Welcome

Investigation of Basement Flooding and Stormwater Runoff Quality Control

Study Areas 21 & 23

Public Information Centre #1

View displays and discuss the study with project staff

Feel free to ask questions and fill out a comment sheet

Purpose of Tonight’s Meeting

• To introduce the problem and study approach • To outline potential factors contributing to surface and/or basement

flooding and stormwater runoff pollution • Present possible alternative solutions and criteria for evaluating the

alternatives • Outline the next steps in the study process • Hear from you! Your input is very important.

Purpose of Our Study

• Examine existing stormwater drainage and sanitary sewer systems to identify the causes of basement flooding and/or surface flooding (severe ponding on streets during extreme storms).

• Assess control measures to improve the quality of stormwater surface runoff as per the City’s Wet Weather Flow Master Plan.

• Make recommendations to: – Reduce the risk of future flooding – Improve the quality of stormwater runoff

before it is discharged to watercourses.

Study Area

• Study Area is made up of two Basement Flooding Areas; 21 & 23.

• Study Area is based on the tributary drainage areas for the sanitary and storm sewer system.

• The City must meet the requirements of Ontario’s Environmental Assessment (EA) Act for infrastructure projects.

• This project requires completion of Phases 1 and 2 of the Class EA process as set out by the Municipal Engineers Association. We are currently in the early stages of Phase 2.

• The EA process is an opportunity for the public and agencies to provide input. Consultation is facilitated via two rounds of Public Information Centres (PICs).

Municipal Class Environmental Assessment Process

PHASE 1 PHASE 2

Problem Or Opportunity

Alternative Solutions

Submit Project File for 30 Day

Review

Project Completion

We are here

PIC #1 & PIC #2

Incorporate Comments

Municipal Class EA Planning and Design Process

Note: This flow chart is meant to be read in conjunction with Part A of the Municipal Class EA

Many steps are involved in the study before solutions can be recommended. This work includes: • Collect and review background data on land use, population, soil conditions, sanitary

sewer and storm drainage systems, flooding history, and operation/maintenance records; • Conduct field surveys to inventory the number of roof leaders disconnected, survey

catchbasins, identify low lying areas, and inventory storm sewer outfalls; • Develop computer models to:

– Analyze the causes of flooding and to predict flows under various weather conditions; – Assess the impacts of stormwater runoff on water quality in receiving watercourses;

• Develop and receive feedback on potential alternatives to address the issue of flooding in each basement flooding area and improve stormwater runoff water quality before it is discharged to the receiving watercourses (1st Public Information Centre);

• Undertake assessment and refinement of alternatives; and • Present recommended alternative (at 2nd Public Information Centre) and finalize the study

recommendations based on input from the public and review agencies.

Investigating Basement Flooding: The Steps Involved

We Are

Here

Stormwater Pollution: The Problem

• Urbanization has altered the pathways through which stormwater finds its way back to rivers and lakes.

• Stormwater collects oil, dirt, pet waste and other pollutants and carries them to rivers and lakes.

• This results in degraded water quality as well as: • Impacts on fisheries and aquatic

habitat • Reduced recreational use and

aesthetics.

Under normal rainfall events, the storm and sanitary sewer systems operate as designed. However, during extreme storms, the following takes place: • Stormwater flow exceeds the storm sewer capacity and overloads the

system. • Directly connected roof drains, especially flat roofs, contribute significant

volumes to the sewer system. • Water remains on the surface and flows

overland along roads. • At low lying areas, water accumulates (ponds)

and enters the sanitary sewer system through manhole covers. This causes the sanitary sewers to surcharge and potentially back-up into basements.

Potential Basement Flooding Factors

During these heavy rainfalls, the ground becomes extremely wet and water enters the sanitary system through cracks or broken pipes, cracked maintenance hole walls and loose joints underground. This contributes to back-up of the sanitary sewers. Other factors related to sanitary sewer back-up include: • Shallow groundwater table intersecting the sanitary sewer • Downspouts connected to the sanitary system through weeping tiles • Water entering the basement from the surface via window sills and reverse-

slope driveways etc. and then through basement floor drains (connected to sanitary sewer)

• Cross-connections between the storm and sanitary sewer systems • Grease build-up and/or blockages.

