HomeMy WebLinkAboutHILL POND RESIDENCES - FDP - FDP160017 - REPORTS - DRAINAGE REPORTJune 15, 2016
FINAL DRAINAGE REPORT
HILL POND RESIDENCES
Fort Collins, Colorado
Prepared for:
Catamount Properties Ltd.
7302 Rozena Drive
Longmont, Colorado 80503
Prepared by:
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158
www.northernengineering.com
Project Number: 620-004
PThis 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.
June 15, 2016
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
Hill Pond Residences
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage Report for your review. This
report accompanies the Final Plan submittal for the proposed Hill Pond Residences
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 Hill Pond Residences 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.
Nicholas W. Haws, PE Andrew Reese
Vice President Project Manager
Hill Pond Residences
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ......................................................... 1
II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 5
III. DRAINAGE DESIGN CRITERIA ......................................................................... 6
IV. DRAINAGE FACILITY DESIGN .......................................................................... 9
V. CONCLUSIONS............................................................................................. 11
References ............................................................................................................. 12
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Hydraulic Computations
B.2 – Detention Facilities
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
APPENDIX E – LID Conformance
APPENDIX F – Standard Operating Procedures (SOP’s) References (Reserved for Final)
MAP POCKET:
DR1 – Drainage Exhibit
DR2 – Existing Drainage Exhibit
Hill Pond Residences
Page|1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
Figure 1 – Vicinity Map
2. The Hill Pond Residences project site is located in the Northwest quarter of Section
23, 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 (refer to Figure 1) is bordered to the north by a single family
residence; to the south by Hill Pond Road; to the east by Gilgalad Way; and to the
west by existing single family residences.
4. There are no major drainageways within or adjacent to the site.
Hill Pond Residences
Page|2
B. Description of Property
1. Hill Pond Residences is comprised of ±2.179 acres.
2. The site is currently a single family residence. It was originally developed as a
neighborhood amenity with two tennis courts, a pool and large green spaces.
Figure 2 – Aerial Photograph
3. The existing groundcover consists of grasses, gravel and concrete.
4. The existing on-site runoff generally drains to both the northeast as well as the
southwest due to a ridge that bisects the property. Flows draining to the northeast
corner are collected by a series of existing low areas that do not have an outfall to any
established drainage facilities. Drainage to the southeast flows to Hill Pond Road and
Gilgalad Way. Those flows are collected by an existing inlet on the northeast corner of
the intersection which conveys flows to Spring Creek.
Project Site
Hill Pond Residences
Page|3
5. A soils report letter (Project No. FC06692-115 | Date: September 16, 2014) was
completed by CTL|Thompson, Inc. The report letter contains the preliminary results
of a complete geotechnical subsurface exploration as well as pertinent geotechnical
recommendations. According to the summary of findings presented in the
aforementioned report,
"Strata encountered in our exploratory borings generally consisted of approximately
0-4-1/2 feet of clay and sand fill, underlain by natural sandy clay and clayey sand
soils which extended approximately 18 to 21 feet.”
6. There are no major drainageways within or adjacent to the project site.
7. The proposed Hill Pond Residences development will consist of 8 residential buildings
that are single family attached units. Other proposed improvements include: a new
concrete and permeable Modular Block Paver (MBP) parking area and landscaping.
8. The proposed land use is residential, single-family attached. This is a permitted use in
the Medium Density Mixed Use Neighborhood District (MMN).
Hill Pond Residences
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C. Floodplain
1. The subject property is not located in a FEMA regulatory or City of Fort Collins
designated floodplain. In particular, the project site is not located within a FEMA
designated 100-year floodplain per Map Number 08069C0987G (Effective date: May
2, 2012).
Figure 4 – FEMA Firmette (Map Number 08069C0987G)
Project Site
Hill Pond Residences
Page|5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Hill Pond Residences is located within the City of Fort Collins Spring Creek major
drainage basin. Specifically, the project site is situated in the central portion of this
major drainage basin. This basin is located in central Fort Collins and has a drainage
area of approximately 5,656 acres. The Spring Creek major drainage basin generally
drains from west to east. Most of the runoff from the Spring Creek major drainage
basin drains into the Poudre River.
