STORMWATER MANAGEMENT REPORT
Presented to: Wal-Mart Canada Corp.
Thursday December 9, 2004 Prepared For: Plaza BNG Inc. 50 Tacoma Drive, Unit 18 Dartmouth, Nova Scotia B2W 3E5 Telephone No.: (902) 468-8688 Facsimile No.: (902) 468-9446 Prepared By: Stantec Consulting Ltd. 7270 Woodbine Avenue Suite 300 Markham, Ontario L3R 4B9 Telephone No.: (905) 474-0455 Facsimile No.: (905) 474-9889 File No.: 606 20063
STORMWATER MANAGEMENT DESIGN BRIEF Yarmouth – NS Wal-Mart Development Starrs Road & Highway 101
Yarmouth, Nova Scotia December 3rd, 2004 Prepared For: Plaza BNG Inc. 50 Tacoma Drive, Unit 18 Dartmouth, Nova Scotia B2W 3E5 Telephone No.: (902) 468-8688 Facsimile No.: (902) 468-9446
Prepared By: Stantec Consulting Ltd. 7270 Woodbine Avenue Suite 300 Markham, Ontario L3R 4B9 Telephone No.: (905) 474-0455 Facsimile No.: (905) 474-9889 File No.: 60620063
File No. 606 20063 December 9, 2004 1st Submission Date: February 20, 2004 2nd Submission Date: April 15, 2004 Revised: December 9, 2004 Mr. Bryce Schnare Plaza BNG Inc. 50 Tacoma Drive, Unit 18 Dartmouth, Nova Scotia B2W 3E5 Dear Mr. Schnare, Re:
Stormwater Management Design Brief Proposed Commercial Development Starrs Road & Highway 101 Yarmouth, Nova Scotia
This third submission is for your review for approval for the development of a Wal-Mart in the Town of Yarmouth, Nova Scotia. The stormwater design brief was prepared to finalize the detailed SWM design. Included in this submission, for your review and approval, are the following: • • • • • • • •
Drawings (SW2, SW3, ESC, D1, Figure 1, Figure 2, and Figure 3); Design brief; and Appendix A – (Allowable Release Rate Calculations) Appendix B – (Control Details) Appendix C – (Modified Rational Storage Calculations) Appendix D – (External Drainage) Appendix E – (SWMHYMO Drainage Analysis) Appendix F – (Stormceptor Sizing Tool Results)
INTRODUCTION This design brief summarizes how the proposed design will meet the stormwater management (SWM) quantity and quality control requirements for the proposed Wal-Mart development. The site is located NE of Starrs Road and Highway 101, in the Town of Yarmouth (‘the Town’), Nova Scotia (please refer to Figure 1). It is currently undeveloped and has a total area of approximately 4.40 hectares (please refer to Figures 1 and 2). Figure 2 illustrates the SWM Plan.
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RELEASE RATES The Town of Yarmouth has requested that no adverse impact occurs as a result of this development. We addressed this request as per the following:
No increase in peak flows from the site for all storms, up to and including the 100year storm; Allow for sufficient capacity of the drainage feature conveying external flows; and Implement SWM practices so that no improvements will be required to the existing culverts crossing Starrs Road.
Based on the above, it is proposed to control 5-year post development flow to existing 2year flow, and to control the 100-year post development flow to 100-year existing flow. The existing flows for the 2-year, 5-year and 100-year design storms from the site are provided in Table 1 (please refer to Appendix A).
Table 1 - Existing Flows Proposed Commercial Development - Starrs Road & Highway 101 Scenario
Existing
Area 1 (ha) 3.86
Peak Flow Rates (L/s) 2-year 2 5-year 2 166 216
100-year 3 554
Notes: 1
The actual site area is 4.40 ha, although 3.86 ha of the total site area is being developed at this time.
On-site detention storage will be provided to ensure that post development flows for the 5year and 100-year design storms will be less than or equal to the existing flows from the site. The proposed post development site flows are provided in Table 2 (please refer to Appendices B and C).
