HomeMy WebLinkAboutHOWES SIX TWO NINE - FDP210025 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT
Final Drainage and Erosion Control Report for
Howes Six Two Nine
Fort Collins, Colorado
December 7, 2021
Prepared for:
Carlson Land Development
Blake Carlson
14570 Clay St.
Broomfield, CO 80023
Prepared by:
301 N. Howes St. Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158
www.northernengineering.com
Project Number: 1590-002
This Drainage Report is consciously provided as a PDF. Please consider
the environment before printing this document in its entirety. When a hard
copy is necessary, we recommend double-sided printing.
December 7, 2021
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
RE: Preliminary Drainage and Erosion Control Report for
Howes Six Two Nine
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the combined Preliminary & Final Plan submittal for the proposed
Howes Six Two Nine Development.
This report has been prepared in accordance with the Fort Collins Stormwater Criteria Manual (FCSCM)
and serves to document the stormwater impacts associated with the proposed Howes Six Two Nine
project. We understand that review by the City of Fort Collins is to assure general compliance with
standardized criteria contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
Northern Engineering Services, Inc.
Austin Snow, PE Danny Weber, PE
Project Engineer Project Manager
Compliance Statement:
I hereby attest that this report for preliminary drainage design for Howes Six Tow Nine was prepared by
me or under my direct supervision, in accordance with the provisions of the Fort Collins Stormwater
Criteria Manual. I understand that the City of Fort Collins does not and will not assume liability for
drainage facilities designed by others.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Table of Contents
Table of Contents
I. General Location and Description ........................................................................ 1
II. Drainage Basins and Sub-Basins .......................................................................... 3
III. Drainage Design Criteria ..................................................................................... 4
IV. Drainage Facility Design ..................................................................................... 7
V. Conclusions ......................................................................................................... 9
VI. References ......................................................................................................... 11
Tables and Figures
Figure 1 – Vicinity Map .............................................................................................. 1
Figure 2 – Aerial Photograph ..................................................................................... 2
Figure 3 – FEMA Firmette (Map Number 08069C0979H) .......................................... 3
Appendices
Appendix A – Hydrologic Computations
Appendix B – Hydraulic Computations
Appendix C – Water Quality/Lid Design Computations
Appendix D – Erosion Control Report
Appendix E – USDA Soils Report
Map Pocket
DR1 – Drainage Exhibit
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 1 of 12
I. General Location and Description
A. Location
1. Vicinity Map
Figure 1 – Vicinity Map
2. The Howes Six Two Nine project site is located within the North half of Lot 2 and
the South half of Lot 3 of Block 93 of the Harrison subdivision, City of Fort
Collins, County of Larimer, State of Colorado.
3. The project site (refer to Figure 1) is bordered on the North and South by parking
lots for multifamily residences; to the West by an inverted-crown alleyway; to
the East by the public right-of-way for South Howes.
B. Description of Property
1. The Howes Six Two Nine development is comprised of ±0.43 acres.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 2 of 12
2. The site is currently occupied by one two-story brick building planned to remain,
a garage adjacent the alleyway which is planned for removal, as well as various
concrete sidewalk and pavers, and an approximately 4240 square-foot asphalt
parking area connected to the alley.
Figure 2 – Aerial Photograph
3. The existing groundcover consists of grasses, concrete, pavers, asphalt, and the
existing structures’ rooftops. The existing on-site runoff generally drains
Westward into the inverted crown alleyway and Eastward to South Howes on
shallow grades (e.g., <2.00%). From there, the drainage follows existing City of
Fort Collins stormwater infrastructure.
4. According to the United States Department of Agriculture (USDA) Natural
Resources Conservation Service (NRCS) Soil Survey website:
(http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx),
the site consists primarily of Fort Collins loam (Hydrologic Soil Group C).
5. The proposed development will consist of one multifamily building consisting of
seven apartment units. Other proposed improvements include: an enlarged
asphalt parking lot, walkways and a courtyard, and landscaping.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 3 of 12
6. The project site is located in the Campus North sub-district of the Downtown
District. The proposed use (Multi-family, 8-units or less/building) is an approved
use in the Downtown District, subject to Type 1 Administrative Review.
7. No significant offsite flows are directed into the site. Off-site flows are prevented
from entering the site by existing topography.
8. The site is not required to provide on-site detention as it is located in the Old
Town Basin and is increasing total impervious area by less than 5,000 square feet.
Additionally, the standard water quality requirement for this site has been
provided for in the City’s Udall water quality facility. This site will meet the
City’s on-site LID treatment requirements via a bioswale included in the design.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain
according to FEMA Firm No. 08069C0979H, effective on 05/02/2012.
2.
Figure 3 – Existing Floodplain(s)
II. Drainage Basins and Sub-Basins
A. Major Basin Description
Howes Six Two Nine is located within the City of Fort Collins Old Town major
drainage basin. Specifically, the project site is situated in the lower center of this
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 4 of 12
major drainage basin. This basin is located in north-central Fort Collins and has a
drainage area of approximately 2,120 acres. The entire basin is urbanized and
generally drains from west to east. Most of the water from the Old Town basin
drains to the Poudre River, just to the east.
B. Sub-Basin Description
1. The outfall for the project site is the Cache la Poudre River, to the east.
2. The subject site can be defined with three (3) historical sub-basins that
encompass the entire project site.
3. The existing site runoff drains to four different places, including the alley to the
west, the parking lot to the north of the site, low areas within the site itself, or
east to the Howes gutter.
4. The project site does not receive notable runoff from off-site properties.
III. Drainage Design Criteria
A. Optional Provisions
There are no optional provisions outside of the FCSCM proposed with the Howes
Six Two Nine project.
B. Stormwater Management Strategy
The overall stormwater management strategy employed with the Howes Six Two
Nine project utilizes the “Four Step Process” to minimize adverse impacts of
urbanization on receiving waters. The following is a description of how the
proposed development has incorporated each step.
Step 1 – Employ Runoff Reduction Practices. The first consideration taken in trying
to reduce the stormwater impacts of this development is the site selection itself. By
choosing an already developed site with public storm sewer currently in place, the
burden is significantly less than developing a vacant parcel absent of any
infrastructure.
The Howes Six Two Nine project aims to reduce runoff peaks, volumes and
pollutant loads from frequently occurring storm events (i.e., water quality (i.e., 80th
percentile) and 2-year storm events) by implementing Low Impact Development
(LID) strategies. Wherever practical, runoff will be routed across landscaped areas or
through an infiltration gallery. These LID practices reduce the overall amount of
impervious area, while at the same time Minimizing Directly Connected Impervious
Areas (MDCIA). The combined LID/MDCIA techniques will be implemented, where
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 5 of 12
practical, throughout the development, thereby slowing runoff and increasing
opportunities for infiltration.
