1. Public Information Centre Slides July 23 and August 11, 2008 Storms
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Public Information Centre Slides July 23 and August 11, 2008 Storms
with added annotations
June 25, 2009
Summer 2008 Flooding

2. July 23, 2008 Storm
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3. August 11, 2008 Storm
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4. Comments on Storms
Radar Loops show intense storms with intensities exceeding 100 mm/hr (see colour bar on right)
10 minute interval does not capture largest peak
Narrow band results in selective flooding
For example, on July 23, no rain south of Taunton
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5. Impacts July 23
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6. Impacts Aug 11(including Sanitary Basement flooding)
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7. Comments on Photos Overland flow on road Flow into parks is desirable
From property line to property line is acceptable
Emergency vehicle access permits no more than 300 mm (1 foot) of water
Flow into parks is desirable
Major – Minor Storm System
Underground sewer handles ‘normal’ storms that occur annually (aka minor system)
Excess flow is handled by overland flow (aka major system) for storms that occur only once every 10 years or less frequently
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8. Analysis - CLOCA
Estimates Based on Rain Gauge Stations at Specific Locations (not in direct path of storm)
CLOCA data based on 15 minute counts of tipping buckets and is used for stream basin analysis. Might not capture intense peaks of short duration required for subdivision analysis. Classification of return period is based on peak intensity and duration factors NOT total rainfall.
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9. Analysis – Town of Whitby (July 23)
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10. Analysis – CLOCA (August 11)
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11. Runoff Rain that soaks into ground does not runoff into storm sewer
On grass 90% typically soaks in
10% runoff
Design assumes 80% to account for hard ground; 20% runoff
For subdivision 50% is assumed to soak into ground
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12. Antecedent Moisture Conditions from CLOCA data
Saturated ground created by several days of rain cannot absorb rainfall on July 23, 2008 resulting in up to double the flow in subdivisions. Since underground sewer (minor system) takes part of flow, overland flow (major system) may be up to triple the normal flow.
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13. Antecedent Moisture Conditions from CLOCA data
Saturated ground created by several days of rain cannot absorb rainfall on August 11, 2008 resulting in up to double the overland flow in subdivisions. Since underground sewer (minor system) takes part of flow, overland flow (major system) may be up to triple the normal flow.
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14. Design Standards Based on Historical Storms from past century
Underground storm sewer (minor system)
designed for most storms
including those that occur only every 5 years
Flow 2/3 full with this storm
Overland flow (major system)
Up to storm that occurs only once every 100 years with 25% safety factor
In this century storms are predicted to be twice as often and more intense
Sanitary sewer designed for ‘Superbowl Sunday toilet flush’ NOT for storm flows
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15. Result of Excess Overland Flow
Extra depth of overland flow pushed extra water into underground storm sewer
For example, a double catch basin
50 mm (2”) => 20 L/s
100 mm (4”) => 90 L/s
150 mm (6”) => 170 L/s
300 mm (12”) => 400 L/s
Based on MTO charts
400 L/s exceeds pipe capacity
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16. Result – Basement Flooding
When underground sewer is full
Downspouts back up
Foundation weepers fill with water
Water seeps into cracks in foundation
If floor drain is connected directly
Water flows quickly into basement
Example: Heber Down Crescent, North Street
Homeowners should modify plumbing to connect floor drain to Sanitary Sewer instead of Storm
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17. Ancillary Sanitary Sewer Backup
Around basement the flow from backup of storm sewer
Infiltrates into nearby sanitary sewer
Through cracks in sanitary clay or plastic pipe
Illegal* weepers attached to sanitary sewer or floor drain
Infiltrates into basement
Cracks in foundation and floor
Flows to floor drain and sanitary sewer
Downspouts ‘illegally’* connected to sanitary sewer
Direct flooding of smaller sanitary sewer
*See new regional by-laws
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18. Analysis Pattern Observed
Clusters of basement flooding occurred at overland flow concentrations
Bayberry, Downey, Rosewood, Kilbride are very clear examples of this clustering
Deep ditches and large inlet controls OR double catchbasins in sag all in overland flow route were adjacent to almost all instances of overland flooding
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19. Summary
Design data from last century would not predict the volumes of overland flow
Reality of Climate Change is increased intensity and frequency of storms
Volume increased by
Peak intensities not measured by CLOC
Saturated Ground
How can we adapt to new reality?
