HomeMy WebLinkAbout16 Stormwater Report 12-21-20
STORMWATER DESIGN REPORT
FOR:
COURTYARD HOTEL BY MARRIOTT
BOZEMAN, MT
Prepared By:
Madison Engineering
895 Technology Blvd Ste 203
Bozeman, MT 59718
(406) 586-0262
DECEMBER 2020
COURTYARD BY MARRIOTT-BOOTHILL
STORMWATER DESIGN REPORT
A. Introduction
The proposed development for the Courtyard Hotel by Marriott will be constructed at 2168
Boot hill Court in Bozeman, MT. The site development consists of one hotel building with
171 guest rooms and associated infrastructure. The following references were used in the
preparation of this report:
a. COB Design Standards and Specifications Policy, 2004 (DSSP). Addendum #7
b. COB Modifications to Montana Public Works Standard Specifications (MPWSS)
B. Stormwater Management
The site is located on Lot 4 of Block 2 of Lewis & Clark Subdivision. It is bordered by two
existing buildings, Boot hill Court, and Interstate 90. The proposed stormwater management
system consists of on-site curb and cutter, curb inlets, conveyance piping, and a retention
pond.
Runoff is directed from the site into the curb and gutter via downspouts, roof drain piping,
and overland sheet drainage. The runoff then enters into curb inlets and stormwater piping,
and is then conveyed via piping into the retention pond. The retention pond includes an
infiltration mechanism, a 5’ radius gravel infiltrator that is excavated to native gravels, lined
with separation fabric, and filled with drain rock.
The proposed design reduces the post-development to less than the pre-development runoff
rate via total retention. Stormwater run-off was calculated based on the Rational Method and
the retention systems were sized per the City of Bozeman’s design standards for a storm
intensity of 10-year frequency and a 2-hour duration. The required retention pond storage
volume is 6,012 cf. At a 1.5 ft depth, the proposed retention pond has a capacity of 6,133 cf.
Stormwater conveyance structures were sized to convey the 25 year, 2-hour storm. The curb
and gutter and proposed piping have adequate capacity to convey the flows.
The stormwater basins, piping, and system are displayed in the attached Stormwater Exhibit.
The stormwater basin, runoff, retention, and conveyance calculations are included in the
appendix. A stormwater maintenance plan is included in the appendix.
C. Soil Conditions and Groundwater Information
The existing site is an empty lot that slopes northward at about 1%. A geotechnical report
was conducted for project 2019 by TD&H Engineering. In general, soil conditions consist of
a layer of topsoil 0.9 to 1.2 ft thick followed by a layer of silts and clays between 4.0 and 7.2
ft depths, followed by alluvial sandy gravel. Groundwater was encountered on the site and
was observed at depths ranging from 4.0 to 7.5 ft below the ground surface at the time of the
geotechnical investigation.
The proposed retention pond was designed to have the bottom of the pond elevation above
the observed groundwater surface. The observed groundwater elevation in Test Pit #3 was
4.25 ft below the existing surface. The pond bottom elevation is approximately 1.5 ft below
existing grade at the lowest point, putting the bottom of the pond about 2.75 ft above the
observed groundwater elevation. The proposed buried gravel infiltration system was
designed to extend into native gravels to facilitate infiltration.
Seasonal high groundwater fluctuations can be estimated via a comparison of groundwater
monitoring data for a nearby project about 1 mile to the northwest, the Palisades
Condominiums, located near the corner of Catamount St and Warbler Way. Groundwater
monitoring was conducted in the spring and summer of 2020, and groundwater fluctuated
less than a foot over the recorded measurements. It is anticipated that groundwater will
fluctuate similarly at the Courtyard Hotel Site, within a foot above the observed
measurements of the Geotechnical report. The Palisades Condominium groundwater
monitoring information is included in the Appendix.
D. Treatment and 0.5” Storm Requirement
All the drainage basins flow into the retention pond, sized to totally retain the 10 year-2 hour
storm, which has an intensity of 0.41 in/hr, exceeding the 0.5” volume.
Appendices
A. Stormwater Calculations
B. Stormwater Maintenance Plan
C. Stormwater Exhibit
D. Palisades Groundwater Monitoring for Comparison
Appendix A:
Stormwater Calculations
25-year Flows for Sizing of Conveyance Structures:
Drainage
Basin No.