Potential Basement Flooding Factors

Typical Causes of Basement Flooding

Note: Typical connections shown, however, private drainage systems can be more complex and each one is unique. For example, there could be interconnection between the sanitary and storm systems or other combinations of connections shown.

Methods for Reducing Basement Flooding and Improving Stormwater Runoff Quality

Source control measures involve managing stormwater where it originates (roofs, roads, driveways), before it enters the City’s sewer pipes.

Source Controls

Conveyance Controls

End-of-Pipe Controls

Conveyance control measures help to control stormwater as it travels along the drainage system (in pipes or along the road).

End-of-pipe control measures control stormwater just before it is discharged to a watercourse (stream, river, or lake).

Potential Solutions SOURCE CONTROLS

Rain Barrels Rain Gardens Tree Planting

Residents can help reduce runoff – the water that flows from hard surfaces into the sewer system. Naturalizing your property lowers the risk of basement flooding and contributes to improving stormwater runoff quality.

Downspout Disconnection

Reduce Toxins Permeable Paving • Eliminate pesticide/fertilizer use • Do not let household

chemicals such as paint, oil, grease, salt, soap, etc. wash to the storm sewer

• Pick-up pet waste

Soakaway Pits Green Roofs

Potential Solutions SOURCE CONTROLS

Sealing Maintenance Hole Covers

Additional source control options: • Sewer Maintenance and Rehabilitation

Involves:

• Sanitary Sewer: CCTV, smoke/dye tests, sewer cleaning, relining, and repair • Storm System: Street sweeping, seasonal leaf pick-up, catchbasin vacuum cleanouts

Surface Flow Path Diversion

Pervious Pavement

These measures can also help reduce the amount of runoff entering the sewer system.

Potential Solutions CONVEYANCE CONTROLS

Description • A vegetated depression and underground trench designed

to filter stormwater runoff to remove pollutants and promote infiltration/evapotranspiration

What Does it Involve?

• Diversion of small overland or piped drainage areas for small storm events

• Excavation of a trench with specific soil mixture, surface plantings and underdrain within an open area such as a boulevard or park

Description • In place of concrete curb and gutter, replace with grassed

ditches and a series of culverts which slows surface water down and encourages infiltration/filtration

What Does it Involve?

• Removal of curb and gutter (if existing) and reconstruction of roadway and boulevard

• Installation of shallow culvert pipes

Alternate Road Cross-Sections (Ditches) (Improve Stormwater Runoff Quality)

Local Bioretention Filters (Improve Stormwater Runoff Quality)

Potential Solutions CONVEYANCE CONTROLS

Increase Number of Catchbasins (Controls Basement Flooding)

Overland (Major System) Control (Controls Basement Flooding)

Description • The diversion of surface drainage away from low lying

areas that have no direct outlet to reduce surface ponding depths

What Does it Involve?

• Addition of “speed bump” or “curb cut” to redirect overland flow to strategic locations

• Interception of road or boulevard flows to dedicated major system sewer with large inlet grate or “curb drain”

Description • Where the storm sewer has existing capacity, add

more catchbasins to capture more flow from the surface

What Does it Involve?

• Minor street excavation for installation of new catchbasin(s) and connection to storm sewer

• Curb replacement and road restoration

Potential Solutions CONVEYANCE CONTROLS

Parking Lot Retrofit for Surface Storage (Controls Basement Flooding)

Catchbasin Inlet Controls (Controls Basement Flooding)

Description • Installation of inlet control devices (ICDs) on

catchbasins to limit release into the storm sewer system to control back-up (surcharge)

What Does it Involve?

• A plastic or metal plate / device installed inside the catchbasin outlet (not visible from surface)

• Minimal effort and time to install • Keeps more water on the surface

Description • Installation of ICDs in parking lots to store stormwater

on surface • Installation of roof drain controls to store stormwater

on large flat roof areas What Does it Involve?

