HomeMy WebLinkAboutWILLOW AND PINE MULTI-FAMILY - PDP - PDP180006 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTApril 16, 2018
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT FOR
WILLOW STREET RESIDENCES
Fort Collins, Colorado
Prepared for:
Richmark Companies
5400 West 20th Street
Greeley, CO 80634
Prepared by:
301 N. Howes, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 1287-005
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
April 16, 2018
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
WILLOW STREET RESIDENCES
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report
for your review. This report accompanies the Project Development Plan submittal for the
proposed Willow Street Residences development.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM),
and serves to document the stormwater impacts associated with the proposed project. We
understand that review by the City is to assure general compliance with standardized criteria
contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Aaron Cvar, PhD, PE
Senior Project Engineer
Willow Street Residences
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain.......................................................................................................................................... 3
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 4
A. Major Basin Description .................................................................................................................... 4
B. Sub-Basin Description ....................................................................................................................... 5
III. DRAINAGE DESIGN CRITERIA ................................................................................... 5
A. Regulations........................................................................................................................................ 5
B. Four Step Process .............................................................................................................................. 5
C. Development Criteria Reference and Constraints ............................................................................ 6
D. Hydrological Criteria ......................................................................................................................... 6
E. Hydraulic Criteria .............................................................................................................................. 6
F. Modifications of Criteria ................................................................................................................... 6
IV. DRAINAGE FACILITY DESIGN .................................................................................... 6
A. General Concept ............................................................................................................................... 6
B. Specific Details .................................................................................................................................. 7
V. CONCLUSIONS ........................................................................................................ 8
A. Compliance with Standards .............................................................................................................. 8
B. Drainage Concept .............................................................................................................................. 8
APPENDICES:
APPENDIX A– Hydrologic Computations
APPENDIX B– Detention Computations
APPENDIX C– Water Quality Computations, LID Information
APPENDIX D – USDA Soils Information
APPENDIX E– Erosion Control Report“Downtown River District (DTRD) Final Design Report”
APPENDIX F– Selected Information from “Downtown River District (DTRD) Final Design Report”
(Ref.4)
Willow Street Residences
Preliminary Drainage Report
LIST OF FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2– Proposed Site Plan ................................................................................................ 3
Figure 3 – Existing Floodplains ............................................................................................. 4
MAP POCKET:
Proposed Drainage Exhibit
Willow Street Residences
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in the northwest quarter of Section 12, Township 7 North,
Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado.
3. The project site is located just east of the intersection of College Ave. and Willow
Street.
4. The project site lies within the Poudre River Basin. Detention will be provided with
an allowable release rate based on historic pervious and impervious areas. Historic
developed area will be granfathered and will be allowed to release at a historic 100-
year rate. Historic undeveloped area will be allowed to release at a historic 2-year
rate. Please see Appendix A for computation of allowable release rate.
5. Water quality treatment for the project site will be provided in the form of LID
treatment within a proposed underground chamber system, as described in further
detail below.
6. As this is an infill site, much of the area surrounding the site is fully developed.
Willow Street Residences
Preliminary Drainage Report 2
B. Description of Property
1. The development area is roughly 2.0 net acres.
Figure 1 – Aerial Photograph
2. The subject property is currently composed of existing buildings, gravel surfaced drive
and parking areas, and landscaped areas. Existing ground slopes are mild to
moderate (i.e., 1 - 3±%) through the interior of the property. General topography
slopes from southwest to northeast.
3. 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 of Paoli Fine Sandy Loam, which falls into Hydrologic Soil Group A.
4. The proposed project site plan is composed of the development of two apartment
buildings and amenities. Associated site work, water, and sewer lines will be
constructed with the development. Onsite water quality treatment is proposed within
an underground chamber system, as discussed in Section IV, below.
PROJECT SITE
Willow Street Residences
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
5. There are no known irrigation laterals crossing the site.
6. The proposed land use is residential/apartments.
C. Floodplain
1. The project site is not encroached by any City designated or FEMA 100-year
floodplain.
Willow Street Residences
Preliminary Drainage Report 4
Figure 3 –Area Floodplain Mapping
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The project site lies within the Poudre River Basin. Detention will be provided with
an allowable release rate based on historic pervious and impervious areas. Historic
developed area will be grandfathered and will be allowed to release at a historic 100-
year rate. Historic undeveloped area will be allowed to release at a historic 2-year
rate. Generally, historic developed areas consist of gravel surfaced drive and parking
areas, which have been accounted for in the computation of the composite historic
release rate from the site. An allowable release rate of 13.15 cfs has been calculated
for the overall site. However, Basins OS1 and OS2 will release undetained into
Willow Street, thus, allowable release rate has been reduced by 0.86 cfs, which is
the peak 100-0year discharge from these basins. Please see Appendix A for
computation of allowable release rate.
2. The entire site area has allowance for water quality treatment in the existing Baysaver
located just southeast of the site. As identified in the “Downtown River District
(DTRD) Final Design Report”, by Ayres Associates, dated February 2012, the current
project area was considered part of master sub-basins 210 and 213, which was
accounted for in the original sizing of the existing Baysaver. Please see the DTRD
Plan, “Exhibit B-Future Development Map for DTRD Area” provided in Appendix F.
3. The Downtown River District (DTRD) Final Design Report accounts for all of Willow
Street Right of Way area in its fully developed condition draining into the recently
completed storm main in Willow Street. Because of this, the project site does not
provide Water Quality or detention for the adjacent half street (Willow Street).
PROJECT SITE
Willow Street Residences
Preliminary Drainage Report 5
4. Please see Appendix B for preliminary detention volume calculations. We will provide
Final level documentation of detention calculations, and underground storage
chamber system information at Final design.
B. Sub-Basin Description
1. The subject property historically drains overland from southwest to northeast. Runoff
from the majority of the site has historically been collected in the adjacent Willow
Street Right of Way, just northeast of the site. There is an existing storm main and a
series of inlets within Willow Street, which collected historic runoff from the existing
site. The proposed outfall for the project site is this existing storm main.
2. A more detailed description of the project drainage patterns is provided below.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the proposed
project.
B. Four Step Process
The overall stormwater management strategy employed with the proposed project utilizes
the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters.
The following is a description of how the proposed development has incorporated each
step.
