HomeMy WebLinkAboutFLATS AT RIGDEN FARM - PDP - PDP140006 - REPORTS - DRAINAGE REPORTFINAL DRAINAGE AND
EROSION CONTROL REPORT
July 16, 2014
THE FLATS AT RIGDEN FARM
RIGDEN FARM 14TH FILING REPLAT
Fort Collins, Colorado
Prepared for:
Landmark Construction Solutions
1170 W. Ash Street #100
Windsor, CO 80550
970-330-4316
Prepared by:
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158
www.northernengineering.com
Project Number: 374-012
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.
RE: Final Drainage and Erosion Control Report for
Rigden Farm 14th Filing Replat
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage and Erosion Control Report for your
review. This report accompanies Project Development Plan submittal for the proposed Rigden
Farm 14th Filing Replat 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.
Stephanie Thomas, PE
Project Engineer
Rigden Farm 14th Filing Replat
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 1
C. Floodplain.......................................................................................................................................... 3
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 4
A. Major Basin Description .................................................................................................................... 4
B. Sub-Basin Description ....................................................................................................................... 4
III. DRAINAGE DESIGN CRITERIA ................................................................................... 4
A. Regulations........................................................................................................................................ 4
B. Four Step Process .............................................................................................................................. 4
C. Development Criteria Reference and Constraints ............................................................................ 5
D. Hydrological Criteria ......................................................................................................................... 5
E. Hydraulic Criteria .............................................................................................................................. 6
F. Floodplain Regulations Compliance .................................................................................................. 6
G. Modifications of Criteria ................................................................................................................... 6
IV. DRAINAGE FACILITY DESIGN .................................................................................... 6
A. General Concept ............................................................................................................................... 6
B. Specific Details .................................................................................................................................. 8
V. CONCLUSIONS ........................................................................................................ 8
A. Compliance with Standards .............................................................................................................. 8
B. Drainage Concept .............................................................................................................................. 8
References ......................................................................................................................... 9
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations (NOT INCLUDED WITH PDP)
B.1 – Storm Sewers (NOT INCLUDED WITH PDP)
B.2 – Inlets (NOT INCLUDED WITH PDP)
APPENDIX C – Erosion Control Report
APPENDIX D – Reference Drainage Plans
Rigden Farm 14th Filing Replat
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2 – Proposed Site Plan ............................................................................................... 3
Figure 3 – Existing Floodplains ............................................................................................. 3
MAP POCKET:
DR1 - Drainage Exhibit
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. Located in the Northwest ¼ of Section 29, Township 7 North, Range 68 West of the
6th Prime Meridian, City of Fort Collins, County of Larimer, State of Colorado. The site
is a part of the Rigden Farm Subdivision.
3. Bounded to the north by Limon Drive, to the west by Illinois Drive, to the south by
Custer Drive, and to the east by Iowa Drive.
4. No significant offsite flows are directed into the site. The majority of off-site flows are
collected in existing inlets or are prevented from entering the site by curb and gutter.
5. The Flats were originally platted as Rigden Farm 14th Filing. Storm Drainage to
convey runoff from Rigden Farm 8th Filing, west of the site, was designed with Rigden
Farm-Northwest Roads.
B. Description of Property
1. The site is approximately 4.08 acres.
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 2
Figure 1 – Aerial Photograph
2. The existing site is comprised of mostly vacant land with bare soils, natural grasses and
vegetation.
3. The majority of the site slopes to the center, while a north portion slopes to the north,
and a south portion slopes to the south.
4. A report by Earth Engineering Consultants dated May 5, 2005 lists the soils for the area
as consisting of layers of sandy clay (CS) and clayey sand (SS). These soils are
classified as Hydrologic Soil Group C and have a low infiltration rate.
5. The proposed project site plan is composed of 3-Story Multi-Family Housing (condos).
This site will employ many water quality features and runoff reduction facilities including
porous pavers, drywells, and subsurface infiltration galleries.
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
6. No existing irrigation facilities are known at this time.
7. The project site is within the Rigden Farm Subdivision Master Plan. The proposed
project is not requesting a change in the land use.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
Figure 3 – Existing Floodplains
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 4
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The Rigden Farm project is located within the Foothills Drainage Basin, which is
located between Prospect Road and Horsetooth Road from north to south and
approximately between Shields Street and Zeigler Road from west to east.