Step 2 – Implement BMPs that Provide a Water Quality Capture Volume (WQCV)
with Slow Release. The efforts taken in Step 1 will help to minimize excess runoff
from frequently occurring storm events; however, urban development of this
intensity will still have stormwater runoff leaving the site. The standard water
quality treatment will occur off-site at the City’s Udall Water Quality facility.
Step 3 – Stabilize Drainageways. The project will pay one-time stormwater
development fees, as well as ongoing monthly stormwater utility fees, both of which
help achieve Citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs. This step
typically applies to industrial and commercial developments.
C. Development Criteria Reference and Constraints
1. The subject property is part of the Old Town basin drainage master plan.
2. The site plan is constrained on the east by a public street, on the west by an alley,
and by existing development on the north and south.
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as
depicted in Figure 3.4-1 of the FCSCM, serve as the source for all hydrologic
computations associated with the development. Tabulated data contained in
Table 3.4-1 has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Chapter 3 of the FCSCM.
3. The Rational Formula-based Federal Aviation Administration (FAA) procedure
has not been utilized for detention storage calculations since detention is not
required for the project.
4. Two separate design storms have been utilized to address distinct drainage
scenarios. The first event analyzed is the “Minor,” or “Initial” Storm, which has a
2-year recurrence interval. The second event considered is the “Major Storm,”
which has a 100-year recurrence interval.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 6 of 12
E. Hydraulic Criteria
1. The drainage facilities proposed for the Howes Six Two Nine project are
designed in accordance with criteria outlined in the FCSCM and/or the Mile
High Flood District’s (MHFD) Urban Storm Drainage Criteria Manual.
2. As stated in Section I.C.1, above, the subject property is not located in any FEMA
or City floodplains.
F. Floodplain Regulations Compliance
1. As previously mentioned, this project is not subject to any floodplain regulations.
G. Modifications of Criteria
No formal modifications are requested at this time. Quantity detention is required in
the Old Town Basin if the site increases impervious area by greater than 5000 square
feet. This site does not exceed/trigger this requirement.
H. Conformance with Water Quality Treatment Criteria
City Code requires that 100% of runoff from a project site receive some sort of water
quality treatment. As per staff guidance, his project will utilize the Udall water
quality facility to provide standard water quality treatment for the site. Additionally,
the site will feature LID treatment for at least the required treatment area. Due to the
physical constraints associated with a project of this nature/size and the prohibition
of providing water quality facilities within the public right-of-way, there are some
small, narrow areas around the perimeter of the project that cannot be captured. The
uncaptured areas tend to be narrow strips of landscaped area between the property
line and buildings or curbs.
While these small areas will not receive formal water quality treatment, most areas
will still see some treatment as runoff is directed across through the landscaped
areas or LID system before outletting to the storm sewer off-site.
I. Conformance with Low Impact Development (LID)
The project site will conform with the requirement to treat a minimum of 75% of the
project site using a LID technique. Please see Appendix C for LID design
information, table, and exhibit(s). As shown in the LID table provided in the
appendix, 86.4% of the proposed site impervious area will receive LID treatment,
which exceeds the minimum required.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 7 of 12
J. Sizing of LID Facilities
Bioswale
1. The bioswale was sized by first determining the required treatment area for the
system (75% of new/modified impervious area). New and modified impervious
area equals approximately 11,591 square feet, so the required treatment area
equals approximately 8,693 square feet.
2. After preliminary placement was identified, the contributing area was delineated
in order to determine if the treatment area requirement in 1, above, was being
met. The treatment area, as designed, equals 8,836 square feet, or 76.2% of the
new & modified impervious area.
3. Once it was determined that the treatment area requirement was met, the
bioswale was sized using the method described in UDFCD/MHFD Treatment
BMP Fact Sheet T-03, referenced in Appendix C (LID Implementation Manual) of
the FCSCM. A modification was applied to this sizing method: the requirement
for storage of 120% of the WQCV as per the FCSCM. The sizing worksheet is
included in the Appendices of this report.
4. A volume calculation utilizing the contributing area flow rate into the bioswale
and the calculated release rate through the filter area was completed as per Fact
Sheet T-03.
IV. Drainage Facility Design
A. General Concept
1. The main objective of the Howes Six Two Nine drainage design is to maintain
existing drainage patterns, while not adversely impacting adjacent properties.
2. No notable off-site runoff passes directly through the project site.
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within
the sections to which the content best applies.
4. Drainage for the project site has been analyzed using thirteen (13) drainage sub-
basins, designated as sub-basins A through G and H-C. The drainage patterns
anticipated for the basins are further described below.
Sub-Basin A
Sub-basin A encompasses approximately 4.5% the total site area. This sub-basin
is comprised primarily of asphalt parking/drive and landscaped area. The sub-
basin will drain to the alley located along the west property line and be captured
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 8 of 12
by an area drain which will then convey runoff from the basin through the storm
drain system off-site. Historically, approximately 360 square feet of impervious
area drains to the alley. The proposed development will increase the impervious
area draining to the alley by 262 square feet to approximately 622 square feet.
Since the increase is less than 350 square feet, as per City staff, drainage analysis
of the alley’s conveyance is not required.
Sub-Basin B
Sub-basin B encompasses approximately 40.6% the total site area. This sub-basin
is comprised primarily of roof area, concrete flatwork, an asphalt parking lot,
and landscaped area. Flows for the sub-basin will drain to a curb-cut in the
southeast corner of the parking lot that flows into Sub-Basin F and the LID
system.
Sub-Basin C
Sub-basin C encompasses approximately 21.4% the total site area. This sub-basin
is comprised primarily of roof area, concrete flatwork and landscaped areas. The
sub-basin will sheet flow to a trench drain, which will then convey flows to an
area inlet leading to the off-site storm sewer in Howes.
Sub-Basin D
Sub-basin D encompasses approximately 2.3% the total site area. This sub-basin
is comprised primarily of landscaped area and roof area. Flows from the sub-
basin will flow to an area inlet which will convey runoff from the basin into the
off-site storm sewer.
Sub-Basin E
Sub-basin E encompasses approximately 16.5% the total site area. This sub-basin
is comprised primarily of roof area. Flows from the sub-basin will flow via
gutters into Sub-Basin F and the LID system.