Step 1 – Employ Runoff Reduction Practices
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low Impact Development (LID) strategies including:
Conserving existing amenities in the site.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, urban
development of this intensity will still generate stormwater runoff that will require
additional BMPs and water quality. The majority of stormwater runoff from the site will
ultimately be intercepted and treated using LID treatment methods prior to exiting the site.
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property. While this step may not
seem applicable to proposed development, the project indirectly helps achieve stabilized
drainageways nonetheless. By providing water quality treatment, where none previously
existed, sediment with erosion potential is removed from downstream drainageway
systems. Furthermore, this project will pay one-time stormwater development fees, as
well as ongoing monthly stormwater utility fees, both of which help achieve City-wide
drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
Willow Street Residences
Preliminary Drainage Report 6
The proposed development will provide LID treatment; thus, eliminating sources of
potential pollution previously left exposed to weathering and runoff processes.
C. Development Criteria Reference and Constraints
The subject property is surrounded by currently developed properties. Thus, several
constraints have been identified during the course of this analysis that will impact the
proposed drainage system including:
Existing elevations along the property lines will generally be maintained.
As previously mentioned, overall drainage patterns of the existing site will be
maintained.
Elevations of existing downstream facilities that the subject property will release to
will be maintained.
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations
associated with the proposed development. Tabulated data contained in Table RA-7
has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 80th percentile rain event, which has been
employed to design the project’s water quality features. The second event analyzed is
the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third
event considered is the “Major Storm,” which has a 100-year recurrence interval.
The fourth storm computed, for comparison purposes only, is the 10-year event.
4. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
1. As previously noted, the subject property maintains historic drainage patterns.
2. All drainage facilities proposed with the project are designed in accordance with
criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District
(UDFCD) Urban Storm Drainage Criteria Manual.
3. As stated above, the subject property is not located in a City designated floodplain.
The proposed project does not propose to modify any natural drainageways.
F. Modifications of Criteria
1. The proposed development is not requesting any modifications to criteria at this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the project drainage design are to maintain existing drainage
patterns, and to ensure no adverse impacts to any adjacent properties.
Willow Street Residences
Preliminary Drainage Report 7
2. Water Quality treatment is provided in the existing Baysaver located just southeast of
the site. LID treatment will be provided in the proposed underground chamber
system, as discussed further below.
3. Drainage patterns anticipated for drainage basins shown in the Drainage Exhibit are
described below. Drainage basins have been defined for preliminary design purposes
and are subject to change at Final design; however, general drainage patterns and
concepts are not expected to be significantly altered.
Basins W1 – W3
Basins W1 through W3 generally consist of paved parking areas, rooftop areas, and
landscaped areas. These basins will generally drain via sheet flow and proposed
concrete pans to collection points and inlets, which will convey flows into the
proposed west underground chamber system.
Basins E1 – E3
Basins E1 through E3 generally consist of paved parking areas, rooftop areas, and
landscaped areas. These basins will generally drain via sheet flow and proposed
concrete pans to collection points and inlets, which will convey flows into the
proposed east underground chamber system.
Basins OS1, OS2
Basins OS1 and OS2 generally consist of paved drive areas, and landscaped areas.
Basin OS1 will sheet flow to proposed curb and gutter which will drain to the adjacent
Willow Street Right of Way. Basin OS2 will sheet flow directly into the adjacent
Willow Street Right of Way. Concrete pavers are proposed in Basin OS1 to provide LID
treatment of the majority of this basin. Allowable overall site release rate has been
reduced to compensate for undetained runoff from Basins OS1 and OS2.
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. An open bottom chamber system is proposed as the primary LID treatment
method for the site. The system will provide standard 12-hour holding time
per UDFCD criteria (please see computations provided in Appendix C). The
chamber system will provide treatment of a minimum of 75% of the proposed
site.
2. Concrete pavers are proposed within Basin OS1, and will treat the majority of
developed runoff generated within this basin.
3. The entire site area has allowance for water quality treatment in the existing Baysaver
located just southeast of the site. As identified in the “Downtown River District
(DTRD) Final Design Report”, by Ayres Associates, dated February 2012, the current
project area was considered part of master sub-basins 210 and 213, which was
accounted for in the original sizing of the existing Baysaver. Please see the DTRD
Plan, “Exhibit B-Future Development Map for DTRD Area” provided in Appendix F.
4. Final design details, and construction documentation shall be provided to the
City of Fort Collins for review prior to Final Development Plan approval.
5. Stormwater facility Standard Operating Procedures (SOP) will be provided by
the City of Fort Collins in the Development Agreement.
Willow Street Residences
Preliminary Drainage Report 8
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the proposed project complies with the City of Fort
Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with this project complies with requirements for the
Poudre River Basin.
3. The drainage plan and stormwater management measures proposed with the
proposed development are compliant with all applicable State and Federal regulations
governing stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit any potential
damage associated with its stormwater runoff by providing detention and water
quality mitigation features.
2. The drainage concept for the proposed development is consistent with requirements
for the Poudre River Basin.
Willow Street Residences
Preliminary Drainage Report 9
References
1. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
2. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
4. Downtown River District (DTRD) Final Design Report, Ayres Associates, February 2012.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado.
APPENDIX A
Hydrologic Computations
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Willow Street Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: B. Mathisen
Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….. 0.50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C
f = 1.00 100-year C
f = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
HN1 15608 0.358 0.261 0.003 0.061 0.022 0.010 0.90 0.90 1.00 92%
HS1 73243 1.681 0.000 0.044 0.097 1.541 0.000 0.54 0.54 0.67 44%
Total 88851 2.040 0.261 0.047 0.158 1.563 0.010 0.60 0.60 0.75 53%
H1 (Impervious) 88396 2.03 0.26 0.05 0.16 1.56 0.00 0.60 0.60 0.75 53%
H1 (Pervious) 455 0.01 0.00 0.00 0.00 0.00 0.01 0.15 0.15 0.19 0%
Existing Impervious Area Breakdown
HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Notes
April 5, 2018
Overland Flow, Time of Concentration:
Project: Willow Street Apartments
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
Rational Method Equation: Project: Willow Street Apartments
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
hn1 HN1 0.36 5 5 5 0.90 0.90 1.00 2.85 4.87 9.95 0.92 1.57 3.57
hs1 HS1 1.68 12 12 9 0.54 0.54 0.67 2.05 3.50 8.03 1.85 3.16 9.07
n/a H1 (Impervious) 2.03 11 11 8 0.60 0.60 0.75 2.17 3.71 8.59 2.66 4.54 13.15
n/a H1 (Pervious) 0.01 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.00 0.01 0.02
HISTORIC RUNOFF COMPUTATIONS
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
B. Mathisen
April 5, 2018
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
C2
Total allowable release from Basin H1
= 13.15
Existing Impervious Area Breakdown
C10
C100
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
Q = C f ( C )( i )( A )
Page 3 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Hist-Direct-Runoff
W
ST ST
X
X
X
X
X
X
X
X
X X
D
M
W
MW
ELEC
BRKR
CONTROL
IRR
MW
MW
MW
MW
D
ELEC
MW
C.O.
