HomeMy WebLinkAbout18 - Design Report - Palisades Apartments - Stormwater DESIGN REPORT
STORMWATER MANAGEMENT
PALISADES APARTMENT COMPLEX
LOT 5C AND LOT 5B
ANNIE SUBDIVISION, PHASE 2
Prepared for:
Bechtle Architects
4515 Valley Commons Drive Ste. 201
Bozeman, MT 59718
Prepared by:
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Engineering and Surveying Inc.
1091 Stoneridge Drive • Bozeman, MT 59718
Phone (406) 587-1115 • Fax(406) 587-9768
www.chengineers.com • info@chengineers.com
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Project Number: 180137
July 2018 �`, �
INTRODUCTION
The Palisades Apartment Complex proposes to develop Lot 5C and Lot 5B of the Annie
Subdivision, Phase 2. The proposed layout of Lot 5C consists of a 3 story 24 unit apartment
building with underground parking, 20 individual row house units, an access driveway and
parking, and associated retention facilities. The proposed layout of Lot 513 consists of a 3 story 18
unit apartment building with underground parking, 11 individual row house units, an access
driveway and parking, and associated retention facilities. The property is located within the
Bozeman city limits and is currently zoned R-4. A combination of site grading, curb and gutter,
and the proposed retention ponds will be used to manage stormwater runoff from the site.
Supporting stormwater calculations are enclosed in appendix B for reference. Installation of N.
25th from Tschache to Oak Street and Breeze Lane from N.27th to N.25th will happen concurrently
with the Palisades Construction. A separate retention facility will be constructed in the Park for
road runoff from Breeze Lane and North 251h Avenue. See the approved N. 25th Avenue and
Breeze Lane storm water design report for details.
LOT 5C STORMWATER DESIGN
The site was divided into 3 drainage areas as shown on the attached Drainage Area Map in
Appendix A. Drainage Area 1 has a total area of 29,666 sf; 14,858 sf of landscape area and 14,808
sf of hardscape area. The City of Bozeman standard 10-year, 2 hour storm intensity is 0.41 in/hr.
This translates to 1,155 ft3 of runoff that is required to be retained; supporting calculations can be
found in Appendix B. In Drainage Area 1 there is an existing storm water retention pond (now
Retention Pond 1)that retains runoff from the eastern half of N.271h Avenue.The volume of runoff
that this portion of N. 27th produces is 2,497 ft3 (see Appendix C for N. 27th storm water design
report). Therefore the total storage volume required for Retention Pond 1 in Drainage Area I is
1,155 + 2,497 = 3,652 ft3. Retention Pond 1 has a volume of 3,785 ft3 with a top elevation at
4741.66 ft, a bottom elevation of 4740.16, and 4:1 (H:V) side slopes. The existing outlet for the
15"HDPE pipe that conveys drainage from N. 27th will be adjusted to drain into the new retention
pond as shown on the civil site plan.The runoff generated by the site will be conveyed to a curb cut
at the low point in the curb and gutter;then to a V wide Swale that will drain into Retention Pond 1.
Drainage area 2 has a total area of 28,252 sf; 16,861 sf of hardscape and 11,391 sf of landscape
(see Appendix A for drainage area map). Using the City of Bozeman design storm, Drainage
Area 2 generates a total runoff volume of 1,240 ft3 that is required to be retained (supporting
calculations can be found in Appendix B). Similar to Drainage Area 1,runoff will be conveyed to
a curb cut at the low point in the curb and gutter,then to a swale that drains into Retention Pond 2.
Retention Pond 2 will have a capacity of 1,365 ft3, a top elevation of 4743.56', a bottom elevation
of 4742.06', and 4:1 (H:V) side slopes.
Drainage Area 3 consists of the roof drainage from the 24 unit apartment building. The roof will
have an area of 13,603 sf. This will generate a runoff volume of 876 ft3. Two drywells, one at
each end of the building,will hold the runoff generated by the roof. Each dry well will be 5' deep
and have a capacity of 488 ft3 (total capacity of 976 ft3). See Appendix B for calculations.