B. Sub-Basin Description
1. Outfalls: There are two existing outfall locations for the project. The first outfall for the
project site is a series of localized low points along the eastern boundary of the
project. The second outfall location for the project is the existing curb and gutter
along Gilgalad Way, along the southeastern boundary of the project site.
2. The existing subject site can be defined with two (2) sub-basins. Refer to the Existing
Drainage Exhibit for additional information.
· Sub-basin EX1 delineates the northern portion of the existing project site,
which was used to approximate the 2- and 100-year existing runoff. Drainage
from the basin generally flows to the northeast, and is collected in localized
low-points along the eastern boundary of the site.
· Sub-basin EX2 delineates the southern portion of the existing project site and
was used to approximate the 2- and 100-year existing runoff. Drainage from
the basin generally flows to the southeast and is collected by Gilgalad Way
and Hill Pond Road, which then conveys flows to the existing inlet on the
northeast corner of the intersection.
3. The project site does not receive notable runoff from contiguous off-site properties.
Hill Pond Residences
Page|6
III. DRAINAGE DESIGN CRITERIA
A. There are no optional provisions outside of the FCSCM proposed with Hill Pond
Residences.
B. The overall stormwater management strategy employed with Hill Pond Residences 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.
Hill Pond Residences 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 Modular Block Pavers (MBPs).
This LID practice reduces 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 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 primary water quality treatment will occur in
the Modular Block Paver (MBP) section in sub-basin B.
Step 3 – Stabilize Drainageways. As stated in Section I.B.5, above, there are no major
drainageways in or near the subject site. While this step may not seem applicable to Hill
Pond Residences, the proposed project indirectly helps achieve stabilized drainageways
nonetheless. Once again, site selection has a positive effect on stream stabilization. By
developing an infill site with existing stormwater infrastructure, combined with LID and
MDCIA strategies, the likelihood of bed and bank erosion is reduced. Furthermore, this
project will pay one-time stormwater development fees, as well as ongoing monthly
stormwater utility fees, both of which help achieve Citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs. This step typically
applies to industrial and commercial developments.
C. Development Criteria Reference and Existing Constraints
1. The subject property is not part of any Overall Development Plan (ODP) drainage
study or similar “development/project” drainage master plan.
2. The site plan is constrained on two sides by public streets, as well as by existing
undeveloped and developed sites along the remaining two sides. As previously
mentioned, the drainage outfall for sub-basin EX1 is a series of localized low points
along the eastern boundary of the project. Basin EX2 drains to the adjacent streets.
Hill Pond Residences
Page|7
3. Peak runoff from the project site during the 2-year event will remain unchanged or
decrease and will decrease during the 100-year storm event.
During the 2-year storm event, runoff to the northeast will decrease from the current
±0.83 cfs to ±0.17 cfs; and during the 100-year storm event runoff will decrease
from ±3.75 cfs to ±0.74 cfs.
During the 2-year storm event, runoff to the southeast will remain unchanged from the
current ±0.95 cfs; and during the 100-year storm event runoff will decrease from
±4.16 cfs to ±3.45 cfs.
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serves as the source for all hydrologic computations
associated with the Hill Pond Residences development. Tabulated data contained in
Table RA-7 has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. The Rational Formula-based Federal Aviation Administration (FAA) procedure has
utilized for detention storage calculations.
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.
E. Hydraulic Criteria
1. The drainage facilities proposed with the Hill Pond Residences project are
designed in accordance with criteria outlined in the FCSCM and/or the Urban
Drainage and Flood Control District’s (UDFCD) Urban Storm Drainage Criteria
Manual.
2. As stated in Section I.C.1, above, the subject property is not located in a
FEMA regulatory or a City of Fort Collins designated floodplain.
F. Floodplain Regulations Compliance
1. As previously mentioned, this project is not subject to any floodplain
regulations.
G. Modifications of Criteria
1. No modifications are requested at this time.
H. Conformance with Low Impact Development (LID)
1. 30,843 sf of paving is proposed with this project, and of the total, 13,422 sf
is proposed to be Modular Block Pavers (MBPs). This means that ± 44% of
Hill Pond Residences
Page|8
the paved areas in the project are pervious, exceeding the minimum
requirement of 25%.
2. The total new impervious area for the project is 71,110 sf. Of that area,
64,537 sf will be treated by LID techniques, primarily Modular Block Pavers
(MBPs) or releasing flows into landscaped areas that will be routed to the
paver subgrade. This means that ± 91% of the site will be treated by LID-
type technology, exceeding the minimum requirement of 50%.