B. Sub-Basin Description
1. The north section of the site drains to a storm sewer within Limon Drive. This storm
sewer flows to a stormwater system within Drake Street. The flows are routed into
Pond 216 of the Overall Drainage Plan for Rigden Farm, which outfalls in the Cache
La Poudre River.
2. The center section of the site drains to an existing inlet and storm sewer bisecting the
site (installed as a part of Rigden Farm 8th Filing) that flows east to an existing swale
that connects to a series of water quality ponds that is a part of the Overall Drainage
Plan for Rigden Farm. The ponds are numbered 212, 217, and 218 by the Rigden
Farm 1st and 6th Filing reports by JR Engineering.
3. The south section of the site drains to an existing inlet in Custer Drive. This inlet is a
part of an existing storm sewer system that outfalls into a water quality pond that
releases to the Foothills Regional Channel. The water quality pond is labeled Water
Quality Pond 2 in the Rigden Farm 1st Filing Drainage Plan.
4. The proposed plan will generally maintain these existing flow patterns.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the Rigden Farm
14th Filing Replat project.
B. Four Step Process
The overall stormwater management strategy employed with the Rigden Farm 14th Filing
Replat 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:
Providing large vegetated open areas throughout the site to reduce the overall
impervious area and to minimize directly connected impervious areas (MDCIA).
Providing permeable paver areas with underground detention area to increase time of
concentration promote infiltration and provide water quality.
Providing Drywells to promote infiltration and water quality throughout the site.
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 5
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, this
development 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 in existing downstream water quality ponds. These ponds have
been designed and built with Filing No. 1 and Filing No. 6.
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property. This property discharges to
existing drainageways that have been designed to accommodate runoff from this project as
a part of the Rigden Farm Master Plan.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
Localized trash enclosures within the development will allow for the disposal of solid
waste.
Snouts and settling basins for water treatment prior to flows entering the subsurface
infiltration galleries and storm systems.
Water Quality measures to protect and prolong the design life of the BMPs delineated
in Step 1.
C. Development Criteria Reference and Constraints
1. The proposed site is has been a part of many different drainage plans and studies in
the past. These plans include Rigden Farm Filing No. 1, Rigden Farm Filing No. 6,
Rigden Farm Filing No. 8 and Rigden Farm – Northwest Roads.
2. The most recent drainage plans (Rigden Farm Filing No. 8 and Rigden Farm –
Northwest Roads) were referenced in the drainage design for this site.
3. The subject property is a part of many drainage plans. As such, several constraints
have been identified during the course of this analysis that will impact the proposed
drainage system including:
Maximum runoff allowable into existing inlets and drainageways based on previous
drainage plans and studies.
Specifically, the Rigden Farm-Northwest Roads Drainage Plan divided the site into
two basins. The north basin was planned to drain to a storm sewer bisecting the
site. The south basin was planned to drain to an existing storm sewer in Custer
Drive. This Drainage Plan defined the maximum allowable runoff generated from
the Flats site to these storm sewers.
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 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. As of this report,
pervious pavers have not been added to Table RO-11. A coefficient of runoff of 0.40
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 6
was assumed for the pervious pavers. This is a value published by Advanced
Pavement Technology.
3. The Rational Formula-based Modified Federal Aviation Administration (FAA)
procedure has been utilized for detention storage calculations. Detention storage
calculations were not necessary for this site.
4. Three 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. The third storm computed, for comparison
purposes only, is the 10-year event.
5. 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 historically drains to the north, east, and
south. The north flows are collected in an existing inlet on Limon Drive then
conveyed to an existing 42” storm sewer that continues down Drake Avenue, the
center flows are collected in a series of water quality ponds designed with the Rigden
Farm Filing No. 1 and No. 6, and the south flows are collected into an existing inlet
on Custer Drive that ultimately discharges to an existing water quality pond designed
with Rigden Farm Filing No. 1.
2. All drainage facilities proposed with the Rigden Farm 14th Filing Replat 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.
3. As stated previously, the subject property is not located within a FEMA regulatory
floodplain.
