HomeMy WebLinkAbout15 - Design Report - Traditions Ph 3 Oak Street Improvements - Stormwater STORMWATER MANAGEMEV)F
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DESIGN REPORT
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TRADITIONS SUBDIVISION PHASE 3
OAK STREET IMPROVEMENTS
Prepared for:
Rosa Construction, Inc.
125 Central Avenue, Bozeman, MT 59718
Prepared by:
C&H Engineering and Surveying, Inc.
1091 Stoneridge Drive, Bozeman, MT 59718
(406) 587-1115
Project Number: 14170.1
AUGUST 2015
INTRODUCTION
Oak Street improvements are proposed during construction of Traditions Subdivision Phase 3 and
will connect West Oak Street from Boulder Creek Subdivision to Twin Lakes Avenue at the
boundary of Flanders Creek Subdivision. The 7.89-acre Lot R1, with frontage along Oak Street,
is situated in the Northeast Quarter of the Southeast Quarter of Section 4, Township 2 South,
Range 5 East of P.M.M., City of Bozeman, Gallatin County, Montana. Lot Rl is a restricted use
lot and zoned R4. This report considers the management of stormwater with Lot R1 in its current
undeveloped state but also provides adequate detention to accommodate the anticipated buildout
of the lot in sizing overflow structures and detention pond volume. A future subdivision or site
plan will address stormwater management on the developed Lot R1 in more detail and additional
stormwater management will be implemented if found to be necessary.
C&H Engineering developed spreadsheets were used for all calculations in this report including
pipe outlet capacities, gutter flow depth and detention pond sizing. Each drainage area,
composite "C" value, total acreage and storm peak runoff was calculated using a C&H
Engineering developed Excel spreadsheet. Data was taken from the Flanders Creek Stormwater
Report and revisions dated June 2005 to model the existing storm sewer facilities in order to
interface the existing system with the proposed. All excel spreadsheet printouts and other sources
can be found at the end of this report.
STORMWATER MANAGEMENT
Design of the stormwater facilities for this project was based on the City of Bozeman Design
Standards and Specifications Policy, March 2004 including Addendums 1 through 5. The future
site plan for Lot R1 was incorporated into the detention pond volume as described in the detention
pond section of this report. For the purposes of determining the volume for Pond 1 the Lot R1
area was assumed to have a future runoff coefficient of 0.7. In the future site plan excess runoff,
which cannot be detained in Pond 1, will be retained on site or an additional detention pond will
need to be designed. Pond 1 is currently shown at its maximum size on Figure D1 found at the
end of this report. The inlet at the corner of Twin Lakes Avenue and Oak Street (Inlet FC-14) is
proposed to be removed during Oak Street improvements. FC-14 currently is piped to a
temporary retention pond located in the Oak Street right of way;this structure will be removed and
Design Report-Page 2 of 5
the contributing drainage area will be graded to drain from the current location of FC-1.4 to
proposed Storm Inlet IA. There is a small section of Oak Street on the far west of the proposed
street (Oak West) which accounts for 4,263 square feet of Oak Street (C=0.82). This small area
will be temporarily drained to Pond 1 until completion of Boulder Creek Subdivision. A
temporary swale is shown on the construction plans for management of this runoff.
DRAINAGE AREA 1
Drainage Area 1 consists of a portion of Oak Street to the north of Lot R1 and a portion of Twin
Lakes Avenue east of Lot R1, as shown on Figure D1. Drainage Area 1 will contribute runoff to
Pond 1 via Storm Inlet IA located on the south side of Oak Street at the low point in the street
profile. This inlet will be piped to a proposed 48-inch manhole (Storm Inlet 2A) via a 15-inch
PVC storm sewer pipe under the curb in Oak Street. From Storm Inlet 2A a 15-inch PVC pipe
will connect with a new 60-inch manhole (SDMH 1) proposed to be installed at the existing
30-inch RCP pipe draining from east to west along the south side of Oak Street in the existing 15
foot stormwater easement. The existing 30-inch RCP pipe is an outlet pipe currently used for the
19,000 cubic foot existing detention pond that was installed with Flanders Creek Subdivision
(existing pond). A 30-inch PVC pipe will be installed downstream from SDMH 1. This pipe
will be the inlet pipe for a new detention pond (Pond 1) proposed to detain runoff from Drainage
Area 1. A composite "C" runoff coefficient was calculated for Drainage Area 1 along with the
post-development time of concentration. The proposed 15-inch,30-inch and 36-inch storm sewer
pipes discussed above all have adequate capacity as calculated on the storm sewer pipe capacity
spreadsheets. Additionally all existing and proposed gutter capacities were checked to verify
adequate freeboard while flowing at the COB maximum gutter flow depth of 0.15 feet below the
top of curb. As can be seen in the attached spreadsheets all gutters have adequate capacity.
STORMWATER DETENTION AT POND 1
Pond 1 is proposed in the designated open space area along the west side of Lot RI. This pond
will retain and release runoff from Drainage Area 1 and it has been oversized for future use
following buildout of the Lot R1 site. The exact drainage area contribution to this pond from Lot
R1 will be determined in the future site plan. Design water depth for the detention pond
Design Report- Page 3 of 5
calculations was limited to 1.5 feet, which is the maximum allowed pond water depth in the COB
stormwater design standards without safety fencing. Drainage area 1 has a total area of 1.14 acres
and a composite "C"runoff coefficient of 0.82. The pre-developed runoff rate was calculated to
be 0.17 ft3/sec. (See end of the report for detailed calculations). The storage volume was
computed by increasing the storm duration and computing the runoff volume minus the release
volume. The release rate is equal to the pre-developed runoff rate. The maximum storage
required occurs at a storm duration of 85 minutes and is equal to 1,579 cubic feet. Detention Pond
#1 has a volume of 10,623 cubic feet as shown on the construction drawings. This volume
accounts for the area of Lot RI (7.89 acres) with a C coefficient of 0.7, the 1.14 acres from
Drainage Area 1 plus the small contribution from Oak West. As shown on the spreadsheet
entitled Detention Pond#1 (Oak Street, Twin Lakes and Lot R1 included) found at the end of this
report the required volume of Pond 1 is 10,299 cubic feet. Therefore the pond as shown on Figure
D1 will be sized to have ample volume to detain the required runoff from Oak Street, Twin Lakes
Avenue, and from the completed Lot RL
OUTLET STRUCTURE AND PIPING—POND 1 AND EXISTING POND
An outlet structure and piping will be installed in the north end of Detention Pond#1. The outlet
structure will be sized per the City of Bozeman Design Standards and will be adjusted to a weir
width of 5.6 inches. Discharge to Baxter Ditch will be limited to 2.88 ft3/sec. which includes 2.71
ft3/sec., the pre-development runoff release rate of the existing pond's 5.3-inch weir, plus the
pre-development runoff release rate of 0.17 ft3/sec. from Drainage Area 1. An adjustable outlet
weir will be used in the outlet structure at Pond 1 in order to increase the overflow rate in the future
if additional detention volume is required during development of the future site plan design. The
weir notch will have a maximum width of 8-inches which will handle the pre-development runoff
from Lot R1, Drainage Area 1 and the current release rate of the outlet weir on the existing pond.
The outlet pipe for the new pond will be sized as a 36-inch PVC pipe with a 0.54% slope
(maximum capacity = 52.72 ft3/sec.). The outlet pipe has been oversized to handle overflow
drainage from Drainage Area 1, Lot R1 and the existing pond. The capacity of this pipe exceeds
the required design flow rate of 35.41 ft3/sec., which includes the existing outlet structure's
overflow rate, Q25 of 20.29 ft3/sec. (Flander's Creek Stormwater Design Report and revisions
Design Report-Page 4 of 5
dated June 2005), plus 15.12 ft3/sec. which is the total amount of overflow from Drainage Area 1
and the anticipated maximum overflow contribution from Lot R1. The detention pond outlet pipe
therefore will provide sufficient overflow capacity from the proposed detention pond to the Baxter
Ditch outfall in a major storm event for the current design and the weir width can be easily adjusted
to handle additional flows from Lot R1 as required.