Please see the LID Treatment Exhibit located in the Appendix for additional
information.
Hill Pond Residences
Page|9
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objective of the Hill Pond Residences 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. The project site has been divided into three (3) drainage sub-basins, designated as
sub-basins A, B & C. The drainage patterns anticipated for each basin are further
described below.
Sub-Basin A
Sub-basin A encompasses ±10 percent of the total site area and runs along the north
and east sides of the property. This sub-basin is comprised of landscaping and private
concrete patios. This basin will continue to surface drain along the boundary of the
project at a decreased 2-year release rate of 0.17 cfs. The basin release rate will also
be reduced in the 100-yr event to a rate of 0.74 cfs.
Sub-Basin B
Sub-basin B encompasses ±60 percent of the total site area. This sub-basin is
comprised of roof area, landscaping and the on-site parking area. This parking area
will be a mix of concrete and Modular Block Pavers (MBPs). Detention will be
provided within in the MBPs (WSEL100-year=5012.63±). The detained flows will then
be directed to the existing curb and gutter along Gilgalad Way. This basin will release
at an adjusted 2-year rate of 0.95 cfs through an orifice plate in the 100-yr event. An
outlet orifice cap located on the east wall of the proposed drain basin will be used to
control the flow rate. See Section B.1 for details on how the release rate was
calculated.
Sub-Basin C
Sub-basin C encompasses the western and southern edge of the project site along the
Hill Pond and Gilgalad Way frontage. It is comprised of public sidewalks and
landscaping, as well as the proposed entry drive. This basin will continue to surface
drain along the boundary of the project at a decreased 2-year release rate of 0.56 cfs.
The basin release rate will also be reduced in the 100-yr event to a rate of 0.2.50 cfs.
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. The release rate for the MBP detention area was determined by calculating the
existing C-value for the entire existing project site (C2=0.37) and multiplying
that value by the area of Sub-Basin B (1.46 acres) and by the 2-yr intensity
factor (1.75). The result is 0.95 cfs. The other areas of the project are not
Hill Pond Residences
Page|10
being significantly affected by development of the site due to the existence of
many large trees on the site and a desire to preserve as many as possible. As
such, these areas will continue to release at levels similar to their existing
condition. In total, the project site will maintain its total release in the 2-year
event at 1.78 cfs and will decrease the total release in the 100-yr event from
the existing 7.91 cfs to 4.19 cfs in the developed condition.
2. The FAA method was used to size the on-site pond for quantity detention.
Calculations for this area, based on the characteristics of sub-basin B and
adjusted release rate, indicate a required detention volume of 11,342 cu. ft.
This includes 2,091 cu. ft. of Water Quality Capture Volume (WQCV). During
water quality events the water quality capture volume will release over 12-
hours. There is no-infiltration accounted for with this design.
3. The storage volume available within the reservoir area (i.e., No. 57 and No. 2
open-graded aggregate) of the MBP section is ±11,353 cu. ft. at WSEL
5012.08. The MBP section is designed with a No.2, open-graded aggregate
material depth that exceeds the minimum required for vehicle loading in order
to provide storage for storm events in excess of the water quality (80th
percentile) storm event. This volume assumes a 30% void space in the open-
graded aggregates per City requirements.
4. A Drain Basin is located at the downstream end of the parking area. This
basin will have an orifice cap installed on the east wall that will limit the
release from the site to the maximum allowable release rate (0.95 cfs).
5. The majority of roof drain downspouts will discharge into the MBP section.
The remaining downspouts will release into landscaped areas.
6. The emergency spill path will be from the parking area onto the lot line, where flows
will proceed along the historic path north and east until they spill into undeveloped
areas north of the project site.
Hill Pond Residences
Page|11
V. CONCLUSIONS
A. Compliance with Standards
1. The design elements comply without variation, and meet all LID requirements.
2. The drainage design proposed with Hill Pond Residences complies with the City of
Fort Collins Master Drainage Plan for the Spring Creek Major Drainage Basin.
3. There are no regulatory floodplains associated with the Hill Pond Residences
development.