4. The Rigden Farm 14th Filing Replat project does not propose to modify any natural
drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, all structures are located outside of any FEMA 100-year
floodplain, and thus are not subject to any floodplain regulations.
G. 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 Rigden Farm 14th Filing Replat drainage design are to
maintain the allowable storm runoffs as outlined within the “Rigden Farm – Northwest
Roads” Utility Plans by JR Engineering, June 29, 2005.
2. 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.
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 7
3. The Rigden Farm 14th Filing Replat project divided the site into three (3) major
drainage basins, designated as Basins A, B, and C. The project further subdivided
Basin B in to twelve (12) sub-basins, designated as Basins B-1, B-2, B-3, B-4, B-5,
B-6, B-7, B-8, B-9, B-10, B-11, and B-12. The drainage patterns anticipated for
each basin and sub-basin are further described below.
Basin A
Basin A consists of proposed multi-family condos, sidewalk, and landscaped areas. A
portion of the runoff from Basin A is collected in an on-site inlet, and a portion of the
runoff from this basin is intercepted by an existing inlet at Iowa Drive and Limon
Drive. The onsite inlet will convey flows from Basin A into the existing inlet at Iowa
Drive and Limon Drive. This existing inlet conveys flows to the existing 42” storm
sewer in Limon Drive. No previous studies had accounted for flows from this lot into
the existing sewer. Calculations based on the upstream flows from Rigden Farm Filing
No. 8 and Rigden Farm – Northwest Roads were conducted to ensure that the existing
storm sewer and existing inlet could handle the increased flows from Basin A. Routed
Hydrologic calculations show an increase from 31.10 cfs to 31.69 cfs during a 100-yr
event. This equates to maximum increase of 0.59 cfs within the 42” storm sewer.
This is considered within the range of error for the pipe. A reduction in the rate is
expected due to the installation of drywells and permeable pavers within the basin.
These improvements will increase the time of concentration in the basin, in addition to
providing stormwater detention.
Basin B
Basin B consists of proposed multi-family condos, sidewalks, landscaped areas,
porous pavers, and asphalt. Basin B is collected in the existing 42” storm sewer that
bisects the site. This storm sewer conveys flows to a series of existing water quality
ponds designed with Filing No. 1. The Drainage Plan for Rigden Farm – Northwest
Roads was referenced to determine the total allowable flows to the existing water
quality ponds. The 2-yr and 10-yr flows from Basin B were calculated at 5.59 cfs
and 9.54 cfs, respectively. These are within the range shown by the Rigden Farm-
Northwest Roads Drainage Plan for the 2- yr and 10-yr events of 5.60 cfs and 9.56
cfs, respectively. The 100-yr event is calculated to produce 30.29 cfs of runoff, this is
more than the 23.68 cfs allowed in the previous drainage plan. As such, a restricter
plate will be installed at the proposed manhole within Basin B-8. During a 100-yr
event, this restricter plate will restrict the flows from Basin B-6, B-7, and B-8 to the
flows allowable as stated in the Rigden Farm – Northwest Roads Drainage Plan.
Additional flows will back up in the system and release at Design Point 8 down a
concrete rundown to the existing inlet in Custer Drive. The sub-basins B-9, B-10, and
B-11 are collected by existing inlets designed in the Filing No. 8 Drainage Plan. The
existing storm sewer was designed with additional capacity. As such, all 100-yr flows
generated by sub-basins B-9, B-10, and B-11 were shown as being intercepted by the
existing inlets.
Basin C
Basin C consists of proposed multi-family condos, sidewalks, and landscaped areas.
All runoff in Basin C-1 is collected in the curb and gutter in Iowa Drive, Custer Drive,
or Illinois Drive, and is conveyed to the existing inlet at Iowa Drive and Custer Drive.
The 2-yr and 100-yr flow calculated for Basin C-1 are 0.65 cfs and 3.24 cfs,
respectively. These flows are well below the 2-yr and 100-yr flows allowed by the
Rigden Farm – Northwest Roads Drainage Report for the existing inlet, 2.74 cfs and
Rigden Farm 14th Filing Replat
Preliminary Drainage Report 8
10.96 cfs. During a 100-yr event additional flows will be directed from Basin B to
the concrete rundown from Basin C.