C.O.
CONTROL
IRR
MW
C
S
E
G
CONTROL
IRR
CONTROL
IRR
ELEC
BRKR
D
ST
ST
ST
ELEC
VAULT
ELEC
CONTROL
IRR
X
MW
MW
WILLOW STREET
HN1
HS1
hs1
hn1
EXISTING INLET
(TO BE REMOVED)
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Willow Street Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90%
Gravel ……….…………………….….…………………………..……………………………….0.. 50 40%
Roofs …….…….………………..……………….…………………………………………….. 0.95 90%
Pavers…………………………...………………..…………………………………………….. 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C
f = 1.00 100-year C
f = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
W1 14482 0.332 0.239 0.000 0.000 0.000 0.000 0.093 0.73 0.73 0.91 72%
W2 8828 0.203 0.158 0.000 0.000 0.000 0.000 0.045 0.77 0.77 0.97 78%
W3 29479 0.677 0.000 0.000 0.677 0.000 0.000 0.000 0.95 0.95 1.00 90%
E1 10430 0.239 0.184 0.020 0.000 0.000 0.000 0.036 0.83 0.83 1.00 84%
E2 4791 0.110 0.042 0.000 0.000 0.000 0.000 0.068 0.45 0.45 0.57 38%
E3 16674 0.383 0.000 0.000 0.383 0.000 0.000 0.000 0.95 0.95 1.00 90%
Overland Flow, Time of Concentration:
Project: Willow Street Apartments
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt
= L / 60V
Tc
= Ti
+ Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf
=1.00)
C*Cf
(10-yr
Cf
=1.00)
C*Cf
(100-yr
Cf
=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
Rational Method Equation: Project: Willow Street Apartments
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
w1 W1 0.33 5 5 5 0.73 0.73 0.91 2.85 4.87 9.95 0.69 1.17 3.00
w2 W2 0.20 5 5 5 0.77 0.77 0.97 2.85 4.87 9.95 0.45 0.76 1.95
w3 W3 0.68 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.83 3.13 6.73
e1 E1 0.24 5 5 5 0.83 0.83 1.00 2.85 4.87 9.95 0.57 0.97 2.38
e2 E2 0.11 8 8 7 0.45 0.45 0.57 2.46 4.21 9.06 0.12 0.21 0.56
e3 E3 0.38 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.04 1.77 3.81
os1 OS1 0.07 5 5 5 0.79 0.79 0.98 2.85 4.87 9.95 0.16 0.27 0.68 0.68 n/a
os2 OS2 0.03 5 5 5 0.65 0.65 0.81 2.85 4.87 9.95 0.05 0.08 0.21 0.21 n/a
Total 13.15
DEVELOPED RUNOFF COMPUTATIONS
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
100-year
Release Rate
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
Basin(s)
8.41
B. Mathisen
April 13, 2018
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
3.85
West
POND ID
East
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
APPENDIX B
Detention Computations
Pond ID WQ Vol (cu. ft.) Detention Vol. (cu. ft.) Total Vol. (cu. ft.) Provided Vol. (cu. ft.) Proposed Release (cfs)
East 699 1419 2118 2119 3.85
West 1227 1746 2973 2994 8.45
Willow Street Residences Drainage Summary
Pond No :
East Pond
100-yr
0.87
5.00 min 1419 ft3
0.73 acres 0.033 ac-ft
Max Release Rate = 3.85 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 1896 1.00 3.85 1154 742
10 7.720 2942 0.75 2.88 1731 1211
15 6.520 3727 0.67 2.56 2308 1419
20 5.600 4268 0.63 2.40 2885 1383
25 4.980 4744 0.60 2.31 3462 1283
30 4.520 5167 0.58 2.24 4039 1129
35 4.080 5442 0.57 2.20 4616 826
40 3.740 5701 0.56 2.16 5192 508
45 3.460 5933 0.56 2.14 5769 164
50 3.230 6154 0.55 2.12 6346 -192
55 3.030 6350 0.55 2.10 6923 -573
60 2.860 6539 0.54 2.08 7500 -961
65 2.720 6737 0.54 2.07 8077 -1340
70 2.590 6909 0.54 2.06 8654 -1746
75 2.480 7088 0.53 2.05 9231 -2143
80 2.380 7255 0.53 2.04 9808 -2553
85 2.290 7417 0.53 2.04 10385 -2968
90 2.210 7579 0.53 2.03 10962 -3383
95 2.130 7711 0.53 2.02 11539 -3828
100 2.060 7850 0.53 2.02 12116 -4266
105 2.000 8002 0.52 2.01 12693 -4690
110 1.940 8132 0.52 2.01 13270 -5138
115 1.890 8282 0.52 2.01 13847 -5564
120 1.840 8414 0.52 2.00 14424 -6010
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
Pond No :
n1
100-yr
0.96
5.00 min 1746 ft3
1.21 acres 0.040 ac-ft
Max Release Rate = 8.45 cfs
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 3467 1.00 8.45 2535 932
10 7.720 5381 0.75 6.34 3803 1578
15 6.520 6816 0.67 5.63 5070 1746
20 5.600 7806 0.63 5.28 6338 1468
25 4.980 8677 0.60 5.07 7605 1072
30 4.520 9451 0.58 4.93 8873 578
35 4.080 9953 0.57 4.83 10140 -187
40 3.740 10427 0.56 4.75 11408 -981
45 3.460 10852 0.56 4.69 12675 -1823
50 3.230 11256 0.55 4.65 13943 -2687
55 3.030 11615 0.55 4.61 15210 -3595
60 2.860 11960 0.54 4.58 16478 -4518
65 2.720 12322 0.54 4.55 17745 -5423
70 2.590 12636 0.54 4.53 19013 -6377
75 2.480 12963 0.53 4.51 20280 -7317
80 2.380 13270 0.53 4.49 21548 -8277
85 2.290 13566 0.53 4.47 22815 -9249
90 2.210 13863 0.53 4.46 24083 -10220
95 2.130 14103 0.53 4.45 25350 -11247
100 2.060 14357 0.53 4.44 26618 -12260
105 2.000 14636 0.52 4.43 27885 -13249
110 1.940 14873 0.52 4.42 29153 -14279
115 1.890 15148 0.52 4.41 30420 -15272
120 1.840 15389 0.52 4.40 31688 -16299
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1287-005
Willow Street Residences
Project Number :
Project Name :
West Pond
A =
APPENDIX C
Water Quality Computations, LID Information
Design
Point
Basin ID Basin Area Treatment Type
LID
System
Area Treated
by LID
System
Percent of Site
Treated by LID
System
w1 W1 0.332 ac.