4. The drainage plan and stormwater management measures proposed with the Hill
Pond Residences 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. Hill Pond Residences will detain for the pervious
area converted to impervious areas to release at the 2-year existing rate during the 2-
year storm and at a significantly decreased rate during the 100-yr storm.
2. The proposed Hill Pond Residences development will not impact the Master Drainage
Plan recommendations for the Spring Creek Major Drainage Basin.
Hill Pond Residences
Page|12
References
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Preliminary Geotechnical Investigation – Proposed Hill Pond Project, September 16, 2014,
CTL | Thompson, Inc. (Project No. FC006692-115).
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Hill Pond Residences
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Reese
Asphalt ……....……………...……….....…...……………….………………………………….0.95 100 . Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 40 .
Roofs …….…….………………..……………….…………………………………………….0.95 . 90
Concrete Pavers…………………………...………………..…………………………………………….0.40 22 .
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….0.15 . 0
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
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.
A 0.18 0.00 0.02 0.00 0.00 0.00 0.16 0.33 0.33 0.41 9.8
B 1.46 0.00 0.32 0.67 0.00 0.31 0.17 0.75 0.75 0.94 65.5
C 0.54 0.00 0.08 0.05 0.00 0.00 0.40 0.42 0.42 0.53 22.3
TOTAL ONSITE 2.18 0.00 0.42 0.72 0.00 0.31 0.73 0.64 0.64 0.80 50.2
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
June 15, 2016
Overland Flow, Time of Concentration:
Project: Hill Pond Residences
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: Hill Pond Residences
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
A A 0.18 5.0 5.0 5.0 0.33 0.33 0.41 2.85 4.87 9.95 0.17 0.29 0.74
B B 1.46 5.8 5.8 5.0 0.75 0.75 0.94 2.76 4.72 9.95 3.04 5.19 13.69
C C 0.54 7.6 7.6 7.2 0.42 0.42 0.53 2.46 4.21 8.80 0.56 0.96 2.50
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
DEVELOPED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
A. Reese
June 15, 2016
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Q = C f ( C )( i )( A )
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational-Calcs_Proposed.xlsx\Direct-Runoff
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100
2-yr Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
A A 0.18 0.33 0.33 0.41 5.0 5.0 5.0 0.17 0.29 0.74
B B 1.46 0.75 0.75 0.94 5.8 5.8 5.0 3.04 5.19 13.69
C C 0.54 0.42 0.42 0.53 7.6 7.6 7.2 0.56 0.96 2.50
DEVELOPED RUNOFF SUMMARY TABLE
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational-Calcs_Proposed.xlsx\Summary Table
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: Hill Pond Residences
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Reese
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100 Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40
Roofs …….…….………………..……………….…………………………………………….0..95 90
Concrete Pavers…………………………...………………..…………………………………………….0.40 . 22
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0 2-year Cf
= 1.00 100-year Cf = 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
Concrete
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.
EX1 53,708 1.23 0.00 0.33 0.02 0.01 0.01 0.85 0.39 0.39 0.48 26.5
EX2 41,204 0.95 0.02 0.15 0.04 0.06 0.00 0.67 0.35 0.35 0.44 23.2
EXISTING 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
June 15, 2016
Overland Flow, Time of Concentration: Hill Pond Residences
Project: Hill Pond Residences
41859.0 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
Hill Pond Residences
Rational Method Equation: Project: Hill Pond Residences
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
EX1 EX1 1.23 17.4 17.4 16.2 0.39 0.39 0.48 1.75 2.99 6.30 0.83 1.42 3.75
EX2 EX2 0.95 5.0 5.0 5.0 0.35 0.35 0.44 2.85 4.87 9.95 0.95 1.63 4.16
EXISTING RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