• Retrofit of City-Owned property (where physically possible)

Potential Solutions CONVEYANCE CONTROLS

Adding New Sewers (Twinning) (Controls Basement Flooding)

Replacement of Existing Storm and/or Sanitary Sewers (Controls Basement Flooding)

Description • Increase the size of the sewer pipe by replacing the old sewer with

a larger pipe What Does it Involve?

• Road excavation within City limits • Removal of old sewer and structures (manholes & catchbasins)

and disconnection of sewer service line(s) • Placement of new sewer, reconnection of sewer service line(s) and

restoration of road and boulevard

Description • Increase the capacity of the sewer system by adding another

sewer pipe in addition to the existing pipe What Does it Involve?

• Road excavation within City limits • Replacement of old structures (manholes & catchbasins) and

reconnection of sewer service line(s), if necessary • Placement of new sewer, reconnection of sewer service line(s) and

restoration of road and boulevard

Potential Solutions END-OF-PIPE CONTROLS

Wet Pond/Wetland (Controls Basement Flooding and Can

Improve Runoff Quality)

Dry Pond (Controls Basement Flooding)

Description • An engineered surface depression that controls the quantity of

inflowing stormwater through storage and slow release to the receiving system

• Typically fills with water during extreme storm events and drains within 24 to 48 hours or less

What Does it Involve?

• Excavation and shaping of a suitable open space • Addition of inlet/outlet structures • Restoration and landscaping; signage

Description • An engineered pond or wetland with a permanent water surface

that controls the quantity and quality of inflowing stormwater through storage and slow release to the receiving system

What Does it Involve?

• Excavation and shaping of a suitable open space • Addition of inlet/outlet structures • Restoration and landscaping (aquatic and side-slope) • Infrequent maintenance (sediment removal)

Potential Solutions END-OF-PIPE CONTROLS

Oil & Grit Separator (Improves Stormwater Runoff Quality)

Underground Storage Tank (Controls Basement Flooding & Can Improve

Stormwater Runoff Quality)

Description • An underground tank or pipe that controls the rate of

inflowing sanitary or stormwater through temporary detention and slow release to the receiving sewer, reducing the potential for flooding

What Does it Involve?

• Excavation and construction of tank or pipe, including inlet and outlet structures

• Infrequent maintenance (monitoring, clean-out)

Description • An underground separation tank that takes the place of a

conventional manhole and provides a measure of treatment for small drainage areas

What Does it Involve?

• Similar to a manhole, minor street excavation for installation of structure

• Road restoration • Annual maintenance (vacuum clean-out)

The following criteria are suggested for evaluating each of the options and identifying the recommended solutions:

Evaluation of Solutions

Natural Environment • Potential Impact on

Terrestrial Systems (Vegetation, Trees, Wildlife)

• Potential Impact on Aquatic Systems (Aquatic Life and Vegetation, Surface Water Quality, Groundwater, Receiving Watercourses)

• Soil and Geology

Socio-Cultural • Effect on Urban

Greenspace (Parks, Ravines, Open Spaces)

• Disruption to Existing Community During Construction (Traffic, Noise)

• Disruption to Existing Community Post Construction (Visual Impact, Odour, Safety)

• Archaeology and First Nations

Technical • Feasibility of Control

Measure (Available Space, Accessibility, Constructability)

• Ability to Improve Stormwater Runoff Quality

• Impact on Upstream, Downstream and Surrounding Areas

• Operations & Maintenance Requirements

• Basement Flooding Prevention Effectiveness

Economic • Capital Cost • Operating and

Maintenance Cost

Thank You for Attending

We welcome your feedback. Please fill out the comment sheet provided. Following this PIC, the study team will review and consider your comments in the

evaluation of alternative solutions.

The next PIC is expected to be held in late 2014 to present the recommended solutions.

Contact Information For more information on this study, to provide your comments, or to be placed on the

project mailing list, please contact: Josie Franch, Public Consultation Unit 55 John Street, Metro Hall, 19th Floor

Toronto, ON M5V 3C6 Phone: 416-338-2859, E-mail: jfranch@toronto.ca

Website: http://www.toronto.ca/involved/projects/basement_flooding/sa_21_23.htm