Design Report-Page 5 of 5
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DETENTION POND #1 (Twin Lakes and Oak Street Only)
REQUIRED VOLUME
2. Calculate Area and Weighted C Factor(Post-Development)
Contributing Area C Area (ft 2) C *Area
ROW 0.82 49504 40593
OS/Park 0.2 0 0
Lot R1 0.7 0 0
Laurel Parkway 0.81 0 0
Durston ROW 0.68 0 0
Total 49504 40593
A =Area(acres) 1.1365
C= Weighted C Factor 0.82'I
3. Calculate Tc (Pre-Development)
Tc Overland Flow
Tc= 1.87(1.1-CCf)D1/2/S1/3
(Storm I
S =Slope of Basin (%) 1 Return (yrs) Cf
C = Rational Method Runoff Coefficient 0.2 12 to 10 11
Cf= Frequency Adjustment Factor 1.1 111 to 25 1.1
D = Length of Basin (ft) 886 :26 to 50 1.21
I51 to 100 1.251
-----------------------------+
Tc(Pre-Development) (minutes) 49
4. Calculate Rainfall Intensity(Duration =Pre-Development Tc)
i =0.64x o.s5 (10-yr Storm, Fig. 1-3, COB Design Standards)
x= storm duration (hrs) 0.82'i(Tc Pre-Development)
i=rainfall intensity(in./hr.) 0.73'
5. Calculate Runoff Rate(Pre-Development)
Q=CiA
C = Rational Method Runoff Coefficient 0.2 (open land)
i = rainfall intensity(in./hr.) 0.73 (calculated above)
A=Area (acres) 1.14 (calculated above)
Q=Runoff Rate (Pre-Development) (cfs) 0.17'
6. Calculate Required Pond Volume
Total Area (acres) = 1.14+acres
Weighted C = 0.82'
Discharge Rate (cfs)= 0.17 cfs(Equal to Pre-Development Runoff Rate)
Duration(min) Duration(hrs) Intensity Qm(cfs) Runoff Release Required
3
(in/hr) Volume Volume Storage (ft)
)
78 1.30 0.54 0.50 2354 777 1577
79 1.32 .0,54 0.50 2364 787 1577
80 1.33 0.53 0.49 2375 797 1578'
81 1.35 0.53 ' 0.49 2385 807 1578':
82 1.37 0.52 0.49 2395 817 1579
83 1.38 0.52 0.48 2405 827 1579'
84 1.40 0.51 0.48 2415 836 1579'
85 1.42 0,51 0.48 2425 846 1579
86 1.43 0.51 0.47 2435 856 1579
87 1.45 0.50 0.47 2445 866 1579'
88 1.47 0,50 0.46 2455 876 ' 1579';
89 1.48 0.50 0.46 2465 886 1579'i
90 1.50 0.49 0.46 2474 896 1578
91 1.52 0.49 0.45 2484 906 1578
92 1.53 0.48 0.45 2494 916 1577
OUTLET STRUCTURE SLOT
Q=CLH 312
QExIsTINc POND = Discharge(cfs) 2.71
QPOND 1 = Discharge (cfs) 0.17
QTOTAL AT POND 1 WEIR= Discharge (cfs) 2.88!
C =Weir Coefficient 3.33;(per COB Design Standards)
H = Head (ft) 1.5
L= Horizontal Length (ft) 0.47
L =Slot Width (inches) 5.6
DETENTION POND #1 (Oak Street, Twin Lakes and Lot R1 included)
REQUIRED VOLUME
2. Calculate Area and Weighted C Factor(Post-Development)
Contributing Area C Area (ft 2) C *Area
ROW 0.82 53767 44089
OS/Park 0.2 0 0
Lot R1 0.7 343838 240687
Laurel Parkway 0.81 0 0
Durston ROW 0.68 0 0
Total 397605 284776
A =Area (acres) 9.1278
C= Weighted C Factor 0.72
3. Calculate Tc (Pre-Development)
Tc Overland Flow
Tc= 1.87(1.1-CCf)D1/2/Sv3
(Storm I
S =Slope of Basin (%) 1 ;Return (yrs) Cf
C = Rational Method Runoff Coefficient 0.2 ;2 to 10 1;
Cf= Frequency Adjustment Factor 1.1 111 to 25 1.1
D = Length of Basin (ft) 886! :26 to 50 1.2i
151 to 100 1.251
Tc(Pre-Development) (minutes) 49
4. Calculate Rainfall Intensity(Duration =Pre-Development Tc)
i = 0.64x'-"(10-yr Storm, Fig. 1-3, COB Design Standards)
x=storm duration (hrs) 0.82i;(Tc Pre-Development)
i=rainfall intensity(in.1hr.) 0.73
5. Calculate Runoff Rate(Pre-Development)
Q =CiA
C = Rational Method Runoff Coefficient 0.2;(open land)
i= rainfall intensity(in./hr.) 0.73'(calculated above)
A=Area (acres) 9.13;(calculated above)
Q=Runoff Rate (Pre-Development)(cfs) 1:33
6. Calculate Required Pond Volume
Total Area (acres) = 9.13 acres
Weighted C = 0.72:
Discharge Rate(cfs)= 1.33 cfs (Equal to Pre-Development Runoff Rate)
Duration min} Duration(hrs} Intensity QI�(cfs) Runoff Release Required
(in/hr) Volume Volume Storage (ft3)
58 097 0.65 4.28 14885 4639 10246
59 0.98 0.65 4.23 14974 4719 10255`
60 1.00 0.64 4,18 15063 4799 10264+
61 1.02 0.63 4.14 15150 4879 10271'
62 1.03 0.63' 4.10 15236 4959 10277
63 1.05 0.62 4.05 15322 5039 10283:
64 1.07 0.61 4.01 15407 6119 ' 10288
65 1.08 0.61 3.97 15490 5199 10292
66 1.10 0.60 3.93 15573 5279 + 10295
67 1.12 0.60 3.89 15656 5359 10297'
68 1.13 0.59 3.86 15737 5439 10298
69 1.15 0.58 3.82 15818 5519 10299
70 1.17 0.58 3.79 15897 5599 10299
71 1.18 0.57 3.75 15977 5679 10298
72 1.20 0.57 3.72 16055 5759 1 10296'
73 1.22 0.56 3.68 16133 5839 10294
74 1.23 0.56 3.65 16210 5919 10291
75 1.25 0.55 3.62 " 16286 5999 10287'
76 1.27 0.55 3.59 16362 6079 10283'
OUTLET STRUCTURE SLOT
Q=CLH 312
QEXISTING POND= Discharge(cfs) 2.71
QPOND 1 = Discharge (cfs) 1.33'
QTOTAL AT POND 1 WEIR= Discharge (cfs) 4.04
C =Weir Coefficient 3.33 (per COB Design Standards)
H = Head (ft) 1:5
L= Horizontal Length (ft) 0.66
L =Slot Width(inches) 7.9
DETENTION POND #1 (Temp. Drainage from Oak West)
REQUIRED VOLUME
2. Calculate Area and Weighted C Factor(Post-Development)
Contributing Area C Area (ft 2) C *Area
ROW 0.82 4263 3496
OS/Park 0.2 ! 0 0"
Lot R1 0.7 0 0
Laurel Parkway 0.81 0 0
Durston ROW 0.68 0 0
Total 4263 3496
A =Area(acres) 0.0979
C= Weighted C Factor 0.82
3. Calculate T, (Pre-Development)
Tc Overland Flow
Tc= 1.87 (1.1-CCf)D1/2/Sv3
(Storm 1
S =Slope of Basin (%) 1 :Return (yrs) Cf
C = Rational Method Runoff Coefficient 0.2 12 to 10 1
Cf= Frequency Adjustment Factor 1.1 ill to 25 1.1
D = Length of Basin (ft) 886' :26 to 50 1.21
151 to 100 1.251
-----------------------------
Tc(Pre-Development) (minutes) 49'
4. Calculate Rainfall Intensity(Duration =Pre-Development Tc)
i =0.64x-'-"(10-yr Storm, Fig. 1-3, COB Design Standards)
x= storm duration (hrs) 0.82 (Tc Pre-Development)
i=rainfall intensity(in./hr.) 0.73
5. Calculate Runoff Rate(Pre-Development)
Q =CiA
C = Rational Method Runoff Coefficient 02 (open land)
i = rainfall intensity(in./hr.) 0.73 (calculated above)
A=Area (acres) 10.10'(calculated above)
Q=Runoff Rate (Pre-Development)(cfs) 0.01
6. Calculate Required Pond Volume
Total Area (acres)= 0.10 acres
Weighted C = 0.82
Discharge Rate (cfs)= 0.01 cfs (Equal to Pre-Development Runoff Rate)
Duration(min) Duration(hrs) Intensity Q,�(cfs) Runoff Release Required
(in/hr) Volume Volume Storage (ft3)
70 1.17 0.58 0.05 195 60 135
71 1.18 0.57 ; 0.05 196 61 ! 135'
72 1.20 0.57 0.05 197 62 135
73 1.22 0.56 0.05 198 63 135
74 1.23 0.56 ', 0.04 199 63 136
75 1.25 0.55 0.04 200 64 136!