StormTech
Chambers
Yes 0.332 ac. 16%
w2 W2 0.203 ac.
StormTech
Chambers
Yes 0.203 ac. 10%
w3 W3 0.677 ac.
StormTech
Chambers
Yes 0.677 ac. 33%
e1 E1 0.239 ac.
StormTech
Chambers
Yes 0.239 ac. 12%
e2 E2 0.110 ac.
StormTech
Chambers
Yes 0.110 ac. 5%
e3 E3 0.383 ac.
StormTech
Chambers
Yes 0.383 ac. 19%
ose1 OSE1 0.070 ac. Concrete Pavers Yes 0.011 ac. 1%
osw1 OSW1 0.026 ac. None No N/A 0%
Total 2.04 ac. 1.955 ac. 96%
LID SUMMARY TABLE
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 80.24%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.264 in
A = 0.73 ac
V = 0.0161 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
699 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
Willow Street Residences April 5, 2018
1287-005 B. Mathisen
Richmark
East Pond
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
east pond
WQ
0.87
5.00 min 471 ft3
0.73 acres 0.01 ac-ft
Max Release Rate = 0.26 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 272 1.00 0.26 78 194
10 1.105 421 1.00 0.26 156 265
15 0.935 534 0.67 0.17 156 379
20 0.805 614 0.63 0.16 195 419
25 0.715 681 0.60 0.16 233 448
30 0.650 743 0.58 0.15 272 471
35 0.585 780 0.57 0.15 311 469
40 0.535 815 0.56 0.15 350 465
45 0.495 849 0.56 0.14 389 460
50 0.460 876 0.55 0.14 428 448
55 0.435 912 0.55 0.14 467 445
60 0.410 937 0.54 0.14 506 431
65 0.385 954 0.54 0.14 545 409
70 0.365 974 0.54 0.14 584 390
75 0.345 986 0.53 0.14 623 363
80 0.330 1006 0.53 0.14 662 344
85 0.315 1020 0.53 0.14 700 320
90 0.305 1046 0.53 0.14 739 307
95 0.290 1050 0.53 0.14 778 271
100 0.280 1067 0.53 0.14 817 250
105 0.270 1080 0.52 0.14 856 224
110 0.260 1090 0.52 0.14 895 195
115 0.255 1117 0.52 0.14 934 183
120 0.245 1120 0.52 0.14 973 147
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
A =
Tc =
Client :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Project Title Date:
Project Number Calcs By:
Client
Basin
0.8
WQCV = Watershed inches of Runoff (inches) 83.08%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq
/100) 0.279 in
A = 1.21 ac
V = 0.0282 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1227 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
Willow Street Residences April 5, 2018
1287-005 B. Mathisen
Richmark
West Pond
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
WQCV (watershed inches)
Total Imperviousness Ratio (i = Iwq
/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
WQCV = a ( 0.91 i 3 − 1 . 19 i 2 + 0 . 78 i )
V * A
12
WQCV
Pond No :
west pond
WQ
0.96
5.00 min 866 ft3
1.21 acres 0.02 ac-ft
Max Release Rate = 0.47 cfs
Time
(min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 1.425 497 1.00 0.47 142 356
10 1.105 771 1.00 0.47 283 488
15 0.935 979 0.67 0.31 283 696
20 0.805 1124 0.63 0.29 354 770
25 0.715 1248 0.60 0.28 425 823
30 0.650 1361 0.58 0.28 495 866
35 0.585 1429 0.57 0.27 566 863
40 0.535 1494 0.56 0.27 637 857
45 0.495 1555 0.56 0.26 708 847
50 0.460 1606 0.55 0.26 778 827
55 0.435 1670 0.55 0.26 849 821
60 0.410 1717 0.54 0.26 920 798
65 0.385 1747 0.54 0.25 991 756
70 0.365 1784 0.54 0.25 1061 722
75 0.345 1806 0.53 0.25 1132 674
80 0.330 1843 0.53 0.25 1203 640
85 0.315 1869 0.53 0.25 1274 596
90 0.305 1916 0.53 0.25 1344 572
95 0.290 1923 0.53 0.25 1415 508
100 0.280 1955 0.53 0.25 1486 469
105 0.270 1979 0.52 0.25 1557 422
110 0.260 1997 0.52 0.25 1627 369
115 0.255 2047 0.52 0.25 1698 349
120 0.245 2052 0.52 0.25 1769 284
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
C =
Tc =
A =
West Pond
Input Variables Results
Design Point
Design Storm Required Detention Volume
Client : Richmark
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Vault ID
Total
Required
WQ Volume
(cf)
Flow,
WQ
(cfs)
Chamber
Type
Chamber Release
Ratea
(cfs)
Chamber
Volumeb
(cf)
Installed Camber
w/ Aggregatec
(cf)
Mimimum
No. of
Chambersd
Total Release
Ratee
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Mimimum
No. of
Chambersf
Storage
Provided
within the
Chambersg
(cf)
Total
Installed
System
Volumeh
(cf)
East Pond 699 0.87 SC-740 0.024 45.90 74.90 10 0.24 471 11 505 824
West Pond 1227 1.49 SC-740 0.024 45.90 74.90 17 0.40 866 19 872 1423
a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.
b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.
c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
d. Number of chambers required to provide full WQCV within total installed system, including aggregate.
e. Release rate per chamber times number of chambers.
f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).
g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.
e. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.