LOT 5B STORMWATER DESIGN
Lot 5B was divided into 2 drainage areas shown on the drainage area map in Appendix A.
Drainage Area 1 has a total area 40,886 sf (25,249 sf of landscape and 15,637 sf of hardscape).
Using the City of Bozeman design storm, Drainage Area 1 on Lot 5B generates a total runoff
volume of 1,837 ft3. The site will drain to a curb cut at the low point in the curb and gutter then to
a small swale that will drain into Retention Pond 3. Retention Pond 3 will have a volume of 1,861
ft3. The pond will have atop elevation of 4742.85',a bottom elevation of 4741.35',and 4:1 (H:V)
side slopes.
Drainage Area 2 will consist of the roof drainage from the 18 unit apartment building. The roof
will have an area of 9,619 sf;which generates 619 ft3 of runoff. Two dry wells,one at each end of
the building, will retain and infiltrate the runoff produced by the roof. The drywells will be 5'
deep and each have a capacity of 488 ft3 (total capacity of 976 ft). See Appendix B for drywell
calculations.
APPENDIX A
DRAINAGE AREA MAP
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APPENDIX B
STORMATER CALCULATIONS
DRAINAGE AREA 1 LOT 5C
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2) C *Area
Hardscape 0.95 14808 14068
Landscape 0.2 14858 2972
Total 29666 17039
A =Area(acres) 0.68
C=Weighted C Factor 0.57
2. Calculate Required Volume
Q=CIA
V=72000
C =Weighted C Factor 0.57
1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm)
A =Area(acres) 0.68
Q = Runoff(cfs) 0.16
V= LOT 5C VOL(ft3) 1155
V= NORTH 27TH VOL(ft3) 2497
V=TOTAL VOL(ft) 3652
DRAINAGE AREA 2 LOT 5C
1. Calculate Area and Weighted C Factor
Contributing Area C Area(ft z C *Area
Hardscape 0.95 16861 16018
Landscape 0.2 11391 2278
Total 28252 18296
A =Area(acres) 0.65
C=Weighted C Factor 0.65
2. Calculate Required Volume
Q=CIA
V=72000
C=Weighted C Factor 0.65
1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm)
A=Area(acres) 0.65
Q=Runoff(cfs) 0.17
V=REQUIRED VOL(ft) 1240
DRAINAGE AREA 3 LOT 5C
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2) C *Area
Hardscape 0.95 13603 12923
Landscape 0.2 0 0
Total 13603 12923
A =Area(acres) 0.31
C=Weighted C Factor 0.95
2. Calculate Required Volume
Q=CIA
V=7200Q
C =Weighted C Factor 0.95
1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm)
A=Area(acres) 0.31
Q= Runoff(cfs) 0.12
V= REQUIRED VOL(ft) 876
PROVIDED VOLUME(2 DRYWELLS) 883
2. Calculate Drywell Volume
Existing Soil Condition Gravelly Sand
Percolation Rate (min/in) 3 (see Circular DEQ 4,
Percolation Rate (ft/hr) 1.67 Table 2.1-1)
Porous Media in Drywell Gravel
Void Ratio of Media 30.00%
Gravel Offset Dist. From Drywell (ft) 3
Drywell Gravel Area (ft2) 89.9
Infilitration Volume(ft) 299.73
Proposed Drywell Depth (ft) 5.25 (round up to nearest 3")
Provided Volume Inc. Perc. (ft) 441
Soil Type Percolation Rate(min/in)
Gravel, gravelly sand, or very coarse sand <3
Loamy sand, coarse sand 3 to<6
Medium sand, sandy loam 6 to<10
Fine sandy loam, loam 10 to<16
Very fine sand, sandy clay loam, silt loam 16 to<31
Clay loam, silty clay loam 31 to<51
Sandy clay 51 to<121
Clays, silts, silty clays 121 to<240
Clays, silts, silty clays >240
DRAINAGE AREA 1 LOT 513
1. Calculate Area and Weighted C Factor
Contributing Area C Area(ft") C*Area
Hardscape 0.95 25249 23987
Landscape 0.2 15637 3127
Total 40886 27114
A =Area(acres) 0.94
C=Weighted C Factor 0.66
12. Calculate Required Volume M
pQ=CIA
'V=7200Q
C=Weighted C Factor 0.66
1= Intensity(in/hr) 0.41 (10 yr, 2hr storm)
A=Area(acres) 0.94
Q=Runoff(cfs) 0.26
V= REQUIRED VOL(ft) 1837
DRAINAGE AREA 2 LOT 5B (ROOF)
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft Z) C *Area
Hardscape 0.95 9619 9138
Landscape 0.2 0 0
Total 9619 9138
A =Area(acres) 0.22
C=Weighted C Factor 0.95
2. Calculate Required Volume
Q=CIA
V=72000
C=Weighted C Factor 0.95