A. Reese
June 15, 2016
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
Q = C f ( C )( i )( A )
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational Calcs_Existing.xlsx\Direct-Runoff
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100
2-yr Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
EX1 EX1 1.23 0.39 0.39 0.48 17.4 17.4 16.2 0.83 1.42 3.75
EX2 EX2 0.95 0.35 0.35 0.44 5.0 5.0 5.0 0.95 1.63 4.16
EXISTING RUNOFF SUMMARY TABLE
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational Calcs_Existing.xlsx\Summary Table
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – STORM
SEWERS
B.2 – DETENTION
FACILITIES
APPENDIX B.1
STORM SEWERS
APPENDIX B.2
DETENTION FACILITIES
Hill Pond Residences
Fort Collins, Colorado
A. Reese Date: June 15, 2016
Pond No.: Paver Parking
B
100-yr
0.94 WQCV 2091 ft
3
Area (A)= 1.46 acres Quantity Detention 11342 ft
3
Max Release Rate = 0.95 cfs Total Volume 11342 ft
3
Total Volume 0.260 ac-ft
Time Time
Ft.Collins
100-yr
Intensity
Q100
Inflow
(Runoff)
Volume
Outflow
(Release) Volume
Storage
Detention
Volume
(mins) (secs) (in/hr) (cfs) (ft
3
) (ft
3
) (ft
3
)
5 300 9.95 13.7 4097 285 3812
10 600 7.72 10.6 6357 570 5787
15 900 6.52 8.9 8053 855 7198
20 1200 5.60 7.7 9223 1140 8083
25 1500 4.98 6.8 10252 1425 8827
30 1800 4.52 6.2 11166 1710 9456
35 2100 4.08 5.6 11759 1995 9764
40 2400 3.74 5.1 12319 2280 10039
45 2700 3.46 4.7 12821 2565 10256
50 3000 3.23 4.4 13299 2850 10449
55 3300 3.03 4.2 13723 3135 10588
60 3600 2.86 3.9 14130 3420 10710
65 3900 2.72 3.7 14558 3705 10853
70 4200 2.59 3.6 14929 3990 10939
75 4500 2.48 3.4 15316 4275 11041
80 4800 2.38 3.3 15678 4560 11118
85 5100 2.29 3.1 16028 4845 11183
90 5400 2.21 3.0 16378 5130 11248
95 5700 2.13 2.9 16662 5415 11247
100 6000 2.06 2.8 16963 5700 11263
105 6300 2.00 2.7 17292 5985 11307
110 6600 1.94 2.7 17572 6270 11302
115 6900 1.89 2.6 17897 6555 11342
120 7200 1.84 2.5 18182 6840 11342
125 7500 1.79 2.5 18424 7125 11299
130 7800 1.75 2.4 18733 7410 11323
135 8100 1.71 2.3 19009 7695 11314
Old Town Flats
Hill Pond Residences
Fort Collins, Colorado
A. Reese Date:
Pond No.: Paver Parking
B
100=yr Void Ratio 30%
2091 ft3
Required
Material
Volume 37808
Design Storm 100-yr
Required Volume= 11342 ft3 WSEL 5012.08 ft.
Minimum
Contour
Maximum
Contour
Incremental
Volume
Cummulative
Volume Conic
(X-values)
ft2 ft. ft3
5,009.29 5,009.40 14.96 14.96
5,009.40 5,009.60 199.48 214.44
5,009.60 5,009.80 658.03 872.47
5,009.80 5,010.00 1427.9 2300.37
5,010.00 5,010.20 2307.24 4607.61
5,010.20 5,010.40 2972.95 7580.56
5,010.40 5,010.60 3350.47 10931.03
5,010.60 5,010.80 3551.52 14482.55
5,010.80 5,011.00 3628.53 18111.08
5,011.00 5,011.20 3631.79 21742.87
5,011.20 5,011.40 3633.52 25376.39
5,011.40 5,011.60 3635.25 29011.64
5,011.60 5,011.80 3636.98 32648.62
5,011.80 5,012.00 3638.71 36287.33
5,012.00 5,012.20 3640.44 39927.77
5,012.20 5,012.40 3642.17 43569.94
5,012.40 5,012.60 1275.17 44845.11
5,012.60 5,012.80 2368.73 47213.84
5,012.80 5,012.13 3645.62 50859.46
Design Point
Design Storm
Require Volume=
Stage - Storage Calculation
Project Number:
Project Location:
Calculations By:
Required Volume Water Surface Elevation (WSE)
June 15, 2016
5,009.50
5,010.00
5,010.50
5,011.00
5,011.50
5,012.00
5,012.50
5,013.00
Contour Elevation
OUTLET RATING CURVE
Subgrade Detention Orifice
Project: Hill Pond Residences
Date: June 15, 2016
By: A. Reese
100-YR ORIFICE RATING
Orifice Dia (in) 4.50
Orifice Area (sf) 0.1104
Orifice invert (ft) 0.00
Orifice Coefficient 0.65
Outlet
Orifice Area Stage release
(SF) (FT) (CFS)
0.1104 0.00 0.00
0.1104 0.25 0.29
0.1104 0.50 0.41
0.1104 0.75 0.50
0.1104 1.00 0.58
0.1104 1.25 0.64
0.1104 1.50 0.71
0.1104 1.75 0.76
0.1104 2.00 0.81
0.1104 2.25 0.86
0.1104 2.50 0.91
0.1104 2.75 0.96
0.1104 3.00 1.00
D:\Projects\620-004\Drainage\Detention\620-004 Orifice rating.xlsx
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
PAVER PARKING AREA