Total Area
(SF)
IMPERVIOUS
(SF) C = 0.9
ROOF (SF)
C=0.9
LANDSCAPED
(SF) C = 0.2
Weighted
C
Basin
Length
(ft)
Slope
%
Tc (min)
Cf = 1.1
i 25-yr
(in/hr)
Q 25
(cfs)Drians To:
Pre-Developed Basins
Existing 130,964 0 0 130,964 0.20 500 1 38 1.05 0.63 Ditch
Post-Developed Basins
A 22,244 10,872 4,928 6,444 0.70 100 1 5 3.83 1.36 Pond
B 43,575 23,160 5,267 15,148 0.66 250 1 5 3.83 2.51 Pond
C 65,145 35,248 10,503 19,394 0.69 350 2 8 2.83 2.93 Pond
Subtotal 130,964 69,280 20,698 40,986 Manual
estimates
Courtyard by Marriott
Peak flow calculations
Drainage Areas
Page 1 of 1
Allowable Pavement Encroachment
Given: T =9 feet (max per city)
W =1.5 feet
Ts =7.5 feet
Sw =0.0625 ft/ft
Sx =0.03 ft/ft
a =0.59 inches
d =3.24 inches
n =0.015
Sw/Sx =2.08
T/W =6
Capacity for Gutter
equations:
Where:
Qs = Discharge within the Roadway
above the depressed section (cfs)
Qw = Discharge within the depressed
(gutter) section (cfs)
Cf = 0.56 for English units
Sx = Pavement cross slope (ft/ft)
Ts = Width of flow in the roadway above
depressed section
So = Gutter longitudinal slope (ft/ft)
Sw = Gutter depression cross slope (ft/ft)
T = Spread (ft)
W = Width of gutter depression (ft)
Capacity solution
Gutter Capacity - Drainage Basin A Gutter Capacity - Drainage Basin B
So =0.0100 So =0.0050
Qs =2.33 cfs Qs =1.65 cfs
Eo =0.42 cfs Eo =0.42 cfs
Q =4.04 cfs Q =2.86 cfs
A =1.215 sf A =1.215 sf
V =3.33 ft/s V =2.35 ft/s
Gutter Capacity - Drainage Basin C
So =0.0100
Qs =2.33 cfs
Eo =0.42 cfs
Q =4.04 cfs
A =1.215 sf
V =3.33 ft/s
BASIN Gutter
Capacity (cfs)
25 Yr Design
Flow (cfs)
Capacity
greater than
25- yr flow?
A 4.04 1.36 Yes
B 2.86 2.51 Yes
C 4.04 2.93 Yes
Summary
Gutter Capacity Calculations
The gutter capacity is adequate for each drainage area.
Courtyard by Marriott
SWQQQ
QEQoW
0
S
E1
QQ
2
1
O3
8
S3
5
X
f
S STSn
CQ
1
8/3
XW
XWo
11T/W
/SS1
/SS1E
Page 1 of 1
Basins A, B & C
East Jordan Iron Works Orifice Flow Calculations: From Manufacturer's Website
Where: Q = Flow (cfs)
A = Open area in grate (in^2)
d = Depth of water over grate (in)
C = Rating Coefficient
C = 0.0108 *From Manufacturer
A = 225 in^2 *From Shop Drawing Submittal
d = 4 in *City Maximum
Q =4.86 cfs
Basin Flows
Basin A - Q 25 1.36 cfs
Basin B - Q 25 2.51 cfs
Basin C - Q 25 2.93 cfs
Summary The Proposed Curb Inlets have sufficient capacity to convey the peak flows
Courtyard by Marriott
Orifice Type (Sag) Curb Inlet Capacity Calculations
𝑄=𝐶∗𝐴∗√𝑑
Courtyard Hotel by Marriott-Boothill
Stormwater Pipe Capacity Summary
Pipe Contributing Basin
Inflow
Q(25) (cfs)Pipe Size Pipe Slope
Pipe
Capacity (cfs)
1 A 1.36 12" 0.50% 3.9
2 A, B 3.87 12" 0.50% 3.9
3 C 2.93 12" 0.50% 3.9
RD 1 Southwest Roof Drain Areas* 0.50 6" 0.50% 0.6
RD 2 Southeast Roof Drain* 0.35 6" 0.50% 0.6
RD 3 Northern Roof Drain* 0.29 6" 0.50% 0.6
RD 4 Parking Canopy Roof Drain* 0.02 4" 0.50% 0.2
*Roof drain flows provided by mechanical engineer
DA Q(25) (cfs)
A 1.36
B 2.51
C 2.93
CIRCULAR CHANNEL
