appendix l: stormwater quality/ quantity control strategy · 2019-05-21 · appendix l - stormwater...

PREPARED BY

London Bus Rapid Transit Transit Project Assessment ProcessEnvironmental Project Report

March 2019

Appendix L: Stormwater Quality/Quantity Control Strategy

Appendix L - Stormwater Quality/Quantity Control Strategy

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1 Introduction .................................................................. 1-1

2 Watershed Overview .................................................... 2-1

3 Storm Drainage ............................................................. 3-1

3.1 Existing Drainage Systems ................................... 3-1

3.2 Storm Drainage Outlets......................................... 3-1

3.3 Potential Drainage Impacts ................................... 3-2

3.3.1 Hydrologic Changes .......................................... 3-2

3.3.2 Storm Sewer Analysis ....................................... 3-2

3.4 Existing Studies/Areas of Interest ......................... 3-3

3.4.1 Watson Park Storm Outlet Municipal Class EA . 3-3

3.4.2 Mud Creek Subwatershed Class Environmental Assessment ....................................................... 3-3

3.4.3 City Center Servicing Study .............................. 3-3

3.4.4 Richmond Street (North of Thames River) ........ 3-4

3.4.5 Richmond Street (Oxford St to Thames River) .. 3-4

3.4.6 Westminster Ponds ........................................... 3-4

3.5 Summary ............................................................... 3-5

4 Stormwater Management ............................................. 4-1

4.1 Current MECP/City of London Requirements ....... 4-1

4.1.1 Quantity Control: ............................................... 4-2

4.1.2 Quality Control (Protection Level for each Subwatershed) ................................................. 4-2

4.2 Trending MECP Requirements: ............................ 4-3

4.3 Rapid Transit Options Assessment: ...................... 4-4

4.3.1 Quantity Control ................................................ 4-4

4.3.2 Quality Control/Runoff Volume Control: ............ 4-5

4.3.3 Erosion Control: ................................................ 4-6

4.4 Summary/Recommendations/Considerations ....... 4-6

5 Regulated Areas ........................................................... 5-1

5.1 Mud Creek ............................................................ 5-1


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5.2 Westminster Ponds ............................................... 5-1

5.2.1 Background ....................................................... 5-1

5.2.2 Existing Conditions ............................................ 5-2

5.2.3 Proposed Conditions ......................................... 5-2

5.2.4 Summary ........................................................... 5-3

5.3 Park and Ride Facility ........................................... 5-3

5.4 River Crossings ..................................................... 5-4

5.4.1 Structure Summary ........................................... 5-4

Wellington Road Bridge over Thames River (South Branch) .............................................................. 5-4

Queens Avenue Bridge over Thames River (North Branch) .............................................................. 5-5

Kensington Bridge over Thames River (North Branch) 5-5

University Drive Bridge over Thames River (North Branch) .............................................................. 5-5

Western Road over Medway Creek ............................. 5-6

Sediment/Erosion Control ............................................ 5-7

Appendix A – Catchment/Outlet Summary

Appendix B – Westminster Ponds

Appendix C – Source Protection


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1 INTRODUCTION

The City of London has proposed the development of a new bus rapid transit (BRT) system to be constructed along 24 km of existing arterial road corridors.

This report provides a summary and analysis of the existing drainage conditions and impact analysis of the proposed works in existing drainage systems, an analysis of mitigation measures, and recommendations for drainage improvements and the implementation of stormwater management controls.

The scope of this Drainage and Stormwater Management Report includes:

An investigation of the existing stormwater drainage system and identification of potential deficiencies that may result from future BRT development;

An assessment of the potential impact of proposed improvements on Regulatory Flood Plains, watercourses, and watercourse crossing structures; and,

The development of a stormwater management plan for all BRT corridors.


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2 WATERSHED OVERVIEW

The project area is within the jurisdictional boundary of the Upper Thames River Conservation Authority (UTRCA). The BRT alignment is located within the sub-watersheds of Medway Creek (Tributary 1), Dingman Creek (Tributary G), Mud Creek (Tributary 1), Pottersburg Creek (Area 6) and the Central Subwatershed (See Figure 1). The tributaries/areas noted are as referenced in each sub-watershed study.


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3 STORM DRAINAGE

3.1 Existing Drainage Systems

The BRT corridor is heavily urbanized and storm water flows for minor storm events (i.e. typically two year City of London design storm) is managed primarily by the City’s underground piped storm sewer system.

Information regarding the existing drainage system along the BRT corridor was

obtained from City of London records. Storm sewer catchment boundaries were defined using topographic data, sewer plans and existing drainage reports. The delineated catchment boundaries are shown in Figures 2, and 2a to 2e. Figure 2 shows an overview of all catchment areas and Figures 2a to 2e show expanded views of the catchments at a larger scale. A total of 36 discreet catchment areas have been identified along the BRT corridors. These areas range in size from less than 1.0 ha to 274.5 ha. Some of these areas were further divided into sub-catchments in order to identify potential impacts specifically within the BRT right-of-way.

