Town of Whitby Town-wide Urban Flooding Study

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Project Information for Public Consultation

• Included is information to provide you with an overview of the Project scope and draft results of the Study.

• Also included is a comment form for your feedback.

• If you have any questions, please contact us through the email or phone number listed at the end of the display panels.

Background

• The Town of Whitby (the Town) is currently undergoing rapid population and economic growth. Growth rates of over 40% are projected by 2031, driven by the Highway 407 extension and construction of the West Durham Line from Highway 407 to 401.

Town of Whitby Town-wide Urban Flooding Study2

• Flood risks throughout the Town, based on existing conditions and infrastructure, must be thoroughly assessed in order to support safe and efficient development, protective of important natural and cultural resources and in consideration of changing climate trends.

• The existing stormwater sewer system is comprised of:

o 7,561 manholes

±

LegendStorm pipes greater than 525 mm

Main Road

Lake

Ridg

e Rd N

Ashb

urn Rd

Thick

son R

d N

Ande

rson S

t

Baldw

in St

N

Highw

ay 41

2 S

Highw

ay 41

2 N

Myrtle Rd W

Highway 407 E Highway 407 W

Townline Rd W

Brawley Rd W

Broc

k St N

Baldw

in St

S

Columbus Rd W

Victoria St E

Dundas St E

Victoria St W Thick

son R

d S

Brock

St S

Dundas St W

Taunton Rd E

Winchester Rd W

Taunton Rd W

Highway 401 E

Rossland Rd E

Lake

Ridg

e Rd S

Rossland Rd W

Henry

St

Consumers Dr

Coch

rane S

t

Hopk

ins St

Columbus Rd E

Baldwin S

t

Myrtle Rd E

Wentworth St

Champlain Ave

Townline Rd E

Brawley Rd E

o 12,513 catch basins

o 7,884 stormwater pipes

o 43 stormwater ponds

Flooding Issues Identified Through Previous Studies

Known issues have previously been reported or identified through the following studies:• 1986 Town of Whitby Stormwater Flooding Study

Identified areas where basement flooding and/or stormwater entry was reported. Recommendations included the installation of storm sewers, reconstruction of select areas to include local storm sewer systems and erosion protection.

• 1994 Downtown Storm Sewer StudyEvaluated existing sewer system in the downtown area to establish a program for addressing deficiencies and developing future design criteria. Recommendations include construction of a stormwater detention facility, initiation of a Sewer Improvement Program and sewer replacements.

• 2003 Annes Street Stormwater Infrastructure Analysis Report

Identified backwater effects and a low lying area in Michael Boulevard and Carter Crescent intersection as storm sewer system constraints. The study recommended inlet control devices, park catch basins, a relief storm sewer on Michael Boulevard, orifice controls and storm sewer upgrades or twinning.

• 2008 Summer Flooding Assessment for Study Area 3Investigated basement and surface flooding along Kilbride Drive, Cahill Court and O’Malley Crescent and portions of Anderson Street. Mitigation measures (e.g., ditch relocation, inlet control devices) to address flooding problems were recommended.

3 Town of Whitby Town-wide Urban Flooding Study

Flooding Issues Identified Through Previous Studies

2008 Whitby/Brooklin Flooding Assessment

• Analyzed two extreme rainfall events that occurred onJuly 19th and August 11th, 2008, producing anextreme storm event based on the following factors.

1. The storm on July 23, 2008 and on August 11, 2008exceeded the storm intensities 1 in a 50-year storm(frequency of occurrence, based on historical records, of1 in 50 years); and

2. Antecedent moisture conditions caused by earlier rainfallhad saturated the ground and prevented the normalinfiltration and resulted in:o creeks flowed at consistently high rates

o exceeded the capacity of the underground storm systems

o overwhelmed the overland drainage system.

o several reports of basement flooding

• The Town completed the assessment and implemented thefollowing measures to minimize basement flooding:

o mapped the Towns overland flow routes and installedinlet control devices on 250 catch basins

o improved overland flow routes to minimize road flooding(e.g., Anderson Street, Kilbride Drive)

o upsized surcharged pipes (e.g., Lupin Drive, HickoryStreet)

o developed a storm sewer model for the entire stormsewer network to evaluate the performance of thestormwater system

Town of Whitby Town-wide Urban Flooding Study4

Problem / Opportunity Statement

Study Purpose / Problem Statement• The Town has initiated a Town-wide Urban Flooding

Study to evaluate the Town's urban storm sewer and overland flow network’s existing capacity, and to determine flood-vulnerable areas during severe rainfall. This study will also provide the Town with a quantitative understanding of climate change impacts on the existing stormwater system. This study covers the entire urban stormwater system of the Town.

Project Objectives• The assessment will include recommendations for

hydraulic capacity improvements that are needed to meet the Town’s design standards, as well as recommendations for future Town flood mitigation projects.

• The study will develop comprehensive flooding remediation plan.

