1.Introduction 1.1 Background Windsor is the one of the most important border crossing between Canada and the United States. More than 16 million cars, trucks and buses travel through the city each year, representing approximately 33 per cent of Canada-United States truck trade. In 2001 alone, this two-way merchandise trade totaled at over $140 billion. Windsor's economy is intricately linked with the international border crossing. As Canadian and American trade and tourism increase through the years, projected traffic volume is also predicted to increase. This has made it apparent to government and commercial officials that there is a need for an additional border crossing which will have the capacity to handle the projected traffic volume. The privately owned Ambassador Bridge currently spans across the Detroit River and links up Detroit and Windsor traffic through the international border crossing facilities on each side of the bridge. One of the main concerns associated to Ambassador Bridge border crossing is that an urban road system links up with the Ambassador Bridge as opposed to a Highways System. This means that before a driver can reach the border crossing they need to cross several street lights within the city core. This causes large traffic jams and impede on the overall traffic ease of the city. This is why the new border crossing is intended to be directly linked to
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the Canadian and American highway systems, such that traffic flow within Detroit and Windsor is much more feasible.
The Detroit River International Crossing Project (DRIC) is a large scale interdisciplinary engineering project currently valued at over one billion dollars. Construction of the New Detroit-Windsor border crossing is intended to begin in late 2009. This border crossing will be built in stages such that the traffic flow matches the facility capacity. Once the preliminary design is complete, the project will be ready for a construction bid. The border crossing is intended to be built as a showcase of leading edge innovation in: water resource engineering, traffic engineering, environmental engineering, energy efficiency, logistics and security.
1.2 Purpose and Scope The purpose of this report is to develop the design of a storm water management system for the projected Windsor Detroit International Border Crossing Plaza site. This report will contain two parts: Firstly, a preliminary report developing and selecting alternatives identifying the hydrological challenges of this project. Secondly, a detailed design report dealing with the hydrological challenges of the preliminary report .In addition to that the technical report should follow best management practices (BMPs) meeting regulated design standards
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outlined in the 2003 Ministry of the Environment storm water management guideline.
1.3 Methodology In order to properly assess the potential use of various alternative drainage systems, the following aspects should be considered: 1)
Compatibility with physical site characteristics;
2)
Compatibility with planning objectives and ease of integration within the road right of way;
3)
Ability to meet stormwater management objectives;
4)
Economics; and
5)
Public acceptance / safety.
6)
Site elevation
The approaches used for stormwater management in this project are: i)
Urban Drainage System Selection Tool (UDSST)
ii)
Rational Method (see Section 5)
Urban Drainage System Selection Tool (UDSST) This tool is developed by J.F. Sabourin and Associates Inc. It is a Microsoft Excel Spreadsheet application for development of different solutions relating to stormwater management. The tool helps to determine which types of alternative drainage features could be used 3
within a site and to compare potential conceptual drainage systems. It is also used to calculate the quantities of materials needed to build a proposed drainage system based on drainage area and imperviousness. This is achieved through the use of the 6 detailed tables (See Appendix 3): •
Table A – Site Characteristics
•
Table B – Development Characteristics
•
Table C – Identification of Compatible Features
•
Table CD – Stormwater Management Objectives
•
Table D – Comparison of SWM Function Potentials
•
Table E – Comparison of Conceptual Drainage Systems
The step by step procedure can be visualized by a flowchart (see Figure 1-1). Table A – Site Characteristic It is used to eliminate specific drainage features which are incompatible with the local site characteristics Table B – Development Characteristics It is used to eliminate options which are incompatible with exisiting or potential development characteristics. Table C – Identification of Compatible Features
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It is used to summarize the results obtained from Tables A and B, and to identify which drainage features could be incorporate in a conceptual system Table CD – Stormwater Management Objectives It is used to summarize the stormwater management objectives and target performance for the drainage system being considered. It is also used to assign variable priorities to the various SWM objectives which are to be met.
Table D – Comparison of SWM Functions It was prepared as a reference and provides an indication of how well a particular drainage feature can respond to a particular SWM objective. SWM objectives were divided into 5 groups: i)
Groundwater recharge
ii) Erosion control iii) Quality control iv) Flood control v) Thermal reduction The water quality control objective was further divided into 4 subgroups:
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i)
Sediment removal
ii) Nutrient removal iii) Bacterial die-off iv) Oil and grease removal. Table E – Comparison of Conceptual Drainage Systems It is used to describe and evaluate possible conceptual drainage systems. The evaluation is based on potential SWM performance, specific design objectives and costs.
Figure 1-1 – Flow Chart of UDSST
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1.4 Preliminary Conclusions Based on the results from UDSST and the site conditions, the solutions retained were storage SWMP’s and oil/grit separators. The storage SWMP’s will provide quality treatment, erosion control and quantity control. Storage SWMP’s will be utilized to match existing peak flow conditions to the receiving watercourses in an effort to emulate existing conditions within the watersheds. Oil/grit separators will provide quality treatment at the upstream areas.