Sub-Basin F
Sub-basin F encompasses approximately 8.2% the total site area. This sub-basin is
comprised primarily of landscaped area. Flows from the sub-basin will enter the
LID system (bioswale) which has been designed to capture the major flows from
the contributing area and features an underdrain conveying flows to the off-site
storm sewer in Howes. An area drain is also featured to collect flows greater than
the major event. Since this Sub-Basin receives flows from multiple other Sub-
Basins, it has been designed to overflow into the Sub-Basin D outlet, an area inlet
that leads directly to the off-site storm sewer, in case of a long-return period
event or clogging in the LID system.
Sub-Basin G
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 9 of 12
Sub-basin G encompasses approximately 6.2% the total site area. This sub-basin
is comprised primarily of roof area, concrete flatwork and landscaped areas.
Flows from this sub-basin cannot be captured due to existing topography at the
property boundary and will flow off-site to the parking lot to the north or the
gutter in Howes, following historical drainage patterns.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the
end of this report.
B. Specific Details
1. Since detention is not required with this site, the existing impervious area has not
been considered in determining allowable release from the property.
2. An allowable release rate was not determined for this project due to an increase
in impervious area less than 5,000 square feet from historical.
3. The FAA method was not used to size the on-site detention volume for quantity
detention since detention is not required.
4. Storm infrastructure was sized to the major event flows from contributing areas
as per the FCSCM.
V. Conclusions
A. Compliance with Standards
1. The design elements comply without variation and meet all LID requirements.
2. The drainage design proposed with the Howes Six Two Nine project complies
with the City of Fort Collins Master Drainage Plan for the Old Town Basin.
3. There are no FEMA regulatory floodplains associated with the development.
4. The drainage plan and stormwater management measures proposed with the
project are compliant with all applicable State and Federal regulations governing
stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit potential
damage associated with its stormwater runoff. The project will not detain for the
pervious area converted to impervious areas to release at the 2-year existing rate
during the 100-year storm as per staff instruction, however, LID will be
implemented to treat new impervious area.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 10 of 12
2. The development will not impact the Master Drainage Plan recommendations for
the Old Town major drainage basin.
Howes Six Two Nine Preliminary Drainage Report December 7, 2021
Carlson Development Page 11 of 12
VI. References
City of Fort Collins Landscape Design Guidelines for Stormwater and Detention
Facilities, November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility
Services.
Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by
Ordinance No. 159, 2018, and referenced in Section 26-500 of the City of Fort Collins
Municipal Code.
Soils Resource Report for Larimer County Area, Colorado, Natural Resources
Conservation Service, United States Department of Agriculture.
Urban Storm Drainage Criteria Manual, Volumes 1-3, Mile High Flood District,
Denver, Colorado, Revised April 2018.
Appendix A
Hydrologic Computations
Project:
Calc. By:
Date:
Description Surface Area
(ft2)
Percent
Impervious
Impervious Area
( ft2)
Rooftop 2,431 90% 2,188
Concrete 1,040 100% 1,040
Asphalt 4,200 100% 4,200
Pavers - 40% -
Gravel 482 40% 193
Landscaping 10,828 2% 217 Imperviousness
Total 18,981 7,837 41.3%
Description
Surface Area
(ft2)
Percent
Impervious
Impervious Area
( ft2)
Rooftop 6,300 90% 5,670
Concrete 1,497 100% 1,497
Asphalt 5,308 100% 5,308
Pavers - 40% -
Gravel - 40% -
Landscaping 5,876 2% 118 Imperviousness
Total 18,981 12,593 66.3%
4,755 25.1%
IMPERVIOUS AREA CALCULATIONS
629 Howes
A. Snow
July 26, 2021
Difference in Impervious Area (ft2)
Developed Impervious Areas
Historic Impervious Areas
Runoff
Coefficient1
Percent
Impervious1
5,007 0.95 100%
2,052 0.95 90%
0 0.50 40%
540 0.50 40%
0 0.10 2%
11,920 0.20 2%
Basin ID Basin Area
(sq.ft.)
Basin Area
(acres)
Asphalt,
Concrete
(sq.ft.)
Asphalt,
Concrete (acres)Rooftop (sq.ft.) Rooftop (acres) Pavers (sq.ft.) Pavers (acres)
Lawns, Clayey
Soil, Flat Slope <
2% (sq.ft.)
Lawns, Clayey
Soil, Flat Slope <
2% (acres)
Percent
Impervious
C2*Cf
Cf = 1.00
C5*Cf
Cf = 1.00
C10*Cf
Cf = 1.00
C100*Cf
Cf = 1.25
H-A 1,418 0.033 202 0.005 158 0.004 0 0.000 1,058 0.02 26%0.39 0.39 0.39 0.49
H-B 17,153 0.394 4,805 0.110 1,485 0.034 540 0.012 10,862 0.25 38%0.49 0.49 0.49 0.61
H-C 409 0.009 0 0.000 409 0.009 0 0.000 0 0.00 90%0.95 0.95 0.95 1.00
Lawns and Landscaping:
2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins
Stormwater Manual (FCSM).
Lawns, Clayey Soil, Flat Slope < 2%
USDA SOIL TYPE: C
Lawns, Sandy Soil, Flat Slope < 2%Composite Runoff Coefficient2
1) Runoff coefficients per Tables 3.2-1 & 3.2 of the FCSM. Percent impervious per Tables 4.1-2 & 4.1-3 of the FCSM.
HISTORIC RUNOFF COEFFICIENT CALCULATIONS
Asphalt, Concrete
Rooftop
Gravel
Pavers
629 Howes
S. Hallauer
March 23, 2020
Project:
Calculations By:
Date:
Character of Surface
Streets, Parking Lots, Roofs, Alleys, and Drives:
Ti = 1.87(1.1-CxCf)√L / (3√S) (Equation 3.3-2 per FCSCM)
Velocity (Channelized Flow), V = (1.49/n)R2/3S1/2 (Equation 5-4 per FCSCM)
Tc2 Tc10 Tc100 C2 C10 C100
I2
(in/hr)
I10
(in/hr)
I100
(in/hr)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
h-a1 H-A 0.033
5.00 5.00 5.00 0.39 0.39 0.49 2.85 4.87 9.95 0.04 0.06 0.16
h-b1 H-B 0.394
5.00 5.00 5.00 0.49 0.49 0.61 2.85 4.87 9.95 0.55 0.94 2.40
h-c1 H-C 0.009 5.00 5.00 5.00 0.95 0.95 1.00 2.85 4.87 9.95 0.03 0.04 0.09
Design
Point Basin Area
(acres)
Runoff CTc (Min)
Tt = L / 60V (Equation 5-5 per FCSCM)
Tc = Ti + Tt (Equation 5-3 per FCSCM)
Intensity, I from Fig. 3.4.1 Fort Collins Stormwater Manual
HISTORIC DIRECT RUNOFF COMPUTATIONS
Intensity Flow
629 Howes
S. Hallauer
March 23, 2020
Project:
Calculations By:
Overland Flow, Time of Concentration:
Channelized Flow, Time of Concentration:
Date:
Rational Equation: Q = CiA (Equation 6-1)
1.87 1.1 ∗ (Equation 3.3-2 per Fort Collins
Stormwater Manual)
Page 1
Runoff
Coefficient1
Percent
Impervious1
6,957 0.95 100%
6,693 0.95 90%
0 0.50 40%
0 0.50 40%
0 0.10 2%
5,270 0.20 2%
Basin ID Basin Area
(sq.ft.)