Chamber Configuration Summary
D:\Projects\1287-005\Drainage\WatQual\1287-005 Chamber Summary.xlsx
Chamber Dimensions SC-160 SC-310 SC-740
Width (in) 25.0 34.0 51.0
Length (in) 84.4 85.4 85.4
Height (in) 12.0 16.0 30.0
Floor Area (sf) 14.7 20.2 30.2
Chamber Volume (cf) 6.9 14.7 45.9
Chamber/Aggregate Volume (cf) 16.0 29.3 74.9
Flow Rate* 0.35 gpm/sf
1 cf = 7.48052 gal
1 gallon = 0.133681 cf
1 GPM = 0.002228 cfs
*Flow rate based on 1/2 of Nov 07 QMAX
in Figure 17 of UNH Testing Report
SC-160 SC-310 SC-740
Flow Rate/chamber (cfs) 0.011426 0.015724 0.023586
StormTech Chamber Data
Chamber Flow Rate
Chamber Flow Rate Conversion (gpm/sf to cfs)
D:\Projects\1287-005\Drainage\WatQual\1287-005 Chamber Summary.xlsx
FortCollins
Fort Collins Rainfall Intensity Data
FIG 3-1
Intensities (iph)
Time WQ Event 2-yr 10-yr 100-yr
minutes 2 3 4 5
5.0 1.425 2.85 4.87 9.95
10.0 1.105 2.21 3.78 7.72
15.0 0.935 1.87 3.19 6.52
20.0 0.805 1.61 2.74 5.60
25.0 0.715 1.43 2.44 4.98
30.0 0.650 1.30 2.21 4.52
35.0 0.585 1.17 2.00 4.08
40.0 0.535 1.07 1.83 3.74
45.0 0.495 0.99 1.69 3.46
50.0 0.460 0.92 1.58 3.23
55.0 0.435 0.87 1.48 3.03
60.0 0.410 0.82 1.40 2.86
65.0 0.385 0.77 1.32 2.72
70.0 0.365 0.73 1.25 2.59
75.0 0.345 0.69 1.19 2.48
80.0 0.330 0.66 1.14 2.38
85.0 0.315 0.63 1.09 2.29
90.0 0.305 0.61 1.05 2.21
95.0 0.290 0.58 1.01 2.13
100.0 0.280 0.56 0.97 2.06
105.0 0.270 0.54 0.94 2.00
110.0 0.260 0.52 0.91 1.94
115.0 0.255 0.51 0.88 1.89
120.0 0.245 0.49 0.86 1.84
APPENDIX D
USDA Soils Information
United States
Department of
Agriculture
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
Larimer County
Natural Area, Colorado
Resources
Conservation
Service
April 4, 2018
Preface
Soil surveys contain information that affects land use planning in survey areas.
They highlight soil limitations that affect various land uses and provide information
about the properties of the soils in the survey areas. Soil surveys are designed for
many different users, including farmers, ranchers, foresters, agronomists, urban
planners, community officials, engineers, developers, builders, and home buyers.
Also, conservationists, teachers, students, and specialists in recreation, waste
disposal, and pollution control can use the surveys to help them understand,
protect, or enhance the environment.
Various land use regulations of Federal, State, and local governments may impose
special restrictions on land use or land treatment. Soil surveys identify soil
properties that are used in making various land use or land treatment decisions.
The information is intended to help the land users identify and reduce the effects of
soil limitations on various land uses. The landowner or user is responsible for
identifying and complying with existing laws and regulations.
Although soil survey information can be used for general farm, local, and wider area
planning, onsite investigation is needed to supplement this information in some
cases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/
portal/nrcs/main/soils/health/) and certain conservation and engineering
applications. For more detailed information, contact your local USDA Service Center
(https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State Soil
Scientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?
cid=nrcs142p2_053951).
Great differences in soil properties can occur within short distances. Some soils are
seasonally wet or subject to flooding. Some are too unstable to be used as a
foundation for buildings or roads. Clayey or wet soils are poorly suited to use as
septic tank absorption fields. A high water table makes a soil poorly suited to
basements or underground installations.
The National Cooperative Soil Survey is a joint effort of the United States
Department of Agriculture and other Federal agencies, State agencies including the
Agricultural Experiment Stations, and local agencies. The Natural Resources
Conservation Service (NRCS) has leadership for the Federal part of the National
Cooperative Soil Survey.
Information about soils is updated periodically. Updated information is available
through the NRCS Web Soil Survey, the site for official soil survey information.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its
programs and activities on the basis of race, color, national origin, age, disability,
and where applicable, sex, marital status, familial status, parental status, religion,
sexual orientation, genetic information, political beliefs, reprisal, or because all or a
part of an individual's income is derived from any public assistance program. (Not
all prohibited bases apply to all programs.) Persons with disabilities who require
2
alternative means for communication of program information (Braille, large print,
audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice
and TDD). To file a complaint of discrimination, write to USDA, Director, Office of
Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or
call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity
provider and employer.
3
Contents
Preface.................................................................................................................... 2
How Soil Surveys Are Made..................................................................................5
Soil Map.................................................................................................................. 8
Soil Map................................................................................................................9
Legend................................................................................................................10
Map Unit Legend................................................................................................ 11
Map Unit Descriptions.........................................................................................11
Larimer County Area, Colorado...................................................................... 13
81—Paoli fine sandy loam, 0 to 1 percent slopes....................................... 13
References............................................................................................................15
4
How Soil Surveys Are Made
Soil surveys are made to provide information about the soils and miscellaneous
areas in a specific area. They include a description of the soils and miscellaneous
areas and their location on the landscape and tables that show soil properties and
limitations affecting various uses. Soil scientists observed the steepness, length,
and shape of the slopes; the general pattern of drainage; the kinds of crops and
native plants; and the kinds of bedrock. They observed and described many soil
profiles. A soil profile is the sequence of natural layers, or horizons, in a soil. The
profile extends from the surface down into the unconsolidated material in which the
soil formed or from the surface down to bedrock. The unconsolidated material is
devoid of roots and other living organisms and has not been changed by other
biological activity.
Currently, soils are mapped according to the boundaries of major land resource
areas (MLRAs). MLRAs are geographically associated land resource units that
share common characteristics related to physiography, geology, climate, water
resources, soils, biological resources, and land uses (USDA, 2006). Soil survey
areas typically consist of parts of one or more MLRA.