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =12.0 Enter Value
Diameter,do (ft) =1.00
Units =1.486
n =0.009
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.0 0.00
0.05 0.90 0.01 0.45 0.03 0.44 0.03 0.00 0.0 7.8 3764.5 1.2 0.02
0.10 1.29 0.04 0.64 0.06 0.60 0.07 0.01 0.1 34.1 16366.5 1.9 0.05
0.15 1.59 0.07 0.80 0.09 0.71 0.10 0.02 0.2 79.4 38105.9 2.4 0.09
0.20 1.85 0.11 0.93 0.12 0.80 0.14 0.04 0.3 143.0 68648.9 2.8 0.13
0.25 2.09 0.15 1.05 0.15 0.87 0.18 0.06 0.5 223.7 107382.8 3.2 0.16
0.30 2.32 0.20 1.16 0.17 0.92 0.22 0.09 0.7 319.8 153516.1 3.6 0.20
0.35 2.53 0.24 1.27 0.19 0.95 0.26 0.12 1.0 429.4 206123.9 3.9 0.24
0.40 2.74 0.29 1.37 0.21 0.98 0.30 0.16 1.2 550.4 264171.6 4.2 0.27
0.45 2.94 0.34 1.47 0.23 0.99 0.34 0.20 1.5 680.3 326526.0 4.4 0.30
0.50 3.14 0.39 1.57 0.25 1.00 0.39 0.25 1.8 816.6 391960.2 4.6 0.33
0.55 3.34 0.44 1.67 0.26 0.99 0.44 0.30 2.1 956.6 459150.7 4.8 0.36
0.60 3.54 0.49 1.77 0.28 0.98 0.50 0.35 2.4 1097.2 526669.2 5.0 0.38
0.65 3.75 0.54 1.88 0.29 0.95 0.57 0.41 2.8 1235.3 592964.0 5.1 0.40
0.70 3.96 0.59 1.98 0.30 0.92 0.64 0.47 3.0 1367.3 656327.6 5.2 0.42
0.75 4.19 0.63 2.09 0.30 0.87 0.73 0.54 3.3 1489.2 714839.5 5.3 0.43
0.80 4.43 0.67 2.21 0.30 0.80 0.84 0.62 3.6 1596.4 766256.2 5.3 0.43
0.85 4.69 0.71 2.35 0.30 0.71 1.00 0.71 3.7 1682.9 807783.2 5.3 0.43
0.90 5.00 0.74 2.50 0.30 0.60 1.24 0.83 3.9 1740.6 835500.2 5.2 0.42
0.95 5.38 0.77 2.69 0.29 0.44 1.77 1.02 3.9 1754.9 842333.8 5.1 0.40
1.00 6.28 0.79 3.14 0.25 0.00 3.6 1633.7 784185.4 4.6 0.33
Pipe Flows Contributing Basin
Pipe 1 1.36 cfs *Basin A
Pipe 2 3.87 cfs *Basin A + B
Pipe 3 2.93 cfs *Basin C
Summary:The proposed pipes have adequate capacity to convey the 25 year flows
Q =
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0.00 0.20 0.40 0.60 0.80 1.00 1.20
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)
ydo
T
THETA
CIRCULAR CHANNEL - 6" Roof Drain Piping
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =6.0 Enter Value
Diameter,do (ft) =0.50
Units =1.486
n =0.009
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.0 0.00
0.03 0.90 0.00 0.23 0.02 0.22 0.02 0.00 0.0 1.2 592.9 0.7 0.01
0.05 1.29 0.01 0.32 0.03 0.30 0.03 0.00 0.0 5.4 2577.6 1.2 0.02
0.08 1.59 0.02 0.40 0.05 0.36 0.05 0.00 0.0 12.5 6001.3 1.5 0.04
0.10 1.85 0.03 0.46 0.06 0.40 0.07 0.01 0.1 22.5 10811.5 1.8 0.05
0.13 2.09 0.04 0.52 0.07 0.43 0.09 0.01 0.1 35.2 16911.7 2.0 0.06
0.15 2.32 0.05 0.58 0.09 0.46 0.11 0.02 0.1 50.4 24177.3 2.3 0.08
0.18 2.53 0.06 0.63 0.10 0.48 0.13 0.02 0.2 67.6 32462.5 2.5 0.09
0.20 2.74 0.07 0.68 0.11 0.49 0.15 0.03 0.2 86.7 41604.4 2.6 0.11
0.23 2.94 0.09 0.74 0.12 0.50 0.17 0.04 0.2 107.1 51424.6 2.8 0.12
0.25 3.14 0.10 0.79 0.13 0.50 0.20 0.04 0.3 128.6 61729.9 2.9 0.13
0.28 3.34 0.11 0.84 0.13 0.50 0.22 0.05 0.3 150.6 72311.7 3.0 0.14
0.30 3.54 0.12 0.89 0.14 0.49 0.25 0.06 0.4 172.8 82945.2 3.1 0.15
0.33 3.75 0.14 0.94 0.14 0.48 0.28 0.07 0.4 194.6 93386.0 3.2 0.16
0.35 3.96 0.15 0.99 0.15 0.46 0.32 0.08 0.5 215.3 103365.1 3.3 0.17