Table 2 - Post Development Flows Proposed Commercial Development - Starrs Road & Highway 101 Scenario
Post-Development2
Area 1 (ha) 3.86
Peak Flow Rates (L/s) 5-year 100-year3 166 275
Notes: (continued from Table 1) 2 Calculated utilizing the modified rational method. 3 Overland spill conveyed to downstream ditch via a weir located at the SE end of parking lot. This spill control is designed to meet the 100-year allowable release rate.
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QUANTITY CONTROL Pipe storage, parking lot storage and rooftop detention storage will be utilized to attenuate the proposed flow to the existing release rates. Rooftop Storage Rooftop control will be provided via installation of roof drain weirs on Building A (Zurn or approved equivalent, see details in Appendix B). The roof drains will meet the following requirements: • • •
The total roof runoff rate will be restricted to a maximum release rate of 42 L/s/ha of rooftop during the 100-year event; The maximum ponding depth will be 0.10 m; relief scuppers will be built in the parapet walls to eliminate any ponding above this depth; and, The roof drains will discharge to the proposed site sewer system.
Parking Lot Storage Ponding in parking lot areas will be limited to a maximum depth of 0.3 m above the catchbasins. Ponding elevations for the 100-year storm event are displayed on Figure 2. Storage requirements for the 100 and 5-year storms were generated utilizing the Modified Rational Method (refer to Appendix C). Along with surface storage (ponding), pipe storage will be utilized using orifice controls. For minor flows, the orifice plate ensures that the release rate from the site to the downstream ditch meets the existing release rate (please refer to details in Appendix A). For major flows, a combination of the orifice plate and weir ensures the release rate from the site into the downstream ditch meets the existing release rate. The proposed locations for the orifice plates and weir controls are illustrated on Figure 2. An orifice plate (#1) located in MH22 will control the release rate for minor events into the downstream ditch. Another small area (0.13 ha) at the west end of the proposed parking lot will be controlled for major events only using an orifice plate (#2) at the east invert of CB26, discharging into the culvert conveying external flows. Tables 3, and 4 outline the storage requirements and release rates for the 100-year and 5-year design storms, respectively. Detailed calculations for these controls can be found in Appendix B.
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Table 3 Proposed Release Rates and Storage Requirements 5-year Storm Outlet ID
Area ID
1
Total (1) Note:
Release Rate1 (m3/s) 0.018 4
Storage Required (m3) 224
Storage Available (m3) 264 5
Orifice Location
Orifice Type
101
Drainage Area (ha) 0.88
Roof
Ponding Depth (m) 0.10
Orifice Size2 (mm) -
Draw Down3 (min) N/A
-
102
2.85
0.122
475
472
MH22
Vertical Plate
0.3
195
0
103
0.13
0.026
0
1
CB26
Vertical Plate
0.3
100
0
-
3.86
0.166
699
748
-
-
-
-
-
1
As per Model/Modified Rational Calculations (refer to Appendix C) See Appendix B for orifice plate details 3 Draw down time calculated based on surface storage only 4 Rooftop control = 42/2 = 21 L/s/ha 5 Available rooftop storage estimated using 3 cm depth over entire roof area 2
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Table 4 Proposed Release Rates and Storage Requirements 100-year Storm Outlet ID
Area ID
1
101 102 103
Total (1) Note:
-
7
Drainage Area (ha) 0.88
Release Rate1,2 (m3/s) 0.037 5
Storage Required (m3) 333
Storage Available (m3) 528 6
Orifice Location
Orifice Type
-
2.85
0.203
774
1035
0.13
0.034
7 1136
3.86
0.275
7
Roof
Ponding Depth (m) 0.10
Orifice Size3 (mm) -
Draw Down4 (min) N/A
MH22
Vertical Plate
0.3
195
34
47
CB26
Vertical Plate
0.3
100
3
1818
-
-
-
-
-
1
As per Model/Modified Rational Calculations (refer to Appendix C) Combined orifice and weir controls provided 3 See Appendix B for orifice plate details 4 Draw down time calculated based on surface storage only 5 Rooftop control = 42 L/s/ha 6 Available rooftop storage estimated using 6cm depth over entire roof area 7 On-site control flow using orifice plates at 100-year W.L. before weir control is activated 2
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Grading Parking lot grades range from 1.17 % to 3.46 % to promote efficient drainage. Existing elevations at the west border of the site (adjacent Loblaws development) will be maintained. The finished floor elevation for the building is set to promote drainage away from the building. On-site grading has been designed to provide major overland flow relief to the downstream ditch through a weir incorporated into the curb at the southern parking lot boundary (please refer to Appendix B). Overland flow routes are shown on Figure 2.