3.2 Storm Drainage Outlets

Figure 1 illustrates the catchment areas along the entire BRT corridor with an arrow indicating the outlet for each area. Most of these areas outlet to existing storm sewer systems that cross the corridor, which in turn outlet directly to the Thames River or a tributary of the Thames River. One exception is the storm outlet to the Westminster Ponds. Currently storm drainage from an isolated section along Wellington Road outlets to the ponds via minor catchbasin outlets and via sheet flow.

It is not expected that new outlets will be required as a result of the BRT, however the outlet to the Westminster Ponds will be modified with a new piped system and the application of treatment measures and modifications to maintain the existing water balance. These proposed works are outlined in Section 5 with catchbasin and outlet details included in Appendix “B”.


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3.3 Potential Drainage Impacts

3.3.1 Hydrologic Changes

The BRT corridor is heavily urbanized and existing land use is comprised primarily of residential and commercial development. The potential for hydrologic impacts exist where the BRT works will result in an increase in impervious area within local storm sewer catchments, however the proposed BRT development is not expected to significantly alter the hydrologic response of the surrounding sub-drainage areas. In general, the BRT modifications will be contained within the existing right-of-way and will result in only a nominal increase in impervious area as compared to the upstream catchment area, including minor road widening along the corridor.

3.3.2 Storm Sewer Analysis

Existing storm sewer capacity was calculated using the Rational Method and based upon existing zoning and right-of-way imperviousness and compared to future flows. Future flows assumed the same existing zoning, however the right-of-way imperviousness was updated to reflect proposed BRT modifications. The two year City of London design storm was used in the analysis.

The analysis included the first run of storm sewer section downstream of the BRT corridors. For the purpose of this study, it was assumed that the existing storm networks from the outlet of BRT corridor were adequate and they were not analysed as part of this exercise. As the incremental increases in flows were minor, any capacity deficiencies in the downstream sewers were deemed to be an existing condition subject to review by others.

From the analysis, it is noted that there are no size replacements directly related to the BRT corridor future impervious (“C”) value. The analysis has shown that the difference in flow is very small or there are other, non-BRT, reasons for replacements such as:

Age;

Storm sewer is already over-capacity;

More flow may be diverted/accounted for from U/S combined sewers;

The City wishes to install a new storm to divert flows to alleviate an U/S outlet issue (i.e. Richmond Street North);

Watson EA, Mud Creek EA and Burbrook area: these areas have current concerns that the City wishes to address;


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Areas where there are no current storm sewers; and

A portion of Wellington Road: currently the east side ditch in the ROW is conveyed elsewhere. The new cross-section will require picking up this drainage in the existing Storm (BRT related).

3.4 Existing Studies/Areas of Interest

Some portions of the storm sewer within the BRT corridor have been included in recently completed studies and Environmental Assessments. Recommendations in these studies are to be incorporated into the final design component of the BRT. In addition, there are some portions of the BRT route that fall within catchments where the City has indicated there are downstream storm issues. Following is a brief summary of studies either recently completed or ongoing by the City of London.

3.4.1 Watson Park Storm Outlet Municipal Class EA

The drainage area for this EA includes Wellington Road from the Thames River to Wilkins Street within the BRT. This study has indicated that a new trunk storm sewer will be required along Wellington Road northerly from approximately Wilkins Street to the Thames River. Water quality control is anticipated to be achieved for the whole of the existing catchment area likely through an end-of-pipe stormwater management facility.

3.4.2 Mud Creek Subwatershed Class Environmental Assessment

Mud Creek crosses the BRT corridor on Oxford Street just east of Proudfoot Lane. Recommendations within the Mud Creek Subwatershed Class Environmental Assessment include the construction of a new larger culvert across Oxford Street West, to convey a realigned Mud Creek. In addition, the existing culvert is to remain in place in order to convey some local upstream drainage.

Recommendations in this report are to be carried forward as part of the detail design of the BRT corridor. Further details are contained in Section 5.

3.4.3 City Center Servicing Study

This report has been prepared by AECOM and covers a portion of the downtown area. This area contains a number of combined sewers, which this study addresses in order to separate into storm and sanitary sewers.


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The study area includes portions of the BRT route on King Street between Richmond Street and Colborne Street; Clarence Street between Dundas Street and King Street; and Wellington Street between Dundas Street and King Street; as well as crossings on King Street at Richmond Street and Wellington Street at York Street.

3.4.4 Richmond Street (North of Thames River)

An existing storm sewer currently flows easterly from the BRT corridor through Masonville Place and the adjacent residential area into Stoney Creek. Due to

existing erosion issues within Stoney Creek, the City of London anticipates constructing a new trunk storm sewer to pick up the existing storm drainage south of Fanshawe Park Road and convey it down Richmond Street to the Thames River. It is anticipated that the existing storm outlet into the Medway Creek will require upsizing or a new outlet to be constructed. This area has not been studied in any detail and it is anticipated that a future study will be required for this new outlet.