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2. Site Description The western edge of the proposed site runs along the Detroit River. The most Southern East point is located at the intersection of Ojbway Parkway and Broadway Street. The site measures 54.3 ha. By looking at geotechnical samples and grade pictures of surrounding site, the pre-existing site terrain inclines towards the South Eastern edge of the proposed site. At the same time, it is fairly flat; the rough elevation difference over 1.45km is 3.5 m. Morrison Hershfield provided design drawings which outlined the proposed site borders and area. The calculations and design specifications were based on those drawings. The map below was
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obtained from Google EarthTM.
Figure 2-1 - Plaza Site Outlined 9
2.1 Existing Land Use and Vegetation The 54.3 hectare area to be used for the proposed Canadian Plaza is currently a mixture of surfaces including grass and asphalt however, the percentage of the paved road/asphalt is very small when compared to the landscape area/grass; this report has taken a conservative approach and assumed that the entire existing area is cultivated land. The resulting runoff coefficients for the existing condition are C = 0.34 and 0.47 for 5 year & 100 year storm event respectively (see Table 2-1).
2.2 Existing Soil and Groundwater Condition The data information was gathered from MNR, DRIC draft environmental assessment reports and geological map of TorontoWindsor area from Geological Survey of Canada. Table 2-1 – Runoff Coefficient for Use in the Rational Method
Character of Surface Undeveloped
Return Period (years) 5
100
0.34
0.47
Asphaltic
0.77
0.95
Concrete/Roof
0.80
0.97
Grass Areas -Poor
0.34
0.47
Cultivated land Flat, 0 – 2% Developed
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condition Flat, 0 – 2% Source: Water Resources Engineering by Larry Mays 2005
The subsurface conditions in the Windsor area are characterized by flat-lying soils including: •
Native deposits of sand and silt
•
Extensive deposits of clayey silt to silty clay beneath the sand
•
Bedrock is encountered at depths of 20 to 35 metres.
Beneath the existing pavement structures, topsoil and / or surficial fill materials, granular materials consisting of sand and gravel, sands and silty sands were identified at a depth of approximately 0.3 metres below existing ground surface. Groundwater levels are expected to be located about 3 metres below ground surface in the clayey silt and silty clay materials. The silty clay, clayey silt, sand and gravel and sands are considered to be slightly erodible and the silty sands are considered to be moderately erodible.
2.3 Topography and Surface Water Drainage Preliminary Drainage Area According to industry standards and property law; when a new structure is built on an undeveloped site, it is critical that the new
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development does not cause excess rainwater to fall into neighboring properties and cause them flood damage. The proposed site is built on a relatively undeveloped site. The construction of the border crossing plaza without a storm water management system would definitely cause excess storm water to flow to neighboring sites. There would be an excess of storm water after construction because the run off coefficient for the soil would increase. The runoff coefficient of asphalt is 0.90, this means that during a typical storm, 10% of the water on the asphalt will be absorbed by the ground, 90% of the water would need to be diverted elsewhere. Therefore, the post development coefficient will be higher than the pre-development coefficient. More water will need to be routed properly. Figure 2-1 is an elevation map outlining a rough contour of the Border crossing plaza site and its surrounding area. This map was obtained from The Atlas of Canada website. The drainage area outlined on Figure 2-2 is based on the natural flow path of water and existence of previously built storm water structures. To illustrate, if a piece of neighboring land has a slope facing the border crossing site, it will be considered part of the total drainage area. However, if a neighboring storm water management pond exists in front of the area with a slope facing the border crossing plaza site, the land will not be considered part of the drainage area. In addition to that, if there is a piece of neighboring land that is connected to a piece of land which
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will lead into the border crossing plaza area, it will be considered part of the drainage area. Figure 2-3 outlines the sub-drainage areas and their drainage directions. These areas are determined based on the flow path of rainwater. Figure 2-3 also outlines the existing flow path of water with arrows. The runoff from total drainage area will naturally flow into the Detroit River.
Figure 2-2 - Outlined drainage area based on rough contour outline Source: The Atlas of Canada – Topographical Map
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Figure 2-3 - Existing flow path of water
The objective of this project is to create a storm water management system with 5 and up to 100 year storm capacity. Runoff will need to be routed properly according to where it lands relative to the border crossing plaza site. Figure 2-4 outlines how the drainage areas will be divided. Main Drainage Area A 14
This area is the most important drainage area of this project. The rainwater that lands on this area will need to be processed for quality and quantity volumes from 5 year up to a 100 year storm. As discussed in the Preliminary report, this area (68.9 ha) will include a main channel which will divert all runoff into the main ponds.
Figure 2-4 - Divided Drainage Areas
Secondary Drainage Area B and C These secondary areas represent the drainage areas outside the project area. The Runoff from these areas will simply need to be diverted into the Detroit River as Quality requirements do not apply.