76 1.27 0.55 0.04 201 65 136
77 1.28 0.54 0.04 202 66 136
78 1.30 0.54 A4 203 67 136'
79 1.32 0.54 0.04 204 68 " 1361i
80 1.33 0.53 0.04 204 69 136
81 1.35 0.53 0.04 205 69 136
82 1.37 0.52 0.04 206 70 136'
83 1.38 0.512 0.04 207 71 136'
84 1.40 0.51 0.04 208 72 136
85 1.42 0.51 0.04 209 ( 73 136
86 1.43 0.51 0.04 210 74 136
87 1.45 0.50 0.04 211 75 136
88 1.47 0.50 0.04 211 75 136!
89 1.48 0.50 0.04 212 76 136
90 1.50 0.49 0.04 213 77 136'
91 1.52 0.49 0.04 214 78 136
92 1.53 0.48 0.04 215 79 136'
93 1.55 0.48 0.04 216 80 136
94 1.57 0.48 0.04 216 81 136':
95 1.58 0.47 0.04 217 81 136
96 1.60 0.47 0.04 218 82 136
97 1.62 0.47 0.04 219 83 136
98 1.63 0.47 0.04 220 84 135
DRAINAGE AREA OAK WEST
Contributing Area C Area (ft 2) C * Area Composite ROW
ROW 0.81957 4263 349 ((0.95*43)+(0.2*17))/60
OS/Park 0.2 0 0.$195652
Lots 0.35 0 , 0
Total 4263 ;3493 $l
C =Weighted C Factor
A =Area(acres) 0:I0
Required Gutter/Pipe Capacity (25-yr Storm)
Tc Overland Flow
Tc = 1.87 (1.1-CC)D1/2/S1/3
Storm
S = Slope of Basin (%) 0.5 Return Cf
C =Rational Method Runoff Coefficient 035 2 to 10 1
Cf=Frequency Adjustment Factor 1,1 11 to 25 1.1
D =Length of Basin (ft) 15 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)
Tc Gutter Flow
Tc =L/V/60
V = (1.486/n)R211 S v2
n =Mannings Coefficient'0 0)3
R= Hydraulic Radius A/P (ft) �< 0 73 (0.15'below top of curb)
S = slope (ft/ft) 0.005
L=length of gutter(ft) 88
V = mean velocity (ft/s)
Tc Gutter Flow (minutes) _ ,3;69
Tc Total (Overland+Gutter)
Q = CIA
C =Weighted C Factor (calculated above)
I = 0.78 Tc°_64(in/hr)
Drainage Area#OAK WEST
A = area(acres) �
Qrequired (CfS)
Provided Gutter Capacity (flowing at 0.15' below top of curb)
Q = (1.486/n)AR"'S"'
n =Mannings Coefficient 0f113'
A = area (ft'`) 4
P =wetted perimeter(ft) 93'
R=Hydraulic Radius A/P(ft) 0 _
S = slope (ft/ft) 0.005
Qprovided (CfS)
GUTTER HAS ADEQUATE CAPACITY
Drainage Area#OAK WEST
DRAINAGE AREA TWIN LAKES WEST
Contributing Area C Area (ft'-) C * Area Composite ROW
ROW 0.81957 24594 2015 ((0.95*43)+(0.2*l7))/60
OS/Park 0.2 0 �0; 0.8195652
Lot RI 0.7 0 , 0
Total 24594 ;:'201564'
C=Weighted C Factor :`,0.
A=Area (acres) (J, 6�
Required Gutter/Pipe Capacity (25-yr Storm)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 0.5 Return Ce
C =Rational Method Runoff Coefficient {};35' 2 to 10 1
Cf=Frequency Adjustment Factor :1 11 to 25 1.1
D = Length of Basin (ft) 15 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes) _ 6n52
Tc Gutter Flow
Tc =L/V/60
V= (1.486/n)R2/1 S 1 is
n=Mannings Coefficient 0 013:
R= Hydraulic Radius A/P(ft) 0 1 '(015' below top of curb)
.. .............:.
S = slope (ft/ft) 0.010
L= length of gutter(ft) 670
V = mean velocity (ft/s)
Tc Gutter Flow (minutes) = :72T
Tc Total (Overland+ Gutter)
Q= CIA
C=Weighted C Factor 0 82=(calculated above)
I=0.78 Tc 0'64(in/hr) 2 4
Drainage Area#TWIN LAKES WEST
A = area(acres) =0;56
Qrequired (Cfs)
Provided Gutter Capacity (flowing at 0.15' below top of curb)
Q= (1.486/n)AR2/1S1/2
n =Mannings Coefficient :,�' 0;�13
A = area (ft2) 14
P = wetted perimeter(ft)
R = Hydraulic Radius A/P (ft) t7: 3'
S = slope (ft/ft) 0.01
Qprovided (Cfs) _ =
GUTTER HAS ADEQUATE CAPACITY
Drainage Area#TWIN LAKES WEST
DRAINAGE AREA 1 (TWIN LAKES WEST AND OAK STREET)
Contributing Area C Area(ft 2) C * Area Composite ROW
ROW 0.81957 45504 37293 ((0.95*43)+(0.2*17))/60
OS/Park 0.2 0 °Q, 0.8195652
Lot RI 0.7 0 (?
