HomeMy WebLinkAboutDrainage Reports - 05/21/2014A�UNITED CIVIL
Design Group LLC
City offt. Colli Plans
Approved By.
Date 5-l —I
Final Drainage Addendum
0
Bella Viva Subdivision
Filing Two
Fort Collins, CO
Prepared for:
Bella Vira Town Homes Inc.
1313 Fairway Five Drive
Fort Collins, CO 80525
May 7, 2014
1501 Academy Ct. Ste. 203 Fort Collins, Colorado 80524 (970) 530-4044
UNITED CIVIL Drainage Addendum
f� `\ Design Group Bella Vira Subdivision Filing Two
Fort Collins, CO
May 7, 2014
' City of Fort Collins
' Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Bella Vira Subdivision Filing Two
Fort Collins, Colorado
Project Number: U13012
Dear Staff:
United Civil Design Group, LLC. is pleased to submit this Final Drainage Addendum for the Bella
Vira Subdivision Filing Two site in Fort Collins, Colorado. In general, this summary serves to
document the stormwater impacts associated with the proposed project and to verify that the
project does conform to the intent and requirements set forth in the approved final drainage
report prepared by Jim Sell Design (JSD) entitled "Final Drainage and Erosion Control Report for
Bella Vira", and dated December 21, 2007.
■ Site Location and Project Description
The Bella Vira Subdivision Filing Two development site (referred herein as "the site") is located
' in Fort Collins and is described as Lot 1 within Bella Vira Subdivision Filing Two located within
the south half of Section 17, Township 7 North, Range 69 West of the Sixth P.M., City of Fort
' Collins, Larimer County, Colorado. The site has a platted area of 3.47 acres and is bounded by
Overland Trail to the east, West Elizabeth Street (currently under construction) to the north,
and The Ponds at Overland Trail Second Filing to the west and south. See the attached
Drainage Plan for additional information.
The planned development for the site will consist of the following:
' • The construction of six (6) single family attached buildings with twenty-five (25)
units.
• The construction of a private drive and parking stalls in support of the building
' construction.
• The construction of utilities to support the proposed buildings including sanitary,
water and storm drainage.
Existing Conditions
' Hydrology
The site, which is located within the Canal Importation Basin, currently exists mainly as
agricultural farm land and is currently covered with grasses and weeds. Storm runoff
1 U13012-DralnageAddendum-Final.doc
UNITED CIVIL Drainage Addendum
Design Group uc Bella Vira Subdivision Filing Two
' Fort Collins, CO
from the site currently drains towards the south and west to an existing City regional
' detention pond located within Tract C of the Bella Vira Subdivision just west of the site.
' Floodplain
A small portion of the southern site is located within a City -regulatory moderate risk
floodway adjacent to the Pleasant Valley and Lake Canal. No improvements are being
' proposed within this area.
Detention
' The City regional detention pond located within Tract C of Bella Vira Subdivision just
west of the site provides both detention and water quality for the site.
' Developed Conditions
In part, the intent of this Drainage Addendum is to verify that the Filing Two project conforms
' to the intent and requirements set forth in the JSD Final Drainage Report for this site. As such,
the following sections of this Addendum compare the proposed design for Filing Two to the
design as shown in aforementioned report.
Hydrology
Basin A as shown in the attached Drainage Plan collects the vast majority of the
developed flows from the site and routes them via swales and storm sewer to the City
regional pond west of the site. Basin A largely corresponds to Basins 20-21b, 25-27, and
29 as were shown in the approved JSD report. A summary of the results of the analysis
of Basin A as compared to the JSD basins is as follows:
Comparison Summary Table
Basin A ' JSD Basins
Overall Area (acres)
3.16
3.54
Impervious Area (acres)
1.75
2.08
% (cfs)
5.67
6.07
Q100 (cfs)
24.21
26.87
As shown in the above table, the proposed improvements for Filing Two of Bella Vira
' result in lower overall and impervious areas and resulting flowrates from those shown
in the approved JSD report. Therefore, the proposed Filing Two improvements appear
t to meet the intent and requirements set forth in the original JSD report and it is
anticipated that the Filing Two improvements will not have a negative impact to the
downstream improvements as designed by JSD.