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20. Solution Inlet Controls Overland Flow enhancements
Restrict flows into the underground storm sewer
Adaptation to new reality of extreme storms
Recommended by recent literature and used in several other municipalities
Overland Flow enhancements
Remove excess overland flow from streets by
Lowering curbs at overland flow route
Lowering grading of boulevard at low point
Removing obstacles in overland flow route
Drawing from IPEX Brochure
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21. Restricting Flows
Major and Minor System – Surface and Underground Storm Sewers
Drawing from IPEX Brochure
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22. Comment on Overland Flow
The additional water on the surface of the road should be minimal
300 mm (1 foot) of water in a 900 mm pipe is less than 30 mm of water on a 9 m wide road
Small increase in depth on surface
curb
Overland flow - Major system
Large reduction in depth
In underground sewer
Minor system
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23. Affected Areas – July 23, 2008 Heber Down Crescent (AECOM Review)
Including Torian and Montgomery south of Vipond
Centre and North Streets
Downey Drive
Underwood Drive, Tremount Street, Durham Street, *Ipswich Place, *Princeton Court
*Bayberry Crescent (Sernas Report)
*Helston Crescent (Sernas Report, SKA Review)
Including Covington Drive, Corsham Drive, Hesham Drive
**Carnwith Condos at Croxall Drive
Consultant reports that ICD was installed
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*not assumed, **private site

24. Affected Areas – August 11, 2008
Kilbride Drive (AECOM Report)
Including Cahill Court, O’Malley Crescent
Anderson and Taunton road flooding
Rosewood Court
Walton Court
*Annes Street (Regional Flooding Study)
Including McCullough Blvd, Michael Blvd, Newman Cres, Gilbert St, Maria St, etc
*Lupin Drive and surrounding streets
*Walton Drive, *Donevan Crescent
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*Regional Sanitary Sewer

25. Heber Down Changes Overland Flow Ditch Inlets Catch Basins
Add inlet controls (about 14)
Catch Basins
Add inlet controls (about 10)
Protect Properties from Overland Flow
Cassels Road from Montgomery to Heber Down
Montgomery at Heber Down – north east corner
Disconnect connections at controlled inlets
Modifications are being checked by an outside consultant
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26. Centre Street West & North Street Changes
Overland Flow
Add inlet controls (4 Ditch Inlets on North Street)
Add inlet controls (2 double catch basins on Centre Street West)
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27. Downey Drive Overland Flow Add inlet controls (2 double catch basins)
Some at Carson Avenue
Add inlet controls (2 ditch inlets in park)
Seal lid on catch basin cover of maintenance hole in overland flow route
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28. *Un-assumed Sites Bayberry Crescent is not assumed
Inlet controls are recommended by the engineering consultant at the double catch basins in sag in the overland flow route
Helston Crescent is not assumed
Inlet controls and modifications to the overland flow route and pond outfall are recommended by the engineering consultant
Modifications are being reviewed by an outside consultant
Princeton Court is not assumed
Inlet controls at the double catch basin at the end of the court in the overland flow route will be recommended and required prior to assumption
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29. **Private Sites Carnwith Condos is a private site
Discussions with engineering consultant and builder have emphasized the need for an inlet control device
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30. Other Flooded Areas July 23, 2008
Isolated reports at
Hanson Crescent
Tremount Street
Durham Street
Kimberly Drive
Ipswich Place
Cassels Road East
Underwood Drive
Hatch Street
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31. Affected Areas – August 11, 2008
Kilbride Drive
Including Cahill Court, O’Malley Crescent
Anderson and Taunton flooding
Rosewood Court
Walton Court
*Annes Street (Regional Flooding Study)
Tributary areas
*Lupin Drive and surrounding streets
*Walton Drive, Donevan Crescent
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32. Kilbride Changes Overland Flow Other
Catch Basins
Add inlet controls (about 2)
Lower Overland Flow Route