• The study will follow the guidance outlined in the Municipal Class EA document (as amended in 2007, 2011, and 2015) for the Schedule B Environmental Assessment Act.

Town of Whitby Town-wide Urban Flooding Study5

Natural Environment Conditions

• An extensive background review of the natural environment conditions within the StudyArea was conducted for the Bridge and Culverts Master Plan – Hydraulic CapacityAssessments study by reviewing the following documents:o Pringle Creek Master Drainage Plan Update (Town and Central Lake Ontario Conservation

Authority [CLOCA] 2018)

o Lynde Creek Master Drainage Plan (Town and CLOCA 2019)

o Municipal Structure Inspection Reports – OSIM (Town 2017)

o Flood Damage Centres Upgrading (CLOCA 2017)

o Lynde Creek Watershed Plan (CLOCA 2017)

o Lynde Creek Watershed Existing Conditions Report (CLOCA 2008)

o Town of Whitby Design Criteria and Engineering Standards (2018)

Town of Whitby Town-wide Urban Flooding Study

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• The background reports will be used to develop environmental opportunities andconstraints for the construction and implementation phase.

• Redside dace are present in section of Lynde Creek; however, no instream habitatwill be disturbed during the implementation of alternatives.

• Opportunities to improve natural environment conditions should be consideredduring the detailed design phase of the Study and may include: avoidingconstruction during the migratory bird period, reducing disturbance to vegetation,and avoiding disturbance to watercourses and wetlands.

• It is anticipated that routine construction work associated with infrastructureimprovements will be temporary.

Overview of the MEA EA Process

Town of Whitby Town-wide Urban Flooding Study7

• Identify the problem or opportunity

• Public consultationto review the problem or opportunity statement

• Notice of Project Commencement issued August 1, 2019

• Identify alternative solutions to the problem or opportunity

• Inventory the natural, social and economic environment

• Identify the impact alternative solutions may have on the environment and associated mitigationmeasures

• Evaluate alternative solutions

We are here: Public Consultation

• Select the preferred solution

• Identify alternative design concepts for the preferred solution

• Provide a detailed inventory of the natural, social and economic environment

• Identify the impact of alternative designs andassociated mitigation measures

• Evaluate alternative designs and a recommended design

• Consult review agencies and public stakeholders

• Select a preferred design

• Complete and Environmental Study Report to be placed on the public record

• Notice of Project Completion sent

• Design, construct and monitor

Phase 5: Implementation

30-Day Review

Phase 4: Environmental Study Report

Phase 3: Alternative Design Concepts

Phase 2: Alternative Solutions

Phase 1: Problem or Opportunity

Existing Flooding Conditions

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• 14% of the storm sewer pipes are 100% surcharging under a 5-year storm event of 6-hour duration with 20 minute time interval

• Some surcharged pipes have been verified by flooding reports for August 11, 2008 storm event (comparable to 5-year storm)

‒Annes Street and Reglan Street

Existing Conditions Storm Sewer Performance

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• Area of the Town selected for dual drainage analysis for detailed review is based on the existing sewer system lying within one of the Town’s oldest neighborhoods and not meeting the Town’s design level of service. Flooding was also reported in the study area for August 11, 2008 storm event further validating the sewer system capacity issue.

• Past modelling shows approximately 50% of sewers surcharging, and it was determined that storm hyetographs need to be re-evaluated along with any issues associated with the model.

• Existing storm sewer System Performance Under 100-Year Storm of 6 hour duration with 20 minute interval

o Basement level assumed to be 2 m below ground surface

o Level of service: Water level in maintenance holes below basement level. In case of shallow sewers with less than 2 m cover depth, no surcharge of maintenance holes or free flow conditions in sewers

o 68% maintenance holes meeting required level of service

o Indicates pipe is free flowing; however, the pipe is less than 2 m below ground surface.

o Indicates pipe is surcharged 100%, however, the water level in the pipe is more than 2 m below ground surface.

Town of Whitby Town-wide Urban Flooding Study

Identified Alternatives

Alternative No. 1: Do-NothingThis alternative would see the urban storm sewer and overland flow network maintain existing capacity, flood-vulnerable areas will remain during severe rainfall.

Alternative No. 2: Inlet Control Devices and Catch BasinsThis alternative would control stormwater flow into storm sewers. Inlet Control Devices and Catch Basins restrict stormwater from major systems (e.g., roads, ditches) getting into the minor systems (e.g., pipes). Inlet Control Devices are specifically designed to limit flow into storm sewers during peak flow events and storing the excess aboveground, reducing surcharges in the storm sewer pipes that may lead to flooding.

Alternative No. 3: Enlarged PipesThis alternative would capture stormwater in large-diameter, interconnected storm sewer pipes. Water is released through an outlet pipe designed to reduce peak water flows during severe rainfall.