3.4.5 Richmond Street (Oxford St to Thames River)

The existing storm sewers in this area consist of a network of small diameter sewers, which are very old, undersized, and are unable to service any anticipated future development growth in this area. Replacement is required due to age and capacity reasons as opposed to BRT construction.

3.4.6 Westminster Ponds

A portion of the south corridor of the BRT route is adjacent to the western portion of the Westminster Ponds. This area is located on Wellington Road just south of Wilkins Street. The Westminster Ponds have been designated as an Environmentally Significant Area (ESA).

Construction of the BRT route along this corridor will create some additional runoff that will have to be considered.

The BRT corridor drainage area currently contributes less than 4% of the minor flows draining into the Westminster Ponds, however the design of the future storm drainage system should take into consideration the water balance within the ponds themselves.

It is proposed to take a portion of the existing minor flows from the future BRT corridor into an oil/grit separator (OGS) and/or other LID measures, and direct these treated flows to the Westminster Ponds in order to maintain the water balance, mainly for runoff volumes. The remainder of the minor flows would be


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directed southerly to an existing 1350 mm storm sewer stub located just north of Southdale Road.

During detail design of the BRT, refined water quality and water balance calculations will be required for approvals.

This area is discussed in further detail in Section 5.

3.5 Summary

In general, it was found that the increase in imperviousness from the construction

of the BRT corridor itself will not affect the existing storm sewers to an extent that replacement will be necessary as a result of capacity issues. This does not include the effects of any further intensification along the corridors or within the storm sewer catchments (i.e. based on existing zoning);

Areas of re-development or intensification along the corridors will be required to implement Stormwater Management (SWM) quantity and quality controls in accordance with City of London standards;

Although storm sewer replacements are not necessary for increased capacity, there will be some areas where storm sewer work will be required as a result of BRT construction as follows:

Storm sewers will require relocation if they are located beneath proposed BRT platforms; and,

New storm sewers will be required in areas that currently do not have any storm sewers and will require them in the future due to the new BRT corridor cross-section. For example, on Wellington Road north of Southdale Road, storm flows currently enter a ditch on the east side of the roadway and flow into the Westminster Ponds. The proposed BRT cross-section will require curb and gutter and a new storm sewer.

Some portions of the storm sewer within the BRT corridor have been included in recently completed studies and Environmental Assessments. Recommendations in these studies are to be incorporated into the final design component of the

BRT. Some of these studies include:

Watson Park Storm Outlet Municipal Class EA (AECOM): Drainage area includes Wellington Road from the Thames River to Wilkins Street within the BRT;

Mud Creek Subwatershed Class Environmental Assessment (September 2017, CH2M Hill Canada Ltd): Study area includes Oxford Street West from east of Wonderland Road to west of Beaverbrook Avenue within the BRT; and,


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City Centre Servicing Study (AECOM): Study area includes portions of the BRT route on King Street between Richmond Street and Colborne Street; Clarence Street between Dundas Street and King Street; and Wellington Street between Dundas Street and King Street; as well as crossings on King Street at Richmond Street and Wellington Street at York Street.

In some areas, replacement of storm sewers is required due to age and capacity reasons, as opposed to BRT construction. It is noted that this is the case along Richmond Street from Oxford Street East to the Thames River and within the older central parts of the BRT corridor downtown.


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4 STORMWATER MANAGEMENT

This section follows from discussions with the City of London regarding the design approach to be applied in the design of stormwater management controls for proposed works within the BRT corridors.

The following provides:

A brief overview of current Ministry of Environment, Conservation and Parks (MECP) and City design standards as they may apply to the subject works;

Anticipated changes to these requirements; and,

Recommendations for the design approach to be taken with respect to the implementation of both stormwater quantity and quality controls for the BRT corridors, to be identified within the current EA.

4.1 Current MECP/City of London Requirements

Provincial guidelines for Stormwater Management in Ontario are provided in the MECP manual, “Stormwater Management Planning and Design Manual”, March 2003 (SMPDD 2003). Further design guidelines can be found within the City of London’s Design Specification and Requirements Manual, as well as individual Subwatershed Studies.

Further to this, in February 2015, the MECP distributed an Interpretation Bulletin regarding expectations for stormwater management. The bulletin noted that going forward, the Ministry expects that stormwater management plans will reflect the findings of watershed, sub-watershed, and environmental management plans, and will employ Low Impact Development (LID) strategies in order to maintain the natural hydrologic cycle to the greatest extent possible.

Stormwater management within existing arterial roadways has become more prevalent since the February 2015 MECP Bulletin. Recent City of London capital projects for road works on arterial roadways include stormwater management controls for water quality and quantity utilizing various strategies such as OGS’s, bioretention cells, inline oversized storm sewers with orifice control, utilizing an existing wet pond SWM facility and dry facility surface detention with surface infiltration.