The existing inlet conveys flows to the existing storm sewer system in Custer Drive,
ultimately outfalling into Water Quality Pond 2 (see Rigden Farm Filing One Drainage
Plan) that releases to the Foothills Regional Channel.
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. Additional details to be provided with the FDP submittal.
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Rigden Farm 14th Filing Replat project
complies with the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Rigden Farm 14th Filing Replat project
complies with the City of Fort Collins’ Master Drainage Plan for the Foothills Drainage
Basin.
3. There are no regulatory floodplains associated with the development.
4. The drainage plan and stormwater management measures proposed with the
development are compliant with all applicable State and Federal regulations governing
stormwater discharge.
5. The site achieves the requirements set forth by the City of Fort Collins for Low Impact
Development (LID) by providing 37% of total paved areas as permeable pavers and
providing 50% of total impervious areas as being treated through an LID treatment.
B. Drainage Concept
1. The drainage design proposed with this project will effectively comply with previous
studies and will limit any potential damage or erosion associated with its stormwater
runoff. All existing downstream drainage facilities are expected to not be impacted
negatively by this development
2. The proposed development will not have any impact on the Master Drainage Plan
recommendations for Rigden Farm.
3. The drainage design is anticipated to be very conservative. We have omitted any
runoff reduction that will manifest due to infiltration from drywells and pervious
pavement. This is currently unable to be calculated with available soils data.
Rigden Farm 14th Filing Replat
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. Preliminary Subsurface Exploration Report, Rigden Farm Northwest Fort Collins, Colorado,
May 5, 2005, Earth Engineering Consultants, Inc.(EEC Project No. 1052053).
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
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
Rigden Farm 14th Filing Replat
CHARACTER OF SURFACE
1
:
Runoff
Coefficient
Percentage
Impervious Project: Rigden Farm - 14th Filing
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: S. Thomas
Asphalt ……....……………...……….....…...……………….………………………………………………………….0.95 . 100% Date: July 15, 2014
Concrete …….......……………….….……….………………..….…………………………………………………….0.95 . 90%
Gravel (packed) ……….…………………….….…………………………..………………………………………….0.50 . 40%
Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90%
Pavers…………………………...………………..……………………………………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….0.15 . 0%
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….0.25 . 0%
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Sub-Basin ID
Sub-
BasinBasin
Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Pavers
(ac)
Area of
Roofs
(ac)
Soil Type and Average
Slope
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite Runoff
Coefficient
Composite
% Imperv.
Basin
Rigden Farm 14th Filing Replat
Overland Flow, Time of Concentration:
Rigden Farm - 14th Filing
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)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