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3. Stormwater Management Design Overview 3.1 Problem Definition Water Quality: The Canadian border crossing site is located in an industrial area which is also connected two major highways. This means that chemical spills can be expected in addition to that surrounding industrial building are built with older generation construction materials such as asbestos, lead and PCB’s. During a rainfall, theses chemicals can make their way into the leachate and contaminate the water system i.e: the Detroit River. This will ultimately endanger the ecosystem and drinking water source. Sediment Control: Water is a highly abrasive medium and with enough time, water will shape any material to its movement. Water abrasion of roads and earth under the roads can compromise the structural integrity of any driving surface. Earth abrasion can create pot-hole, earth vacancies and landslides. For the safety of drivers these large driving surfaces cannot afford to be structurally compromised, secondly it is also important to mitigate the cost of repairing damaged driving surfaces. 16
In addition to this, it is important to note that, storm water from the North and the East sides of the site may contain large amounts of sediments during the construction stage. This sediment laden runoff can cause sewers to be filled with sediment and destroy fish habitat in the river. Road Safety: The border crossing area is intended to be used as a high traffic area for vehicles of all sizes, it is imperative that storm water be properly drained such that driving surfaces are un-slippery and safe enough to drive on. In addition to that, we want to make sure that during a heavy 100 year rainfall, water is properly diverted from driving surfaces and vehicle submersion in water is unlikely.
3.2 Considerations The Canadian Plaza is approximately 54.3 ha, consisting primarily of pavement and commercial buildings. Stormwater management for the Plaza requires quality, quantity and erosion controls for runoff flows from the Plaza, as the increase in impervious area will increase the overall peak flows from the site, as well as the overall pollutant loading. This will lead to erosion issues downstream, as well as impact the ecological condition of the Detroit River. The principle concern for large sites with a high imperiousness and vehicular traffic is providing stormwater treatment for frequent vehicular pollutants (oil, gasoline, coolant, etc), roadside grit and 17
garbage (gravel, sand, and cigarette butts), infrequent pollutant spills, and controlling increase of overland runoff to the receiving watercourses. Enhance Quality treatment will also be required in accordance to the MOE document “ Stormwater Management Planning and Design Guidelines”, date 2003, Level 1 protection which states removal of a minimum of 80% total suspended solids (TSS). It is to be designed based on a 100-year design flow and be controlled for all storm events up to and including 100-year storm event. Based on the results and the site conditions, the solutions retained were storage SWMP’s and oil/grit separators. The storage SWMP’s will provide quality treatment, erosion control and quantity control. Storage SWMP’s will be utilized to match existing peak flow conditions to the receiving watercourses in an effort to emulate existing conditions within the watersheds. Oil/grit separators will provide quality treatment at the upstream areas. The stormwater management plan consists of creating a two-cell facility in the green spaces south of the proposed plaza and a linear open channel feature. These green spaces can be converted to stormwater management facilities utilizing the existing drain to connect the facilities, discharging to the Detroit River via an outlet channel. The pond system provides closer outlets for the sewer system, lowering the overall grading requirements of the Plaza. The linear feature would be designed such that there would always be an
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open portion to ensure that there is no restriction to the conveyance of flow from one pond to the other. The pond system would control the release rate to the Detroit River. In the event of a contaminant spill with the Plaza, a shut off valve or alternative damming procedure will be required within the pond.
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4. Main Channel Design This section will include the technical design of the major storm water management structures built within the border crossing plaza site. The design portion will be split into two parts the design of stormwater management system within the Main Drainage Area A and the design of the stormwater management structures outside the plaza area: Secondary Drainage Area B and C.
4.1 Main Drainage Area A Pond and Main Channel Positioning From the conceptual report, the Best Management Practice (BMP) of storm water management system would include ponds and a large channel leading up to the pond. The quality and quantity pond would be located at the most western edge of proposed site as shown on Figure 4-1 because: 1. Construction contingencies only allow the wet pond to be located at the western edge of the site 2. Water has a much shorter distance to flow into the Detroit River if there is a larger than expected storm that occurs. 3. Post development slope will lead water towards pond
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The main storm water channel leading up to the pond will be placed along the southern edge of the site. The channel will be in this configuration because: Figure 4-1 - Channel and pond configuration
1. The channel will be at the bottom of the site slope in such a way that excess rainwater is forced to flow towards channel and does not pool in critical traffic areas 2. It will run along the greatest length of the site, catching a majority of the excess rainwater.
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3. The border crossing plaza has the greatest free space
allocation along the southern edge of the site.