t
2 U13012-DminageAddendum-Final.doc
' UNITED CIVIL Drainage Addendum
Design Group LL� Bella Vira Subdivision Filing Two
' Fort Collins, CO
Storm Sewer
' Storm Sewer Line 1 is located in the center of the proposed development and collects
water from Basins Al and A4-A6. In order to eliminate as much surface water as
' possible through Basin AS, several downspouts within Basin A6 are being collected and
piped directly into the storm drain. Due to the collection of some roof areas, the minor
flows that are to be collected, and the desire to eliminate as much surface flow through
' Basin Al due to erosion concerns, Storm Line 1 has been designed to convey the 100-
year flows away from the site and into the downstream pond.
t Detention and Water Quality Requirements
As previously mentioned, the site is provided with detention and water quality from the
City regional pond just west of the site. With the Filing Two improvements not
exceeding those assumed during the design of the regional facility, no further detention
or water quality improvements are required with Filing Two.
' Low Impact Development (LID) Requirements
In February of 2013, City Council adopted the LID policy and criteria. Filing Two of Bella
' Vira is required to meet the newly adopted criteria. Per the criteria, the site must:
• Treat no less than 50% of any newly added impervious area using one or a
combination of LID techniques.
• Treat no less than 25% of any newly added pavement area using a permeable
pavement.
In communication with City personnel, this site, as it was originally approved prior to
t the LID requirements, will not be required to provide the permeable pavement J the
development proposes to treat more than 50% of the newly added impervious area.
For this development, Basin A contains all the impervious area associated with the
project which totals 1.75 acres. In order to accommodate the above mentioned
requirement, the development is proposing to treat the newly added impervious area
' as follows:
• The upstream basins of A4-A6 (totaling 1.31 acres of impervious area) will be
treated with a series of grass lined swales prior to entering the storm drain
' system. Once in the storm drain system, the entirety of the impervious area
within said basins will be treated within Inlet 1-2 using a Snout BMP along
with an associated bioskirt. Upon exiting the storm drain runoff will then be
' directed to a level spreader with bioretention sand media to further treat
stormwater and promote groundwater infiltration. Refer to the Drainage
Plan and Construction Documents for additional information.
' • Basin A2 (with 0.22 acres of impervious area) will be treated with a grass line
swale prior to entering a bioswale with underdrain proposed at the
' downstream end of the basin. This bioswale (which has total length of 135-
feet) will treat the entirety of the impervious area within the basin prior to
directing the runoff to the downstream pond.
3 U13012-DrainageAddendum-Final.doc
UNITED CIVIL DrainageAddendurri
Design Group uc Bella Vira Subdivision Filing Two
Fort Collins, CO
In total, the development is proposing to collect and treat 1.53 acres of the newly
' added impervious area using a series of LID techniques. The percentage of the
impervious area within the site being treated with LID techniques totals 87%. Due to
' the percentage of the site that is proposed to be treated, and based upon
communication with City personnel, the development team is proposing to not provide
any pervious pavement with Filing Two of this project.
Four Step Process
With the adoption of the USDCM, the City has also adopted the "Four Step Process"
that is recommended in Volume 3 of the USDCM in selecting structural BMPs for the
redeveloping urban areas. The following portions of this addendum describe each step
and how it has been utilized for this project:
Step 1— Employ Runoff Reduction Practices
The objective of this step is to reduce runoff peaks and volumes and to employ the
technique of "minimizing directly connected impervious areas" (MDCIA). This project
accomplishes this by:
• Providing grass buffers throughout the site between impervious areas to
minimize directly connected impervious areas.
• Routing flows through a series of vegetated swales to increase time of
concentration, promote infiltration and provide initial water quality.
• Routing a portion of the site through a bioswale to promote infiltration and
provide additional water quality.
Step 2 — Provide Water Quality Capture Volume (WQCV)
The objective of providing WQCV is to reduce the sediment load and other pollutants
that exit the site. For this project WQCV is provided within the regional pond located
west of the site, so no additional WQCV is required.
Step 3 — Stabilize Drainageways
The site is adjacent to the Pleasant Valley and Lake Canal. The project is not directly
stabilizing this manmade drainageway; however, the project is indirectly maintaining
the existing stability of the drainageway by directing the vast majority of onsite flows
away from the canal and to the existing regional pond west of the site. Additionally,
this project will pay stormwater development and stormwater utility fees which the City
uses, in part, to maintain the stability of the City drainageway systems.
Step 4 — Consider Need for Industrial and Commercial BMPs
This step is generally considered for industrial and commercial sites. As this
development is proposing single family attached dwellings only, no specialized BMPs
have been considered for this project.
