx Page 3 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:I = rainfall intensity (in/hr)
Q n = n -yr peak discharge (cfs)P 1 = one-hour point rainfall depth (in)
C n = n -yr runoff coefficient t c = time of concentration (min)
I n = n -yr rainfall intensity (in/hr) P 1-2yr =0.82 in
A n = Basin drainage area (ac)P 1-10yr =1.40 in
P 1-100yr =2.86 in
BASIN SUMMARY:
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)
H1 H1 0.218 8.21 0.43 0.09 2.38 0.22 8.21 0.43 0.09 4.07 0.38 7.08 0.53 0.12 8.75 1.01
OS1 OS1 0.575 12.18 0.43 0.25 2.04 0.50 12.18 0.43 0.25 3.49 0.86 12.00 0.53 0.31 7.16 2.20
D1 D1 0.180 5.00 0.77 0.14 2.85 0.40 5.00 0.77 0.14 4.87 0.68 5.00 0.97 0.17 9.95 1.73
D2 D2 0.038 5.00 0.47 0.02 2.85 0.05 5.00 0.47 0.02 4.87 0.09 5.00 0.59 0.02 9.95 0.23
10-yr Peak Runoff 100-yr Peak Runoff
335 E. Magnolia Street
DEVELOPED PEAK RUNOFF
DESIGN CRITERIA:
Design
Point Sub-basin Area (acres)
D.Egger
Highland Development Services
20-1021-00
February 19, 2021
2-yr Peak Runoff
City of Fort Collins Stormwater Criteria Manual
nnnnAICQ=(0.786651)
1
)10(
5.28
ct
PI
+
=
20-1021-00 Rational Calcs (2021-02-17).xlsx Page 4 of 4 Highland Development Services
Appendix C
APPENDIX C – LOW IMPACT DEVELOPMENT CALCULATIONS
VANDNDNDNDNDNDNDNDNDNDNDNFIRE RISERHIGHLANDDEVELOPMENT SERVICES6355 FAIRGROUNDS AVENUE, SUITE 100 | WINDSOR, CO 80550PHONE: 970.674.7550 | EMAIL: Info@Highland-DS.com | www.Highland-DS.comOFSHEET
DRAWN BY
CHECKED BY
DATE
SCALE (H)
HDS PROJ #
SCALE (V)335 EAST MAGNOLIA STREETLID EXHIBIT02/19/21
1" = 20'
N/A
DTE
JTC
20-1021-00
LID
1 1
N
W E
S
DRAINAGE BASIN BOUNDARY
AREA CONTRIBUTING TO LID
TREATMENT
0
SCALE: 1" = 20'
2010
LEGEND
BASIN COEFFICIENT (100-YR)
BASIN DESIGNATION
BASIN AREA
DESIGN POINT
DRAINAGE FLOW ARROW
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
9,492 0.22 6,385 75% 4,789
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
D1 D1 7,827 69.9% 5,851 0.22 143 Storm Chamber
4,789
5,851
122.2%
Area (sq-ft) Area (acres) Treatment Ratio
7,827 0.18 82.5%
1,665 0.04 17.5%
9,492 0.22Total Improvement Area
Water Quality Area Treatment Summary
Description
Total Area Treated by LID
Total Area unable to be Treated
335 E. Magnolia Street
Low Impact Development
Total % Required 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.