The soils and miscellaneous areas in a survey area occur in an orderly pattern that
is related to the geology, landforms, relief, climate, and natural vegetation of the
area. Each kind of soil and miscellaneous area is associated with a particular kind
of landform or with a segment of the landform. By observing the soils and
miscellaneous areas in the survey area and relating their position to specific
segments of the landform, a soil scientist develops a concept, or model, of how they
were formed. Thus, during mapping, this model enables the soil scientist to predict
with a considerable degree of accuracy the kind of soil or miscellaneous area at a
specific location on the landscape.
Commonly, individual soils on the landscape merge into one another as their
characteristics gradually change. To construct an accurate soil map, however, soil
scientists must determine the boundaries between the soils. They can observe only
a limited number of soil profiles. Nevertheless, these observations, supplemented
by an understanding of the soil-vegetation-landscape relationship, are sufficient to
verify predictions of the kinds of soil in an area and to determine the boundaries.
Soil scientists recorded the characteristics of the soil profiles that they studied. They
noted soil color, texture, size and shape of soil aggregates, kind and amount of rock
fragments, distribution of plant roots, reaction, and other features that enable them
to identify soils. After describing the soils in the survey area and determining their
properties, the soil scientists assigned the soils to taxonomic classes (units).
Taxonomic classes are concepts. Each taxonomic class has a set of soil
characteristics with precisely defined limits. The classes are used as a basis for
comparison to classify soils systematically. Soil taxonomy, the system of taxonomic
classification used in the United States, is based mainly on the kind and character
of soil properties and the arrangement of horizons within the profile. After the soil
5
scientists classified and named the soils in the survey area, they compared the
individual soils with similar soils in the same taxonomic class in other areas so that
they could confirm data and assemble additional data based on experience and
research.
The objective of soil mapping is not to delineate pure map unit components; the
objective is to separate the landscape into landforms or landform segments that
have similar use and management requirements. Each map unit is defined by a
unique combination of soil components and/or miscellaneous areas in predictable
proportions. Some components may be highly contrasting to the other components
of the map unit. The presence of minor components in a map unit in no way
diminishes the usefulness or accuracy of the data. The delineation of such
landforms and landform segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, onsite
investigation is needed to define and locate the soils and miscellaneous areas.
Soil scientists make many field observations in the process of producing a soil map.
The frequency of observation is dependent upon several factors, including scale of
mapping, intensity of mapping, design of map units, complexity of the landscape,
and experience of the soil scientist. Observations are made to test and refine the
soil-landscape model and predictions and to verify the classification of the soils at
specific locations. Once the soil-landscape model is refined, a significantly smaller
number of measurements of individual soil properties are made and recorded.
These measurements may include field measurements, such as those for color,
depth to bedrock, and texture, and laboratory measurements, such as those for
content of sand, silt, clay, salt, and other components. Properties of each soil
typically vary from one point to another across the landscape.
Observations for map unit components are aggregated to develop ranges of
characteristics for the components. The aggregated values are presented. Direct
measurements do not exist for every property presented for every map unit
component. Values for some properties are estimated from combinations of other
properties.
While a soil survey is in progress, samples of some of the soils in the area generally
are collected for laboratory analyses and for engineering tests. Soil scientists
interpret the data from these analyses and tests as well as the field-observed
characteristics and the soil properties to determine the expected behavior of the
soils under different uses. Interpretations for all of the soils are field tested through
observation of the soils in different uses and under different levels of management.
Some interpretations are modified to fit local conditions, and some new
interpretations are developed to meet local needs. Data are assembled from other
sources, such as research information, production records, and field experience of
specialists. For example, data on crop yields under defined levels of management
are assembled from farm records and from field or plot experiments on the same
kinds of soil.
Predictions about soil behavior are based not only on soil properties but also on
such variables as climate and biological activity. Soil conditions are predictable over
long periods of time, but they are not predictable from year to year. For example,
soil scientists can predict with a fairly high degree of accuracy that a given soil will
have a high water table within certain depths in most years, but they cannot predict
that a high water table will always be at a specific level in the soil on a specific date.
After soil scientists located and identified the significant natural bodies of soil in the
survey area, they drew the boundaries of these bodies on aerial photographs and
Custom Soil Resource Report
6
identified each as a specific map unit. Aerial photographs show trees, buildings,
fields, roads, and rivers, all of which help in locating boundaries accurately.
Custom Soil Resource Report
7
Soil Map
The soil map section includes the soil map for the defined area of interest, a list of
soil map units on the map and extent of each map unit, and cartographic symbols
displayed on the map. Also presented are various metadata about data used to
produce the map, and a description of each soil map unit.
8
9
Custom Soil Resource Report
Soil Map
4493250 4493270 4493290 4493310 4493330 4493350 4493370 4493390 4493410 4493430
4493250 4493270 4493290 4493310 4493330 4493350 4493370 4493390 4493410 4493430
493600 493620 493640 493660 493680 493700 493720 493740
493600 493620 493640 493660 493680 493700 493720 493740
40° 35' 30'' N
105° 4' 32'' W
40° 35' 30'' N
105° 4' 25'' W
40° 35' 23'' N
105° 4' 32'' W
40° 35' 23'' N
105° 4' 25'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 45 90 180 270
Feet
0 10 20 40 60
Meters
Map Scale: 1:962 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 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
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
81 Paoli fine sandy loam, 0 to 1
percent slopes
2.5 100.0%
Totals for Area of Interest 2.5 100.0%
Map Unit Descriptions
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, 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 and some minor
components that belong to taxonomic classes other than those of the major soils.
Most minor soils 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. Other minor components, however, have properties
and behavioral 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.
Custom Soil Resource Report
11
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.
Soils that have profiles that are almost alike make up a soil series. Except for
differences in texture of the surface layer, all the soils of a series have major
horizons that are similar in composition, thickness, and arrangement.
Soils of one 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.