Basin Area
(acres)
Asphalt,
Concrete
(sq.ft.)
Asphalt,
Concrete (acres)Rooftop (sq.ft.) Rooftop (acres)
Lawns, Clayey
Soil, Flat Slope <
2% (sq.ft.)
Lawns, Clayey
Soil, Flat Slope <
2% (acres)
Percent
Impervious
C2*Cf
Cf = 1.00
C5*Cf
Cf = 1.00
C10*Cf
Cf = 1.00
C100*Cf
Cf = 1.25
A 862 0.020 650 0.015 0 0.000 212 0.00 76%0.77 0.77 0.77 0.96
B 7,715 0.177 4,658 0.107 1,504 0.035 1,553 0.04 78%0.80 0.80 0.80 1.00
C 4,050 0.093 1,386 0.032 1,592 0.037 1,072 0.02 70%0.75 0.75 0.75 0.94
D 443 0.010 147 0.003 0 0.000 296 0.01 35%0.45 0.45 0.45 0.56
E 3,129 0.072 0 0.000 3,129 0.072 0 0.00 90%0.95 0.95 0.95 1.00
F 1,551 0.036 0 0.000 0 0.000 1,551 0.04 2%0.20 0.20 0.20 0.25
G 1,170 0.027 116 0.003 468 0.011 586 0.01 47%0.57 0.57 0.57 0.72
DEVELOPED RUNOFF COEFFICIENT CALCULATIONS
Asphalt, Concrete
Rooftop
Gravel
Pavers
629 Howes
S. Hallauer
October 14th, 2021
Project:
Calculations By:
Date:
Character of Surface
Streets, Parking Lots, Roofs, Alleys, and Drives:
Lawns and Landscaping:
2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins
Stormwater Manual (FCSM).
Lawns, Clayey Soil, Flat Slope < 2%
USDA SOIL TYPE: C
Lawns, Sandy Soil, Flat Slope < 2%Composite Runoff Coefficient2
1) Runoff coefficients per Tables 3.2-1 & 3.2 of the FCSM. Percent impervious per Tables 4.1-2 & 4.1-3 of the
FCSM.
Ti = 1.87(1.1-CxCf)√L / (3√S) (Equation 3.3-2 per FCSCM)
Velocity (Channelized Flow), V = (1.49/n)R2/3S1/2 (Equation 5-4 per FCSCM)
Tc2 Tc10 Tc100 C2 C10 C100
I2
(in/hr)
I10
(in/hr)
I100
(in/hr)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
a A 0.020
5.00 5.00 5.00 0.77 0.77 0.96 2.85 4.87 9.95 0.04 0.07 0.19
b B 0.177
5.00 5.00 5.00 0.80 0.80 1.00 2.85 4.87 9.95 0.40 0.69 1.76
c C 0.093
5.00 5.00 5.00 0.75 0.75 0.94 2.85 4.87 9.95 0.20 0.34 0.87
d D 0.010
5.00 5.00 5.00 0.45 0.45 0.56 2.85 4.87 9.95 0.01 0.02 0.06
e E 0.072
5.00 5.00 5.00 0.95 0.95 1.00 2.85 4.87 9.95 0.19 0.33 0.71
f F 0.036
5.00 5.00 5.00 0.20 0.20 0.25 2.85 4.87 9.95 0.02 0.03 0.09
g G 0.027 5.00 5.00 5.00 0.57 0.57 0.72 2.85 4.87 9.95 0.04 0.08 0.19
DEVELOPED DIRECT RUNOFF COMPUTATIONS
Intensity Flow
629 Howes
S. Hallauer
October 14th, 2021
Project:
Calculations By:
Overland Flow, Time of Concentration:
Channelized Flow, Time of Concentration:
Date:
Rational Equation: Q = CiA (Equation 6-1)
Design
Point Basin Area
(acres)
Runoff C
Tt = L / 60V (Equation 5-5 per FCSCM)
Tc = Ti + Tt (Equation 5-3 per FCSCM)
Intensity, I from Fig. 3.4.1 Fort Collins Stormwater Manual
Tc (Min)
1.87 1.1 ∗ (Equation 3.3-2 per Fort Collins
Stormwater Manual)
Appendix B
Hydraulic Calculations
Appendix C
Water Quality/LID Design Computations
Project:
Calc. By:
Date:
0.436 <-- INPUT from impervious calcs
66.30 <-- INPUT from impervious calcs
0.6630 <-- CALCULATED
12 hours <-- from UDFCD Vol. 3 Table 3-2
0.8 <-- from UDFCD Vol. 3 Table 3-2
0.207 <-- UDFCD Vol. 3 Equation 3-1
0.00754 <-- UDFCD Vol. 3 Equation 3-3
Basin Area =
Basin Percent Imperviousness =
Basin Imperviousness Ratio =
WQCV (watershed inches) =
WQCV (ac-ft) =
Drain Time Coefficient =
Drain Time =
April 13, 2020
WATER QUALITY POND DESIGN CALCULATIONS
Primary Pond
Required Storage & Outlet Works
629 Howes
F. Wegert
Bioretention T-3
November 2015 Urban Drainage and Flood Control District B-5
Urban Storm Drainage Criteria Manual Volume 3
The following steps outline the design procedure and criteria, with Figure B-1 providing a corresponding
cross-section.
2. Basin Storage Volume: Provide a storage volume based on a 12-hour drain time.
Find the required WQCV (watershed inches of runoff). Using the imperviousness of the tributary
area (or effective imperviousness where LID elements are used upstream), use Figure 3-2 located
in Chapter 3 of this manual to determine the WQCV based on a 12-hour drain time.
Calculate the design volume as follows: 𝑉 = �WQCV12�𝐴 Equation B-1
Where:
V= design volume (ft3)
A = area of watershed tributary to the rain garden (ft2)
3. Basin Geometry: UDFCD recommends a maximum WQCV ponding depth of 12 inches to
maintain vegetation properly. Provide an inlet or other means of overflow at this elevation.