Project: Hill Pond Residences
By: A. Reese
REQUIRED STORAGE & OUTLET WORKS:
BASIN AREA (acres)= 1.200 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 100.00 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 1.0000 <-- CALCULATED
Drain Time (hrs) 12 <-- INPUT
Drain Time Coefficient 0.8 <-- CALCULATED from Figure Table 3-2
WQCV (watershed inches) = 0.400 <-- CALCULATED from Figure EDB-2
WQCV (ac-ft) = 0.040 <-- CALCULATED from UDFCD DCM V.3 Section 6.5
Adjusted WQCV (ac-ft) = 0.048 <-- CALCULATED (20% Sedimentation Accumulation)
Adjusted WQCV (cu-ft) = 2091 <-- CALCULATED (20% Sedimentation Accumulation)
WATER QUALITY CONTROL STRUCTURE PLATE
June 15, 2016
APPENDIX D
EROSION CONTROL REPORT
Hill Pond Residences
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 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 C001 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 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 E
LID CONFORMANCE
APPENDIX F
STANDARD OPERATING PROCEDURES (SOPS) REFERENCES
STANDARD OPERATING PROCEDURES (SOPs)
A. Purpose
In order for physical stormwater Best Management Practices (BMPs) to be effective, proper maintenance is
essential. Maintenance includes both routinely scheduled activities, as well as non-routine repairs that may be
required after large storms, or as a result of other unforeseen problems. Standard Operating Procedures (SOPs)
should clearly identify BMP maintenance responsibility. BMP maintenance is typically the responsibility of the
entity owning the BMP.
Identifying who is responsible for maintenance of BMPs and ensuring that an adequate budget is allocated for
maintenance is critical to the long-term success of BMPs. Maintenance responsibility may be assigned either
publicly or privately. For this project, the privately owned BMPs shown in Section B below are to be maintained
by the property owner, homeowner’s association (HOA), or property manager.
B. Site-Specific SOPs
The following stormwater facilities contained within the Scott Plaza development are subject to SOP
requirements:
- Permeable Modular Block Pavers (MBPs)
- Storm Drains and Tree Roots
The location of said facilities can be found on the Utility Plans and Landscape Plans for Scott Plaza. Inspection
and maintenance procedures and frequencies, specific maintenance requirements and activities, as well as
BMP-specific constraints and considerations shall follow the guidelines outlined in Volume 3 of the Urban
Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual.
SOP Maintenance Summary Table
Stormwater Facility /
BMP
Ownership /
Responsibility UDFCD Maintenance Reference
Permeable Modular Block
Pavers (MBPs) Private
Follow guidelines for Permeable Modular Block Pavers
(Chapter 6 – Section 11.0)
The complete UDFCD BMP maintenance references listed above, except for the roof gutters and downspouts,
can be found in Chapter 6 of Volume 3. Applicable BMP maintenance excerpts can be found at the end of this
document.
Permeable Modular Block Pavers (MBPs)
There are several MBP sections throughout the project serving a critical role in the drainage system. These systems
provide storage and important water quality benefits.
Proper maintenance is critical to ensure lasting performance and integrity of the system. The more frequent and diligent
the routine maintenance procedures are, the more likely it is to avoid and/or postpone significant repair and replacement
actions. Such major remedies would include removal of the surface pavers to access (and potentially replace) the
underlying sub-base material and/or underdrain pipes should either become clogged or otherwise fail to function
properly.
Routine Maintenance Table for Permeable Pavement Systems
Required Action Maintenance Objective Frequency of Action
Inspection
Inspect the pavement condition and
observe infiltration either during a rain
event or with a garden hose to ensure
that water infiltrates into the surface.