4 U33012-DrainageAddendum-Final.doc
UNITED CIVIL
Design Group LLc
Drainage Addendum
Bella Vira subdivision Filing Two
Fort Collins, CO
Standard Operating Procedures (SOPs)
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 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 Appendix C of
' this Addendum are to be maintained by the property owner, homeowner's
association (HOA), or property manager.
Conclusions
In conclusion, the drainage system proposed within this Drainage Addendum provides
adequate conveyance of the developed stormwater runoff from the proposed development to
existing discharge locations and drainage systems. In addition, the calculations provided show
that the proposed drainage system does meet the intent and requirements set forth in the
original JSD Final Drainage Report. It should also be noted that with this addendum and the
corresponding design, every attempt has been made to minimize any negative impacts on the
downstream receiving waters. With the incorporation of the LID techniques throughout the
development, the site will discharge a lower sediment load and less runoff than the design
originally proposed with the Bella Vira Subdivision project.
We understand that review by the City of Fort Collins is to assure general compliance with
standardized criteria contained in the Fort Collins Stormwater Criteria Manual (FCSCM). This
addendum was prepared in compliance with technical criteria set forth in both the Urban
Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual and the
FCSCM.
If you should have any questions or comments as you review this drainage summary, please
feel free to contact us at your convenience.
Sincerely,
United Civil Design Group, LLC
Kevin Brazelton, PE
Engineering Manager
5 U13012-DrainageAddendum-Final.doc
APPENDIX A
Hydrology Calculations
1
' Bella Vira Filing 2 j�UNITED CIVIL
Fort Collins, CO Runoff Summary Design Group
' Area Cie Qioo
Basin Design Point %I C2 COO
' (acre) (cfs) (cfs)
Proposed Basins -Filina 2
Al
Al
0.28
27%
0.45
0.57
0.35
1.55
A2
A2
0.60
35%
0.51
0.64
0.87
3.82
A3
A3
0.46
29%
0.46
0.58
0.60
2.62
A4
A4
0.78
80%
1 0.86
1.00
1.90
7.73
A5
A5
0.64
69%
0.77
0.96
1.39
6.07
A6
A6
0.32
47%
0.60
0.76
0.56
2.42
O51
O51
0.27
2%
0.25
0.31
0.16
0.68
052
052
0.10
2%
0.25
0.31
0.06
0.27
rOn;i7te Total
3.44
47%
0.61
0.76
5.67
24.21
Modified Phase 1 Basins
19
19
0.35
78%
0.82
1.00
0.82
3.52
23
23
0.06
82%
0.84
1.00
0.15
0.63
Calculations by. KRB
' Date: 1211912013 D: jDropbox`Projects►U13012 Bella ViralDrainagelHydrologyIU13012-Runoff Final.xlsx
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APPENDIX B
Hydraulic Calculations
[- CURB OPENING INLET IN A SUMP
Project = Bella Vira - Filing 2
Inlet ID = Inlet 1-2
Wy Lu ` ` WPC
nv Direction
3n Information (Input)
th of a Unit Inlet
LL, =
10.00 It
Depression, if any (not part of upstream Composite Gutter)
a,., =
3.00 inches
it of Curb Opening in Inches
H =
6.00 inches
Width for Depression Pan
WP =
3.00 ft
ding Factor for a Single Unit (typical value = 0.1)
C� =
0.20
of Throat (see USDCM Figure ST-5)
Theta =
63.4 degrees
e Coefficient (see USDCM Table ST-7)
CP =
0.67
Coefficient (see USDCM Table ST-7)
CN, =
3.00
Number of Units in the Curb Opening Inlet
No =
1
a Weir
sign Discharge on the Street (from Street Hy)
Q, =
7.4 cfs
[ter Depth for the Design Condition
Yo =
8.37 inches
al Length of Curb Opening Inlet
L =
10.00 ft
)acity as a Weir without Clogging
Ci„ =
26.9 cfs
gging Coefficient for Multiple Units
Coef =
1.00
gging Factor for Multiple Units
Clog =
0.20
mcity as a Weir with Clogging
Q,„a =
23.4 cfs
an Orifice
:)acity as an Orifice without Clogging
Qo; =
18.5 cfs
:)acity as an Orifice with Clogging
QP =
14.8 cfs
pacify for Design with Clogging
Qa =
14.8 cfs
pture Percentage for this Inlet = Qo / QP =
C% =
100.00 %
Note: Unless additional ponding depth or spilling over the curb is acceptable, a capture
percentage of less than 100% in a sump may indicate the need for additional inlet units.