Depending on the type of vegetation planted, a greater depth may be utilized to detain larger
(more infrequent) events. The bottom surface of the rain garden, also referred to here as the filter
area, should be flat. Sediment will reside on the filter area of the rain garden; therefore, if the
filter area is too small, it may clog prematurely. If the filter area is not flat, the lowest area of the
filter is more likely to clog as it will have a higher sediment loading. Increasing the filter area
will reduce clogging and decrease the frequency of maintenance. Equation B-2 provides a
minimum filter area allowing for some of the volume to be stored beyond the area of the filter
(i.e., above the sideslopes of the rain garden).
Note that the total surcharge volume provided by the design must also equal or exceed the design
volume. Where needed to meet the the required volume, also consider the porosity of the media at 14
percent. Use vertical walls or slope the sides of the basin to achieve the required volume. Sideslopes
should be no steeper than 4:1 (horizontal:vertical).
AIAF02.0=
Equation B-2
Where:
AF= minimum (flat) filter area (ft2)
A = area tributary to the rain garden (ft2)
I = imperviousness of area tributary to the rain garden (percent expressed as a decimal)
V = (WQCV/12) A
WQCV = 0.207 WSI
A = 12061 ft2
So, V = (0.207 in./12) * 12061 ft2
V = 208 ft3
120% = 250 ft3
Af = 0.02 A I
A = 12061 ft2 I = 66.3%
So, Af = 0.02(12061)(.663)
Af = 159.93 ft2
Bioswale has been designed to store 250 ft3 of water (278.4
total) with a flat filter area of 160 ft2.
FORT COLLINS STORMWATER CRITERIA MANUAL Water Quality (Ch. 7)
6.0 Low Impact Development
6.0 Low Impact Development
Page 13
Reference: Calculating effective imperviousness and quantifying volume reduction as
discussed in the 2015 UDFCD Manual, Volume 3, Section 4.0 are not allowed. The City of
Fort Collins does not allow for extended detention basins to be designed using the Excess
Urban Runoff Volume (EURV) and Full-Spectrum Detention method, as described in the
UDFCD Manual.
6.0 Low Impact Development
This Section of this Chapter presents information that is specific to the City of Fort Collins and may be a
significant deviation from the information presented in the UDFCD Manuals. Utilizing UDFCD
methodologies for Low Impact Development (LID) designs may not be accepted by FCU.
In February 2013, Fort Collins City Council adopted Ordinance No. 152, 2012, to incorporate provisions
implementing LID principles; with the goal to declare that the purpose of the City Stormwater Utility is
to provide an integrated, sustainable stormwater management program that reflects the community’s
values of protecting and restoring the City’s watersheds. This was subsequently modified and updated in
January 2016 with Ordinance No. 007, 2016 to allow for some added flexibility in the implementation of
the LID policy.
Reference: Both the initial LID ordinance, Ordinance No. 152, 2012, and the subsequent
ordinance, Ordinance No. 007, 2016, can be found on the City of Fort Collins website.
LID is simply defined as an integrated, sustainable stormwater management program that requires a
distributed, closer to the source stormwater runoff control that simulates natural processes and relies
mainly on filtration and infiltration to locally treat and manage stormwater runoff.
Integration of LID systems into the drainage design is required for all development projects in order to
comply with the City’s policies on LID, the requirements of this Manual, the City Code and the Land Use
Code. LID systems provide a higher degree of stormwater quality treatment than that provided with
standard water quality design. The implementation of LID systems requires one of the following two
options:
1) 50% of the newly added or modified impervious area must be treated by LID techniques and
25% of new paved (vehicle use) areas must be pervious.
2) 75% of all newly added or modified impervious area must be treated by LID techniques.
Impervious surfaces are defined as hardscape surfaces that do not allow stormwater to infiltrate into
the ground. Impervious surfaces include asphalt and concrete surfaces, concrete curbs, gutters,
sidewalks, patios and rooftops. (Impervious surface areas must be assumed for single family residential
lots when overall impervious areas are being determined for residential developments. The assumed
areas must then be included in LID calculations.)
FORT COLLINS STORMWATER CRITERIA MANUAL Water Quality (Ch. 7)
6.0 Low Impact Development
6.0 Low Impact Development
Page 14
“Added” impervious area stated in
the two options above is further
defined as existing vegetation (or
pervious) areas becoming
hardscape (or impervious) areas.
“Modified” impervious area stated
in the two options above is further
defined as existing impervious
areas on an existing site being
removed and replaced with other
impervious surfaces through a
redevelopment process (i.e.
existing asphalt surface becoming a rooftop surface). Mill and overlay of asphalt areas is not considered
a “modified” impervious area.
“Paved” areas, as stated in option 1 above are generally considered to be private vehicle use areas only.
Reference: Refer to the City of Fort Collins LID Implementation Manual in Appendix C for
detailed information and requirements on LID systems.
6.1 General Requirements
Included here are some general design requirements applicable for all types of LID system designs in
Fort Collins.
• Overall added or modified impervious areas that amount to less than 1000 square feet (<
1000 sf) on a site will not require LID system treatment for water quality.
• For development sites that are adding or modifying 1000 square feet of imperviousness or
more (≥ 1000 sf) are required to implement LID system treatment at the site. The LID system
is allowed to treat existing imperviousness in exchange for the newly added imperviousness
if the surface character is similar (e.g. existing pavement may be treated in lieu of newly
added rooftop)
• For single-family residential developments, LID must be placed in tracts or common areas
for ownership and maintenance by the HOA. LID systems installed as part of the
development requirement shall not be placed on single-family lots.
• LID is not required for private, single-family residential improvement projects that are not a
part of a larger subdivision project. (i.e. an existing lot in an older part of Fort Collins that is
being re-built)
OPTIONS FOR MEETING WATER QUALITY
TREATMENT REQUIREMENTS
50% SITE TREATED WITH “STANDARD” WATER QUALITY
+ 50% SITE TREATED WITH LID (INCLUDING PAVERS)
100% OF SITE TREATED (REQUIREMENTS MET)
OR
25% SITE TREATED WITH “STANDARD” WATER QUALITY
+ 75% SITE TREATED WITH LID
100% OF SITE TREATED (REQUIREMENTS MET)
FORT COLLINS STORMWATER CRITERIA MANUAL Water Quality (Ch. 7)
6.0 Low Impact Development
6.0 Low Impact Development
Page 15
• LID systems are not allowed to be placed in the public right-of-way to treat runoff from
development sites. Stormwater runoff from development must be treated within the
confines of the development and therefore cannot be treated and/or placed within a public
right-of-way. Stormwater runoff generated within the public right-of-way, however, is still
required to be captured and treated for water quality.