Cahill Court - Work with home owners in easement
Kilbride – Lower path into park
Anderson – Lower west boulevard at creek
Other
Debris proof pond outlets
Remove indirectly connected downspout connections
Modifications are being recommended by an AECOM, an outside consultant
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33. Rosewood Court Changes
Overland Flow
Add inlet controls (2 double catch basins)
Other
Remove indirectly connected downspout connections
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34. Lupin Drive and surrounding area
Overland Flow
Follow recommendations of consultant’s report
Other
Remove indirectly connected downspout connections (57 locations)
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35. Michael Blvd and surrounding area
Overland Flow
Follow recommendations of consultant’s report
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36. *Sanitary Sewer Flooding Regional Reports
Region is taking the lead on all other August 11, 2008 flooding investigations
Town is cooperating with any required changes to storm sewer system
Town is advising Region of locations where overland flow may infiltrate sanitary sewer through maintenance hole covers
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37. Other Flooded Areas August 11, 2008
Isolated reports at many other areas are currently under review by the Region
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38. Other Causes of Basement Flooding
Grading
Slopes can push water toward foundation
Unprotected openings in foundation below flood elevations can let surface water in
Downspout flows towards foundation wall can flood weepers
Blocked drainage swales can cause backyard ponding against foundation
Blocked weepers
For example, Old clay tiles filled with roots or silt can prevent drainage of ground water
High water table, natural springs, extra depth basements (below water table) can overwhelm foundation weepers
Extra sump pumps with backup power may be required
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39. Causes of Basement Flooding
See
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Typically the weeping tile connects to the storm sewer.

40. Handbook for reducing Basement flooding
What to look for in this diagram (shown in red)
This diagram shows a home that is at risk of basement flooding from infiltration flooding, overland flooding and sewer backup. In this diagram:
The cracks in the foundation wall and basement floor are unsealed.
Downspouts are connected to the municipal sewer system or are discharging too close to the foundation.
The yard is improperly graded and sloped toward the home.
The weeping tiles are connected to the sanitary sewer lateral.
The weeping tiles have not been maintained and are damaged.
There is no backwater valve in place.
The sewer laterals have not been maintained, are cracked and have loose joints.
The storm sewer lateral has not been severed and is prone to exfiltration.
The backfill area beside the foundation wall is uncapped.
The sewer cleanout is uncapped and unsealed.
There is no window well cover in place.
by Institute for Catastrophic Loss Reduction
Reproduced by permission.
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41. Methods of Connection Sewers
New construction (Typical in Whitby and Brooklin since 1980s)
Storm sewer lateral - Front downspouts, weepers
Sanitary sewer lateral – Floor drain, other plumbing
Some (Bradford Court, Lynde Shores)
Foundation Collector lateral – weepers ONLY, no storm sewer lateral
NO downspout connection permitted
Ditches (Newman, Maria, Gilbert, Henry, Cochrane, Heber Down, etc)
Sanitary sewer – floor drain, weepers, etc
Current or Former Septic Tank
Basement Floor Drain goes to sump pump
Former Sump Pump
Sump and weepers connected to storm sewer lateral
Backwater valve is now RECOMMENDED on storm sewer lateral
Downspout connection is not normally recommended
Floor Drain should be REDESIGNED to connect to sanitary sewer
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42. Other Things to Check Clear basement floor drain
Seepage from walls or floor or leakage from hot water tank or water in windows or other openings should all drain to floor drain
Ensure a clear path from all locations to floor drain
Basement floor drain is connected to sanitary sewer
Except Heber Down Crescent, Torian Avenue, Montgomery Avenue, North Street and all houses that originally had sumps and septic systems.
