The specific reasons for a home to experience flooding have to be investigated on a case-by-case basis. Possible causes could be foundation wall seepage, failure of a backwater valve or sump pump, excessive flows the sump pump cannot handle, and/or excessive street flooding.
The central older parts of Edmonton built before 1960 are serviced by a combined sewer system. This system carries both sewage from the home and stormwater runoff from streets and rooftops in one pipe. Residents with this type of servicing should disconnect their downspouts and direct them onto the surface. This will reduce the amount of water that enters the combined sewer system and will reduce the risk of sewer backup.
Almost all areas of Edmonton built between 1960 and 1980 are serviced by both a sanitary and storm sewer. The sanitary sewer system carries sewage from the home and drainage from weeping tiles located around the foundation of the house. The storm sewer system carries stormwater from the streets and household downspouts.
Residents in areas with sanitary and storm sewers should be aware that disconnecting the downspout from the storm sewer system may not reduce the risk of basement flooding. Instead, doing this may increase the risk of surface flooding if the lot is not properly graded to drain water away from the home. Should a homeowner choose to disconnect the downspout, they need to ensure their lot grading directs water from the downspout away from the home towards a city street or lane, rather than onto a neighbouring property.
Many homes in older areas had their downspouts connected to the storm system. Flooding often occurs during a heavy rainstorm when the storm system is flowing at high capacity, causing the system to back up. Disconnecting the downspouts from the storm system allows roof drainage to flow onto the ground before reaching the catch basin in the street. However, this will cause problems if the grading around the house and adjacent properties is not adjusted to accommodate the flow.
Good lot grading keeps surface water away from your home and your weeping tile system. Ideally a lot should be sloped steeply away from the home in a way that allows surface water to flow onto City property (e. g. , streets and lanes), rather than onto a neighbouring property. A disconnected downspout and sump pump should discharge at least six feet away from the home to ensure water does not seep down the side of the house and into the home's weeping tile. For more information, see Lot Grading.
Because sanitary sewers are not watertight, stormwater can get into the sanitary sewer in a number of ways:
- at manholes, through manhole covers, and through cracks and voids around the manhole
- from the surrounding ground, through cracks or separations in the sewers and from private service connections
- from weeping tile (foundation drainage) systems at private homes and buildings, since poor lot grading contributes to weeping tile flows
- from downspouts that have been incorrectly connected to the sanitary sewer system rather than the storm sewer system.
Also, during larger storm events, like the ones that occurred in July 2004, much more water pools on the surface than normal. This can cause an increased amount of water to enter the sanitary sewer.
Using stormwater management lakes for flood control only became common practice in neighbourhoods designed since 1980. By capturing rainfall and storing peak flows, these community lakes are a very effective means to prevent neighbourhood surface flooding. As part of the engineering review currently underway, the City plans to explore how to best manage peak flows and assess the potential to add stormwater facilities to existing neighbourhoods.
Check your own lot grading. Most homes over five years have settlement around the foundation walls. Remember, downspouts only pick up roof drainage. If both houses have proper slope away and proper drainage swales then the discharge of the downspout and/or sump pump would be directed off the lot. Have you ever considered where your surface runoff would go if your neighbour's house was not there?
A new house built in an older area is called in-fill housing. In these cases, the builders must conform to the provisions of the Drainage Bylaw, which prohibits drainage onto adjacent properties. Matching the existing grade at the common property line is normal practice for these developments. Adjacent homeowners must consider their own grading. They should be aware that under the Alberta Building Code and Surface Drainage Bylaw, new homes are required to have a 10% slope away from the foundation walls.
Check your own lot grading and foundation drainage. Then speak with your neighbour. Remember, surface water will follow the grade of least resistance. If you have a poor or negative grade, the surface water will flow towards your foundation wall increasing the risk of basement flooding.
Effective side-lot drainage requires the co-operation of both property owners. Check your own lot grading and foundation drainage, then speak with your neighbour. Ask them if they can construct a retaining wall to catch the surface drainage, or re-direct the downspout discharge or sump pump discharge to force the surface drainage to flow toward the front street or back lane.
Community Flood Prevention
The City has responded to drainage problems in communities that previously experienced a high frequency of flooding. Drainage work has been undertaken in Mill Woods, Lago Lindo, Dunluce Warwick, Ottewell, Kenilworth, Mayfield, High Park, McQueen and Laurier Heights.
There are two main reasons. Neighbourhoods built before 1980 were not required to have a major overland flow escape route, which carries away rainwater that storm sewer pipes cannot handle. In the absence of an overland flow escape route, flooding may occur in basements and on residential streets. Communities built before 1980 that have natural overland escape routes are also less prone to flooding than other older areas that do not.
Another reason is that storm events are random and tend to be concentrated in small areas. Often one community will be hit with a short duration, high intensity rainfall event that causes flooding. Meanwhile, a nearby community may be hit with the same storm but the intensity is lower and no flooding occurs.
Though this is not common, there could be a number of reasons for this occurrence. One side of the street may have basements that are lower than the other, due to the natural slope of the land. The height differential could be difficult to detect with the naked eye but is enough to cause flooding.
Likewise, in neighbourhoods with back alleys, one side of the street may be serviced with a different piping system than the other. This can result in a slightly different level of service, which may contribute to flooding.
Lot grading, the absence of a backwater valve, incorrect positioning of a downspout, a malfunctioning sump pump, leaking weeping tile, and even the style of home can contribute to flooding.
The level of drainage service is a concern for many communities throughout the city. The City is making better flood protection a top priority and is committed to do what is possible to improve drainage in local neighbourhoods. However, until the engineering studies are completed, it is premature to say what can and will be done for specific neighbourhoods.
Yes. The City will inform affected residents and communities of the engineering studies' findings and will consult on potential flood protection solutions. Community input and support is key because system improvements will require cooperation from the City, individual neighbourhoods and private landowners.
The maintenance of catch basins and sewer pipes depends on the history of the particular neighbourhood. During normal flow conditions, local problem areas are identified, investigated and scheduled for maintenance. Typically, the sewer pipes are flushed and cleaned, and debris is removed from the catch basins. In more severe cases, a sewer may require re-lining. A problem drainage location may be visited by a crew once a year, with the cleaning operation taking about two hours.
Catch basin sumps along bus routes and major roads that are sanded get cleaned once a year. All other catch basins are only cleaned if a specific problem is noticed or reported.
No. Flooding events are typically not related to maintenance. Flooding tends to occur because the system is unable to handle a high volume of water as seen during a severe storm event. In this situation, water pools on the surface because the sewer pipes are full of water and have reached capacity.