• LID systems are generally required to be placed outside of a detention basin area.
• LID systems may only drain to drywells if a gravity outfall for the water quality storm is not
available.
• LID systems are required to be sized for the entire area tributary to the LID basin (including
any offsite contributing areas)
• LID systems are required to be placed outside of any existing wetlands (jurisdictional and
non-jurisdictional), streams or other waters of the U.S.
• LID systems design must comply with the excerpts of the City of Fort Collins Landscape
Design Standards and Guidelines for Stormwater and Detention Facilities, dated November
5, 2009 included as Appendix B to this Manual.
6.2 Permeable Pavement
The term “permeable pavement” is a general term to describe any one of several pavement systems
that allow infiltration of water into the layers below the pavement through openings within the
pavement surface. Use of permeable pavements is an accepted Low Impact Development (LID) practice
in Fort Collins and is often used in combination with other BMPs to provide full treatment and slow
release of the WQCV. In addition, there are some installations in Fort Collins that have also been
designed with an outlet control and increased depth of aggregate material in order to provide quantity
detention in excess of the water quality (80th percentile) storm event. Design considerations for
permeable pavement systems are presented in the LID Implementation Manual, included in Appendix C.
However, there are several design parameters specified below that are also required for all permeable
pavement system designs specific to meeting the LID requirements for Fort Collins.
FORT COLLINS STORMWATER CRITERIA MANUAL Water Quality (Ch. 7)
6.0 Low Impact Development
6.0 Low Impact Development
Page 17
6.3 Bioretention (Rain Gardens)
A BMP that utilizes bioretention is an engineered, depressed landscape area designed to capture and
filter or infiltrate the water quality capture volume (WQCV). BMPs that utilize bioretention are
frequently referred to as rain gardens or porous landscape detention areas (PLDs). In an effort to be
consistent with terms most prevalent in the
stormwater industry, this document generally
refers to the treatment process as
“bioretention” and to the BMP as a “rain
garden”.
This infiltrating BMP requires consultation with
a geotechnical engineer when proposed
adjacent to a structure. A geotechnical engineer
can assist with evaluating the suitability of soils,
identifying potential impacts, and establishing
minimum distances between the BMP and
structures.
Design and construction detailing for
bioretention systems, alternatively referred to
as “rain gardens” are presented in the LID
Implementation Manual in Appendix C.
Additionally, included in Figure 6.4-1 below are
some key design parameters for rain gardens
that are specific to Fort Collins.
6.4 Sand Filter
A sand filter is a filtering or infiltrating BMP that consists of a surcharge zone underlain by a sand bed
with an underdrain system. During a storm, accumulated runoff collects in the surcharge zone and
gradually infiltrates into the underlying sand bed, filling the void spaces of the sand. The underdrain
gradually dewaters the sand bed and discharges the runoff to a nearby channel, swale, storm drain or
detention basin. It is similar to a BMP designed for bioretention in that it utilizes filtering, but differs in
that it is not specifically designed for vegetative growth. The absence of vegetation in a sand filter allows
for active maintenance at the surface of the filter, (i.e., raking for removing a layer of sediment). For this
reason, sand filter criteria allows for a larger contributing area and greater depth of storage. Sand filters
can also be placed in a vault. Underground sand filters have additional requirements.
Design and construction detailing for sand filters are presented in the LID Implementation Manual.
Included in Figure 6.4-1 below are some key design guides for sand filters.
NOTES ABOUT DRYWELLS
• DRYWELLS MAY BE UTILIZED AS AN
OUTFALL FOR LID FACILITIES ONLY
WHEN A GRAVITY OUTFALL TO THE
SURFACE OR STORMWATER
INFRASTRUCTURE IS NOT AVAILABLE
• DRYWELLS ARE NOT ALLOWED TO BE
UTILIZED AS A PRIMARY OUTFALL
FOR DETENTION BASINS OR STORM
PIPING SYSTEMS
• INCLUSION OF A DRYWELL IN DESIGN
PLANS MUST BE ACCOMPANITED BY
A GEOTECHNICAL ANALYSIS AND
RECOMMENDATIONS
• DRYWELL AGGREGATE MATERIAL
MUST EXTEND TO WELL-DRAINING
SOILS AS IDENTIFIED IN A
GEOTECHNICAL ANALYSIS
FORT COLLINS STORMWATER CRITERIA MANUAL Water Quality (Ch. 7)
6.0 Low Impact Development
6.0 Low Impact Development
Page 18
Figure 6.4-1. Design Criteria for Rain Gardens and Sand Filters
6.5 Linear Bioretention
Linear bioretention has low longitudinal slopes and broad cross-sections that convey flow in a slow and
shallow manner, thereby facilitating sedimentation and filtering (straining) while limiting erosion. Berms
or check dams may be incorporated into the facility to reduce velocities and encourage settling and
infiltration. When using berms, an underdrain system should be provided. Linear bioretention is an
integral part of the LID concept and may be used as an alternative to a curb and gutter system.
Design and construction detailing for linear bioretention systems are presented in the LID
Implementation Manual in Appendix C. Included below are some additional design parameters that are
specific to the City of Fort Collins.
Figure 6.5-1. Design Criteria for Linear Bioretention
LOCATION
•Generally, Rain
Gardens and Sand
Filters shall be
placed "offline"
from the detention
basin
VOLUME
•Rain Gardens and Sand
Filters are sized for the
WQCV
•Forebay shall be
included and is to be
sized for 1% of the
WQCV and have a
minimum depth of 12"
•UD-BMP workbook may
be utilized for sizing
•Maximum depth is 12"
for Rain Gardens
OVERFLOW
•Area inlet or
overflow required
at the WQCV depth
(12" above the rain
garden finished
grade surface)
UNDERDRAINS
•Underdrain piping
is required
•Underdrain
cleanouts are
required for
flushing and
inspection
SLOPES
•Minimum longitudinal
slope is 0.5%
•Maximum longitudinal
slope is 1.0%
GEOMETRY
•Minimum bottom width is
24"
•Maximum side slopes 4:1
2-YR STORM DESIGN
•Froude No. ≤ 0.5
•Velocity ≤ 1 fps
•Depth ≤ 12"
X X X X X X X X X X XLID BIOSWALE EXTENTS
250 CUBIC FEET CAPACITY
7.2" MAXIMUM WATER DEPTHLID BIOSWALE
BOTTOM FILTER AREA
160 SQUARE FEET
IMPERMEABLE LINER
SheetHOWES SIX TWO NINEThese drawings areinstruments of serviceprovided by NorthernEngineering Services, Inc.and are not to be used forany type of constructionunless signed and sealed bya Professional Engineer inthe employ of NorthernEngineering Services, Inc.NOT FOR CONSTRUCTIONREVIEW SETENGINEERNGIEHTRONRNFORT COLLINS: 301 North Howes Street, Suite 100, 80521GREELEY: 820 8th Street, 80631970.221.4158northernengineering.comof 15
( IN FEET )
0
1 INCH = 10 FEET
10 10
LEGEND
BIOSWALE TREATMENT AREA
UNTREATED AREA
NOTES:
1.AREA NOT TREATED BY LID CONSISTS OF COURTYARD/WALKWAY,
EXISTING ROOFTOP AREA, LANDSCAPING AND LAWNS.