0.38 4.19 0.16 1.05 0.15 0.43 0.36 0.10 0.5 234.5 112580.2 3.3 0.17
0.40 4.43 0.17 1.11 0.15 0.40 0.42 0.11 0.6 251.4 120677.8 3.3 0.17
0.43 4.69 0.18 1.17 0.15 0.36 0.50 0.13 0.6 265.0 127217.9 3.3 0.17
0.45 5.00 0.19 1.25 0.15 0.30 0.62 0.15 0.6 274.1 131583.0 3.3 0.17
0.48 5.38 0.19 1.35 0.14 0.22 0.88 0.18 0.6 276.4 132659.3 3.2 0.16
0.50 6.28 0.20 1.57 0.13 0.00 0.6 257.3 123501.5 2.9 0.13
Pipe Flows
Southwest Roof Drain 0.50 cfs *Flows provided by the Mechanical Engineer
Southeast Roof Drain 0.35 cfs *Flows provided by the Mechanical Engineer
Northern Roof Drain 0.29 cfs *Flows provided by the Mechanical Engineer
Summary:The proposed pipes have adequate capacity to convey the 25 year flows
Q =
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)
ydo
T
THETA
CIRCULAR CHANNEL - 4" Roof Drain Piping
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =4.0 Enter Value
Diameter,do (ft) =0.33
Units =1.486
n =0.009
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.0 0.00
0.02 0.90 0.00 0.15 0.01 0.15 0.01 0.00 0.0 0.4 201.1 0.6 0.01
0.03 1.29 0.00 0.21 0.02 0.20 0.02 0.00 0.0 1.8 874.2 0.9 0.01
0.05 1.59 0.01 0.27 0.03 0.24 0.03 0.00 0.0 4.2 2035.5 1.2 0.02
0.07 1.85 0.01 0.31 0.04 0.27 0.05 0.00 0.0 7.6 3667.0 1.4 0.03
0.08 2.09 0.02 0.35 0.05 0.29 0.06 0.00 0.0 12.0 5736.0 1.6 0.04
0.10 2.32 0.02 0.39 0.06 0.31 0.07 0.01 0.0 17.1 8200.3 1.7 0.05
0.12 2.53 0.03 0.42 0.06 0.32 0.09 0.01 0.1 22.9 11010.4 1.9 0.05
0.13 2.74 0.03 0.46 0.07 0.33 0.10 0.01 0.1 29.4 14111.2 2.0 0.06
0.15 2.94 0.04 0.49 0.08 0.33 0.11 0.01 0.1 36.3 17441.9 2.1 0.07
0.17 3.14 0.04 0.52 0.08 0.33 0.13 0.02 0.1 43.6 20937.2 2.2 0.08
0.18 3.34 0.05 0.56 0.09 0.33 0.15 0.02 0.1 51.1 24526.3 2.3 0.08
0.20 3.54 0.05 0.59 0.09 0.33 0.17 0.02 0.1 58.6 28132.9 2.4 0.09
0.22 3.75 0.06 0.63 0.10 0.32 0.19 0.03 0.1 66.0 31674.1 2.4 0.09
0.23 3.96 0.07 0.66 0.10 0.31 0.21 0.03 0.2 73.0 35058.8 2.5 0.10
0.25 4.19 0.07 0.70 0.10 0.29 0.24 0.03 0.2 79.6 38184.3 2.5 0.10
0.27 4.43 0.07 0.74 0.10 0.27 0.28 0.04 0.2 85.3 40930.8 2.5 0.10
0.28 4.69 0.08 0.78 0.10 0.24 0.33 0.05 0.2 89.9 43149.1 2.5 0.10
0.30 5.00 0.08 0.83 0.10 0.20 0.41 0.05 0.2 93.0 44629.6 2.5 0.10
0.32 5.38 0.09 0.90 0.10 0.15 0.59 0.07 0.2 93.7 44994.7 2.4 0.09
0.33 6.28 0.09 1.05 0.08 0.00 0.2 87.3 41888.6 2.2 0.08
Pipe Flows
Parking Canopy Roofdrain 0.02 cfs *Flows provided by the Mechanical Engineer
Summary:The proposed pipes have adequate capacity to convey the 25 year flows
Q =
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)
ydo
T
THETA
Courtyard Hotel by Marriott
Lot 4 Block 2 of Lewis and Clark Commercial Subdivision
Stormwater Detention/Retention Calculations
11/3/2020
Calculation of Required Volume for Storm Detention Pond
(Reference: Bozeman Stormwater Master Plan - 1982)
Design Rainfall Freq. 10 year (see page III - 5 of master plan)
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
C
Areas (ft2):Landscaping 40,986 0.20