4.2 Main Channel Design Pre-development conditions: Based on site elevation provided by the city of Windsor, it is obvious to see that the site is highly flat. The existing elevation difference between the highest and lowest part of the channel is 2.72m over a 1110m span. The MOE 2003 storm water management guideline outlines that grass swales are ideal storm water management structures for flat terrain. Thus the main channel leading up to the pond will be a grassed swale. Grass swales also work effectively in the quality processing of runoff. The length of the swale was determined based on a preliminary drawing provided by Morrison Hershfield. This length extends from the swale entrance to the projected pond entrance along the southern edge of the site. The elevation data was obtained from the City of Windsor official website. Design Constraints The design constraints of the proposed site are mainly the flatness and ground water table elevation. Figure 4-2 describes the design
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constraints of the channel. The highest elevation at the eastern swale entrance is 178.72m. The current ground level of the pond entrance is 176.53 m. This point is highly important, as it will determine the level
Figure 4 -2 - Existing main channel elevation profile
at which the Main Swale will enter the pond. The Detroit River Website measured that the highest water level of the ground water table to be
3m below ground level. Through shear optimization and coordination a 2.25m
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4.3 Runoff Routing Drainage Area A The Main Drainage Channel is designed to route all of the runoff from Drainage Area A into the Wet/Dry ponds designed in Section 5. This section will roughly describe the post development runoff pattern. As seen from Figure 2-4 in Section 2, runoff from Drainage area B and C will flow into Main Drainage Area A. However because there will be secondary drainage channels routing all excess runoff from drainage area B and C directly into the Detroit River, the excess runoff will not need to be considered in this section. Figure 4-3 outlines the projected Drainage pattern for Drainage Area A. The routing will be accomplished by sloping the land in the direction of the Main Drainage Swale. This terrain will force runoff landing on drainage area A to flow towards the main drainage swale.
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Figure 4-3 - Post Development Drainage Pattern For Drainage Area A
4.4 Channel Design using Manning’s equation Now that the elevation profile for the main swale is known, a swale height can be determined based on the designed constraints outlined in Section 4.2. By looking at Figure 4-2 the height available for between the swale floor at the pond entrance and the ground level of the most eastern point of the swale is 2.98m. The MOE also states that a one foot clearance between the 100 year water elevation of the swale and the ground level above the swale is required. Thus, the swale design requires that the sum of the 100 year water level of the swale and the elevation difference due to the channel slope not exceed 2.675m. Through optimization of the manning’s equation described below it was found that the swale would not exceed 1m in depth for a 100 year storm and that the optimal slope is 0.125%. The Manning’s equation is industry recognized and will be used to determine the water level of our channel for a 100 year storm. The water elevation is a key parameter of determining the main swale cross-sectional dimensions. The equation is as follows: V=1n*R23*S0.5
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By multiplying both sides by the area of the channel the modified Manning’s equation is: Q=1n*AR23S0.5
Where
n = the roughness coefficient. For grass channels, n
= 0.03 A = the cross sectional area of the channel R = the Hydraulic radius and S is the slope Q = 100 year Post Development flow m3/s. For the proposed site area it is 9.3305 m3/s V = Mean Runoff Velocity m3/s S = Channel Slope, after optimization the best slope to use given the site constraints is 0.125%. This is a very minor slope however given the water table depth, site elevation and resulted channel depth this value is the most optimal. MOE 2003 STMWTR Guideline specifies that the swale will need a trapezoidal form thus area is defined as: A=(B+Zy)y
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Where B = the Base of the swale, 6m. However due to the fact that the site is very flat 7m were used as the base of the swale. Z = the horizontal distance per meter of the side slope, 2.5m y = the height and water level of the trapezoid for a 100 year storm it is the unknown that will be solving for. R - Hydraulic radius for a trapezoid defined as: R=(B+Zyy/(B+2*y1+Z20.5)^(23)
Now that all values are defined, solve for y in the following equation: 0=B+ZyyB+ZyyB+2*y1+Z20.523-Q*n/S0.5
Due to the fact that many channels were designed in this project, a manning’s equation worksheet on Excel to solve for Y was created. The 100 year Main Drainage Swale Depth is YMDS=1.00m. For a 5 year storm, Q=4.4675m3/s was used Y5MDS=0.67m
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For a 100 year storm, Q=9.3305m3/s was used Y100MDS=1.00m Now that the water level is found, Figure 4-5 outlines the profile view of the section.
Foot 6m 2.5:1m Unknown: Base Clearance Side (MOE Y Slope 2003)
Figure 4-4 – Swale Design Outline
4.5 Main Drainage Swale Conclusion In conclusion, according design Section 4, The Main Drainage Swale has a 5 year and a 100 year storm rainfall capacity. All excess 28
rain rater from Drainage Area A will be routed towards the Main Drainage Channel by natural slope gravity. The runoff flowing in the Main Drainage Swale will lead into the Wet/Dry pond designed in Section 5.
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Figure 4-5 – Post Development Swale Elevation
Figure 4-6 - Main Drainage Swale Cross sectional Dimensions in
5. End of Pipe Extended Detention Meters
Facilities
(Quantity and Quality Control) Overview A two-cell facility which separates water quality and erosion control from quantity control will be discussed in this section. The quality
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control cell was designed as an artificial wet pond, and the quantity control cell was designed as a dry detention area to receive flows only when quality pond filled. The design criteria for the facility were: •
Quantity/Flood Control The Essex County Conservation Authority requires postdevelopment peak flows to be controlled to pre-development levels for the lands draining to the facility for 5 to 100 year design storm events. Detention must therefore be provided for any increase in post-development run-off. In addition, supplementary flood control storage was incorporated to ensure peak flows further downstream in the Detroit River remained at pre-development levels.
•
Erosion Control 24 hour detention for the runoff from a 25 mm storm was incorporated.