2.BIOSWALE LID TREATMENT AREA CONSISTS OF ROOF AREA OF
NEW BUILDING(S), THE PORTION OF THE ASPHALT PARKING AREA
NOT DRAINING TO THE ALLEY, AND LANDSCAPED AREAS THAT ARE
TRIBUTARY.
LID1 LID EXHIBIT NA
Howes Six Two Nine LID Summary
Project Summary
Total New/Modified Impervious Area 10,847 sf
Target Treatment Percentage 75%
Minimum Area to be Treated by LID Measures 8,135 sf
LID - Bioswale
Total Area Treated by LID 8,480 sf
Percent of New/Modified Impervious Area
Treated 78.2%
Appendix D
Erosion Control Report
October 15, 2021
Erosion Control Report
Erosion Control Report
A comprehensive Erosion and Sediment Control Plan (along with associated details) has been
included with the final construction drawings. It should be noted, however, that any such
Erosion and Sediment Control Plan serves only as a general guide to the Contractor. Staging
and/or phasing of the BMPs depicted, and additional or different BMPs from those included
may be necessary during construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be
implemented during construction, as well as permanent erosion control protection. Best
Management Practices from the Volume 3, Chapter 7 – Construction BMPs will be utilized.
Measures may include, but are not limited to, silt fencing and/or wattles along the disturbed
perimeter, gutter protection in the adjacent roadways and inlet protection at existing and
proposed storm inlets. Vehicle tracking control pads, spill containment and clean-up
procedures, designated concrete washout areas, dumpsters, and job site restrooms shall also be
provided by the Contractor.
Grading and Erosion Control Notes can be found on Sheet CS2 of the Utility Plans. The Final
Utility Plans will also contain a full-size Erosion Control Plan as well as a separate sheet
dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets,
the Contractor shall be aware of, and adhere to, the applicable requirements outlined in any
existing Development Agreement(s) of record, as well as the Development Agreement, to be
recorded prior to issuance of the Development Construction Permit. Also, the Site Contractor
for this project may be required to secure a Stormwater Construction General Permit from the
Colorado Department of Public Health and Environment (CDPHE), Water Quality Control
Division – Stormwater Program, before commencing any earth disturbing activities. Prior to
securing said permit, the Site Contractor shall develop a comprehensive Storm Water
Management Plan (SWMP) pursuant to CDPHE requirements and guidelines. The SWMP will
further describe and document the ongoing activities, inspections, and maintenance of
construction BMPs.
Appendix E
USDA Soils Report
Soil Map—Larimer County Area, Colorado
(Howes Street Project)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/16/2021
Page 1 of 3449199044920004492010449202044920304492040449199044920004492010449202044920304492040493080493090493100493110493120493130493140493150493160493170
493080 493090 493100 493110 493120 493130 493140 493150 493160 493170
40° 34' 44'' N 105° 4' 54'' W40° 34' 44'' N105° 4' 50'' W40° 34' 42'' N
105° 4' 54'' W40° 34' 42'' N
105° 4' 50'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 20 40 80 120
Feet
0 5 10 20 30
Meters
Map Scale: 1:440 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 Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
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.
Soil Map—Larimer County Area, Colorado
(Howes Street Project)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/16/2021
Page 2 of 3
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
35 Fort Collins loam, 0 to 3
percent slopes
0.7 100.0%
Totals for Area of Interest 0.7 100.0%
Soil Map—Larimer County Area, Colorado Howes Street Project
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/16/2021
Page 3 of 3
Map Unit Description
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions in this
report, along with the maps, can be used to determine the composition and
properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or
more major kinds of soil or miscellaneous areas. A map unit is identified and
named according to the taxonomic classification of the dominant soils. Within a
taxonomic class there are precisely defined limits for the properties of the soils.
On the landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is
made up of the soils or miscellaneous areas for which it is named, soils that are
similar to the named components, and some minor components that differ in use
and management from the major soils.
Most of the soils similar to the major components have properties similar to those
of the dominant soil or soils in the map unit, and thus they do not affect use and
management. These are called noncontrasting, or similar, components. They
may or may not be mentioned in a particular map unit description. Some minor
components, however, have properties and behavior characteristics divergent
enough to affect use or to require different management. These are called
contrasting, or dissimilar, components. They generally are in small areas and
could not be mapped separately because of the scale used. Some small areas of
strongly contrasting soils or miscellaneous areas are identified by a special
symbol on the maps. If included in the database for a given area, the contrasting
minor components are identified in the map unit descriptions along with some
characteristics of each. A few areas of minor components may not have been
observed, and consequently they are not mentioned in the descriptions,
especially where the pattern was so complex that it was impractical to make
enough observations to identify all the soils and miscellaneous areas on the
landscape.
The presence of minor components in a map unit in no way diminishes the
usefulness or accuracy of the data. The objective of mapping is not to delineate
pure taxonomic classes but rather to separate the landscape into landforms or
landform segments that have similar use and management requirements. The
delineation of such segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned,
however, onsite investigation is needed to define and locate the soils and
miscellaneous areas.
An identifying symbol precedes the map unit name in the map unit descriptions.
Each description includes general facts about the unit and gives important soil
properties and qualities.
Map Unit Description: Fort Collins loam, 0 to 3 percent slopes---Larimer County Area,
Colorado
Howes Street Project
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/16/2021
Page 1 of 4
Soils that have profiles that are almost alike make up a soil series. All the soils of
a series have major horizons that are similar in composition, thickness, and
arrangement. Soils of a given series can differ in texture of the surface layer,
slope, stoniness, salinity, degree of erosion, and other characteristics that affect
their use. On the basis of such differences, a soil series is divided into soil
phases. Most of the areas shown on the detailed soil maps are phases of soil
series. The name of a soil phase commonly indicates a feature that affects use or
management. For example, Alpha silt loam, 0 to 2 percent slopes, is a phase of
the Alpha series.
Some map units are made up of two or more major soils or miscellaneous areas.
These map units are complexes, associations, or undifferentiated groups.