Storm Inlet 1-1.xls, Curb-S 12/19/2013, 2:02 PM
Bella Vira - Filing 2
Fort Collins, CO
Area Inlet Capacity
' INLET ID: Inlet 1-7 (Basin A6)
Governing Equations:
Inlet capacity equation at low flows (weir calculation): Y = .0 P
Where:
' P-2(L+W)
H = depth of water above the flowline
fZ UNITED CIVIL
/ Design Group
Inlet capacity equation at higher flows (orifice calculation):
Q =
0.67 A l 2 gH
' Where:
A = open area of the inlet grate
' H = depth of water above the centroid of the cross -sectional area (A)
Input Parameters:
Grate:
15 Nyloplast (1599CGD)
'
Wier Perimeter:
3.93
Open Area of Grate (ft`):
0.80
QZ = 0.56 cfs
' Flowline Elevation (ft):
5127.62
Q100 = 2.42 cfs
Allowable Capacity:
50%
' Depth vs. Flow:
Shallow
Orifice
Actual
Depth Above Inlet
Elevation
Weir Flow
Flow
Flow
(ft)
(n)
(cfs)
(cfs)
(cfs)
0.00
5127.62
0.00
0.00
0.00
0.10
5127.72
0.19
0.68
0.19
0.21
5127.83
0.56
0.98
0.56 02
'
0.10
5127.72
0.19
0.68
0.19
0.30
5127.92
0.97
1.18
0.97
' 0.40
5128.02
1.49
1.36
1.36
0.50
5128.12
2.08
1.52
1.52
0.60
5128.22
2.74
1.67
1.67
t 0.70
5128.32
3.45
1.80
1.80
0.80
5128.42
4.22
1.93
1.93
0.90
5128.52
5.03
2.04
2.04
Calculations by: KRB
' Date:1211912013 D:�Dropbox) Projects 1iU13012Bella VirolDrainage�InletsIU13012-AreaInlets.xlsx
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Channel Report
Hydraflow Express Extension for AutoCAD® Civil 3D® 2013 by Autodesk, Inc.
Swale - Upstream Basin A5 (Between Buildings 5&6)
Thursday, Dec 19 2013
User -defined
Highlighted
Invert Elev (ft)
= 5126.64
Depth (ft)
= 0.35
Slope (%)
= 1.75
Q (cfs)
= 1.800
N-Value
= 0.025
Area (sqft)
= 0.75
Velocity (ft/s)
= 2.40
Calculations
Wetted Perim (ft)
= 4.35
Compute by:
Known Q
Crit Depth, Yc (ft)
= 0.36
Known Q (cfs)
= 1.80
Top Width (ft)
= 4.29
EGL (ft)
= 0.44
(Sta, El, n)-(Sta, El, n)...
( 0.00, 5128.50)-(0.10, 5128.00, 0.013)-(7.50, 5127.96, 0.013)-(13.00, 5126.64,
0.025)-(24.00, 5128.00, 0.025)-(24.10, 5132.75,
0.013)
Elev (ft)
1.80cfs is equal to (Basin A6 100-year flowrate) -
(roof area piped directly to Storm Line 1) + (1500sf
of Basin A5 landscape area)
Section
-5 0 5 10 15 20 25
Sta (ft)
Depth (ft)
6.36
5.36
4.36
3.36
2.36
1.36
0.36
-0.64
-1.AA
30
APPENDIX C
Standard Operating Procedures
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 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 Bella Vira Subdivision Filing Two are
subject to SOP requirements:
- Vegetated Swales
- Bioswale
- Snout BMP
- Level Spreader with Bioretention Sand Media
The location of said facilities can be found on the Utility Plans for Bella Vira Subdivision
Filing Two. Inspection and maintenance procedure 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 for the Vegetated Swales and
Bioswale. Note that the Level Spreader shall follow the same criteria as those for
Bioswales. Inspection and maintenance procedure and frequencies, specific maintenance
requirements and activities for the Snout BMP shall adhere to guidelines provided by the
manufacturer.
SOP Maintenance Summary Table
Stormwater Facility /
Ownership /
Maintenance Reference
BMP
Responsibility
Vegetative Swales
Private
Follow applicable guidelines for
Vegetative Swales within UDFCD.
Bioswale
Private
Follow applicable guidelines for
Bioretention and Vegetative Swales within UDFCD.