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43. What Can Home Owners Do? Disconnect downspouts
ALL Rear downspouts except for Townhouses
Temporarily disconnect Front downspouts until your plumber verifies that storm water from your roof cannot infiltrate to sanitary plumbing
Downspouts connected to Sanitary Sewer must be disconnected – contact Region
Direct downspouts to splash pads away from house
Protect Openings from surface drainage
Use window wells
Use sealed windows and doors near ground
Slope patios and driveways away from your foundation (2% slope)
Do not raise the grade along property line
Leave a minimum 0.60 m (2 feet) buffer
Remove obstacles
Watch out for driveway widenings, walkways between house, landscaping which have all been shown to cause basement flooding
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44. Downspout Disconnection
Sanitary Sewer lateral has no capacity to handle flows from downspouts
Storm Sewer lateral can handle about ½ of a roof and not more than 100 m² (1000 sf)
Exception – all of a small townhouse roof
Flows from downspouts can directly enter basement under some conditions
Through infiltration and direct or indirect sanitary sewer connections
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45. If You Were Flooded
Consider installing sewer backflow preventers on sewer line from basement floor drain
Disconnect your downspouts
Cost is less than $15 per downspout
Have your storm and sanitary sewer lines inspected by a plumber
Sanitary can be inspected from basement cleanout
Storm can be inspected from downspout connection to storm
Town (storm) and Region (sanitary) is responsible for blockages outside of the property
If your plumber finds this type of blockage, call us
Home owner is responsible for blockages inside the property lines
Clean out your foundation weepers
May require a dig up to access weepers
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46. Sewer Backflow Preventer
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47. No Plumbing Permit Fee for Installation*
To encourage the proper installation of backflow preventers
Town will effectively waive Plumbing Permit Fee
*A grant equivalent to the cost of the plumbing permit will be given at the time of application
*Grant is only available for one year
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48. Warnings – Backflow Preventers
Inside installation only effective at preventing flooding from basement floor drain
Outside installation on storm sewer is possible but not if floor drain and foundation weepers connects to storm sewer
Improper or poorly maintained installation may result in basement flooding
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49. Other Sources of Information
City of Toronto – Wet Weather Flow Management and other documents
City of Edmonton – Homeowner’s Guide to Flood Prevention
Institute for Catastrophic Loss Reduction
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50. Five Quick, Inexpensive Ways To Get You Started City of Edmonton
1 Plug the leaks.
A ladder, silicone, and time are all you need to seal holes or cracks in your eaves troughs, downspouts, extensions, sidewalks, patio and driveway.
2 Repair or replace downspout extensions.
This might be a matter of simply putting down the extension that’s already there or putting back the splash pad. Purchasing and installing extensions or splash pads is inexpensive but very important in getting water away from foundation walls.
3 Clean your eaves troughs and downspouts.
The downspout extensions have little value if leaves, and other debris are preventing water from getting down the downspout. A gloved hand (or garden spade), ladder and garden hose are what you need to get the job done.
4 Backfill under steps and decks.
This is often the weak spot in lot grading. Dirt and some shovel work is all it takes to fill the depression and get the ground sloping downhill away from the house again.
5 Top up sunken areas around the foundation.
Ground around your basement settles over time. Raising that up with some dirt and shovel work will re-establish a positive grade again at little or no cost.
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51. Contacts Town of Whitby Public Works Emergency Sewer Backups
Arthur Smith x 2227
Antony Manoharan x 2346
Emergency Sewer Backups
Town Operations Centre 7:30 am to 4:00 pm
(Storm related)
Region Works Dept 8:00 am to 5:00 pm
(Sanitary related)
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