1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm)
A=Area(acres) 0.22
Q= Runoff(cfs) 0.09
V= REQUIRED VOL(ft3) 619
PROVIDED VOLUME (2 DRYWELLS) 869
2. Calculate Drywell Volume
Existing Soil Condition Gravelly Sand
Percolation Rate(min/in) 3„ (see Circular DEQ 4,
Percolation Rate(ft/hr); 1.67 Table 2.1-1)
Porous Media in Drywell Gravel
Void Ratio of Media 30.00%
Gravel Offset Dist. From Drywell(ft) 3
Drywell Gravel Area(ft2) 89.9
Infilitration Volume(ft) 299.73
Proposed Drywell Depth (ft) 5 (round up to nearest 3")
Provided Volume Inc. Perc. ft3 435
Soil Type Percolation Rate(min/in)
Gravel, gravelly sand, or very coarse sand <3
Loamy sand, coarse sand 3 to<6
Medium sand, sandy loam 6 to<10
Fine sandy loam, loam 10 to<16
Very fine sand, sandy clay loam, silt loam 16 to<31
Clay loam, silty clay loam 31 to<51
Sandy clay 51 to<121
Clays, silts, silty clays 121 to<240
Clays, silts, silty clays >240
APPENDIX C
NORTH 27th STORMWATER REPORT
Tfp- 11Ed,
SEP 2 8 2M6
Stortnwater Investigation
For
Fellowship Baptist Church
North 27'h Avenue Improvements
Prepared For:
Fellowship Baptist Church
Bozeman,MT 59715
Prepared By:
HKM Engineering Inc.
601 Nikles Dr.,Ste.2
Bozeman,MT 59715
September 22,2006
04C364.102
North 27`h Avenue—Stormwater Investigation August,2006
Table of Contents
Page
Purpose ...........................................................................................................................................3
ProjectOverview............................................................................................................................3
Preliminary Conditions Summary...................................................................................................3
Basisof Calculations.......................................................................................................................3
StormwaterRetention.....................................................................................................................3
Stormwater Treatment and Release................................................................................................6
ConveyanceFacilities.....................................................................................................................6
Maintenance....................................................................................................................................7
A. Inspection Program..............................................................................................................7
B. Maintenance Program..........................................................................................................7
Conclusion .....................................................................................................................................7
Tables
Table 1 -North 27`h Avenue Storage Stormwater Quantities.........................................................4
Table 2-North 27'h Avenue Conveyance Capacity.......................................................................7
Figures
Figure 1 -Storm Water Plan-Layout: ..........................................................................................5
Appendices
Appendix A-Peak Runoff Rate and Detention Pond Volume Calculations
Appendix B-Conveyance Facility Calculations
Page 2 of 7
North 27`h Avenue—Stormwater Investigation August,2006
Purpose
This engineer's report is intended to address the stormwater management system for the
northbound lane of North 27'h Avenue,from Oak Street to Tschache Lane. This report will
determine the recommended sizing of the stormwater retention basins and conveyance facilities
within the northbound lane only. This report was prepared in accordance with the design criteria
set forth in the current edition of the City of Bozeman's Design Standards and Specifications
Policy.
