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Common Reasons For Basement Flooding


Drainage 101

In the City of Lethbridge, private and public drainage systems work together to channel and move wastewater and stormwater safely away from homes and neighbourhood streets.
The private system includes things like eavestroughs, downspouts, weeping tiles, lot grading and sump pumps and is the responsibility of residential and commercial property owners. The public system is owned and operated by the City of Lethbridge and includes the wastewater and stormwater pipes that run under the streets and alleys.
The wastewater system deals with all water disposed of inside the home. Water from showers, toilets, sinks, dishwashers, clothes washers and floor drains is channeled to a pipe under your basement floor. This pipe is connected to a larger wastewater pipe located under the street or alleys. The wastewater flows through these pipes to our Wastewater Treatment Plant where it is cleaned and then released into the Oldman River.
The stormwater system deals with roof and surface water that comes from rainfall or snowmelt. Sloped lawns and driveways direct water from the roof and the ground to the street or alleys, where stormdrains are located. The stormdrains are connected to large underground stormwater pipes which flow to storm ponds and directly into the Oldman River. Water that seeps through the ground is collected by weeping tile (foundation drain) located at the bottom of your home's foundation. Your foundation drain is either connected to a sump pump or to a wastewater pipe under your basement floor.



Inflow from foundation drains

Inflow from foundation drains is a major contributor to overloading of the wastewater collection system. Approximately two thirds of homes in Lethbridge have their foundation drains connected to the wastewater system.
Rain water can enter the foundation drain through:
  • poor lot grading
  • basement window wells
  • exterior drains 
  • down spouts not properly extended
  • street flooding and manholes-it is important to keep your storm drains clear of debris. Click here​ to find out more about our storm drain cleaning programs, including Adopt-​A-Stormdrain and Gutter Buddy!

The following diagrams show how foundation drains are connected.

 Before 1995

In homes built before 1995 foundation drains were connected to the wastewater collection system. During heavy rains the wastewater system can become overwhelmed and cause basement flooding. In older areas of Lethbridge the wastewater collection system was designed to only accommodate wastewater flows.


Between 1995 and 2005

In 1995 Lethbridge prohibited the practice of connecting foundation drains to the wastewater collection system. Homes built between 1995 and 2005 had their foundation drains connected to a sump pump that discharged to the lawn.


After 2005

In 2005 Lethbridge made another change and required new homes to have sump pumps connected to the stormwater collection system. During heavy rains the stormwater system can become overwhelmed. The stormwater collection system, sewer pipes and catchbasins, are only designed to accommodate the runoff from minor rainfall events.