•
Water Quality Storage was based on the 2003 SWMP Manual requirements for enhanced protection including 40 m3/ha of active storage.
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This active storage was in addition to that provided for flood and erosion control.
10 20 30 40 50 5.1 5.1 Water Quantity Control The following subsections cover flow calculations pertaining to the design of the systems. Detailed calculations were enclosed in the Appendix 2 5.1.1 Runoff Computation Rational method was used in determining for the peak flows of both pre-development and post-development along with storage volume. Qpeak = C*i*A /360 Where
Q = Peak Flow (m3 /s) A = Drainage Area (ha)
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i = Average rainfall intensity (mm/hr) for a duration equal to the time of concentration for a particular storm frequency. C = Runoff coefficient (see Table 5.1) 5.1.2 Drainage Area The drainage area to be used in the design should include all those areas which will reasonable or naturally drain to the storm system. The area term in the Rational Method formula represents the total area tributary under consideration. For this proposed site, the drainage area is 63.8965 ha (please refer to main drainage area in Figure 2-4). 5.1.3 Runoff Coefficient As noted in Section 2.1, the runoff coefficients used to determine pre-developed flows are C = 0.34 for 5 year event, and C = 0.47 for 100 year event. For the post-development conditions, as depicted in Figure 5-1, approximately 29 ha of proposed site will be covered in asphalt, with a further 1.7 ha of building area. The remaining 33.2 ha of the site is proposed to be landscaped area. The proposed site has a composite runoff coefficient value of 0.5472 for 5 year and 0.7009 for 100 year (please refer to calculation in Appendix 2) and has an increase runoff potential compared to existing conditions. The final
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drainage area breakdown for the post-development condition, along with their coefficients is shown in Table 5.1. Table 5.1 – Drainage Areas, Land Covers and Runoff Coefficients for Post-development Description
Area (m2)
Area (ha)
Building
16629
Paved Area Landscape
Runoff Coefficient 5 year
100 year
1.6629
0.8
0.97
290083
29.0083
0.77
0.95
332244
33.2244
0.34
0.47
34
35
Under the requirement of City of Windsor, 5 year and up to 100 year storm events are needed to be taken into account. Time of concentration is the time required for flow to reach the pond from the most remote part of the drainage area.
Upland method was used for
Figure 5 -1 – Layout of the Canadian Plaza Crossing Study Website
5.1.4 Rainfall Intensity and Time of Concentration
Source: Detroit River International
determining the time of concentration. As stated in the “Water Resources Engineering” by Larry Mays 2005, upland method is based on defining the time of concentration as a ratio of the hydraulic flow length to the velocity. Tc = L / (3600 * V)
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Where
Tc = time of concentration (hrs) L = hydraulic flow length (ft) V = velocity (ft/s)
The velocity can be estimated by knowing the land use and the slope (see Figure 5-2). From the figure, the velocity is estimated to be 2.75 ft/s for the paved area and 0.5 % slope. The rainfall intensity can be estimated from intensity durationfrequency curve (IDF curve) with specified time of concentration. The IDF curve used for this project was obtained from Atmospheric Environment Service of Canada (See Figure. 5-3). The time of concentration calculated as 35.3 minutes, the rainfall intensity which corresponding to this time is 46 mm/hr and 75 mm/hr for 5 year and 100 year storm event respectively.
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Figure 5.2 –
Velocities for upland method of estimating tc
Source: U.S Department of Agriculture Soil Conservation Service 1986
38
Figure 5.3 – - City of Windsor
Intensity Duration-Frequency Curve (IDF Curves) 39
Source: Environment Canada – Atmospheric Environment Services
40 4.1 5.1.5 Design Details of Proposed Pond
The proposed quantity control pond is indicated on Figure 5-4. The tributary area of the pond will be 63.9 hectares of which 33.2 hectares will be covered by grass. Drainage will enter the pond via a 12m × 9m × 1.5m flow diversion structure (see Section 5.1.6) and via an overland flow swale (see Figure 5-5). The outfall from the channel to the pond shall be modified to prevent erosion by use of large rip-rap placed over filter cloth. Outlet control will be provided by means of a 5.25 m width × 0.4 m height weir placed within the embankment. The pond bottom will be graded at 0.23% to reduce the possibility of ponding during low flow run-off events. The pond invert (175.2m) at the outlet is above the level of the local water table (173.5 m), and the side slope gradient has been reduced to 4:1 to ensure slope stability during water level fluctuations. Inlet areas should be protected to reduce erosion. The 2 m pool benches are important for safety reasons and establishment of emergent vegetation. The proposed pond was calculated into the 5 and 100 year postdevelopment and the results were compared to pre-development peak
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flows. The pre-developed flows are 2.7759 m3/s and 6.2564 m3/s for 5 year and 100 year storm events respectively with an existing runoff coefficient of 0.34 for 5 year and 0.47 for 100 year storm events and a time of concentration of 35.3 minutes. The post-development flows are 4.4675 m3/s and 9.3305 m3/s for 5 year and 100 year storm events respectively with calculated post-development composite runoff coefficient of 0.5472 for 5 year and 0.7009 for 100 year storm events and a time of concentration of 35.3 minutes. Calculations were
41
42
Figure 5-4 – Layout of the ponds and channels
Figure 5-5 – Cross-Section of Overflow Swale – to Quantity Pond
43
enclosed in the Appendix 2. Table 5.2 shows the design parameters and Table 5.3 provides a summary of flows and storage volumes. The maximum water level during the 1:100 storm event will be approximately 176.5m. Maximum water depth will therefore be 1.3 m. The detention storage is
Table 5.2 – Design Parameters
Pre-development
Items Area (ha) Runoff Coefficient
Post-development
5 yr
100 yr
5 yr
100 yr
63.8956
63.8956
63.8956
63.8956
0.34
0.47
0.5472
0.7009
The design events used in the analysis were as follows: •
5 Year City of Windsor Storm
•
100 Year City of Windsor Storm
Time of Concentration:
35.3 minutes
Table 5.3 – Summary of Quantity Volume and Peak Flows
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Storm Events
Peak Flows (m3/s) Storage Volume (m3)
Pre-
Post-
development
development
5 yr
4783.6521
2.7759
4.4675
100 yr
8693.129
6.2564
9.3305
8693.13 m3. Detailed calculations can be found in Appendix 2. An emergency overland outlet from the pond to the adjacent Detroit River will be available at the downstream end of the pond at an invert of 175.2 m. Existing topography at this location will direct pond overflow to the Detroit River.