EXTERNAL DRAINAGE Two 1200 mm storm sewers legs (referred to as the ‘proposed culverts’) will replace the existing ditch on the proposed site (please refer to Figure 2). The proposed culverts will discharge into the existing ditch downstream of the site, which drains to two culverts under Starrs Road. The proposed culverts were sized to convey existing external 100-year flows (please refer to Appendix D) to the existing downstream ditch. The sizing of the culverts assumes that there will be no future development upstream in the Broad Brook watershed area, or that the developed areas will provide on-site controls to match pre development flow rates for all storms. A drainage analysis has also been performed to address the Town’s concerns regarding the impact of the proposed development on the Broad Brook watercourse system (please refer to Appendix E). The calculated external drainage flows are in good agreement with the information presented in the Town of Yarmouth Stormwater Management Plan prepared by Beasy Nicoll Engineering Ltd. in August of 1995. In conclusion, the proposed commercial development will not have any negative impacts on the downstream culverts and will meet the allowable peak flow release rates for the 2-year, 5-year and 100-year storms.
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QUALITY CONTROL Quality control will be provided for the site to reduce the sediment loading into the receiving ditch, and to prevent oil and floating pollutants from leaving the site. A Stormceptor was sized using Stormceptor Sizing Tool Version 4.0.0 to remove a minimum of 70% of TSS (refer to Appendix F for results). Table 5 illustrates the size and location of the proposed oil/grit separator.
Stormceptor Manhole Location D/S MH25
Drainage Area 1 (ha) 3.08
Table 5 – Stormceptor® Sizing Impervious Controlled 5-year Type of % TSS ® Drainage Release Rate Removal Stormceptor Area (ha) (L/s) 2.77 186 STC1500 70
Note: 1 Drainage Area does not include clean flow from roof.
We trust the information provided will assist you in completing your review of the SWM for this site. Should you require any additional information, please contact the undersigned.
Yours very truly, STANTEC CONSULTING LIMITED
Walter Toth, MBA, P.Eng. Principal
Serge Ristic, P.Eng. (Ontario) Senior Water Resources Engineer
c. Stantec – Steve Auger, Tanya Gibson Encl.
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APPENDIX A Allowable Release Rate Calculations
APPENDIX B Control Details
On-Site Detention Storage - Orifice Outlet Project Description Project No. Area Id
5 Year storm and 100 year storm
Yarmouth - NS 60620063 102
1/2 Orifice Equation: Q = CdA(2gh)
Area: g= Cd =
Type of Control: Location:
405 mm 2 0.000 m 9.81 m/sec 0.62
2
Parking Lot Storage - 100
Pipe Storage
Surface Area = Depth =
2 2349 m 0.25 m
Volume =
3 196 m
Parking Lot Storage - 5 Surface Area = Depth =
2 0m 0m
Volume =
3 0m
Stage Invert E.L. Ground E.L. 5 Year WL 100 Year WL
26.00 29.15 29.15 29.40
CBMH18
Head* (m) 0.00 0.05 0.05 0.00
MH Storage
Diameter (mm)
Area (m2)
250 300 375 450 525 600