1 A-1 No 0.76 0.76 0.94 81 2.31% 4.4 4.4 2.0 47 0.94% 1.94 0.4 5.0 5.0 5.0
2 B-1 No 0.89 0.89 1.00 102 1.56% 3.4 3.4 1.6 0 N/A N/A N/A 5.0 5.0 5.0
3 B-2 No 0.88 0.88 1.00 38 0.74% 2.9 2.9 1.3 32 0.44% 1.32 0.4 5.0 5.0 5.0
4 B-3 No 0.85 0.85 1.00 89 1.53% 3.8 3.8 1.5 48 0.52% 1.44 0.6 5.0 5.0 5.0
5 B-4 No 0.72 0.72 0.90 70 2.07% 4.6 4.6 2.4 151 0.87% 1.87 1.3 6.0 6.0 5.0
Rigden Farm 14th Filing Replat
Rational Method Equation: Project: Rigden Farm - 14th Filing
Calculations By:
Date:
Rainfall Intensity:
1 A-1 0.11 5 5 5 0.76 0.76 0.94 2.85 4.87 9.95 0.23 0.40 1.02
2 B-1 0.37 5 5 5 0.89 0.89 1.00 2.85 4.87 9.95 0.95 1.62 3.71
3 B-2 0.12 5 5 5 0.88 0.88 1.00 2.85 4.87 9.95 0.31 0.53 1.23
4 B-3 0.16 5 5 5 0.85 0.85 1.00 2.85 4.87 9.95 0.39 0.67 1.61
5 B-4 0.77 6 6 5 0.72 0.72 0.90 2.76 4.72 9.95 1.53 2.61 6.89
6 B-5 0.39 5 5 5 0.94 0.94 1.00 2.85 4.87 9.95 1.05 1.79 3.88
7 B-6 0.23 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.63 1.08 2.34
8 B-7 0.42 12 12 8 0.62 0.62 0.78 2.05 3.50 8.38 0.53 0.91 2.71
9 B-8 0.30 6 6 5 0.83 0.83 1.00 2.67 4.56 9.95 0.67 1.14 3.00
10 B-9 0.06 5 5 5 0.77 0.77 0.96 2.85 4.87 9.95 0.13 0.23 0.58
11 B-10 0.11 5 5 5 0.74 0.74 0.92 2.85 4.87 9.95 0.23 0.39 1.01
12 B-11 0.08 5 5 5 0.66 0.66 0.82 2.85 4.87 9.95 0.14 0.24 0.62
13 B-12 0.42 6 6 5 0.65 0.65 0.81 2.67 4.56 9.95 0.72 1.22 3.34
TOTAL BASIN B 3.43 12 12 7 0.78 0.78 0.98 2.09 3.57 9.06 5.59 9.54 30.29
14 C-1 0.54 15 15 11 0.63 0.63 0.79 1.90 3.24 7.57 0.65 1.11 3.24
July 15, 2014
Intensity,
i10
(in/hr)
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
PROPOSED 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)
Sub-Basin(s)
S. Thomas
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Q C f C i A
Rigden Farm 14th Filing Replat
CHARACTER OF SURFACE
1
:
Runoff
Coefficient
Percentage
Impervious Project: Rigden Farm-14th Fil. & 8th Fil.
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: S. Thomas
Asphalt ……....……………...……….....…...……………….………………………………………………………….0.95 . 100% Date: July 15, 2014
Concrete …….......……………….….……….………………..….…………………………………………………….0.95 . 90%
Gravel (packed) ……….…………………….….…………………………..………………………………………….0.50 . 40%
Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90%
Pavers…………………………...………………..……………………………………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….0.15 . 0%
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….0.25 . 0%
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Sub-Basin ID
Sub-
BasinBasin
Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Pavers
(ac)
Area of
Roofs
(ac)
Soil Type and Average
Slope
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite Runoff
Coefficient
Composite
% Imperv.
A-1 0.11 0.00 0.01 0.00 0.07 Clayey | Average 2% to 7% 0.030 0.76 0.76 0.94 65%
Rigden Farm 14th Filing Replat
Overland Flow, Time of Concentration:
Rigden Farm-14th Fil. & 8th Fil.
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + 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)
Up Stream
Elevation
Down
Stream
Elevation
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Up
Stream
Elevation
Down
Stream
Elevation
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
Rigden Farm 14th Filing Replat
Rational Method Equation: Project: Rigden Farm-14th Fil. & 8th Fil.