The SMPDD 2003 recognizes that there can be constraints related to providing SWM measures such as cost, municipal standards and physical constraints such


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as land area. The SMPDD 2003 manual gives the following guidelines with respect to providing quantity/quality and erosion control:

4.1.1 Quantity Control:

Excerpt from: From Section 3.5 of the MECP SWMP 2003 Manual

“Generally, accepted criteria are that maximum peak flow rates must not exceed

pre-development values for storms with return periods ranging from 2 to 100 years.”

Generally this is the same criteria given in the City’s subwatershed studies, with minor exceptions applied on a watershed basis, where some subwatershed areas have tighter controls particularly for the more frequent events.

4.1.2 Quality Control (Protection Level for each Subwatershed):

The SMPDD 2003 gives volumetric water quality criteria based on a 24 hour drawdown time for various SWMP types and levels of protection. Three levels of protection are identified and they are characterized as: enhanced, normal and basic. The application of each level of control is dependent upon the sensitivity of the receiving watercourse into which the storm system outlets.

Each protection level corresponds to an end-of-pipe storage volume required for the long-term average removal of suspended solids given as:

80% removal (enhanced);

70% removal (normal); and,

60% removal (basic).

The volume criteria is intended to cover end-of-pipe solutions such as pond facilities, however it is noted that any SWM strategy that can be demonstrated to meet the required long-term suspended solids removal for the selected protection levels, is deemed acceptable for water quality objectives.

Based on our preliminary analysis, the majority of the Rapid Transit corridors within London will fall within areas requiring a “normal” protection level. One exception would be the Westminster Ponds area, which would likely require an “enhanced” level of protection should there be any increase in the amount of storm discharge directed to the ponds areas.


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4.2 Trending MECP Requirements:

As noted above, as of February 2015, the MECP requires Low Impact Development (LID) strategies in order to maintain the natural hydrologic cycle to the greatest extent possible. Subsequent to this, two documents have been developed for the MECP as follows: "Jurisdictional Scan of Canadian, US and International Stormwater Management Volume Control Criteria Draft Final Report" and, "Runoff Volume Control Targets for Ontario Final Report". The information in these documents, and the public comments on these documents will help inform the content of the MECP’s draft Low Impact Development Stormwater Guidance Manual. The purpose of the LID Guidance Manual, once

finalized, is to clarify the Ministry’s expectations with regard to LID stormwater management, and related runoff volume and water quality control expectations. Similar to the 2003 Stormwater Management Planning and Design Manual, this Guidance Manual will provide the framework for Ministry staff involved in assessing and approving stormwater management proposals.

LID techniques can be applied to reduce the volume of runoff from urban areas and help maintain the hydrologic cycle. A mandatory control hierarchy is expected to be implemented in order to achieve the required amount of runoff volume control as follows:

Control Hierarchy Approach 1 - Retention

The target volume is controlled and not later discharged to the municipal sewer network or surface runoffs and does not become runoff.

Control Hierarchy Approach 2 - LID Volume Capture and Release

The controlled volume is filtered and released to the municipal sewer network or surface waters at a reduced rate and volume (a portion of LID Volume Capture and Release may be infiltrated or evapotranspirated).

Control Hierarchy Approach 3 - Other Volume Detention and Release

The controlled volume is treated and released to the municipal sewer network or surface water at a reduced rate.

Some examples of LID’s within road right-of-ways include the following. These can fall into either Control Hierarchy Approach 1 or 2 depending upon whether there is an overflow outlet to either the municipal sewer network or as surface runoff.

Bioretention (within planters, curb extensions, bioretention units)

Swales (Enhanced grass swales, bioswales)

Perforated pipes

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Prefabricated Modules (precast tree planters, soil support systems, phosphorus removal, proprietary stormwater treatment devices)

Permeable pavement (pervious concrete, porous asphalt, permeable pavers)

Examples of stormwater treatment methods for Control Hierarchy Approach 3 would include technologies which utilize filtration, hydrodynamic separation and/or sedimentation, such as oil/grit separators and end-of-pipe facilities (detention ponds etc).

Such strategies cannot be universally applied effectively - either singularly or in

combination, and their application is largely dependent on the local physical environment. In addition, the current documents giving input to the future LID Guidelines, note a possibility that volume control of the entire corridor may be required to be implemented in the case of full corridor reconstruction. In the case where there is no full reconstruction, it is noted that only the increase in imperviousness may require volume control.

4.3 Rapid Transit Options Assessment:

As noted above, stormwater management within existing arterial roadways has become more prevalent since the February 2015 MECP Bulletin. Recent City of London capital projects for road works on arterial roadways include stormwater management controls for water quality and quantity utilizing various strategies such as OGS’s, bioretention cells, inline oversized storm sewers with orifice control, utilizing an existing wet pond SWM facility and dry facility surface detention with surface infiltration.