Protect Overview
This portion of North 27'"Avenue is being constructed in conjunction with the Fellowship
Baptist Church project, bounded on the west by North 27'"Avenue,on the east by the proposed
North 25`" Avenue, on the north by Tschache Lane and on the south by Oak Street.North 27'"
Avenue is classified as a collector in the Bozeman Transportation Plan.
Preliminary Conditions Summary
The pre-development condition of the proposed North improvements is agricultural with no
residential structures on site. North 271"Avenue is currently being constructed from Oak Street
to Baxter Lane,with the southbound lane for the entire distance and the northbound lane from
Tschache Lane to Baxter Lane being constructed by others.The current topography of the site
can be generalized as flat with a consistent slope of approximately 1.4%from south to north.
Basis of Calculations
The calculations and recommendations within this report are based on the regulations set forth in
the City of Bozeman Design Standards and Specifications Policy. The Rational Method was
used to determine the pre-developed release rate and,in turn,the post-developed minimum
required storage volume. All calculations associated with the release rate and required storage
volumes were based on a 10-year,2-hour storm event. The conveyance facilities,described
further in this report,are based on a 25-year,2-hour storm event. Calculations are provided in
the appendix of this report.
Stormwater Retention
The proposed system will discharge from North 27'h Avenue eastward to the adjacent property
prior to Tschache Lane.Stormwater retention is proposed for this property(Fellowship Baptist
Church). Stormwater retention facilities for the church are being designed by others.HKM
understands that these facilities will include retention storage for post development runoff from
North 276'Avenue.
Page 3 of 7
North 27th Avenue—Stormwater Investigation August,2006
The site has been analyzed as a single runoff basin.A summary of the pre-developed peak runoff
rate and the post-developed required storage is shown below in Table 1.
Table 1
North 27th Avenue
—Oak Street to Tscbache Lane(Northbound Lane)—
Stora e Requirements
Pre-Developed host-Developed
Peak Runoff Rate cfs Min.Required Storage fl
0.50 2,497
The drainage basis is 0.94 acres in size,and composed entirely of the paved northbound lane of
North 27th Avenue and the east half of the raised median.For purposes of this calculation,the
entire area is assumed to be pavement in the post-development analysis.Runoff from the basin
flows north and will be collected in standard storm drain inlets(COB Standard Drawing 02720-1
and 02720-1B)at three locations.Proposed inlet locations are shown on Figure 1.The calculated
minimum storage volume for runoff from North 27th Avenue is 2,497 cubic feet,under
developed conditions.
Page 4 of 7
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North 271h Avenue—Stormwater Investigation August,2006
Stormwater Treatment and Release
The stormwater retention ponds for the adjacent Fellowship Baptist Church property are being
design by others.Thus,stormwater treatment and release is not addressed here.
Conveyance Facilities
Stormwater runoff from this site will be conveyed to stormwater retention ponds by means of
curb and gutter,catch basins and storm main. All conveyance facilities on the site have been
sized to handle the 25-year,2-hour storm event as required in the City of Bozeman Design
Standards and Specifications Policy. Table 2 summarizes the post-developed runoff rate and
required pipe diameter.The storm sewer mains are shown on Figure 1.
The PVC storm mains are the minimum required 15"diameter. The rational method and
Manning's Equation were used to size the storm main. All calculations can.be found in the
Appendix of this report.
Standard 36"standard storm drain inlets(C.O.B Standard Drawing No.02720-1)will be used to
capture the stormwater runoff at the points specified on Figure 1.