Level Spreader w/
Private
Follow applicable guidelines for
Bioretention Sand Media
Bioretention and Vegetative Swales within UDFCD.
Snout BMP
Private
Follow applicable guidelines for
Snout BMP provided by the manufacturer.
The complete UDFCD BMP maintenance references listed above can be found in Chapter
6 of Volume 3. The complete Snout BMP maintenance references "Maintenance
Considerations for SNOUT Stormwater Quality Systems" , and can be found at
www.bmpinc.com. Applicable excerpts for 'Routine' maintenance requirements for each
BMP can be found below. Additionally, it is strongly recommended that the Guidelines
for Use of Pesticides, Herbicides and fertilizers (UDFCD Fad Sheet S-8), and the
Landscape Maintenance procedures (UDFCD Fad Sheet S-9) be followed, not just within
the drainage facilities themselves, but for the entire development.
Vegetative Swales Routine Maintenance Table (Summary from Chapter 6 of UDFCD)
Required
Maintenance Objective
Frequency of Action
Action
Maintain irrigated grass at 2 to 4 inches tall
Lawn mowing
and nonirrigated native grass at 6 to 8 inches
Routine — As needed.
and Lawn care
tall. Collect cuttings and dispose of them
offsite or use a mulching mower.
Debris and Litter
Keep the area clean for aesthetic reasons,
Routine — As needed by
removal
which also reduces floatables being flushed
inspection, but no less than two
downstream.
times per year.
Routine — As needed by
Remove accumulated sediment near culverts
inspection. Estimate the need to
Sediment
and in channels to maintain flow capacity.
remove sediment from 3 to 10
removal
Replace the grass areas damaged in the
percent of total length per year,
process.
as determined by annual
inspection.
Check the grass for uniformity of cover,
Routine — Annual inspection is
Inspections
sediment accumulation in the swale, and near
suggested.
culverts.
Bioswale & Level Spreader Routine Maintenance Table (Summary from Chapter 6 of UDFCD)
Required Action
Maintenance Objective
Frequency of Action
Occasional mowing of grasses and weed
Lawn mowing and
removal to limit unwanted vegetation.
Routine — Depending on aesthetic
vegetative care
Maintain irrigated turf grass as 2 to 4 inches
requirements.
tall and nonirrigated native turf grasses at 4
to 6 inches.
Routine — Including just before annual
Debris and Litter
Remove debris and litter from bioswale area
storm seasons (that is, April and May),
end of storm season after leaves have
removal
to minimize clogging of the sand media.
fallen, and following significant rainfall
events.
The bioretention sand media and landscaping
Every 5 to 10 years, depending on
Landscaping
layer will clog with time. This layer will need
infiltration rates needed to drain the
removal and
to be removed and replaced, along with all
WQCV in 12-hours or less. May need to
replacement
turf and other vegetation growing on the
do it more frequently if exfiltration rates
surface, to rehabilitate infiltration rates.
are too low to achieve this goal.
Inspect bioswale area to determine if the
Routine — Bi-annual inspection of
Inspections
sand media is allowing acceptable infiltration.
hydraulic performance.
Snout BMP Routine Maintenance Table (Summary from Manufacturer Recommendations)
Required Action
Maintenance Objective
Frequency of Action
Monitor new installation after site has been
Routine — Monthly for first year. Determine
Monitoring
stabilized. Measure sediment depth and
yearly schedule from monitoring performed.
note surface pollutants in the structure.
Routine — Optimally completed when sump is
half full of sediment. Routine schedule
Remove sediment from sump. Maintenance
should be determined during first year
Sediment removal
is best completed with a vacuum truck.
monitoring. Structures should also be
cleaned if a spill or other incident causes a
larger than normal accumulation of pollutants.
Routine - Optimally completed when 6" of
floating material accumulates on surface
above static water level. Routine schedule
Floatable and
Remove floatables and trash from sump.
should be determined during first year
trash removal
monitoring. Structures should also be
cleaned if a spill or other incident causes a
larger than normal accumulation of pollutants.
Maintain/replace Bio-Skirt. "Maintenance"
includes wringing out of the unit to remove
Routine — Optimally completed when more
Bio-Skirt service
accumulated oils and then washed in an
than 213 of the boom is submerged,
or replacement
industrial washing machine with warm water.
indicating a nearly saturated state. At a
The Bio-Skirt may then be re -deployed as
minimum, annual service or replacement is
long as the material maintains it's structural
required.
integrity.
APPENDIX D
Drainage Plan
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