Total5504 , 3729 :5
C =Weighted C Factor 82'
A =Area (acres) a104
Required Gutter/Pipe Capacity (25-_yr Storm)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/51/3
Storm
S = Slope of Basin (%) 0.5 Return Cr
C =Rational Method Runoff Coefficient 0.,35 2 to 10 1
Cf=Frequency Adjustment Factor 11 to 25 1.1
D =Length of Basin (ft) 15 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes) -52:
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2i3 S 1/2
n=Mannings Coefficient (JGl3
R=Hydraulic Radius A/P (ft) 0 1'3'(0.15' below top of curb)
S = slope (ft/ft) 0.005
L=length of gutter(ft) 968
V = mean velocity (ft/s)
Tc Gutter Flow (minutes)
Tc Total (Overland +Gutter)
Q = CIA
C =Weighted C Factor 0 82 (calculated above)
0 I= 0.78 Tc '64(in/hr)
A = area (acres) 04=
Qrequired (CfS) _ 1: r
Provided Gutter Capacity (flowing at 0.15' below top of curb)
Q= (1.486/n)AR2/1S1/2
n =Mannings Coefficient 0.013`
A area (ft) 1,24:
P= wetted perimeter(ft) :23
R = Hydraulic Radius A/P (ft) 013
S = slope (ft/ft) 0.01
Qprovided (CfS)
GUTTER HAS ADEQUATE CAPACITY
DRAINAGE AREA LOT RI
Contributing Area C Area(fe) C * Area Composite ROW
ROW 0.81957 0 Q ((0.95*43)+(0.2*17))/60
OS/Park 0.2 0 �`: <0 0.8195652
Lot R1 0.7 346141 42299
Total 346:141 242299
C =Weighted C Factor
A =Area (acres) � ;75
Required Gutter/Pipe Capacity (25-yr Storm)
Tc Overland Flow
Tc = 1.87 (1.1-CCr)D1/2/S1/3
Storm
S = Slope of Basin (%) 0.5 Return Ce
C =Rational Method Runoff Coefficient :0,35 2 to 10 1
Cf=Frequency Adjustment Factor l;'1 11 to 25 1.1
D =Length of Basin (ft) 15 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)
Tc Gutter Flow
Tc =L/V/60
V = (1.486/n)R2r3 S vz
n =Mannings Coefficient
R= Hydraulic Radius AlP(ft) 013�(0.15'below top of curb)
S = slope (ft/ft) 0.010
L=length of gutter(ft) 670
V = mean velocity (ft/s) .00;
Tc Gutter Flow (minutes)
Tc Total (Overland +Gutter)
Q=CIA
C=Weighted C Factor 0 7<,0 (calculated above)
I=0.78 Tc 0�64(in/hr)
Drainage Area#LOT R1
A = area (acres) - 79
Qrequired (cfs) = 1344
Provided Gutter Capacity (flowing at 0.15' below top of curb)
Q = (1.486/n)AR113S Ill
n =Mannings Coefficient
A = area (ft') 124
P= wetted perimeter(ft) 2 �
R=Hydraulic Radius AT (ft)
S = slope (ft/ft) 0.01
Qprovided (cfs) = 3.72'
CAPACITY PROBLEM
Drainage Area#LOT R1
R"' =0.2623 ft
S = 0.0060 ft/ft
S 112=0.0775 ft/ft
Q= (1.486/0.013)(1.24)(0.2623)(0.0775)=2.88 cfs.
2.81 cfs < 2.86 cfs — Gutter capacity is adequate
DRAINAGE AREA#2
Drainage Area#2 consists of a total of 490,865 ft'-, with 79,295 ft'-of that being right of way,
263,990 ft2 of park land, and 147,580 ft2 of medium density lots. Drainage area#2 will be
divided into four subareas, three for each area that contributes to a catch basin that will be
utilized, plus the portion of the park that will drain into the detention pond. The time of
concentration for each sub-area needs to be calculated to determine the intensity of storm that
will contribute to the catch basin.
The time of concentration for sub-area#24 is calculated below:
Time of Concentration
Overland flow(115 ft @ 1.00%, C=0.35) = 14.3 min.
Gutter flow(830 ft @ 1.00% avg. slope on Rosa Way)
V= (1.486/n)R2i3S1i2 (n=0.013,A=1.24 ft, P=9.23, R2/3=0.2623, S1/2=0.1000)
V= 3.00ft/s
T= 830 ft/3.00 ft/s/60s/min =4.6 min
Total Time of Concentration = 18.9 minutes (0.32 hours)
For a 25-year storm event Its =0.78X-.64= 0.78(0.32)--64= 1.62 in/hr
Q25 Lots =CIA =0.35(1.62 in/hr)(1.7553 acres) = 1.00 cfs
Q25 r/w =CIA = 0.70(1.62 in/hr)(0.6123 acres) =0.69 cfs
Q25 Total = (1.00+0.69) = 1.69 cfs =Total flow rate entering catch basin#4
The time of concentration for sub-area#2-2 is calculated below:
Time of Concentration
Overland flow(110 ft @ 1.00%, C=0.35) = 14.0 min.
Gutter flow(830 ft @ 1.0% avg. slope on Rosa Way)
V= (1.486/n)R2/1S1/1 (n=0.013, A=1.24 ft, P=9.23, Rv3=0.2623, S"2=0.1000)
V= 3.00 ft/s
T= 830 ft/3.00 ft/s/60s/min =4.6 min
Total Time of Concentration = 18.6 minutes(0.31 hours)
For a 25-year storm event Its = 0.78X-.64=0.78(0.31)--64= 1.65 in/hr
Q25 Lots =CIA = 0.35(1.65 in/hr)(1.656 acres) =0.96 cfs
Q25 r/w = CIA =0.70(1.65 in/hr)(0.9431 acres) = 1.09 cfs
Q25 Total = (0.96+1.09) = 2.05 cfs =Total flow rate entering catch basin#5
The time of concentration for sub-area#2-3 is calculated below:
Time of Concentration
Overland flow(13.5 ft @ 2.0%, C=0.46) = 3.2 min.
Gutter flow(150 ft @ 0.60% avg. slope on Annie Street)
V= (1.486/n)R2/3S1/2 (n=0.013, A=1.24 ft, P=9.23, R'-/3=0.2623, S 112=0.07746)
V= 2.32 ft/s
T= 150 ft/2.32 ft/s/60s/min = 1.1 min
Total Time of Concentration =4.3 minutes (0.09 hours)
For a 25-year storm event I25 = 0.78X-.64= 0.78(0.07)-.64=4.21 in/hr
Q25 r/w =CIA = 0.70(4.21 in/hr)(0.2649 acres) =0.78 cfs
Q25 Total= 0.78 cfs=Total flow rate entering catch basin#6
Q25 Total for Storm Sewer#2 = (1.69+2.05+0.78)=4.52 cfs
DRAINAGE AREA#3
Drainage Area#3 consists of a total of 421,020 ft2, with 85,620 ft2 of that being right of way,
151,785 ft2 of park land, and 183,615 ft2 of medium density lots. Drainage area#3 will be
divided into three subareas, one for each catch basin that will be utilized. The time of
concentration for each sub-area needs to be calculated to determine the intensity of storm that
will contribute to the catch basin.
The time of concentration for sub-area#3-1 is calculated below:
Time of Concentration
Overland flow(13.5 ft @ 2.0%, C=0.46) = 3.2 min.
Gutter flow(115 ft @ 0.60% avg. slope on Sherwood Way)
V= (1.486/n)R2/35112 (n=0.013, A=1.24 ft, P=9.23, R213=0.2623, S 112=0.07746)
V= 2.32 ft/s
T= 115 ft/2.32 ft/s/60s/min =0.8 min
Total Time of Concentration =4.0 minutes(0.07 hours)
For a 25-year storm event I25 =0.78X-.fi4=0.78(0.07)-.64=4.30 in/hr
Q25 r/w =CIA =0.70(4.30 in/hr)(0.1625 acres) = 0.49 cfs
Q25 Total =0.49 cfs =Total flow rate entering catch basin#7 & 8
Q25 Total for Storm Sewer#3 =0.49 cfs
The time of concentration for sub-area#3-2 is calculated below:
Time of Concentration
Overland flow(I15 ft @ 1.0%, C=0.35) = 14.3 min.