Roof Area 20,698 0.90
Impervious 69,280 0.90
Total: 130,964
total area: 3.007 acres
composite C: 0.68
Retention Pond Calculations:
Q = CIA
C = 0.68 (post-development)
I = 0.41 in/hr (10-yr, 2-hr storm)
A = 3.01 acres
Q =0.83 cfs
required retention storage (ft3) =6,012 ft3
Volume held between contours:
Cumulative
Contour Area (ft2) Delta V (ft3) Volume (ft3)
4716.50 1523
4717.0 3338 1,215 1,215
4717.5 5142 2,120 3,335
4718.00 6049 2,798 6,133
Design storage at 1.5' depth (ft3) =6,133
Retention pond COB.xls
Appendix B:
Stormwater Maintenance Plan
Courtyard Hotel by Marriott-Boothill
Storm Water Maintenance Plan
Owner’s responsibility for routine inspection and maintenance:
1. Perform quarterly inspection of and keep the curb and gutter, curb cut, sidewalk chase, curb
inlets, conveyance piping and round rock drainage swale areas free of leaves, rocks,
sediment, and other debris.
2. Re-sod or seed damaged or maintained areas immediately.
3. Retention Pond: Perform yearly inspection of the retention pond and remove sediment if it
accumulates to 3” above design grade. Keep the pond free of trash and other debris.
4. Stormwater facilities shall be maintained by the owner or other responsible party in a
condition so that the facilities will function as designed.
5. Waste shall be disposed of from maintenance of facilities in accordance with applicable
federal, state and local laws and regulations.
7. The owner or other responsible party shall create and maintain records of installation and
maintenance and repair for the life of the development and shall be made available to the
engineering department upon request.
8. Owner to maintain and fund Operation and Maintenance of facilities.
Owner, Courtyard Hotel
Appendix C:
Stormwater Exhibit
B
O
O
T
H
I
L
L
C
O
U
R
T
UP
UP
FITNESS036
MECH/WH/FIRE026
POOLEQUIPMENT028
POOLCHEMICAL029
POOL/SPA032
MEETINGROOM041
LOBBY019
RECEPTION017
LUGGAGE015
COMP/TELECOM016
ELEVATORLOBBY190
EMPLOYEEBREAKROOM006
LINEN007
LAUNDRY193
WORKROOM012
SALESOFFICE013
MANAGERSOFFICE014
CRATE018
BAR020
FOOD PREP021 MEETINGROOMSTORAGE031
DHU027
POOLVEST.033
CORRIDOR034
ENTRYVESTIBULE001
LOUNGE042
VEST.035
ELECTRICAL025
KING128
KING130KING132KING134KING136
PUBLICSPACE138
QUEEN/QUEENACC. R.I.S.139
QUEEN/QUEENACC. R.I.S.137 QUEEN/QUEEN135
STAIR 2152
STAIR 1150
EMP.RESTROOM005
FIRERISER
WATERHEATER
MECHANICAL
RESTROOM044
PREFUNCTIONAREA039
MEETINGROOM040
WOMENS127
MENS129
GUESTLAUNDRY141
VESTIBULE142
QUEEN/QUEEN133
ICE140
ELEV.EQUIP.143
LINEN144
BASIN A
22,244 SF
IMPERVIOUS = 10,872 SF
ROOF = 4,928 SF
LANDSCAPED = 6,444 SF
C = 0.70
BASIN B
43,575 SF
IMPERVIOUS = 23,160 SF
ROOF = 5,267 SF
LANDSCAPED = 15,148 SF
C = 0.66
BASIN C
65,145 SF
IMPERVIOUS = 35,248 SF
ROOF = 10,503 SF
LANDSCAPED = 19,394 SF
C = 0.69
COURTYARD HOTEL
BY MARRIOTT
FFE 4723.00
LEGEND
1" =
0
SCALE
30'
601530
EXHIBITMADISON ENGINEERING
895 TECHNOLOGY BLVD, STE 203, BOZEMAN, MT 59718
PHONE (406) 586-0262
COURTYARD BY MARRIOTT
STORMWATER EXHIBIT