Town of Whitby Town-wide Urban Flooding Study10

Identified Alternatives

Town of Whitby Town-wide Urban Flooding Study11

This alternative includes green infrastructure to capture, reduce or slow down stormwater before it reaches the sewer system and can include the beneficial use of rain water. Examples include:

• Incorporating natural vegetation surfaces into streets and adjacent impervious land features to absorb stormwater

• Replacing parking lots with porous pavement to promote infiltration

• Vegetated rooftops to capture stormwater

• Rainwater storage for beneficial re-use (e.g., irrigation)

• Capturing stormwater underground

This alternative would capture stormwater from surrounding areas in a series of underground pipes. Stored water is then released through an outlet pipe or diversion designed to reduce peak stormwater flows to storm sewers.

Alternative No. 4: Low Impact Development/Green Infrastructure

Alternative No. 5: Additional Pipe Storage

Identified Alternatives

Town of Whitby Town-wide Urban Flooding Study12

Alternative No. 6: Lot/Source Control

Alternative No. 7: Stormwater Management Ponds

This alternative would include the implementation of lot controls such as:

• downspout disconnection to reduce inflow to the storm sewers (e.g., downspout disconnection programs)

• on-lot infiltration of stormwater

• reduction of impervious areas (e.g., driveways) to promote more infiltration

This alternative includes a stormwater pond to collect stormwater that runs over impermeable surfaces such as parking lots and roads.

Surface flow path

diversion

Disconnecting downspouts

Alternatives Evaluation Framework

Alternative flood mitigation measures have been evaluated based on their ability to address the Study’s purpose, stakeholder input, and their potential impacts. Criteria used in the evaluation include:

Town of Whitby Town-wide Urban Flooding Study13

Natural Environment• Surface Water Quality• Terrestrial Habitat• Aquatic Habitat• Groundwater Quality

Technical• Flood Control• Conveyance Control• Constructability,

Implementation and Work Scope

• Operations and Maintenance

• Compatibility with Development and Growth

• Compatibility with existing and planned infrastructure

Socio-Cultural• Public Health and

Safety• Occupational

health and Safety• Public Lands Use

Impacts• Archeological and

Cultural Resources• First Nations

Communities• Public Disruption

Cost• Capital Costs• Operations and

Maintenance Costs

• Life-Cycle Costs

Recommended Flood Control Alternatives

Alternative Flood Mitigation Measures Evaluation(a)

Criteria Categories Do-Nothing

Inlet Control Devices and Catch

basins

Enlarged Pipes

Low Impact Development/Green

Infrastructure

Additional Pipe Storage

Lot/Source Controls

StormwatManagem

Ponds

Environmental Fail Pass Pass Pass Pass Pass Pass

Technical Fail Pass Pass Pass Pass Pass Fail

Social/Cultural Fail Pass Pass Pass Pass Pass Pass

Economic Pass Pass Pass Pass Pass Pass Pass

er ent

Note (a): Alternative must "PASS" in all Criteria Categories to be recommended as a preferred option for flood management

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Town of Whitby Town-wide Urban Flooding Study

Future Storm Sewer Performance with the Preliminary Preferred Alternatives

Preferred Alternativeso A combination of enlarged pipes, inline

storage, and inlet capacity modifications.

Performance Under 100-Year Design Storm of 6 hour duration with 20 minute interval

o Basement level assumed to be 2 m below ground surface

o Level of service: Water level in maintenance holes below basement level. In case of shallow sewers with less than 2 m cover depth, no surcharge of maintenance holes or free flow conditions in sewers

o 92% maintenance holes meeting required level of service

o Indicates pipe is free flowing; however, the pipe is less than 2 m below ground surface

o Indicates pipe is surcharged, however, the water level in the pipe is more than 2 m below ground surface

o Detailed investigation is required to finalize the preliminary preferred alternatives.

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Next Steps

Next Steps in the EA Process include:1. Provide final recommendations for hydraulic

capacity improvements and future Town flood mitigation projects (March 2020)

2. Complete the Schedule B Project File Report (March 2020)

3. Issue the Notice of Completion and Post the Project File (Environmental Study Report) for 30-day public review (April 2020)

4. Finalize the Study after the 30 day review is complete (May 2020)

5. Implementation Phase (schedule still to be finalized)• Detailed design• Natural environment and Archeological/cultural

heritage surveys, as needed• Permit approvals• Construction of recommended measures

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Thank you for participating!

Your questions and comments are important and we value your input.

Please fill out the comment sheet available online at https://www.whitby.ca/en/townhall/currentstudies.aspand email a copy of the comment sheet or list your answers in an email to either of the Project team members listed below by April 10, 2020.

If you have any questions or concerns about this study, please feel free to contact any member of the Project team, including:

Town of Whitby Town-wide Urban Flooding Study17

Tom Mahood, P. Eng.Project ManagerJacobs Engineering Group72 Victoria St. S, Suite 300Kitchener, ON N2G 4Y9519-579-3500 x73241Tom.Mahood@jacobs.com

Antony Manoharan, P.Eng.Water Resources Engineer, Program ManagerTown of Whitby575 Rossland Road EastWhitby, ON L1N 2M8905-430-4925manoharana@whitby.ca