Gutter flow(320 ft @ 1.10% avg. slope on Rosa Way)
V= (1.486/n)R2i3S1i2 (n=0.013, A=1.24 ft, P=9.23, R213=0.2623, 5112=0.1049)
V= 3.14 ft/s
T= 320 ft/3.14 ft/s/60s/min = 1.7 min
Gutter flow(200 ft @ 0.60% avg. slope on Sherwood Way)
V= (1.486/n)R2/3S1/2 (n=0.013,A=1.24 ft, P=9.23,R2/3=0.2623, S1/2=0.0775)
V= 2.32 ft/s
T= 200 ft/2.32 ft/s/60s/min = 1.4 min
Total Time of Concentration = 17.4 minutes (0.29 hours)
For a 25-year storm event I25 =0.78X-.64=0.78(0.29)--64= 1.72 in/hr
Q25 Lots = CIA =0.35(1.72 in/hr)(0.7118 acres) =0.43 cfs
Q25 r/w = CIA =0.70(1.72 in/hr)(0.7375 acres) =0.89 cfs
Q25 Total = (0.43+0.89) = 1.32 cfs=Total flow rate entering catch basin#9
The time of concentration for sub-area#3-3 is calculated below:
Time of Concentration
Overland flow(145 ft @ 1.0%, C=0.35) = 16.1 min.
Gutter flow(620 ft @ 0.80% avg. slope on Parkview Avenue)
V= (1.486/n)R2/3S112 (n=0.013, A=1.24 ft, P=9.23, R"3=0.2623, S'/2=0.0894)
V= 2.68 ft/s
T= 620 ft/2.68 ft/s/60s/min = 3.9 min
Gutter flow(270 ft @ 0.60% avg. slope on Parkview Avenue)
V= (1.486/n)R2i3S112 (n=0.013, A=1.24 ft, P=9.23, R2i3=0.2623, S112=0.0775)
V=2.32 ft/s
T= 270 ft/2.32 ft/s/60s/min = 1.9 min
Total Time of Concentration =21.9 minutes (0.37 hours)
For a 25-year storm event 125 = 0.78X-�64= 0.78(0.37)".64= 1.47 in/hr
Q25 Lots =CIA = 0.35(1.47 in/hr)(3.5035 acres) = 1.80 cfs
Q25 r/w =CIA= 0.70(1.47 in/hr)(1.0655 acres) = 1.10 cfs
Q25 Total = (1.80+1.10) =2.90 cfs =Total flow rate entering catch basin#10
Q25 Total for Storm Sewer#3 = (1.32+2.90) =4.22 cfs
DRAINAGE AREA#4
Drainage Area#4 consists of a total of 474,050 ft2, with 143,825 ft2 of that being right of way,
40,660 ft'- of park land, and 289,565 ft2 of high density lots. Drainage area#4 will be divided
into three subareas, one for each catch basin that will be utilized. The time of concentration for
each sub-area needs to be calculated to determine the intensity of storm that will contribute to the
catch basin.
The time of concentration for sub-area#4-1 is calculated below:
Time of Concentration
Overland flow(13.5 ft @ 2.0%, C=0.46) = 3.2 min.
Gutter flow(625 ft @ 1.20% avg. slope on Rosa Way)
V= (1.486/n)R2/3S'/2 (n=0.013, A=1.24 ft, P=9.23, R213=0.2623, S'12=0.1095)
V= 3.28 ft/s
T= 625 ft/3.28 ft/s/60s/min = 3.2 min
Total Time of Concentration = 6.4 minutes(0.11 hours)
For a 25-year storm event 125 = 0.78X-.64=0.78(0.11),64 = 3.20 in/hr
Q25 r/w = CIA =0.70(3.20 in/hr)(0.5342 acres) = 1.20 cfs
Q25 Total = 1.20 cfs =Total flow rate entering catch basin#11
The time of concentration for sub-area#4-2 is calculated below:
Time of Concentration
Overland flow(280 ft @ 1.0%, C=0.60) = 13.8 min.
Gutter flow(262.5 ft @ 0.60% avg. slope on A Street)
V= (1.486/n)R2/3S'/2 (n=0.013,A=1.24 ft, P=9.23, R'-/3=0.2623, S'/'-=0.0775)
V= 2.32 ft/s
T= 262.5 ft/2.32 ft/s/60s/min = 1.89 min
Total Time of Concentration = 15.7 minutes (0.26 hours)
For a 25-year storm event 125 = 0.78X-.64=0.78(0.26)-.64 = 1.85 in/hr
Q25 Lots = CIA =0.60(1.85 in/hr)(1.4415 acres) = 1.60 cfs
Q25 r/w = CIA =0.70(1.85 in/hr)(0.47 acres) = 0.61 cfs
Q25 Total = (1.60 +0.61) = 2.21 cfs =Total flow rate entering catch basin#15
Time of Concentration
Overland flow(280 ft @ 1.0%, C=0.60) = 13.8 min.
Gutter flow(262.5 ft @ 0.60% avg. slope on A Street)
V= (1.486/n)R2/3S112 (n=0.013, A=1.24 ft, P=9.23, R'-/3=0.2623, S'/2=0.0775)
V= 2.32 ft/s
T=262.5 ft/2.32 ft/s/60s/min = 1.89 min
Total Time of Concentration = 15.7 minutes (0.26 hours)
For a 25-year storm event 125 =0.78X-.64=0.78(0.26)-.64 = 1.85 in/hr
Q25 Lots = CIA=0.60(1.85 in/hr)(1.2609 acres) = 1.40 cfs
Q25 r/w = CIA =0.70(1.85 in/hr)(0.47 acres)= 0.61 cfs
Q25 Total = (1.40 + 0.61) =2.01 cfs =Total flow rate entering catch basin#12
Q25 Total for Storm Manhole#2= (2.21 + 2.01) =4.22 cfs
The time of concentration for sub-area#4-3 is calculated below:
Time of Concentration
Overland flow(280 ft @ 1.0%, C=0.60) = 13.9 min.
Gutter flow(300 ft @ 1.20% avg. slope on Rosa Way)
V= (1.486/n)R"'S'/2 (n=0.013, A=1.24 ft, P=9.23, RZis=0.2623, S'12=0.1095)
V= 3.28 ft/s
T= 300 ft/3.28 ft/s/60s/min = 1.5 min
Total Time of Concentration = 15.4 minutes (0.26 hours)
For a 25-year storm event 125 =0.78X-.64= 0.78(0.26)-.64= 1.85 in/hr
Q25 Lots =CIA= 0.60(1.85 in/hr)(1.9050 acres)=2.11 cfs
Q25 r/w =CIA =0.70(1.85 in/hr)(0.6319 acres) = 0.82 cfs
Q25 Total = (2.11+0.82) = 2.93 cfs =Total flow rate entering catch basin#13
The time of concentration for sub-area#44 is calculated below:
Time of Concentration
Overland flow(280 ft @ 1.0%, C=0.60) = 13.9 min.
Gutter flow(300 ft @ 1.60% avg. slope on Rosa Way)
V= (1.486/n)R2/3S1/2 (n=0.013,A=1.24 ft, P=9.23, R'-/3=0.2623, S'12=0.1265)
V= 3.79 ft/s
T= 300 ft/3.79 ft/s/60s/min = 1.3 min
Total Time of Concentration = 15.2 minutes (0.25 hours)
For a 25-year storm event 125 = 0.78X-.64=0.78(0.25)-.64 = 1.89 in/hr
Q25 Lots =CIA = 0.60(1.89 in/hr)(1.7423 acres) = 198 cfs
Q25 r/w =CIA =0.70(1.89 in/hr)(0.8160 acres) = 1.08 cfs
Q25 Total= (1.98+1.08) = 3.06 cfs =Total flow rate entering catch basin#14
Q25 Total for Storm Sewer#4= (1.20+4.42+2.93+3.06) = 11.61 cfs
Drainage Area#1
15" PVC from Catch Basin #1 to Catch Basin#2
This pipe carries the storm water from drainage sub-area#1-1. As previously calculated we
should anticipate a flowrate of 1.02 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
0.40 feet with a velocity of 3.00 ft/sec.
15" PVC from Catch Basin#2 to Catch Basin#3
This pipe carries the storm water from drainage sub-areas 1-1 & 1-2. As previously calculated
we should anticipate a flowrate of(1.02 + 2.81) = 3.83 cfs from a 25-year storm event.