0.049 0.071 0.110 0.159 0.216 0.283
0 0 0 0 0 0
750 825 900 1050
0.442 0.535 0.636 0.866
0 0 0 0 Total Volume
Storage (m3) 0 11 11 207
Length (m)
Volume (m3)
Diameter (mm)
Area (m2)
0.0 0.0 0.0 0.0 0.0 0.0
1200 1200 1500 1500 1800 1800
1.131 1.131 1.767 1.767 2.545 2.545
0 0 0 0 0 0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0
2400 2400 2400 2400
4.524 4.524 4.524 4.524
0 0 0 0 Total Volume
0.0 0.0 0.0 0.0 0.0
Discharge (m3/s) 0.00 0.000 pipe storage 0.000 0.000 pipe+surface storage
*Head calculated from tailwater from 103
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Depth (m)
Volume (m3)
CB Storage Size (m)
Area (m2)
0.6 0.6
0.360 0.360
Depth (m) 2.00 1.50
Volume (m3) 0.72 0.54
No. of CB's
15 0 Total Volume
Volume (m3) 10.80 0.0 10.8
On-Site Detention Storage - Orifice Outlet Project Description Project No. Area Id
5 Year storm and 100 year storm
Yarmouth - NS 60620063 102
1/2 Orifice Equation: Q = CdA(2gh)
Orifice Diameter: Area: g= Cd =
Type of Control: Location:
195 mm 2 0.030 m 9.81 m/sec 0.62
2
Parking Lot Storage - 100
Pipe Storage
Surface Area = Depth =
2 5630 m 0.3 m
Volume =
3 563 m
Parking Lot Storage - 5 Surface Area = Depth =
2 0m 0m
Volume =
3 0m
Stage Invert E.L. Ground E.L. 5 Year WL 100 Year WL
26.07 29.10 29.10 29.40
Vertical MH22
Head (m) 0.00 2.93 2.93 3.23
MH Storage
Diameter (mm)
Area (m2)
250 300 375 450 525 600
0.049 0.071 0.110 0.159 0.216 0.283
69 55 0 39 0 86
750 825 900 1050
0.442 0.535 0.636 0.866
0 0 68 450 Total Volume
Storage (m3) 0 472 472 1035
Length (m)
Volume (m3)
Disharge (m3/s) 0.00 0.140 pipe storage 0.140 0.147 pipe+surface storage
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Diameter (mm)
Area (m2)
Depth (m)
Volume (m3)
3.4 3.9 0.0 6.2 0.0 24.2
1200 1200 1500 1500 1800 1800
1.131 1.131 1.767 1.767 2.545 2.545
0 0 0 0 0 0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 43.3 389.2 470.1
2400 2400 2400 2400
4.524 4.524 4.524 4.524
0 0 0 0 Total Volume
0.0 0.0 0.0 0.0 0.0
CB Storage Size (m)
Area (m2)
0.6 0.6
0.360 0.360
Depth (m) 1.50 1.50
Volume (m3) 0.54 0.54
No. of CB's
4 0 Total Volume
Volume (m3) 2.16 0.0 2.2
On-Site Detention Storage - Orifice Outlet Project Description Project No. Area Id
100 year storm
Yarmouth - NS 60620063 Weir flow - 102 Q = CwBH3/2
Weir Equation: Base (Weir Length) = Cw =
Type of Control: Location:
22 m 1.49
Parking Lot Storage - 100
Pipe Storage
Surface Area = Depth =
2 0m 0.02 m
Volume =
3 0m
Parking Lot Storage - 5 Surface Area = Depth =
2 0m 0m
Volume =
3 0m
Stage Invert E.L. 100 Year WL Flow over Weir = Cross-sectional area = Velocity =
0
29.38 29.40
Head (m) 0.00 0.00
Diameter (mm)
Area (m2)
250 300 375 450 525 600
0.049 0.071 0.110 0.159 0.216 0.283
0 0 0 0 0 0
0.0 0.0 0.0 0.0 0.0 0.0
750 825 900 1050
0.442 0.535 0.636 0.866
0 0 0 0 Total Volume
0.0 0.0 0.0 0.0 0.0
Storage (m3) 0 0
Length (m)
Volume (m3)
Disharge (m3/s) 0.00 0.093 pipe+surface storage
3 0.09 m /s 2 0.44 m 0.21 m/s
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Site: Job No.:
Yarmouth - NS 60620063
12/9/2004 8:46
100 Year
Catchment ID
101 102 103 Weir flow - 102 Total
Building No.
Runoff Coef.