Table 2
North 27th Avenue
—Oak Street to Tschache Lane(Northbound Lane)—
Conveyance Capacity
Post-Developed Pipe Diameter Pipe Capacity
Runoff Rate(cfs) (in) (cfs)
1.97 15 4.09
Page 6 of 7
North 27th Avenue—Stormwater Investigation August,2006
Maintenance
The storm drainage system within the publicly dedicated right-of-way is defined as a public
system. The public system shall be maintained by the City of Bozeman. The private system,
those facilities that do not lie within the publicly dedicated right-of-ways,will be maintained by
the property owner.
Due to sediment in the storm runoff and other variables,regular maintenance will be required by
the City to maintain proper performance of the storage and drainage network. The following
steps are minimum requirements for the maintenance of the storm facilities.
A) Inspection Program—On an annual basis,the following elements of the storm water
facilities should be inspected for excessive sediment deposits:
1) Catch Basins
2) Curb Cut Openings
3) Storm Mains
4) Detention/Retention Ponds
B) Maintenance Program—The following maintenance measures should be completed
based on the inspection program:
1) Catch Basin.&Curb Cut Openings—excessive sediments shall be removed either
manually(with a shovel)or with a vacuum truck and flushed.
2) Storm Mains—Mains shall be flushed if necessary.
3) Detention/Retention Ponds—A stake will be set six(6)inches above the original
bottom of the basin. If sediment is over the stake,it must be removed and the basin
must be revegetated according to the original landscape plan.
Conclusion
This report establishes the projected stormwater flows,retention requirements and conveyance
recommendations for the northbound lane of North 27th Avenue(Oak Street to Tschache Lane).
These facilities will be constructed in conjunction with improvements to property owned by
Fellowship Baptist Church,located at the intersection of Oak Street and North 271h Avenue in
Bozeman.
Page 7 of 7
A
P
PEAK RUNOFF RATE P
AND RETENTION POND
VOLUME CALCULATIONS
N
D
I
X
A
North 27th Avenue Storm Drainage Fellowship Baptist Church
04C364.102 Retention Volume Calculations Bozeman, MT
Drainage Basin-North 27th Avenue ROW(Oak St to Tschache Ln)
The following calculations were used to determine the minimum required storage volume for storm
water runoff. The volumes were calculated using the Rational Method,and the retention facilities were
sized based on a 10-year 2-hour storm event.
Area= 0.94 Acre
C= 0.9 Impervious
I= 0.41 In./hr.
Determine post-developed runoff rate:
Q= CxIxA
0.34686 cis
Determine minimum required storage volume:
V= 7200 x Q
2497.392 of
Va.�u M
HOVMR
G NO INN L N I NO
Appendix A Page 1 of 1
A
p
CONVEYANCE FACILITY p
CALCULATIONS
N
D
X
B
North 27th Avenue Storm Drainage Fellowship Baptist Church
04C364.102 Retention Volume Calculation Bozeman,MT
Storm Drainage Main-North 27th Avenue
The following calculations were used to size the conveyance facilities for stormwater runoff.
The volumes were calculated using the Rational Method,and the conveyance facilities were
sized based on a 25-year 2-hour storm event.
Contributing Basin(s)
A= 0.94 Acre
C= 0.9 Paved Roadway
Calculate Time of Concentration(T j
Developed Conditions:
S=1.40%
0.9 Paved Roadway
Find Sheet/Shallow Concentrated To
Assume: L=700 ft(300 ft-sheet flow 1400 ft-shallow flow)
From Figure 1-1,T,(sn= 10 min.
Find Channel Flow Tc(Gutter Flow)
Using Mannings Equation,n=0.013,S=1.4%,calculate channel flow
L= 550 ft
R= 0.92 it
v= 11.09 ft/sec
Tam= 0.83 min
Find Total Tr
Tc=TC(an+Tc(cF)
Total Tc(enlnF)= 10.83 min
CalculatePre-developed Storm Intensity at TQ
From Figure 1-3,using the 25 year event,I=0.78T-0B'
I= 2.33 In/hr
Calculate Post-developed Peak Runoff Rate
Q=ciA,using the above parameters.