Custom Soil Resource Report
12
Larimer County Area, Colorado
81—Paoli fine sandy loam, 0 to 1 percent slopes
Map Unit Setting
National map unit symbol: jpxx
Elevation: 4,800 to 5,600 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 135 to 150 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Paoli and similar soils: 85 percent
Minor components: 15 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Paoli
Setting
Landform: Stream terraces
Landform position (three-dimensional): Tread
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Alluvium
Typical profile
H1 - 0 to 30 inches: fine sandy loam
H2 - 30 to 60 inches: fine sandy loam, sandy loam, loamy sand
H2 - 30 to 60 inches:
H2 - 30 to 60 inches:
Properties and qualities
Slope: 0 to 1 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Very low
Capacity of the most limiting layer to transmit water (Ksat): High (2.00 to 6.00
in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 15 percent
Salinity, maximum in profile: Nonsaline to very slightly saline (0.0 to 2.0
mmhos/cm)
Available water storage in profile: Very high (about 16.5 inches)
Interpretive groups
Land capability classification (irrigated): 1
Land capability classification (nonirrigated): 3c
Hydrologic Soil Group: A
Ecological site: Overflow (R067BY036CO)
Hydric soil rating: No
Custom Soil Resource Report
13
Minor Components
Caruso
Percent of map unit: 6 percent
Hydric soil rating: No
Table mountain
Percent of map unit: 6 percent
Hydric soil rating: No
Fluvaquentic haplustolls
Percent of map unit: 3 percent
Landform: Terraces
Hydric soil rating: Yes
Custom Soil Resource Report
14
References
American Association of State Highway and Transportation Officials (AASHTO).
2004. Standard specifications for transportation materials and methods of sampling
and testing. 24th edition.
American Society for Testing and Materials (ASTM). 2005. Standard classification of
soils for engineering purposes. ASTM Standard D2487-00.
Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of
wetlands and deep-water habitats of the United States. U.S. Fish and Wildlife
Service FWS/OBS-79/31.
Federal Register. July 13, 1994. Changes in hydric soils of the United States.
Federal Register. September 18, 2002. Hydric soils of the United States.
Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydric
soils in the United States.
National Research Council. 1995. Wetlands: Characteristics and boundaries.
Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service.
U.S. Department of Agriculture Handbook 18. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/national/soils/?cid=nrcs142p2_054262
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for
making and interpreting soil surveys. 2nd edition. Natural Resources Conservation
Service, U.S. Department of Agriculture Handbook 436. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053577
Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department of
Agriculture, Natural Resources Conservation Service. http://
www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053580
Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service and
Delaware Department of Natural Resources and Environmental Control, Wetlands
Section.
United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps of
Engineers wetlands delineation manual. Waterways Experiment Station Technical
Report Y-87-1.
United States Department of Agriculture, Natural Resources Conservation Service.
National forestry manual. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/
home/?cid=nrcs142p2_053374
United States Department of Agriculture, Natural Resources Conservation Service.
National range and pasture handbook. http://www.nrcs.usda.gov/wps/portal/nrcs/
detail/national/landuse/rangepasture/?cid=stelprdb1043084
15
United States Department of Agriculture, Natural Resources Conservation Service.
National soil survey handbook, title 430-VI. http://www.nrcs.usda.gov/wps/portal/
nrcs/detail/soils/scientists/?cid=nrcs142p2_054242
United States Department of Agriculture, Natural Resources Conservation Service.
2006. Land resource regions and major land resource areas of the United States,
the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook
296. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?
cid=nrcs142p2_053624
United States Department of Agriculture, Soil Conservation Service. 1961. Land
capability classification. U.S. Department of Agriculture Handbook 210. http://
www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf
Custom Soil Resource Report
16
APPENDIX E
Erosion Control Report
Willow Street Residences
Preliminary Erosion Control Report
EROSION CONTROL REPORT
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at 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 the Utility Plans. The Final Plans will contain a
full-size Erosion Control sheet 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 the Development Agreement for the development. Also,
the Site Contractor for this project will be required to secure a Stormwater Construction General
Permit from the Colorado Department of Public Health and Environment (CDPHE), Water Quality
Control Division – Stormwater Program, prior to any earth disturbance activities. Prior to securing
said permit, the Site Contractor shall develop a comprehensive StormWater Management Plan
(SWMP) pursuant to CDPHE requirements and guidelines. The SWMP will further describe and
document the ongoing activities, inspections, and maintenance of construction BMPs.
APPENDIX F
Selected Information from “Downtown River District (DTRD) Final
Design Report”
MAP POCKET
SS
SS
SS SS
SS
X
X
X
X
X
X X X
X
X
X X
X
X
X X X
X
X X
X
X
D
ST
ST
D
ST
ST
ST
ST
CONTROL
IRR
T
ST
ST
ST
S
N
YLOPLAST
DO NOT POLLUTE DRAINS TO WATERWAYS
NYLOPLAST
DO NOT POLLUTE DRAINS TO WATERWAYS
S
NYLOPLAST
DO NOT POLLUTE DRAINS TO WATERWAYS
NYLOPLAST
DO NOT POLLUTE DRAINS TO WATERWAYS
NYLOPLAST
DO NOT POLLUTE
DRAINS WATERWAYS TO
DO NOT POLLUTE DRAINS TO WATERWAYS
NYLOPLAST DUCTILE IRON
NYLOPLAST
DO DRAINS NOT TO POLLUTE
WATERWAYS
DO NOT POLLUTE DRAINS TO WATERWAYS
NYLOPLAST DUCTILE IRON
UD
MONITORING WELL
TRAFFIC RATED
UD UD UD UD UD
UD
UD
UD
UD
UD
UD
MONITORING WELL
TRAFFIC RATED
MONITORING WELL
TRAFFIC RATED
MONITORING WELL
TRAFFIC RATED
w1
w2
e1
e2
WILLOW STREET
w3
e3
W3
OS1
E3
E1
W2
E2
W1
OS2
"WEST POND"
34 SC-740 STORMTECH CHAMBERS
23 SC-740 ISOLATOR CHAMBERS
"EAST POND"
21 SC-740 STORMTECH CHAMBERS
21 SC-740 ISOLATOR CHAMBERS
SEE SHEET C-300
FOR STORM SEWER
INFORMATION
POROUS PAVERS
± 732 SQ. FT. OF
RUNOFF FLOWING
OVER THE PUBLIC
SIDEWALK
INLET
INLET
INLET
INLET
INLET
INLET
2' CONCRETE
PAN
2' CONCRETE
PAN
os2
os1
Sheet
WILLOW STREET RESIDENCES These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
REVIEW SET
ENGINEER ING
N O R T H E RN
FORT COLLINS: 301 North Howes Street, Suite 100, 80521
GREELEY: 820 8th Street, 80631
970.221.4158
northernengineering.com
of 09
NORTH
C-500
DRAINAGE EXHIBIT
08
( IN FEET )
0
1 INCH = 20 FEET
20 20 40 60
GRAPHIC SCALE:
LEGEND:
PROPOSED STORM SEWER
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED STORM INLET
EXISTING CURB & GUTTER
PROPOSED OVERLAND FLOW
EXISTING MAJOR CONTOUR
PROPOSED MAJOR CONTOUR
RUNOFF SUMMARY:
A2
a3
DRAINAGE BASIN AREA
DRAINAGE BASIN ID
DRAINAGE BASIN MINOR/MAJOR COEFF.