At least annually.
Debris Removal,
Sweeping and
Vacuuming
Use a regenerative air or vacuum
sweeper to maintain infiltration rates.
Replace infill aggregate as needed.
As necessary - the frequency depends on use types
(e.g., foot traffic only versus vehicle traffic) and
patterns as well as specific site conditions such as
tributary basin characteristics.
Snow Removal
DO NOT apply sand to the MBP surface.
Mechanical snow and ice removal
should be used.
As necessary.
Full and Partial
Replacement of
the Pavement or
Infill Material
If the surface is completely clogged and
rendering minimal surface infiltration
rate, restoration of surface infiltration
can be achieved by removing the first ½
to 1 inch of soiled aggregate infill
material with a vacuum sweeper. Refill
the openings with clean aggregate infill
materials.
Routine – Annual inspection of hydraulic and
structural facilities. Also check for obvious problems
during routine maintenance visits, especially for
plugging of outlets.
Storm Drain Lines Maintenance Plan
The storm drain lines to be constructed with the proposed project may be located in proximity to trees. The situation is
unavoidable; therefore, special maintenance has been identified to ensure these storm drain systems perform as they
were designed.
Routine Maintenance Table
Required Action Maintenance Objective Frequency of Action
Inspection
Use a video camera to inspect the
condition of the storm drain pipes.
Cleanout pipes as needed. If the integrity
of the pipe is compromised, then repair
the damaged section(s).
Every two to five years.
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
D:\Projects\620-004\Drainage\Detention\620-004_Detention.xlsm\
140 8400 1.67 2.3 19252 7980 11272
145 8700 1.63 2.2 19462 8265 11197
150 9000 1.60 2.2 19763 8550 11213
155 9300 1.57 2.2 20038 8835 11203
160 9600 1.54 2.1 20290 9120 11170
165 9900 1.51 2.1 20516 9405 11111
170 10200 1.48 2.0 20718 9690 11028
175 10500 1.45 2.0 20895 9975 10920
180 10800 1.42 1.9 21047 10260 10787
185 11100 1.40 1.9 21327 10545 10782
190 11400 1.38 1.9 21591 10830 10761
195 11700 1.36 1.9 21838 11115 10723
200 12000 1.34 1.8 22068 11400 10668
205 12300 1.32 1.8 22282 11685 10597
210 12600 1.30 1.8 22480 11970 10510
215 12900 1.28 1.8 22661 12255 10406
220 13200 1.26 1.7 22826 12540 10286
225 13500 1.24 1.7 22974 12825 10149
230 13800 1.22 1.7 23106 13110 9996
235 14100 1.21 1.7 23415 13395 10020
240 14400 1.20 1.6 23715 13680 10035
Detention Pond Calculation | FAA Method
Project:
Project Location:
Calculations By:
Input Variables Results
Design Point
Design Storm Required Detention Volume
Developed "C" =
D:\Projects\620-004\Drainage\Detention\620-004_Detention.xlsm\
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
EX1 EX1 No 0.25 0.25 0.31 284 3.6 17.4 17.4 16.2 0 0.0 0.00 N/A 0 0.0 0.00 N/A 17.4 17.4 16.2
EX2 EX2 No 0.25 0.25 0.31 13 5.3 3.3 3.3 3.1 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.0 5.0 5.0
EXISTING TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
A. Reese
June 15, 2016
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational Calcs_Existing.xlsx\Tc-2-yr_&_100-yr
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational Calcs_Existing.xlsx\C-Values
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
A A No 0.25 0.25 0.31 10 15.0 2.0 2.0 1.9 0 0.0 0.00 N/A 248 4.0 3.00 1.4 5.0 5.0 5.0
B B No 0.95 0.95 1.00 113 0.5 3.8 3.8 2.5 174 0.5 1.41 2.1 0 0.0 0.00 N/A 5.8 5.8 5.0
C C No 0.25 0.25 0.31 26 3.8 5.2 5.2 4.8 0 0.0 0.00 N/A 217 1.0 1.50 2.4 7.6 7.6 7.2
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
A. Reese
June 15, 2016
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational-Calcs_Proposed.xlsx\Tc-2-yr_&_100-yr
D:\Projects\620-004\Drainage\Hydrology\620-004_Rational-Calcs_Proposed.xlsx\C-Values