Calculations By: S. Thomas
Date:
Rainfall Intensity:
1
TOTAL BASIN TO LIMON STORM
SEWER WITHOUT A-1 5.80
21 21 19 0.83 0.83 0.93 1.59 2.71 5.75 7.62 13.01 31.10
1
TOTAL BASIN TO LIMON STORM
SEWER WITH A-1 5.91
21 21 19 0.83 0.83 0.93 1.59 2.71 5.75 7.75 13.23 31.69
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
July 15, 2014
PROPOSED 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)
Sub-Basin(s)
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Intensity,
i10
(in/hr)
C10
Q C f C i A
7/15/2014 10:17 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Design Point 1 - Filing 8th and 14th and NW.xlsx\Runoff
APPENDIX C
EROSION CONTROL REPORT
Rigden Farm 14th Filing Replat
Preliminary 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 Sheet CS2 of the Utility Plans. The Utility
Plans at final design 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 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,
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 D
REFERENCE DRAINAGE PLANS
This unofficial copy was downloaded on Jan-02-2014 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
This unofficial copy was downloaded on Jan-02-2014 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
This unofficial copy was downloaded on Jan-02-2014 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
MAP POCKET
DR1 – OVERALL DRAINAGE EXHIBIT
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
1
TOTAL BASIN TO LIMON STORM
SEWER WITHOUT A-1
No 0.83 0.83 0.93 50 2.00% 2.8 2.8 1.8 1232 29.34 25.20 0.34% 1.16 17.7 20.6 20.6 19.5
1
TOTAL BASIN TO LIMON STORM
SEWER WITH A-1
No 0.83 0.83 0.93 50 2.00% 2.9 2.9 1.8 1232 29.34 25.20 0.34% 1.16 17.7 20.6 20.6 19.5
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
PROPOSED TIME OF CONCENTRATION COMPUTATIONS
S. Thomas
July 15, 2014
Design
Point
Sub-Basin
Overland Flow Pipe Flow Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
7/15/2014 10:17 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Design Point 1 - Filing 8th and 14th and NW.xlsx\Tc
Rigden Farm 8th Filing 01-15-04
C1 0.04 Clayey | Average 2% to 7% 0.15 0.15 0.19
C2 0.03 Clayey | Average 2% to 7% 0.15 0.15 0.19
C3 0.27 Clayey | Average 2% to 7% 0.31 0.31 0.35
C4 1.53 Clayey | Average 2% to 7% 0.95 0.95 1.00
C5 0.21 Clayey | Average 2% to 7% 0.76 0.76 0.81
C6 0.09 Clayey | Average 2% to 7% 0.95 0.95 1.00
C7 0.10 Clayey | Average 2% to 7% 0.95 0.95 1.00
C8 0.18 Clayey | Average 2% to 7% 0.95 0.95 1.00
C9 0.09 0.95 0.95 1.00
C10 0.61 Clayey | Average 2% to 7% 0.70 0.70 0.85
OC1 0.23 Clayey | Average 2% to 7% 0.83 0.83 0.88
OC2 0.23 Clayey | Average 2% to 7% 0.95 0.95 1.00
OC3 0.06 Clayey | Average 2% to 7% 0.95 0.95 1.00
OC4 0.02 0.95 0.95 1.00
Rigden Farm Northwest Roads 06-29-
05
103b 0.93 Clayey | Average 2% to 7% 0.85 0.85 1.00
104 0.41 Clayey | Average 2% to 7% 0.81 0.81 1.00
105 0.69 Clayey | Average 2% to 7% 0.82 0.82 1.00
OS-2 0.04 Clayey | Average 2% to 7% 0.81 0.81 1.00
OS-3 0.04 Clayey | Average 2% to 7% 0.81 0.81 1.00
TOTAL BASIN TO LIMON STORM
SEWER WITHOUT A-1
5.80 Clayey | Average 2% to 7% 0.83 0.83 0.93
TOTAL BASIN TO LIMON STORM
SEWER WITH A-1
5.91 Clayey | Average 2% to 7% 0.83 0.83 0.93
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Composite Runoff Coefficient with Adjustment
7/15/2014 10:16 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Design Point 1 - Filing 8th and 14th and NW.xlsx\Composite C
7/15/2014 10:19 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Proposed_Rational_Calcs.xlsx\Runoff
6 B-5 No 0.94 0.94 1.00 70 1.87% 2.0 2.0 1.3 73 0.47% 1.36 0.9 5.0 5.0 5.0
7 B-6 No 0.95 0.95 1.00 56 1.84% 1.7 1.7 1.1 37 0.51% 1.43 0.4 5.0 5.0 5.0
8 B-7 No 0.62 0.62 0.78 182 0.92% 12.4 12.4 8.4 0 N/A N/A N/A 12.4 12.4 8.4
9 B-8 No 0.83 0.83 1.00 132 1.16% 5.5 5.5 2.0 81 0.90% 1.90 0.7 6.2 6.2 5.0
10 B-9 No 0.77 0.77 0.96 46 2.35% 3.2 3.2 1.3 31 0.65% 1.61 0.3 5.0 5.0 5.0
PROPOSED TIME OF CONCENTRATION COMPUTATIONS
S. Thomas
July 15, 2014
Design
Point
Sub-Basin
Overland Flow Gutter/Pipe Flow Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
7/15/2014 10:18 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Proposed_Rational_Calcs.xlsx\Tc
10 B-9 No 0.77 0.77 0.96 46 2.35% 3.2 3.2 1.3 31 0.65% 1.61 0.3 5.0 5.0 5.0
11 B-10 No 0.74 0.74 0.92 55 3.51% 3.3 3.3 1.6 31 2.06% 2.87 0.2 5.0 5.0 5.0
12 B-11 No 0.66 0.66 0.82 70 3.19% 4.7 4.7 2.9 17 2.94% 3.43 0.1 5.0 5.0 5.0
13 B-12 No 0.65 0.65 0.81 64 1.16% 6.5 6.5 4.2 0 N/A N/A N/A 6.5 6.5 5.0
TOTAL BASIN B No 0.78 0.78 0.98 182 0.92% 8.3 8.3 3.2 407 1.01% 2.01 3.4 11.7 11.7 6.6
14 C-1 No 0.63 0.63 0.79 130 0.79% 10.7 10.7 7.1 406 0.79% 1.78 3.8 14.5 14.5 10.9
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
7/15/2014 10:18 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Proposed_Rational_Calcs.xlsx\Tc
Treated thru
LID?