Calculations are enclosed in the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch
pipe will flow at a depth of 0.88 feet with a velocity of 4.17 ft/sec.
15" PVC from Catch Basin#3 to Pond #1
This pipe carries the storm water from drainage sub-areas 1-1, 1-2 & 1-3. As previously
calculated we should anticipate a flowrate of(1.02+ 2.81+0.93) =4.76 cfs from a 25-year storm
event. Calculations are enclosed in the Appendix for a 15" PVC pipe at 0.50% slope. The
15-inch pipe will flow at a depth of 1.08 feet with a velocity of 4.22 ft/sec.
Detention Pond#1
The total area served by Detention Pond#1 is 6.11 acres with a weighted C-factor of 0.464 after
development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 1.07 cfs. Calculations are
also enclosed in the Appendix for sizing the detention pond by varying the storm duration and
holding the release rate at 1.07 cfs. The required storage for Detention Pond#1 is 3,215 cubic
feet. The weir must also be sized to insure the discharge never exceeds the allowable release
rate. The weir in the discharge structure for Detention Pond#1 will be 2.09 inches in width.
These calculations are included with the calculations for sizing the pond.
Drainage Area#2
15" PVC from Catch Basin#4 to Catch Basin#5
This pipe carries the storm water from drainage sub-area 2-1. As previously calculated we
should anticipate a flowrate of 1.69 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
0.53 feet with a velocity of 3.44 ft/sec.
15" PVC from Catch Basin#6 to Catch Basin#5
This pipe carries the storm water from drainage sub-area 2-3. As previously calculated we
should anticipate a flowrate of 0.78 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.75% slope. The 15-inch pipe will flow at a depth of
0.32 feet with a velocity of 3.21 ft/sec.
15" PVC from Catch Basin#5 to Storm MH#1 to Detention Pond#2
This pipe carries the storm water from drainage sub-area 2-1, 2-2, & 2-3. As previously
calculated we should anticipate a flowrate of(1.69+0.78+2.05) =4.52 cfs from a 25-year storm
event. Calculations are enclosed in the Appendix for a 15" PVC pipe at 0.50% slope. The
15-inch pipe will flow at a depth of 1.01 feet with a velocity of 4.24 ft/sec.
Detention Pond#2
The total area served by Detention Pond#2 is 11.270 acres with a weighted C-factor of 0.326
after development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 1.801 cfs.
Calculations are also enclosed in the Appendix for sizing the detention pond by varying the storm
duration and holding the release rate at 1.801 cfs. The required storage for Detention Pond#2 is
3,610 cubic feet. The weir must also be sized to insure the discharge never exceeds the
allowable release rate. The weir in the discharge structure for Detention Pond#2 will be 3.53
inches in width. These calculations are included with the calculations for sizing the pond.
Drainage Area#3
15" PVC from Catch Basin#7-8 to Pond#3
This pipe carries the storm water from drainage sub-area 3-1. As previously calculated we
should anticipate a flowrate of 0.49 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 1.00% slope. The 15-inch pipe will flow at a depth of
0.23 feet with a velocity of 3.10 ft/sec.
Detention Pond#3
The total area served by Detention Pond#3 is 2.23 acres with a weighted C-factor of 0.367 after
development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 0.367 cfs.
Calculations are also enclosed in the Appendix for sizing the detention pond by varying the storm
duration and holding the release rate at 0.367 cfs. The required storage for Detention Pond#3 is
525 cubic feet. The weir must also be sized to insure the discharge never exceeds the allowable
release rate. The weir in the discharge structure for Detention Pond#3 will be .72 inches in
width. These calculations are included with the calculations for sizing the pond.
15" PVC from Catch Basin#10 to Catch Basin#9
This pipe carries the storm water from drainage sub-area 3-3. As previously calculated we
should anticipate a flowrate of 2.90 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
0.72 feet with a velocity of 3.94 ft/sec.
15" PVC from Catch Basin#9 to Pond#4
This pipe carries the storm water from drainage sub-area 3-2 & 3-3. As previously calculated
we should anticipate a flowrate of(2.90+1.32) =4.22 cfs from a 25-year storm event.
Calculations are enclosed in the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch
pipe will flow at a depth of 0.95 feet with a velocity of 4.22 ft/sec.
Detention Pond #4
The total area served by Detention Pond#4 is 7.440 acres with a weighted C-factor of 0.3.96
after development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 1.11 cfs.
Calculations are also enclosed in the Appendix for sizing the detention pond by varying the storm
duration and holding the release rate at 1.11 cfs. The required storage for Detention Pond#4 is
3,340 cubic feet. The weir must also be sized to insure the discharge never exceeds the
allowable release rate. The weir in the discharge structure for Detention Pond#4 will be 2.18
inches in width. These calculations are included with the calculations for sizing the pond.
Drainage Area#4
15" PVC from Catch Basin#14 to Catch Basin#13
This pipe carries the storm water from drainage sub-area 4-4. As previously calculated we
should anticipate a flowrate of 3.06 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
0.75 feet with a velocity of 3.99 ft/sec.
15" PVC from Catch Basin#12 to Storm MH#2
This pipe carries the storm water from drainage sub-area 4-2. As previously calculated we
should anticipate a flowrate of 2.21 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
0.61 feet with a velocity of 3.69 ft/sec.
15" PVC from Catch Basin#15 to Storm MH#2
This pipe carries the storm water from drainage sub-area 4-2. As previously calculated we
should anticipate a flowrate of 2.01 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
0.58 feet with a velocity of 3.60 ft/sec.
15" PVC from Storm MH#2 to Catch Basin#13
This pipe carries the storm water from drainage sub-area 4-2. As previously calculated we
should anticipate a flowrate of 4.22 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.50% slope. The 15-inch pipe will flow at a depth of
1.39 feet with a velocity of 4.23 ft/sec.
18" PVC from Catch Basin#13 to Catch Basin #11
This pipe carries the storm water from drainage sub-area 4-2, 4-3, &4-4. As previously
calculated we should anticipate a flowrate of(4.22+2.93+3.06) = 10.21 cfs from a 25-year storm
event. Calculations are enclosed in the Appendix for a 18" PVC pipe at 1.00% slope. The
18-inch pipe will flow at a depth of 1.20 feet with a velocity of 6.77 ft/sec.
18" PVC from Catch Basin#11 to Detention Pond #5
This pipe carries the storm water from drainage sub-area 4-1, 4-2, 4-3, &4-4. As previously
calculated we should anticipate a flowrate of(1.20+4.22+2.93+3.06) = 11.41 cfs from a 25-year
storm event. Calculations are enclosed in the Appendix for a 18" PVC pipe at 1.50% slope.
The 18-inch pipe will flow at a depth of 1.10 feet with a velocity of 8.22 ft/sec.
Detention Pond#5
The total area served by Detention Pond#5 is 10.88 acres with a weighted C-factor of 0.596 after
development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 1.61 cfs.
Calculations are also enclosed in the Appendix for sizing the detention pond by varying the storm
duration and holding the release rate at 1.61 cfs. The required storage for Detention Pond#5 is
9,200 cubic feet. The weir must also be sized to insure the discharge never exceeds the
allowable release rate. The weir in the discharge structure for Detention Pond#5 will be 3.16
inches in width. These calculations are included with the calculations for sizing the pond.
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Scale In Feet
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Scale In Meters
4770
June 22, 2006
City of Bozeman Engineering Dept.
Attn: Sue Stodola,P.E.