5.1.6 Flow Diversion Structure A flow splitter or flow diversion structure was used to direct the first fraction of runoff (commonly called the “first flush”) into the quality pond, while bypassing excess flows from 100 year event around the facility into a bypass channel. The bypass then enters to a detention/quantity pond. Runoff water is conveyed to the quality pond via the main open channel. Once the main open channel reaches its 5 year water capacity, water backs up in the channel and into the flow splitter itself. When the water level reaches the bypass elevation, stormwater begins to bypass to the overflow swale and enters to the quantity 45
pond. The bypass is created and controlled by a weir in the flow splitter structure. Bypass Elevation – the elevation of the bypass weir dictates the maximum elevation of the water in the channel. Therefore, the bypass elevation is set to equal to the design water elevation (which is 5 year storm event – 176.42m).
Using this method, the flow will only
start to bypass the weir once the channel has conveyed the design runoff volume. (see Figure 5-6a & 5-6b)
46
Figure 5-6a – Plan View of Flow Diversion Structure
Figure 5-6b – Cross-Section of Flow Diversion Structure
47
5.2 Water Quality Control Design Criteria As indicated on Figure 5-4, the proposed development will discharge into Detroit River. The report entitled “Practical Alternatives Evaluation Working Paper, Natural Heritage” dated July 2007, was conducted to determine potential impacts on vegetation, wildlife, and fish habitat, as well as fishery habitat classification. Information on fish habitat for the receiving watercourses is integrated with the design of stormwater management facilities, as adequate stormwater quality treatment from the proposed development will be required for watercourses with sensitive fishery habitat. From this report, Detroit River is classified as coldwater fish habitat. Design criteria for water quality control features are included in “Stormwater Management Practices Planning and Design Manual 2003” from Ministry of Environment. This manual presents a method for determining the level of water quality. Level 1 protection is the most stringent and involves the highest degree of stormwater quality control, while Level 4 is least stringent. Due to the presence of a cold water fishery, stormwater quality features for this project were designed using the Level 1 criteria.
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Based on the above information, and with reference to Table 3.2 in the “Stormwater Management Practices Planning and Design Manual 2003”, the following criteria apply: •
210 m3/ha of permanent storage (dead storage)
•
40 m3/ha of active storage (live storage)
All storm runoff should be conveyed through an oil/grit separator (OGS) prior to discharge into the stormwater systems to remove suspended solids and oils. The detailed design of OGS will not be discussed in the report. Like the quantity pond, the drainage will enter the pond via a 12m × 9m × 1.5m flow diversion structure and via an overland flow swale (see Figure 5-8). The outfall from the channel to the pond shall be modified to prevent erosion by use of large rip-rap placed over filter cloth. Outlet control will be provided by means of 250mm diameter pipe to quantity pond. The pond bottom will also be graded at 0.23% to reduce the possibility of ponding during low flow run-off events. The pond invert at the outlet is 173.9 and the side slope gradient has been reduced to 4:1 to ensure slope stability during water level fluctuations. Inlet areas should be protected to reduce erosion. The maximum water level during the 5 year storm event will be approximately 175.7m. Maximum water depth will therefore be 1.75 m. The active storage is 2555.824 m3. The permanent pool level is 49
at 175.42m and its storage is 13418.08 m3. Detailed calculations can be found in Appendix 2.