4.3.1 Quantity Control

Within the majority of the proposed Rapid Transit corridors, there will only be a nominal increase in imperviousness, which will in-turn result in a nominal increase in peak storm flows, as the majority of the corridors can already be characterized as having a high level of development. In some locations, such as

the fully developed downtown or Old East Village areas, there will be no net increase in impervious areas. In other areas, such as Wharncliffe Road between Oxford Street West and Riverside Drive, no improvements are planned and there will be no increase in imperviousness.

For new large-scale developments, current conventional methods to provide quantity control tend to involve end-of-pipe solutions such as stormwater management ponds. In some site plan developments, oversized pipes or some form of underground storage can be applied. These type of methods can


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sometimes be impractical within a confined right-of-way corridor due to limitations on land area, utility conflicts, cost, and maintenance issues, however they should be implemented where possible when no other alternative is available.

The application of LID strategies within the corridors will help to provide some level of both quantity and quality control and it is expected that going forward, the upcoming Ministry LID guidelines will require the application of these strategies where practical. Given the timing for future rapid transit corridor improvements, the consideration of LID measures should be carried forward for consideration as part of detail design and appropriate cost allowances be included at the preliminary engineering design stage for project cost estimates.

4.3.2 Quality Control/Runoff Volume Control:

As noted previously, the current documents giving input to the future LID Guidelines, note a possibility that volume control of the entire corridor may be required to be implemented in the case of full corridor reconstruction. In the case where there is no full reconstruction, it is noted that only the increase in imperviousness may require volume control.

Design of the reconstructed corridors providing BRT are expected to implement LID measures wherever possible in accordance with the hierarchy noted above in Section 4.2 or in accordance with the MECP and City of London requirements at the time of detail design.

LID measures using Control Hierarchy Approach 1 is the preferred alternative. Many of these measures require an overflow to an existing storm sewer or as surface runoff in which case the Control Hierarchy Approach 2 is achieved. Examples of these types of LID’s are contained in Section 4.2 above.

Once the above measures have been implemented where possible, a Control Hierarchy Approach 3 method can be utilized such as oil/grit separators (OGS’s). Oil and grit separators are generally recognized as providing effective treatment for smaller areas whether used singularly or within a network of facilities, collectively treating areas of up to five hectares. Practical use of oil and grit separators for the provision of water quality treatment within road corridors is

limited by their costs, the physical size of the units, the size of the drainage area and the maintenance costs associated with ongoing cleaning of the units. Notwithstanding these constraints, oil and grit separators remain one of the most practical forms of providing water quality treatment for storm runoff within arterial road corridors.

Given this recent trend by government bodies and agencies to provide a higher level of treatment for all new works, it is recommended that at the EA level and functional design level for the RT corridors, that the assumption be made that a “normal” level of water quality treatment be applied for all BRT reconstruction


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works - regardless of whether there is a net increase in the overall impervious area. It is recommended that the oil and grit separators be designed and sized such that the entire road allowance is treated for quality control. This may require the use of some off-line local storm sewers to collect road drainage only.

There are a number of concerns with the extensive use of oil and grit separators:

a) They are expensive to both install and maintain;

b) They are relatively large devices and it can be challenging to find locations for their installation within spatially challenged road allowances;

c) Efficacy is limited to areas less than 5.0 hectares which increases the concerns raised by items a) and b) above.

Given the above concerns and limitations, it will be necessary to take a strategic approach to the application of quality controls within the RT corridors as it may not always be possible or practical to install the facilities necessary to provide the full level of treatment desired.

End-of-pipe stormwater facilities are another form of Control Hierarchy Approach 3. For example, the EA for the Watson Park Storm Outlet is proposing a SWM pond that will treat the future BRT corridor of Wellington Road south of the Thames River, as well as the remainder of the drainage area.

4.3.3 Erosion Control:

Providing storage with an over-restriction for smaller events is generally not considered practical within road corridors as the land area to provide the volume is not available, nor the practicality of maintaining the system. Once again, the provision of LID’s within the corridors themselves will assist in providing erosion control for the downstream receiving watercourse.

4.4 Summary/Recommendations/Considerations

In all corridors, consideration is to be given to the installation of LID measures wherever feasible in accordance with the latest MECP and City of London requirements and guidelines in order to meet quantity/quality/runoff volume control targets. The implementation of these measures are contingent upon available land area, native soils, capital costs and maintenance costs. A mandatory control hierarchy is expected to be implemented in order to achieve the required amount of runoff volume control as follows:


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1) Control Hierarchy Approach 1 - Retention

2) Control Hierarchy Approach 2 - LID Volume Capture and Release

3) Control Hierarchy Approach 3 - Other Volume Detention and Release

Some examples of LID’s within road right-of-ways include the following. These can fall into either Control Hierarchy Approach 1 or 2 depending upon whether there is an overflow outlet to either the municipal sewer network or as surface runoff.