20 E. Olive Street
P.O. Box 1230
Bozeman, MT 59771-1230
RE: Flanders Creek Subdivision, Storm Water Design Report Revisions (05189)
Dear Sue,
Please find the enclosed revisions for the storm water design report for the above referenced
project. These revisions are in response to a letter from you dated February 8, 2006. A brief
narrative of the revisions and additional information requested are as follows:
1. Upon further review of the drainage calculations, inconsistencies were found in the
calculations for the overland flow distance and time of concentration. By correcting the
runoff coefficient "C" and the overland flow distance, the gutter capacity was found to be
below the maximum allowed. Therefore additional outlets are not needed. Calculations
are included to show this.
2. a. The 24" PVC from Catch Basin #9 to Detention Pond #3 was installed as a 24"
diameter pipe, which is larger than the previously approved size, but more than
adequate to handle the storm water load.
b. The 15" PVC from Catch Basin #10 to Detention Pond #3 is now consistent at a
0.5% slope on both the design report and the plans, with calculations included.
C. Calculations are included for the 15" PVC pipe running from Catch Basin #10 to
Detention Pond#3 at a 6.01% slope which matches the plans.
3. Detention Pond #1 is now labeled as 2000cf on plan Sheet C1.0 to match the design
report. The weir that was installed in the outlet control structure was 18" H x 1.95" W.
The correct weir for this outlet control structure is 18"H x 1.29"W. The plan sheet is
now correctly labeled to match the design report. The weir dimensions will be corrected
to the size indicated.
4. The calculations for Detention Pond #2 which is now a Retention Pond are included.
Sheet C 1.0 is still labeled Retention Pond.
5. The weir for Detention Pond#3 was installed at 18" H x 9.77" W. In the design report,
the height dimension was called out as 12", not 18". The correct width for an 18" weir is
5.31". This is now correctly labeled in the plans, with the calculations attached. A new
weir will be ordered and installed in the outlet structure.
6. Sheets C1.0, C4.10 and C4.11 are now labeled with a 30" sewer instead of 36" sewer.
The storm easement was adjusted to accommodate the 30" storm sewer line.
7. On sheet C1.0 the legend now includes proposed Storm Sewer Main and proposed Storm
Sewer Manhole. The drawing is also to scale.
8. On sheet C4.11 it is now clearly labeled as a 60" diameter Storm Sewer Manhole.
This summarizes the extent of the modifications from the previous plan and design report
submittal. If any other changes occur, we will notify you immediately. Please review this
material for your approval and contact us if any additional information is needed.
Sincerely,
Jon Jupka,E.I.
Enc.
GAc&h\05\05189\0ffice\05189 Stodola storm revisions 061906.wpd
Storm Sewer revisions:
The following calculations are included for the revisions to the outlet pipe from Pond #3 to
Baxter Ditch.
The time of concentration for sub-area#3-1 is calculated below:
Time of Concentration
Overland flow(140 ft @ 1.0%, C=0.35) = 15.82 min.
Gutter flow(580 ft @ 1.10% avg. slope on Cottonwood Road)
V= (1.486/n)R213SI/I (n=0.013,A=1.24 ft, P=9.23, R2/3=0.2623, S"2=0.1049)
V= 3.14 ft/s
T= 580 ft/3.14 ft/s/60s/min = 3.1 min
Gutter flow(260 ft @ 0.60% avg. slope on Sherwood Way)
V= (1.486/n)R21351/2 (n=0.013, A=1.24 ft, P=9.23, R'-/3=0.2623, S1/'-=0.0775)
V= 2.32 ft/s
T= 260 ft/2.32 ft/s/60s/min = 1.9 min
Total Time of Concentration = 20.82 minutes(0.347 hours)
For a 25-year storm event Its = 0.78X--64= 0.78(0.347)-.64 = 1.53 in/hr
Q25 Medium Density Lots =CIA =0.35(1.53 in/hr)(3.4023 acres) = 1.83 cfs
Q25 r/w =CIA= 0.70(1.53 in/hr)(1.6478 acres) = 1.76 cfs
Q25 Total = (1.83+1.76) = 3.59 cfs =Total flow rate entering catch basin#6
The time of concentration for sub-area#3-2 is calculated below:
Time of Concentration
Overland flow(135 ft @ 1.0%, C=0.35) = 15.36 min.
Gutter flow(585 ft @ 0.85% avg. slope on Flanders Creek Avenue)
V= (1.486/n)R21IS112 (n=0.013, A=1.24 ft, P=9.23, RZi3=0.2623, S1i2=0.0922)
V= 2.76 ft/s
T= 585 ft/2.76 ft/s/60s/min =3.5 min
Gutter flow(245 ft @ 0.60% avg. slope on Sherwood Way)
V= (1.486/n)R2/3S1i2 (n=0.013, A=1.24 ft, P=9.23, R2/3=0.2623, S1i2=0.0775)
V= 2.32 ft/s
T= 245 ft/2.32 ft/s/60s/min = 1.8 min
Total Time of Concentration = 20.84 minutes (0.347 hours)
For a 25-year storm event 125 =0.78X-.64=0.78(0.347)-.64 = 1.53 in/hr
Q25 Medium Density Lots = CIA=0.35(1.53 in/hr)(3.2849 acres) = 1.76 cfs
Q25 r/w =CIA =0.70(1.53 in/hr)(1.2770 acres) = 1.37 cfs
Q25 Total = (1.76+1.37) = 3.13 cfs =Total flow rate entering catch basin#7
The time of concentration for sub-area#3-3 is calculated below:
Time of Concentration
Overland Flow (140 ft @ 1.0%, C=0.60) = 9.7 min.
Gutter Flow (143.5 ft @ 0.75% avg. slope on Twin Lakes Drive)
V= (1.486/n)RZi3Sii2 (n=0.013, A=1.24 ft, P=9.23, R213=0.2623, S"2=0.08660)
V= 2.60 ft/s
T= 143.5 ft/2.60 ft/s/60 s/min =0.92 min.
Total Time of Concentration = 10.62 minutes (0.177 hours)
For a 25-year storm event Its = 0.78X-.64= 0.78(0.177)-.64= 2.36 in/hr
Q25 High Density Lots = CIA =0.60(2.36 in/hr)(0.8744 acres) = 1.24 cfs
Q25 r/w = CIA =0.70(2.36 in/hr)(0.20 acres)= 0.33 cfs
Q25 Total= (1.24+0.33) = 1.57 cfs =Total flow rate entering catch basin#8
Time of Concentration
Overland Flow (140 ft @ 1.0%, C=0.60) = 9.7 min.
Gutter Flow (218.42 ft @ 0.75% avg. slope on Twin Lakes Drive)
V= (1.486/n)R2/3S1/2 (n=0.013, A=1.24 ft, P=9.23, R2/3=0.2623, 5112=0.08660)
V= 2.60 ft/s
T= 218.42 ft/2.60 ft/s/60 s/min = 1.40 min.
Total Time of Concentration = 11.1 minutes (0.185 hours)
For a 25-year storm event Its =0.78X-.64= 0.78(0.185),64 =2.30 in/hr
Q25 High Density Lots =CIA =0.60(2.30 in/hr)(1.1937 acres) = 1.65 cfs
Q25 r/w =CIA=0.70(2.30 in/hr)(0.30 acres) = 0.48 cfs
Q25 Total = (1.65 +0.48) = 2.13 cfs =Total flow rate entering catch basin#9
The capacity of the curb and gutter, at a 0.75% slope, with a depth of water 0.15'below the top of
curb is calculated as follows:
Q=(1.486/n)AR2/35112
n = 0.013 for Concrete
A= 1.24 ft'-
P=9.23 ft
R =A/P= 1.24/9.23 =0.1343 ft
R213 =0.2623 ft
S =0.0075 ft/ft
S112=0.08660 ft/ft
Q= (1.486/0.013)(1.24)(0.2623)(0.08660)= 3.21 cfs.
1.57 cfs < 2.13 cfs < 3.21 cfs - Gutter capacity is adequate
Q25 Total for Storm Sewer#3 = (3.58+3.13+1.57+2.13) =10.41 cfs
The time of concentration for sub-area#34 is calculated below:
Time of Concentration
Overland flow(140 ft @ 1.0%,C=0.60) =9.7 min.