Figure 5–8 – Cross-Section of Overflow Swale- to Quality Pond
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Figure 5.9 – Cross-Section of Quality and Quantity Ponds
5.3 Other Considerations •
The end-of-pipe facility should be designed with a sediment forebay to improve pollutant removal by trapping larger particles near the inlet of the pond. It is important for maintenance and longevity of a stormwater treatment pond. The sediment forebay sizing must be done in accordance with MOE’s guideline 2003 and it should be constructed with a maintenance access route to permit future monitoring and maintenance as well as provide access in the event of an emergency. The forebay should be 1-2m deep to minimize the
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potential for re-suspension and to prevent the conveyance of resuspended material to the pond outlet. The forebay dimensions should be selected to provide maximum dispersion of the inflow to the pond, thereby reducing velocities in the cell. •
Oil/grit Separators (pre-treatment controls) can pre-treat the road runoff prior to discharge to the channel by removing sediments. This, in turn, will minimize any long-term deterioration of the pond function.
•
A landscaping plan for a stormwater pond and its buffer should be prepared to indicate how aquatic and terrestrial areas will be vegetatively stabilized and established. Wherever possible, wetland plants should be encourage in a pond design, either along the aquatic bench, the safety bench and side slopes or within shallow areas of the pool itself
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6 Secondary Drainage Channels Figure 2-2 and 2-3 demonstrates there is a considerable amount of runoff draining around the border crossing plaza site due to the pre existing drainage pattern discussed in Section 2.3. By official standards and law, new construction cannot interfere with the natural flow pattern of neighboring sites. Although runoff must pass through the border crossing site, the runoff does not need to be processed and meet provincial quality standards. This design section will consider all runoff predicted to enter the site from Secondary Drainage Areas B and C, refer to Figure 2-4. Figure 6-1 is an illustrative diagram of the secondary drainage channels and swales of the site which will route the runoff for up to a 100 year storm directly into the Detroit River.
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Figure 6-1 - Secondary Drainage Channels Layout
There will be 4 secondary drainage channel designs: 1. The Minor Drainage Swale represented by P6-P5-P4-P3-P2 will route runoff from Secondary Drainage Area B into Major and Minor Drainage Swale MMDS. 2. The Major Drainage Swale represented by P6-P7-P8-P9-P10P11 will route runoff from Secondary Drainage Area C into the Major Drainage Culvert MajDC. 3. The Major Drainage Culvert represented by P2-P7 will route runoff from MajDS into the Major and Minor Drainage Swale MMDS. The culvert will be placed under ground such that it 54
does not mix with the runoff expected to land on the main border crossing plaza site. The culvert will be underground and incased with cement with a 25 cm thickness. 4. The Major and Minor Drainage Swale represented by P1-P2 will route runoff from MajDC and MinDS into the Detroit River.
Figure 6-2 - Secondary Drainage Channel Outline
6.1 Existing Profiles of Secondary Channels 6.1.1 Minor Drainage Swale MinDS: The line representing P6-P5-P4-P3-P2 will collect the water from Secondary Drainage Area B and route it to point P2. Figure 6-3 is pre
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existing elevation profile of Line P6-P5-P4-P3-P2. This line will represent the Minor Drainage Swale MinDS
Figure 6-3 - Pre existing elevation profile of Line P6-P5-P4-P3-P2, MinDS
6.1.2 Major Drainage Swale MajDS: The line representing P6-P7 will collect the water from Secondary Drainage Area C and route it to point P7 which is the entrance of the 56
major drainage culvert MajDC. In addition to that, the line representing P7-P8-P9-P10-P11 will collect the water from Secondary Drainage Area B and route it to point P7 which is the entrance of the major drainage culvert MajDC as well. Figure 6.4 the pre existing elevation profile of Line P6-P7-P8-P9-P10-P11 which will represent the
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Major Drainage Swale MajDS.
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Figure 6-4 - Pre existing elevation profile of Line P6-P7-P8-P9-P10-P11, MajD
6.1.3 Major Drainage Culvert MajDC: The line representing P2-P7 will collect the water from MajDS and route it to point P2 which is the entrance of the Major and Minor Drainage Swale MMDS. Figure 6.5 is pre existing elevation profile of Line P2-P7 which will represent the Major Drainage Culvert MajDC.
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Figure 6.5 - Pre existing elevation profile of Line P2-P7, MajDC
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Figure 6-6 - Pre existing elevation profile of Line P1-P2, MMDS
6.1.4 Major and Minor Drainage Swale MMDS: The line representing P1-P2 will collect the water from MinDS and MajDC and route it directly into the Detroit River. Figure 6-6 is the pre existing elevation profile of Line P1-P2 which will represent the Major and Minor Drainage Swale MMDS.