LID Treated
Impervious Area
(ac)
A-1 0.11 0.00 0.01 0.00 0.07 Clayey | Average 2% to 7% 0.030 0.76 0.76 0.94 65% NO 0.00
B-1 0.37 0.08 0.10 0.00 0.16 Clayey | Average 2% to 7% 0.033 0.89 0.89 1.00 84% NO 0.00
B-2 0.12 0.03 0.01 0.00 0.06 Clayey | Average 2% to 7% 0.013 0.88 0.88 1.00 83% NO 0.00
B-3 0.16 0.03 0.05 0.00 0.05 Clayey | Average 2% to 7% 0.022 0.85 0.85 1.00 80% NO 0.00
B-4 0.77 0.13 0.15 0.18 0.20 Clayey | Average 2% to 7% 0.105 0.72 0.72 0.90 67% YES 0.52
B-5 0.39 0.14 0.06 0.00 0.18 Clayey | Average 2% to 7% 0.005 0.94 0.94 1.00 93% NO 0.00
B-6 0.23 0.06 0.04 0.00 0.13 Clayey | Average 2% to 7% 0.001 0.95 0.95 1.00 92% YES 0.22
B-7 0.42 0.06 0.05 0.12 0.09 Clayey | Average 2% to 7% 0.102 0.62 0.62 0.78 55% YES 0.23
B-8 0.30 0.08 0.04 0.05 0.12 Clayey | Average 2% to 7% 0.009 0.83 0.83 1.00 81% YES 0.24
B-9 0.06 0.00 0.00 0.00 0.04 Clayey | Average 2% to 7% 0.016 0.77 0.77 0.96 67% NO 0.00
B-10 0.11 0.00 0.01 0.00 0.07 Clayey | Average 2% to 7% 0.034 0.74 0.74 0.92 63% NO 0.00
B-11 0.08 0.00 0.00 0.00 0.04 Clayey | Average 2% to 7% 0.031 0.66 0.66 0.82 53% NO 0.00
B-12 0.42 0.00 0.07 0.00 0.17 Clayey | Average 2% to 7% 0.181 0.65 0.65 0.81 51% YES 0.21
TOTAL BASIN B 3.43 0.61 0.59 0.36 1.32 Clayey | Average 2% to 7% 0.552 0.78 0.78 0.98 72%
C-1 0.54 0.00 0.06 0.00 0.23 Clayey | Average 2% to 7% 0.242 0.63 0.63 0.79 49% NO 0.00
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
Permeable Pavement LID Treatment
Total Pavement (ac)= 1.94 Total Impermeable Area(ac)= 2.81
Total Permeable Pavement (ac)= 0.72 Total Impermeable Area Treated with LID(ac)= 1.42
Percent Permeable Pavement= 37% Percent Treated with LID= 50%
LID Requirements
Composite Runoff Coefficient with Adjustment LID Treatment
PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
7/15/2014 10:18 AM D:\Projects\374-012\Drainage\Hydrology\374-012_Proposed_Rational_Calcs.xlsx\Composite C