Gutter flow(340 ft @ 0.75% avg. slope on Twin Lakes Drive)
V= (1.486/n)R2/3S1/2 (n=0.013,A=1.24 ft, P=9.23, R2/3=0.2623, 5112=0.08660)
V= 2.60 ft/s
T= 340 ft/3.67 ft/s/60s/min =2.2 min
Gutter flow(260 ft @ 0.87% avg. slope on A Street)
V= (1.486/n)R2/3S1J2 (n=0.013, A=1.24 ft, P=9.23, R213=0.2623, 51/2=0.0933)
V= 2.78 ft/s
T=260 ft/2.78 ft/s/60s/min = 1.6 min
Gutter flow(350 ft @ 1.5% avg. slope on Parkview Avenue)
V= (1.486/n)R213S1/2 (n=0.013, A=1.24 ft, P=9.23, RZ/3=0.2623, S1/2=0.1225)
V= 3.67 ft/s
T= 350 ft/3.28 ft/s/60s/min = 1.6 min
Total Time of Concentration = 15.1 minutes (0.25 hours)
For a 25-year storm event Its =0.78X-.64= 0.78(0.25)-.64= 1.89 in/hr
Q25 High Density Lots =CIA =0.60(1.89 in/hr)(2.008 acres) = 2.27 cfs
Q25 r/w =CIA=0.70(1.89 in/hr)(1.5327 acres) = 2.03 cfs
Q25 Total = (2.27+2.03) =4.30 cfs =Flow rate entering catch basin#10
Time of Concentration (Oak Street)
Gutter flow(600 ft @ 0.5% avg. slope on Oak Street)
V= (1.486/n)Rv3S1/2 (n=0.013, A=1.24 ft, P=9.23, R2-/1=0.2623, S1/2=0.07071)
V=2.63 ft/s
T= 600 ft/2.63 ft/s/60s/min =4.72 min
Total Time of Concentration =4.72 minutes (0.079 hours)
For a 25-year storm event I25 = 0.78X-.64=0.78(0.079)".64= 3.95 in/hr
Q25 r/w =CIA =0.70(3.95 in/hr)(0.8276 acres) = 2.29 cfs
Q25 Total = 2.29 cfs = Flow rate entering catch basin#10
Q25 Total for Storm Sewer#4=4.30 cfs+ 2.29 cfs = 6.59 cfs
The capacity of the curb and gutter, at a 1.5% slope for Parkview Avenue, with a depth of water
0.15'below the top of curb is calculated as follows:
Q=(1.486/n)AR2/3S1/2
n =0.013 for Concrete
A= 1.24 ft'-
P= 9.23 ft
R= A/P= 1.24/9.23 =0.1343 ft
R2/1 =0.2623 ft
S = 0.015 ft/ft
S1/2=0.1225 ft/ft
Q = (1.486/0.013)(1.24)(0.2623)(0.1225)=4.55 cfs.
4.31 cfs < 4.55 cfs - Gutter capacity on Parkview Avenue is adequate
The capacity of the curb and gutter, at a 0.5% slope for Oak Street, with a depth of water 0.15'
below the top of curb is calculated as follows:
Q= (1.486/n)AR213S1/2
n =0.013 for Concrete
A= 1.24 ft2
P= 9.23 ft
R=A/P = 1.24/9.23 =0.1343 ft
R2/2 =0.2623 ft
S =0.015 ft/ft
S 112 =0.07071 ft/ft
Q= (1.486/0.013)(1.24)(0.2623)(0.07071)= 2.63 cfs.
2.29 cfs < 2.63 cfs - Gutter capacity on Oak Street is adequate
The time of concentration for sub-area#3-5 is calculated below:
Time of Concentration
Gutter flow(615 ft @ 1.1% avg. slope on Cottonwood Road)
V= (1.486/n)R2/3Su2 (n=0.013, A=1.24 ft, P=9.23, R213=0.2623, 512=0.1049)
V= 3.14 ft/s
T= 615 ft/3.14 ft/s/60s/min = 3.3 min
Total Time of Concentration = 3.3 minutes (0.06 hours)
For a 25-year storm event I25 =0.78X--64= 0.78(0.06)`64 =4.721 in/hr
Q25 r/w =CIA =0.70(4.721 in/hr)(0.9936 acres) = 3.28 cfs
Q25 Total for Storm Sewer#5 = 3.28 cfs =Flow rate entering catch basin#11
The capacity of the curb and gutter, at a 1.1% average slope for Cottonwood Road, with a depth
of water 0.15'below the top of curb is calculated as follows:
Q= (1.486/n)AR2r3Sii2
n=0.013 for Concrete
A= 1.24 ft2
P= 9.23 ft
R= A/P= 1.24/9.23 =0.1343 ft
R2/3 =0.2623 ft
S = 0.011 ft/ft
SI/2 = 0.10488 ft/ft
Q= (1.486/0.013)(1.24)(0.2623)(0.10488)= 3.89 cfs.
3.28 cfs < 3.89 cfs - Gutter capacity on Cottonwood Road is adequate
24" PVC from Catch Basin#9 to Detention Pond#3
This pipe carries the storm water from drainage sub-areas 3-1 & 3-2 &3-3. As previously
calculated we should anticipate a flowrate of(3.58 + 3.13 + 1.57 + 2.13) = 10.41 cfs from a
25-year storm event. Calculations are enclosed in the Appendix for a 24" PVC pipe at 1.85%
slope. The 24-inch pipe will flow at a depth of 1.18 feet with a velocity of 5.42 ft/sec.
15" PVC from Catch Basin#10 to Detention Pond#3
This pipe carries the storm water from drainage sub-area 3-4. As previously calculated we
should anticipate a flowrate of 6.59 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 0.5% slope. The 15-inch pipe will flow at a depth of 1.02
feet with a velocity of 6.13 ft/sec.
15" PVC from Catch Basin#11 to Detention Pond#3
This pipe carries the storm water from drainage sub-area 3-5. As previously calculated we
should anticipate a flowrate of 3.28 cfs from a 25-year storm event. Calculations are enclosed in
the Appendix for a 15" PVC pipe at 6.01% slope. The 15-inch pipe will flow at a depth of
0.39 feet with a velocity of 10.18 ft/sec.
Detention Pond#3
The total area served by Detention Pond#2 is 20.593 acres with a weighted C-factor of 0.524
after development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 2.71 cfs.
Calculations are also enclosed in the Appendix for sizing the detention pond by varying the storm
duration and holding the release rate at 2.71 cfs. The required storage for Detention Pond#3 is
15,175 cubic feet. The weir must also be sized to insure the discharge never exceeds the
allowable release rate. The weir in the discharge structure for Detention Pond#3 will be 5.32
inches in width. These calculations are included with the calculations for sizing the pond.
The discharge pipe from Pond#3 to Baxter Ditch will be designed to handle a flow rate of 20.29
cfs. The discharge pipe will be 30" RCP at a slope of 0.22%. Calculations are attached for this
section of pipe.
Detention Pond#1
The total area served by Detention Pond#1 is 3.62 acres with a weighted C-factor of 0.483 after
development. The storage basin can have a release rate equal to the pre-development flow.
The calculations for the pre-development time of concentration and flows are included in the
Appendix. The pre-development flow (acceptable release rate) is 0.658 cfs.
Calculations are also enclosed in the Appendix for sizing the detention pond by varying the storm
duration and holding the release rate at 0.658 cfs. The required storage for Detention Pond#1 is
2,000 cubic feet. The weir must also be sized to insure the discharge never exceeds the
allowable release rate. The weir in the discharge structure for Detention Pond#1 will be 1.29
inches in width. These calculations are included with the calculations for sizing the pond.