Bioretention (within planters, curb extensions, bioretention units)

Swales (Enhanced grass swales, bioswales)

Perforated pipes

Prefabricated Modules (precast tree planters, soil support systems, phosphorus removal, proprietary stormwater treatment devices)

Permeable pavement (pervious concrete, porous asphalt, permeable pavers)

Examples of stormwater treatment methods for Control Hierarchy Approach 3 would include technologies which utilize filtration, hydrodynamic separation and/or sedimentation, such as oil/grit separators and end-of-pipe facilities (detention ponds etc.).

Areas adjacent to and tributary to local storm sewers within the BRT corridor would be expected to provide their own quality and quantity treatment as development or re-development occurs.

The appropriate cost allowances be included in the cost estimates for rapid transit corridor improvements to account for the application of the measures recommended in this memo.

The actual design of both stormwater quality and quantity controls to be applied within the corridors will be determined during the final design stage of the project.


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5 REGULATED AREAS

5.1 Mud Creek

The Mud Creek Subwatershed Class Environmental Assessment was completed in September 2017, as prepared by CH2M Hill Canada Ltd. The study area for this EA includes Oxford Street West from east of Wonderland Road to west of Beaverbrook Avenue within the BRT network.

Recommendations within this report include the construction of a new larger culvert across Oxford Street West, to convey a realigned Mud Creek, which will assist in decreasing the upstream floodlines. The existing culvert is to remain in place in order to convey some local upstream drainage.

Recommendations in this report are to be carried forward as part of the detail design of the BRT corridor.

5.2 Westminster Ponds

5.2.1 Background

A portion of the south corridor of the BRT route is adjacent to the western portion of the Westminster Ponds. This area is located on Wellington Road just south of Wilkins Street. The Westminster Ponds have been designated as an Environmentally Significant Area (ESA).

Construction of the BRT route along this corridor will require the construction of curbs and gutters, sidewalks and some asphalt widening of the corridor. This will create additional runoff that will have to be considered. A meeting with the Upper Thames River Conservation Authority (UTRCA) on November 23, 2016 confirmed that they will require consideration be made to the water balance within the Westminster Ponds area. Environmental aspects will be discussed

under separate cover by others.

Minor flows consist of runoff from more frequent storm events, generally less than the City of London two year design storm, that is collected by storm sewers and ditches and flow to an outlet. Major flows consist of runoff from larger, less frequent storm events that the minor system cannot handle. In this circumstance, runoff then flows overland to an outlet point.


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5.2.2 Existing Conditions

Figure ST-01 in Appendix B shows three ponds within the Westminster Ponds area along with their associated drainage areas, Spettigue Pond, Tumbleson Pond and Saunders Pond. The total drainage area is approximately 121 ha. Existing drainage conditions are also shown on this figure. Currently there is a 4.27 ha drainage area (Area A) consisting of Wellington Road itself, as well as the fronting commercial properties to the west draining both major and minor flows directly into the Saunders Pond. These flows are directed either directly into the ponds by ditches or into catchbasins that outlet directly into the Saunders Pond at a low point in the Wellington Road profile. In addition, there is a 2.68 ha residential area (Area B) directly west of this in which only the major flows are directed to Saunders Pond. Minor flows from this area are directed northerly and then westerly within an existing storm sewer. Therefore the external drainage area contributing to the Westminster Ponds, by the Wellington Road corridor and west, consist of approximately 3.5% of the minor flow and 5.7% of the major flows to the Westminster Ponds.

5.2.3 Proposed Conditions

The option of directing the minor storm flows from the proposed BRT corridor to an existing 1350 mm storm stub located just north of Southdale Road was examined. This existing 1350 mm storm sewer has the capacity to take in these additional flows. A water balance calculation indicates that this option will decrease the overall runoff conveyed to the Westminster Ponds themselves by just less than 20%. Therefore a strategy is required in order to maintain the water balance as closely as possible to existing conditions.

It is proposed to convey a portion of these minor flows to an oil/grit separator (OGS) and/or other Low Impact Development (LID) measures, which will then convey these treated minor flows toward the Ponds. The remainder of the minor flows will be directed to the existing 1350 mm storm sewer located north of Southdale Road.

Figure ST-02 in Appendix B shows the proposed drainage conditions. Area A has been split into Area A1 and A2. Area A1 (approximately 3.77 ha) has both major and minor flows directed to the Westminster Ponds after some quality treatment with an OGS. Area A2 (approximately 0.50 ha) will have minor flows directed southerly towards the existing 1350 mm storm sewer and major flows will continue to flow into the Westminster Ponds.