EXISTING STORM SEWER ST
PROPOSED DIRECT FLOW
BASIN DELINEATION
1. REFER TO "PRELIMINARY DRAINAGE REPORT FOR WILLOW STREET
RESIDENCES" PREPARED BY NORTHERN ENGINEERING ON 04/16/2018 FOR
ADDITIONAL INFORMATION.
NOTES:
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
Q2
(cfs)
Q100
(cfs)
W1 0.332 0.73 0.91 0.69 3.00
W2 0.203 0.77 0.97 0.45 1.95
W3 0.677 0.95 1.00 1.83 6.73
E1 0.239 0.83 1.00 0.57 2.38
E2 0.110 0.45 0.57 0.12 0.56
E3 0.383 0.95 1.00 1.04 3.81
OS1 0.070 0.79 0.98 0.16 0.68
OS2 0.026 0.65 0.81 0.05 0.21
City Engineer Date
Date
Date
Date
Date
Stormwater Utility
Parks & Recreation
Traffic Engineer
Date
Water & Wastewater Utility
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
Environmental Planner
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what's below.
Call before you dig.
R
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 12, Oct 10, 2017
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Mar 20, 2015—Oct
15, 2016
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Custom Soil Resource Report
10
Project Name : Willow Street Residences
Project Number : 1287-005
Page 4 of 7
1287-005 Chamber Summary.xlsx
=
12 hr
Richmark
Willow Street Residences
1287-005
Project Name :
Project Number :
East Pond
Page 2 of 7
1287-005 Chamber Summary.xlsx
=
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Project Number :
Project Name :
East Pond
Page 1 of 1
1287-005_FAA East Pond.xls
Q = C f ( C )( i )( A )
Page 6 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Direct-Runoff
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
w1 W1 No 0.73 0.73 0.91 15 3.21% 1.8 1.8 0.9 160 1.10% 2.10 1.3 0.5 N/A N/A 5 5 5
w2 W2 No 0.77 0.77 0.97 N/A N/A N/A 82 1.25% 2.24 0.6 1.5 N/A N/A 5 5 5
w3 W3 No 0.95 0.95 1.00 N/A N/A N/A N/A N/A N/A N/A N/A N/A 5 5 5
e1 E1 No 0.83 0.83 1.00 N/A N/A N/A N/A 2.00% N/A N/A 1.5 N/A N/A 5 5 5
e2 E2 No 0.45 0.45 0.57 46 2.00% 6.5 6.5 5.4 193 2.00% 2.83 1.1 2.5 N/A N/A 8 8 7
e3 E3 No 0.95 0.95 1.00 N/A N/A N/A N/A N/A N/A N/A N/A N/A 5 5 5
os1 OS1 No 0.79 0.79 0.98 53 1.90% 3.4 3.4 1.3 N/A N/A N/A N/A N/A 5 5 5
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter/Internal Building Flow Swale Flow
Design
Point
Basin
Overland Flow
B. Mathisen
April 13, 2018
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
= −
Page 5 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr
OS1 3031 0.070 0.050 0.002 0.000 0.000 0.011 0.006 0.79 0.79 0.98 74%
OS2 1136 0.026 0.016 0.000 0.000 0.000 0.000 0.010 0.65 0.65 0.81 62%
TOTAL 88851 2.040 0.689 0.022 1.060 0.000 0.011 0.281 0.85 0.85 1.00 81%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf
= 1.00
April 13, 2018
**Soil Classification of site is Sandy Loam**
B. Mathisen
Page 4 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\C-Values
NORTH
( IN FEET )
0
1 INCH = 60 FEET
60 60 120 180
GRAPHIC SCALE:
LEGEND:
PROPERTY BOUNDARY
EXISTING STORM INLET
EXISTING CURB & GUTTER
EXISTING OVERLAND FLOW
EXISTING MAJOR CONTOUR
RUNOFF SUMMARY:
A2
a3
DRAINAGE BASIN AREA
DRAINAGE BASIN ID
DRAINAGE BASIN MINOR/MAJOR COEFF.
EXISTING STORM SEWER ST
BASIN DELINEATION
1. REFER TO "PRELIMINARY DRAINAGE REPORT FOR WILLOW STREET
RESIDENCES" PREPARED BY NORTHERN ENGINEERING ON 04/10/2018 FOR
ADDITIONAL INFORMATION.
NOTES:
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
Q2
(cfs)
Q100
(cfs)
HN1 0.358 0.90 1.00 0.92 3.57
HS1 1.681 0.54 0.67 1.85 9.07
H1 (Impervious) 0.000 0.00 0.00 2.66 13.15
H1 (Pervious) 0.000 0.00 0.00 0.00 0.02
HISTORIC DRAINAGE EXHIBIT
APPENDIX
FORT COLLINS, CO
WILLOW STREET RESIDENCES
ENGINEER ING
N O R T H E RN
04.11.2018
D:\PROJECTS\1287-005\DWG\DRNG\1287-005_HIST_DRNG.DWG
ROOF
GRAVEL
CONCRETE
ASPHALT
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
hn1 HN1 No 0.90 0.90 1.00 93 2.68% 2.6 2.6 1.3 N/A N/A N/A N/A N/A N/A 5 5 5
hs1 HS1 No 0.54 0.54 0.67 275 2.84% 12.3 12.3 9.4 N/A N/A N/A N/A N/A N/A 12 12 9
n/a H1 (Impervious) No 0.60 0.60 0.75 275 2.84% 10.9 10.9 7.6 N/A N/A N/A N/A N/A N/A 11 11 8
n/a H1 (Pervious) No 0.15 0.15 0.19 20 4.65% 4.8 4.8 4.6 N/A N/A N/A N/A N/A N/A 5 5 5
Existing Impervious Area Breakdown
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
B. Mathisen
Design
Point
Basin
Overland Flow Gutter Flow Swale Flow Time of Concentration
April 5, 2018
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
= −
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10-year Cf
= 1.00
**Soil Classification of site is Sandy Loam**
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
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