Public Bulletin 2

February 18, 2005

This is the second in a series of information bulletins to residents about the City's Flood Prevention Strategy and its program activities. To be added to the mailing list or to receive future updates and notices by e-mail, please call 780-496-5539.

The Flood Prevention Strategy is a direct response to the severe flooding caused by major rainstorms in July 2004. Additional information is available by contacting a Flood Prevention Project Leader:

Flood Investigation Studies Completed

Engineering studies of the hardest hit communities of Edmonton have been completed. The studies analyzed the degree of flooding, looked at existing infrastructure and identified system weaknesses. The City now has a good idea of what the core surface and underground problems are and some possible options for correcting those problems.

Ward 1 (West Edmonton)

The most heavily flooded areas in Ward 1 were Elmwood, Lynnwood, Rio Terrace, Quesnell Heights and Laurier Heights. Some of the common characteristics of the 744 homes (an average of 149 homes per neighbourhood) that flooded in July were:

  • In about 60% of the homes, the yard elevation above the street curb was half a metre or less.
  • In 37% of the homes, landscaping or lot grading caused surface water to drain towards the houses.
  • In 30% of the homes, there were no roof leader extensions or the extensions were less than the recommended minimum length of 1. 5 metres.
  • At the time, only three per cent of the homes had backwater valves.

The study also revealed that:

  • The water volume created by the rainstorms exceeded the trunk storm sewer system's capacity, contributing to surface flooding and sanitary sewer backup.
  • The most common methods by which rainwater got into the sanitary sewer system was through manholes covers, household foundation weeping tiles and leakage from storm water pipes.

Ward 5 (South Central Edmonton)

Some of the most heavily flooded areas in Ward 5 were McKernan, Parkallen, Lendrum Place, Pleasantview and Malmo Plains. Some of the common characteristics of the 470 homes (an average of 94 homes per neighbourhood) that flooded in July were:

  • About 78% of the flooding was due to sewer backup.
  • In 21% of the homes, landscaping or lot grading caused surface water to drain towards the houses.
  • 32% of the homes had downspouts that were connected to the weeping tile or sanitary sewer lines.
  • At the time, about 8% per cent of the homes had backwater valves and 9% had basement sump pumps.

The study also revealed that:

  • The water volume created by the rainstorms exceeded the storm and sanitary sewer systems' capacity, contributing to surface flooding and sanitary sewer backup.
  • In two neighbourhoods, there are interconnections between storm and sanitary sewer systems. This allowed stormwater to overflow into the sanitary system putting added stress on the sanitary sewer system during the major rainstorms.
  • Each neighbourhood has a natural low area towards which all surface water in the neighbourhood flows.
  • The most common methods by which rainwater got into the sanitary sewer system was through manholes covers and household foundation weeping tiles.
  • Maintenance records indicate the July flooding was not likely caused by blockage in the stormwater or sanitary sewer systems.

Wards 3, 4 & 6 (northeast, Central and southeast Edmonton)

The most heavily flooded areas in Wards 3, 4 & 6 were Knottwood, Lakewood and North Millbourne in Mill Woods. Some of the common characteristics of the 259 homes (an average of 86 homes per neighbourhood) that flooded there in July were:

  • In 17% of the homes, landscaping or lot grading caused surface water to drain towards the houses.
  • Many homes had downspouts that were connected directly to the weeping tile, placing added pressure on the system.

The study also revealed that:

  • In certain locations, the water volume created by the rainstorms exceeded the storm and sanitary sewer systems' capacity, contributing to surface flooding and sanitary sewer backup.
  • The most common methods by which rainwater got into the sanitary sewer system was through household foundation weeping tiles and leakage from storm water pipes.
  • Most manhole covers in the area are sealed, preventing surface water from getting into the sanitary sewer system.

Results of Other Neighbourhoods Studied

A more cursory analysis was done of less severely flooded areas in the City. Although not as detailed, analysis of flood reports and the local drainage system of an additional 41 neighbourhoods concluded that contributing factors to flooding were:

  • In many cases, downspouts were directly connected to a home's sanitary sewer line. This can cause the line to overload and cause sanitary sewer backup.
  • Very few homes had a sanitary sewer backwater valve or basement sump pump to deal with excess water volume.
  • Street sanitary sewer mains were unable to handle the unusual amount of water volume caused by the July storms.
  • Hail and other debris plugged many catch basins, causing water to pool and spill onto residential property.
  • In some cases, poor lot grading or plugged eavestroughs led to water flowing towards basement walls rather than away from them.

In Ward 1, the analysis included the neighbourhoods of Aldergrove, Summerlea, Belmead, La Perle, Callingwood North, Callingwood South, Patricia Heights, Westridge, Lymburn, Thorncliff, West Meadowlark Park, Meadowlark Park, Sherwood, Jasper Park, Parkview, and Oleskiw. In these 16 neighbourhoods, 969 homes were flooded (an average of 61 homes per neighbourhood).

In Ward 5, the analysis included the neighbourhoods of Bearspaw, Duggan, Steinhauer, Greenfield, Royal Gardens, Belgravia, Sweet Grass, Rideau Park, Keheewin, Queen Alexandra, Ermineskin, Allendale, Empire Park, Aspen Gardens, Westbrook Estates, and Grandview Heights. In these 16 neighbourhoods, 686 homes were flooded (an average of 43 homes per neighbourhood).

In Wards 3 and 4, the analysis included the neighbourhoods of Highlands, Bellevue, Cloverdale, Westmount, Bonnie Doon, Garneau, Strathcona, Strathearn, Forest Heights, and Holyrood. In these 10 neighbourhoods, 141 homes were flooded (an average of 14 homes per neighbourhood).

Neighbourhood Consultations Slated for March and April 

Neighbourhood consultation sessions are being organized for March and early April to review the findings of the flood investigations and discuss with residents options for reducing the risk of flooding. Locations, dates and times will be advertised as soon as they are finalized. In addition to newspapers and direct mail, the information will be posted on the City's website at www.edmonton.ca/floodprevention

The purpose of the sessions is to review the results of the studies and to get the community's input and feedback regarding various options. Drainage Services will take this input and incorporate it into an overall flood prevention implementation plan. This plan will be reviewed with the community before it is implemented.

It is important that flood prevention measures reflect community needs and preferences. The flood studies have shown that better flood prevention requires a commitment from both the City and private landowners. This means working together to make homes and neighbourhoods more flood resistant.

Full implementation of the Flood Prevention Strategy will require funding approval from City Council. However, there may be initiatives Drainage Services can embark upon this spring and summer. These will also be discussed with residents at the neighbourhood consultation sessions.

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