6.2 Secondary Drainage Channels Design Constraints As described in the Main Channel Design, the Border crossing plaza area is very flat. Elevation is a primary design consideration. In the
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main channel design section 4.2.1 the Ground Water Table was the elevation constraint, however for the secondary drainage channels, the Detroit River water level is the design constraint. The channel floor must be higher than the highest Detroit water elevation. The highest water level report of the Detroit River is 175.00m. Thus the channel floor cannot be lower than 175.00m. The manning equation parameters will be determined based the River Water Level and slope elevation difference. The design begins by looking at the longest path runoff will have to travel before reaching the river. By investigating Figure 6-1 that path is obviously P11-P10-P9-P8-P7-P2-P1. By combining the elevation profile of MMDS, MajDC and MajDS. Figure 6-7 displays the P11-P10-P9-P8-P7-P2-P1 elevation profile. Figure 6-7 clearly outlines there is a 3.30 meter difference between the highest and the lowest point of the Secondary Drainage Channels. In design it is important to consider that any swale design must have a minimum of a 30.5cm clearance. We will also use a 0.125% slope as the Main Channel Design used this slope. The
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Figure 6.7 - Elevation Profile For P11-P10-P9-P8-P7-P2-P1.
elevation difference due to the slope at 0.125% is 2.16m. Thus the remaining elevation availability for the 100 year storm water level in the swales and culvert is 83.25cm. The 0.125% slope was obtained by optimization using the manning equation excel worksheet displayed in the Appendix 1.
6.3 Secondary Drainage Channels Design using Manning’s equation
The following section will explain the inputs of the Manning’s equation Minor Drainage Swale (MinDS):
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The MinDS will route all the excess rainwater from Minor Secondary Drainage area to MMDS at point P2. The Minor Secondary drainage area was determined to be 77642m2, with 15695m2 paved with concrete (C=0.95) and 619500m2 with grass (C=0.47). The intensity of a 100 year storm is 75mm/h for 35 minutes. By using Rational method (Q=CiA) the resulting flow is 2.3107m3/s. by using approached outlined in Section 4 inputs in the Manning’s equation are as follows: Q=2.3107m3/s, n=0.03, S=0.125%,Z=2.5m, B=6m. After applying Manning’s formula, we solve for y=0.50m. Figure 6-8 outlines the MinDS cross section and Figure 6-9 is the Post Development MinDS Elevation Profile.
Figure 6-8 - MinDS cross section
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Figure 6-9 - Post Development MinDS Elevation Profile
Major Drainage Swale (MajDS): The MajDS will route all the excess rainwater from Major Secondary Drainage area to MMDS, P7. The Major Secondary drainage area was determined to be 434983m2, with 109285m2 paved with concrete (C=0.95) and 325698m2 with grass (C=0.47). The intensity of a 100 year storm is 75mm/h for 35 minutes. By using Rational method (Q=CiA) the resulting flow is 5.3521m3/s. by using approached outlined in Section 4 inputs in the Manning’s equation are as follows: Q=5.3521m3/s, n=0.03, S=0.125%,Z=2.5m, B=6m. After applying Manning’s formula, we solve for y=0.79m Figure 6-10 outlines the MajDS cross section and Figure 6-11 outlines the Post Development MajDS Elevation Profile.
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Figure 6-10 - MajDS cross section
Figure 6-11 -Post Development MajDS Elevation Profile
Major Drainage Culvert (MajDC) The Culvert will route all the excess rainwater from MajDS to the MMDS. The culvert will be designed to go underneath the border crossing plaza’s roads and buildings it will be incased in reinforced concrete with strength able to sustain the weight of the largest truck 66
multiplied by a safety factor of 3. The culvert will be trapezoidal as all of our other channels are trapezoidal: The inputs of the Manning’s equation are as follows:
Figure 6-12 - MajDC cross section
Figure 6-13- Post Development MajDC Elevation Profile
Q=5.3521m3/s, n=0.017 (for Sewer Concrete), S=0.125%, Z=2.5m, B=6m. After applying Manning’s formula, we solve for y=0.52m. 67
Figure 6-12 outlines the MajDC cross section and Figure 6-13 Outlines the Post Development MajDC Elevation Profile. Major and Minor Drainage Swale (MMDS) The Swale will route all the excess rainwater from surrounding sites, P2, to the Detroit River. The flow value is simply the sum of the 100 peak flow for MinDS and the MajDS which is Q=7.6628m3/s. The culvert will be trapezoidal as all of our other channels are trapezoidal: The rest of the inputs of the Manning’s equation are as follows: n=0.03 (for Grass), =0.125%,Z=2.5m, B=8.5m (minimum width given elevation constraints). After applying Manning’s formula, we solve for y=0.68m. Figure 6-14 outlines the MMDS cross section and Figure 6-15 Outlines the Post Development MMDS Elevation Profile.
Figure 6-14- MMDS cross section
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Figure 6-15 - Post Development MMDS Elevation Profile
6.4 Secondary Drainage Conclusion In conclusion, according design Section 6, the secondary storm water channels system has a 100 years rainfall capacity. All excess rain rater from surrounding areas B and C will be routed into the Detroit River by natural slope gravity. According to profile drawings: Figure 6-9, Figure 6-11, Figure 6-13, Figure 6-15 earth filling is minimized.
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7. Conclusions and Recommendations This report adheres to municipal, provincial and federal regulations, such that the development of this site will not result in adverse effects to the downstream conveyance systems. The implementation of the proposed conceptual SWM strategy and measures outlined in this report will ensure that the natural habitat of the area is not disturbed in the long term and that the sediment transported on site does not leave the site but rather is contained within the downstream conveyance systems.
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