Area (ha)
Release Rate (l/s)
A
0.95 0.95 0.95
0.88 2.85 0.13
37 203 34
333 797 7
3.86
274.6
1136
Allowable Release Rate
Site: Job No.:
553.9
Storage Ponding Depth Required (m3) (m)
0.10 0.30 0.30 0.02 Notes:
L/s
Storage Available (m3)
Draw Down Time (mins)
528 1035 47
n/a 37 3
Orifice Size (mm) or Weir Length (m)
Orifice Release Rate (l/s) or Weir Discharge Rate (l/s)
Location of Orifice or Weir
Invert
HORIZONTAL/ VERTICAL/TUBE Control
roof 195 100 22 -
147 34 93 -
0.0 MH22 CB26 0.0 -
26.070 27.600 -
Vertical Vertical -
1818 Area 101 is in series with 102 Area 102 is in series with 103 The site area is recognized to be 4.40 ha. However, the downstream uncontrolled area is not considered in this analysis to size orfice plates on-site to meet required storage and allowable release rates. Weir discharge included in subcatchments 102 and 103 release rates.
Yarmouth - NS 60620063
12/9/2004 8:46
5 Year
Catchment ID
101 102 103
Building No.
Runoff Coef.
Area (ha)
Release Rate (l/s)
A
0.95 0.90 0.90
0.88 2.85 0.13
18 122 26
224 475 0
166.4
699
Total Total Site Allowable Release Rate
166.0
5 Year Storage Available (m3)
Draw Down Time (mins)
Orifice Size (mm)
Orifice Release Rate (l/s)
0.10 0.00 0.00
264 472 1
n/a 0 0
roof 195 100
140 26
0.30
748
-
Storage Ponding Depth Required (m3) (m)
L/s
Notes:
Area 101 is in series with 102 Area 102 is in series with 103 The site area is recognized to be 4.40 ha. However, the downstream uncontrolled area is not considered in this analysis to size orfice plates on-site to meet required storage and allowable release rates.
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Site: Job No.:
Yarmouth - NS 60620063
12/9/2004 8:46
100 Year Catchment ID
102 103 Weir flow - 102
Surface Ponding (m2)
5630 469.3
Pipe Length
Ponding Depth (m)
Type of Control
0.3 0.3 0.02
Vertical Vertical -
Location of MH
Ground Invert
Invert
MH22 CB26
29.100 29.100 29.400
26.070 27.600 29.400
Pipe Diameter (mm)
250 69
Pipe Diameter (mm)
300 55
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Pipe Diameter (mm)
Pipe Diameter (mm)
375
450 39
Pipe Diameter (mm)
Pipe Diameter (mm)
525
600 86
Pipe Diameter (mm)
750
Pipe Diameter (mm)
Pipe Diameter (mm)
825
900 68
Pipe Diameter (mm)
1050 450
APPENDIX C Modified Rational Storage Calculations
MOD_RTNL 100.xls 12/8/2004 17:04 Modified Rational Method Project Name : Yarmouth - NS 101 Building Project No. : 60620063 Area = "C" = AC= Tc = Time Increment = *Release Rate = Max.Storage =
0.88 0.95 0.836 10.0 5.0 37.0 333
Mainstream Length (km) :- L = Mainstream Slope (m/km) :- S = Bransby Williams:-Tc = Time
A
ha *Roof controls @ 42 l/s/ha min min l/s m3
Yarmouth - NS a= b= c=
100yr 1964.068 16.512 0.823
0.0
Rainfall
Storm
Runoff
Released
Storage Volume
Intensity
Runoff
Volume
Volume
(min)
(mm/hr)
(l/s)
(m3)
(m3)
(m3)
10.0
132.3
307.55
184.5
22.2
162.4
15.0
114.8
266.79
240.1
33.3
206.8
20.0
101.7
236.33
283.6
44.4
239.2
25.0
91.5
212.64
319.0
55.4
263.5
30.0
83.3
193.64
348.6
66.5
282.0
35.0
76.6
178.04
373.9
77.6
296.3
40.0
71.0
164.97
395.9
88.7
307.2
45.0
66.2
153.85
415.4
99.8
315.6
50.0
62.1
144.26
432.8
110.9
321.9
55.0
58.5
135.91
448.5
122.0
326.5
60.0
55.3
128.56
462.8
133.1
329.8
65.0
52.5
122.03
475.9
144.1
331.8
70.0
50.0
116.20
488.0
155.2
332.8
75.0
47.7
110.95
499.3
166.3
332.9
80.0
45.7
106.19
509.7
177.4
332.3
85 0
43 8
101 87
519 5
188 5
331 0