A complex consists of two or more soils or miscellaneous areas in such an
intricate pattern or in such small areas that they cannot be shown separately on
the maps. The pattern and proportion of the soils or miscellaneous areas are
somewhat similar in all areas. Alpha-Beta complex, 0 to 6 percent slopes, is an
example.
An association is made up of two or more geographically associated soils or
miscellaneous areas that are shown as one unit on the maps. Because of
present or anticipated uses of the map units in the survey area, it was not
considered practical or necessary to map the soils or miscellaneous areas
separately. The pattern and relative proportion of the soils or miscellaneous
areas are somewhat similar. Alpha-Beta association, 0 to 2 percent slopes, is an
example.
An undifferentiated group is made up of two or more soils or miscellaneous areas
that could be mapped individually but are mapped as one unit because similar
interpretations can be made for use and management. The pattern and
proportion of the soils or miscellaneous areas in a mapped area are not uniform.
An area can be made up of only one of the major soils or miscellaneous areas, or
it can be made up of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is
an example.
Some surveys include miscellaneous areas. Such areas have little or no soil
material and support little or no vegetation. Rock outcrop is an example.
Additional information about the map units described in this report is available in
other soil reports, which give properties of the soils and the limitations,
capabilities, and potentials for many uses. Also, the narratives that accompany
the soil reports define some of the properties included in the map unit
descriptions.
Larimer County Area, Colorado
35—Fort Collins loam, 0 to 3 percent slopes
Map Unit Setting
National map unit symbol: 2tlnc
Elevation: 4,020 to 6,730 feet
Mean annual precipitation: 14 to 16 inches
Mean annual air temperature: 46 to 48 degrees F
Frost-free period: 135 to 160 days
Map Unit Description: Fort Collins loam, 0 to 3 percent slopes---Larimer County Area,
Colorado
Howes Street Project
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/16/2021
Page 2 of 4
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Fort collins and similar soils:85 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Fort Collins
Setting
Landform:Stream terraces, interfluves
Landform position (three-dimensional):Interfluve, tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Pleistocene or older alluvium and/or eolian
deposits
Typical profile
Ap - 0 to 4 inches: loam
Bt1 - 4 to 9 inches: clay loam
Bt2 - 9 to 16 inches: clay loam
Bk1 - 16 to 29 inches: loam
Bk2 - 29 to 80 inches: loam
Properties and qualities
Slope:0 to 3 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Well drained
Runoff class: Low
Capacity of the most limiting layer to transmit water
(Ksat):Moderately high to high (0.20 to 2.00 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Calcium carbonate, maximum content:12 percent
Maximum salinity:Nonsaline to very slightly saline (0.1 to 2.0
mmhos/cm)
Available water capacity:High (about 9.1 inches)
Interpretive groups
Land capability classification (irrigated): 3e
Land capability classification (nonirrigated): 3e
Hydrologic Soil Group: C
Ecological site: R067BY002CO - Loamy Plains
Hydric soil rating: No
Minor Components
Nunn
Percent of map unit:10 percent
Landform:Stream terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Map Unit Description: Fort Collins loam, 0 to 3 percent slopes---Larimer County Area,
Colorado
Howes Street Project
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/16/2021
Page 3 of 4
Map Pocket
DR1 –Drainage Exhibit
FF=5004.17
FF=5004.60
FF=5005.37
ST
ST
ST
ST STSTSTSTSTSTSTSTSTSTSTSTXXXXXXXXXX X X X X C S
S
C
G
C S
C.O.
C S
C S
W
W
G G
D
D
D
D
STSTSTSTSTSTSTSTST ST ST
STSTSTX X X X X X XEEEEEE
E
E
E
E E
EEE
E
UD UD UD UD UD UD
G
G G
FLATS AT THE OVAL
SUBDIVISION
N1
2 LOT 3,
HARRISON'S ADDITION
0.02 ac.
A
0.18 ac.
B
0.09 ac.
C
0.03 ac.
G
0.01 ac.
D
0.07 ac.
E
0.04 ac.
F
a1
b1
f1
e1
c1
d1
g1
LID - BIOSWALE
REQUIRED BOTTOM FILTER SURFACE AREA: 159.9 SF
SURFACE AREA PROVIDED: 160 SF
RIP RAP AROUND
FOREBAY (1.1%)HOWES STREETALLEYSheetHOWES SIX TWO NINEThese drawings areinstruments of serviceprovided by NorthernEngineering Services, Inc.and are not to be used forany type of constructionunless signed and sealed bya Professional Engineer inthe employ of NorthernEngineering Services, Inc.NOT FOR CONSTRUCTIONREVIEW SETENGINEERNGIEHTRONRNFORT COLLINS: 301 North Howes Street, Suite 100, 80521GREELEY: 820 8th Street, 80631970.221.4158northernengineering.comof 15
DR1 OVERALL DRAINAGE PLAN 15
NORTH
( IN FEET )
1 inch = ft.
Feet01515
15
30 45
NOTES:
1.REFER TO THE PRELIMINARY DRAINAGE REPORT FOR ADDITIONAL INFORMATION.
LEGEND:
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
PROPOSED CONTOUR
PROPOSED STORM SEWER
PROPOSED SWALE
EXISTING CONTOUR
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED INLET
A
DESIGN POINT
FLOW ARROW
DRAINAGE BASIN LABEL
DRAINAGE BASIN BOUNDARY
PROPOSED SWALE SECTION
11
A
DEVELOPED DRAINAGE SUMMARY
Design
Point Basin ID
Total
Area
(acres)
C2 C100 2-Yr Tc
(min)
100-Yr Tc
(min)
Q2
(cfs)
Q100
(cfs)
a A 0.020 0.77 0.96 5.00 5.00 0.04 0.19
b B 0.177 0.80 1.00 5.00 5.00 0.40 1.76
c C 0.093 0.75 0.94 5.00 5.00 0.20 0.87
d D 0.010 0.45 0.56 5.00 5.00 0.01 0.06
e E 0.072 0.95 1.00 5.00 5.00 0.19 0.71
f F 0.036 0.20 0.25 5.00 5.00 0.02 0.09
g G 0.027 0.57 0.72 5.00 5.00 0.04 0.19
Howes Six Two Nine LID Summary
Project Summary
Total New/Modified Impervious Area 10,847 sf
Target Treatment Percentage 75%
Minimum Area to be Treated by LID Measures 8,135 sf
LID - Bioswale
New/Modified Impervious Area Treated by LID 8,480 sf
Percent of New/Modified Impervious Area
Treated 78.2%
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 4/16/2021 at 5:15 PM 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°5'11"W 40°34'58"N
105°4'33"W 40°34'31"N
Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020