Preliminary water balance calculations indicate that this approximate split in flows will mimic existing runoff volume amounts to the Westminster Ponds. Infiltration will decrease somewhat (less than 1.5%), however in the report “Master Plan Update 2005, Westminster Ponds/Pond Mills Environmentally Significant Area”, it


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is noted in Section 3.4.2 (Groundwater), that the “Saunders, Spettigue and Tumbleson Ponds are underlain by Port Stanley Till, which is characterized by low permeability silty clay and clayey silt till soils, resulting in a relatively slow flow of groundwater between the ponds (Gartner Lee Ltd. and Monteith Zelinka Ltd. 1993). As a result, the wetland ecosystems between the ponds are maintained primarily by surface water flow rather than by high groundwater flow rates and restricted outlet conditions, virtually all runoff becomes pond storage." Therefore infiltration is not as large of a concern.

It is recognized that water quality treatment from an OGS does not address salts, however it is noted that currently salts are directly being introduced with the

current drainage pattern and plant life in the area has adapted, therefore there will be no net increase in this effect.

Preliminary water balance calculations were performed to confirm the above. During detail design of the BRT, more refined water quality and water balance calculations will be required for approvals.

5.2.4 Summary

The BRT corridor drainage area currently contributes less than 4% of the minor flows draining into the Westminster Ponds, however the design of the future storm drainage system should take into consideration the water balance within the ponds themselves.

Current storm drainage entering the ponds from the proposed BRT corridor and westerly consist of approximately 4.27 ha of minor flows and a total of 6.95 ha of major flow area as shown on Figure ST-01. This accounts for approximately 3.5% of the minor flow and 5.7% of the major flows to the Westminster Ponds.

It is proposed to take a portion (approximately 88%) of the existing minor flows from the future BRT corridor into an OGS and direct these treated flows to the Westminster Ponds in order to maintain the water balance, mainly for runoff volumes. The remainder of the minor flows would be directed southerly to an existing 1350 mm storm sewer stub located just north of Southdale Road. Figure ST-02 shows the proposed drainage conditions.

Preliminary water balance calculations were performed to confirm the above. During detail design of the BRT, more refined water quality and water balance calculations will be required for approvals.

5.3 Park and Ride Facility

A Park and Ride facility is being considered south of Exeter Road and east of Wellington Road South. It would be located between the existing OPP station


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and the Hydro One corridor. The Murray Drain is adjacent to the south side of this area which is located within the Dingman Creek Subwatershed.

Discussions with the Upper Thames River Conservation Authority (UTRCA) have noted that this area is within the floodplain. Detailed hydraulic/hydrologic modelling is required to better determine the floodfringe in this area and if a reduction in the floodplain at this site may be possible by addressing a flow restriction associated with an undersized culvert crossing Wellington Road just downstream. Any design of the Park and Ride facility would need to comply with the UTRCA’s most current policies on floodfringe development.

Low Impact Development (LID) technologies are to be considered to address

stormwater flows from the paved parking lot prior to discharge to the Murray Drain. The design is to comply with the latest Dingman Creek Subwatershed Study requirements as well as MECP guidelines.

5.4 River Crossings

Some existing structures over the Thames River and Medway Creek will be affected as part of the Bus Rapid Transit (BRT) project. The following memo provides a technical civil engineering summary of these five structures located within the BRT corridors.

5.4.1 Structure Summary

Wellington Road Bridge over Thames River (South Branch)

The existing bridge structure over the Thames River on Wellington Street is within the proposed Bus Rapid Transit (BRT) route. This existing structure is to be maintained. A widening of approximately 8.4 meters is proposed to the east including the extension of the deck and piers, therefore in-stream work is required. The existing piers are founded on piles.

In addition, the existing pathway requires reconfiguration at the northeast

quadrant of the bridge to accommodate the widening and to meet AODA requirements. This may also mean lowering of the pathway with nominal hydraulic effects.

Existing hydraulic (Hec-Ras) modelling was obtained from the Upper Thames River Conservation Authority (UTRCA) for the Thames River floodlines in this area. The Wellington Bridge is located at Section 2370 within this model. The bridge data at this section was modified to include the preliminary data for the proposed widening of this bridge deck and piers. The modelling confirmed that there are minimal effects on the floodlines for the 250 year storm event (0.01 m


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increase). This does not consider the reconnection of the multi-use pathway, however, in general, if the pathway revisions are not increasing the amount of fill in the floodplain, there should be also minimal, if any, effects on the floodlines and flow conveyance. It is noted that the limited upstream area affected by the small increase in the 250 year floodline is mainly contained within the steeper undeveloped bank portions of the Thames River with little to no lateral spread. This does not create any further safety concerns during flood events above what already exists in the area. It is noted also that the modelling performed for this study is very preliminary in nature in order to get a general idea of the floodline effects with the bridge modifications. More in depth modelling will be required during the detail design of the bridge where it may even be possible to have a zero effect to the floodlines. Ultimately a submission will be required, as part of detail design, to the UTRCA in order to confirm that their Riverine Flooding Hazard Policies are met.

Queens Avenue Bridge over Thames River (North Branch)

The Queens Avenue Bridge is also within the proposed BRT route. There are no instream works proposed at this location. A very small widening (less than 0.5 m) is proposed on the north side of this structure. This can be accommodated by widening the deck only. No pier work is anticipated.