Q= 1.97 ds
Calculate Pipe Capacity Provided
Q=(1.486/n)•A"R'"S72
Given: n= 0.013 Pipe Diameter=15"
A= 1.22718 sf Material=PVC
R= 0.31250 ft
S= 0.00400 fi/ft
Q= 4.08653 cis> 1.07 cis ok
V= 3.32919 fps
Appendix B 1 of 1
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APPENDIX D
STORMATER MAINTENANCE PLAN
STORMWATER MAINTENANCE PLAN FOR PALISADES APARTMENT COMPLEX
The following areas, facilities will be inspected and the identified deficiencies shall be corrected.
Clean-out must include the removal and legal disposal of any accumulated sediments and debris
from the entire stormwater management system.
Storm Water Facilities:
1. Retention Ponds/Detention Ponds:
Inspect ponds annually and after major storms (following three days of dry weather after
a storm event exceeding '/4 inch of precipitation.) and correct any identified deficiencies
to ensure that it is working in its intended fashion and that it is free of trash and debris.
Failure for water to percolate or pass through outlet structure within this time period
indicates clogging or poor-draining soils. Replace/repair as necessary. Remove and
properly dispose of any accumulated sediment or debris as needed. Inspect the
embankments and drainage structures for settlement, slope erosion,and downstream
swamping.
Mow the embankment to control woody vegetation. Remove woody debris from the
bottom of the pond. Inspect for channelization at bottom of pond and remove any
channels observed. Regrade as required if any channels are found that are not an element
of the original design. Remove grass clippings, litter, and debris from ponds.
2. Vegetated Areas:
Inspect slopes and embankments early in the growing season to identify active or
potential erosion problems. Replant bare areas or areas with sparse growth. Where rill
erosion is evident, armor the area with an appropriate lining or divert the erosive flows to
on-site areas able to withstand the concentrated flows. The facilities will be inspected
after major storms and any identified deficiencies will be corrected.
3. Ditches, Swales, Stormwater Chases and other Open Stormwater Channels:
Inspect 2 times per year(preferably lli Spring and Fall}to c:.sure they arc worl.irg-in
their intended fashion and that they are free of sediment and debris. Remove any
obstructions to flow, including accumulated sediments and debris and vegetated growth.
Repair any erosion of the ditch lining. Vegetated ditches will be mowed at least annually
or otherwise maintained to control the growth of woody vegetation and maintain flow
capacity. Any woody vegetation growing through riprap linings must also be removed.
Repair any slumping side slopes as soon as practicable. If the ditch has a riprap lining,
replace riprap on areas where any underlying filter fabric or underdrain gravel is showing
through the stone or where stones have dislodged. Correct any erosion of the channel's
bottom or side slopes. The facilities will be inspected after major storms and any
identified deficiencies will be corrected. For concrete stormwater chase structures with
metal "no slip" cover. Inspect covers to ensure metal edges aren't protruding above the
concrete surface. Correct deficiencies if found. Repair damaged or badly cracked
stormwater chases if observed.
Standard Maintenance Summary:
1. Remove sediment and oil/grease from retention ponds.
2. Inspect and remove debris from drainage swales, catch basins, and detention ponds.
3. Monitor health of vegetation and revegetate as necessary to maintain full vegetative
cover.
4. Inspect for the following issues: differential accumulation of sediment,drain time, signs of
petroleum hydrocarbon contamination (odors, oil sheen in pond water), standing water,
trash and debris blockages.
Note on sediment disposal:
In most cases, sediment from a detention pond does not contain toxins at levels posing a hazardous
concern. However, sediments should be tested for toxicants in compliance with current disposal
requirements and if land uses in the drainage area include commercial or industrial zones, or if
visual or olfactory indications of pollution are noticed. Sediments containing high levels of
pollutants should be disposed of in accordance with applicable regulations and the potential
sources of contamination should be investigated and contamination practices terminated.
ACCEPTED BY PALISADES APARTMENT COMPLEX OWNERS ASSOCIATION,BY
1
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