Impervious Area Treated (sq-ft)
Impervious Area Required for LID Treatment (sq-ft)
LID Treatment Summary
LID Treatment Areas
D.Egger
Highland Development Services
20-1021-00
February 18, 2021
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Description
Total Redeveloped Area
Allowed FilterFabric Flow Ratea(cfs)0.35 gpm/sq-ftSC-106LP 14 10 6 6 85.4 25 12 14.8 0.012 6.9 15.0SC-310 18 8 6 6 85.4 34 16 20.2 0.016 14.7 31.0SC-740 18 8 6 6 85.4 51 30 30.2 0.024 45.9 74.9DC-780 18 12 6 9 85.4 51 30 30.2 0.024 46.2 78.4MC-3500 24 8 12 9 90 77 45 48.1 0.038 109.9 178.9 14.9 46MC-4500 24 7 12 9 52 100 60 36.1 0.028 106.5 162.6 35.7 108.7LIDFacilityChamberTypeTotalRelease Ratef(cfs) WQ Flowg(cfs)Req'd StorageVolumeh(cu-ft)Minimum No. of ChambersiChamberStoragej(cu-ft)No. ofEndcapskEndcapStoragel(cu-ft)Total ChamberVolumem(cu-ft)Total InstalledSystem Volumen(cu-ft)WQCV12-hr(cu-ft)D1 SC-310 0.06 0.2156 4 56 12 0 56 205 143Max Cover(ft)Min Cover(in)ChamberModelD.EggerHighland Development Services20-1021-00February 18, 2021Min InstalledChamber/AggregateVolumec(cu-ft)335 E. Magnolia StreetLow Impact DevelopmentStormTech Chamber Configuration SummaryStormTech Chamber DataDesign Engineer:Design Firm:Project Number:Date:Length(in)Width(in)Height(in)Floor Area(sq-ft)ChamberVolumeb(cu-ft)MinAggregate Base(in)Min Aggregate Cover(in)NegligibleEndcapVolumed(cu-ft)Min InstalledEndcap/AggregateVolumee(cu-ft)NegligibleNegligibleNegligibleNote:a. Release rate per chamber, limited by flow through geotextile with accumulated sediment. City acceptable flow rates determined to be approximately 1/2 of the Nov-07 Qmaxfrom Figure 17 of the "Final Report on Field Verification Testing of the StormTech Isoloator Row Treatement Unit", prepard by the University of New Hamphire Stormwater Center, dated Setpember 2010.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. Volume within endcap only, not accounting for void spaces in surrounding aggregate.e. Volume includes endcap and void spaces (40%) in surrounding aggregate, per chamber unit.f. Release rate per chamber times number of chambers. This is used as the allowed release rate for the FAA calculations.g. WQ flow, equal to 1/2 of the 2-yr peak runoff rate, referenced to size flow control structure.h. Required detention volume determined using the FAA Method based on the acceptable release rate of sediment accumulated filter fabric of the chambers and the 1/2 of the 2yr in flow rate.i. Number of chambers required to provide required FAA storage volume stored within the chamber and endcaps only (no aggregate storage).j. Total volume provided in chambers only (no aggregate storage).k. Number of endcaps based on desired chamber layout.
DESIGN CRITERIA
0.73
1.00
0.73 ft3 acre-ft
0.18 acres 56 0.00
0.06 cfs
Time
(min)
1/2 2-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Accumulative
Release Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.000 0.00 0 0 0 0.00
5 1.425 0.19 56 18 38 0.00
10 1.105 0.14 87 36 51 0.00
15 0.935 0.12 110 54 56 0.00
20 0.805 0.11 127 72 55 0.00
25 0.715 0.09 141 90 50 0.00
30 0.650 0.09 153 108 45 0.00
35 0.585 0.08 161 126 35 0.00
40 0.535 0.07 168 144 24 0.00
45 0.495 0.06 175 162 13 0.00
50 0.460 0.06 181 180 1 0.00
55 0.435 0.06 188 199 -10 0.00
60 0.410 0.05 194 217 -23 0.00
Adjusted Runoff Coefficient (CC f )
Area (A )
Allowed Release Rate
- City of Fort Collins - Storm Water Criteria Manual
- City of Fort Collins accepts 1/2 of the 2-yr runoff as the WQ inflow rate
WQ Treatment Volume Calculation - D1 Filtration Chamber
Runoff Coefficient (C )
Frequency Factor (C f )Required Detention
335 E. Magnolia Street
WQ Treatment Volume - FAA Method
D.Egger
Highland Development Services
20-1021-00
February 18, 2021
Design Engineer:
Design Firm:
Project Number:
Date:
User Inputs
Chamber Model: SC-310
Outlet Control Structure: Yes
Project Name: 335 E. Magnolia St
Engineer: N/A
Project Location:
Measurement Type: Imperial
Required Storage Volume: 144 cubic ft.
Stone Porosity: 40%
Stone Foundation Depth: 6 in.
Stone Above Chambers: 6 in.
Average Cover Over Chambers: 18 in.
Design Constraint Dimensions:(15 ft. x 30 ft.)
Results
System Volume and Bed Size
Installed Storage Volume: 205.05 cubic ft.
Storage Volume Per Chamber: 14.70 cubic ft.
Number Of Chambers Required: 4
Number Of End Caps Required: 4
Chamber Rows: 2
Maximum Length:20.75 ft.
Maximum Width: 8.77 ft.
Approx. Bed Size Required: 181.90 square ft.
System Components
Amount Of Stone Required: 13.54 cubic yards
Volume Of Excavation (Not Including
Fill):
15.72 cubic yards