Due to the minor nature of this work, it is anticipated that there will be little to no effect on the flow conveyance/existing floodlines within this area, therefore no preliminary modelling was produced for this proposed work.

Kensington Bridge over Thames River (North Branch)

The Kensington Bridge is located just south of the Queens Avenue Bridge and links Riverside Drive to Dundas Street. There are no works planned for this structure as part of the BRT project.

University Drive Bridge over Thames River (North Branch)

The University Drive Bridge is located on University Drive within the Western University Campus and crosses over the North Branch of the Thames River. This structure is to be completely replaced with both a wider span and a wider width. This will require in-water construction activities. The proposed bridge will have a span of approximately 109 m and a total width of 21.5 m as compared to the existing span of approximately 90 m and a width of 12 m. The proposed bridge will have two piers constructed in a different location than the existing two piers.


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It is noted that another consultant is currently updating the floodlines through the University using a 2D model. As access to this model is unavailable, we have utilized the most current HecRas model obtained from the UTRCA for this branch of the Thames River. The University Bridge is located at Section 3910 within this model. The bridge data at this section was modified to include the preliminary data for the proposed new bridge deck and piers. The modelling confirmed that there are minimal effects on the floodlines for the 250 year storm event (0.02 m decrease).

It was noted by the UTRCA that there is a sizable restriction on the Thames River at this location. It has been determined that the existing bridge is not the

full cause of this restriction. The valley itself in this area is providing a restriction for upstream and causing backwater effects. As noted in the modelling, the replacement of the bridge itself will not help reduce the upstream floodlines substantially. The new structure will have a minimal positive effect on the 250 year floodlines by decreasing the floodline elevations in the immediate area upstream of the structure.

Western Road over Medway Creek

This bridge is located on Western Road immediately south of Windermere Road and crosses over the Medway Creek. This existing structure, approximately 24 m in width, is to be maintained. A widening of approximately 14 m is proposed to the east including the extension of the deck, abutment and pier, therefore in-stream work is required.

The City has some existing preliminary hydraulic (Hec-Ras) modelling (not yet completed/adopted) for the Medway Creek floodlines in this area. Without updating this incomplete model, it is anticipated that there will be minimal effects on the floodlines for the 250 year storm event (same as the Wellington Bridge). . It is noted that the limited upstream area affected by any small increase in the 250 year floodline is mainly contained within the steeper undeveloped bank portions of the Thames River with little to no lateral spread, however there are some small parking lots already within the floodway that may have some minor effects. It is felt that this does not create any further safety concerns during flood events above what already exists in the area. Detail design of the bridge will need to either ensure no impact to flood elevations or that any impact is minimal enough that there is no adverse result. Ultimately a submission will be required, as part of detail design, to the UTRCA in order to confirm that their Riverine Flooding Hazard Policies are met.


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Sediment/Erosion Control

As part of the future detail design of any work within regulated areas, such as encroachments or bridge replacements / widenings, a sediment and erosion control (SEC) plan will need to be developed/approved and included as part of the construction drawing set in accordance with the City of London’s Sediment and Erosion Control Requirements outlined in their Design Specifications & Requirements Manual. These guidelines rely on the Ministry of Natural Resources Guidelines on erosion and sediment control for urban construction sites.

The following brief summary gives some examples of what this plan will need to consider:

Construction within and in close proximity of an open watercourse: Construction along the banks of the river will require measures such as silt fencing, erosion control blanket and best practices such as prompt reseeding in order to prevent the migration of sediment into the watercourse. Construction within the watercourse itself will require isolation of the construction with coffer dams or similar methods to prevent any sediment from entering into the watercourse. Refueling and cleaning of equipment is to occur away from the watercourse;

Construction within close proximity to natural areas: These areas should be delineated by construction fencing to prevent construction equipment from entering and disturbing any existing vegetation, animal species or other natural items that are to be protected;

Monitoring: During construction the site is to be monitored regularly and before/after significant rainfall events to ensure that SEC measures are in place and maintained properly. Any failures of SEC measures are to be reported and rectified in short order;

Contingency plan: the purpose of the contingency plan is to minimize the risk or consequence of failure of the sediment and erosion control works. The plan should include such items as:

o Any emergency contact list for emergency situations, including the design consultant, the City of London, and MECP;

o Items such as silt fence, straw bales and stakes, sandbags, appropriate sized rip-rap, and clean gravel fill should be available for emergency installation;

o Gas powered pumps, appropriate sized hoses, filtration socks and filtercloth should be available for emergency dewatering;

o Heavy equipment should be on standby for emergency works; and,


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o Fuel spill equipment should be available for emergency spills of deleterious substances.

A contact list for any further required equipment or materials should be prepared and made available for emergency use.

appendix l: stormwater quality/ quantity control strategy · 2019-05-21 · appendix l - stormwater...

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