Urban flooding a severe and continuing problem for municipalities

Basement flooding are you prepared for mothers natures little nasty reminders when you are away at work and not home or your family is left to clean up?

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More often than not, basement flooding is a result of overland flooding, infiltration flooding or sewer backup, or a combination of two or all three of these types of flooding. After a few days of steady rain, when spring snow-melt occurs or during an extreme rainfall event, the soil around your home can become saturated with water. Steady snow-melt and precipitation can also raise the ground water level to a point where it is higher than your basement floor.

This groundwater can infiltrate into basements through cracks in basement walls (or foundation walls) and cracks in basement floors. Infiltration flooding can be a significant problem in older homes where mortar has weakened over the years and cracks have developed in stone or cinder block foundations.

Think about and assess the risks just like at work have you done a risk assessment review?

• Talk to your municipal government about basement flooding
• Inform your municipal government about basement flooding that you’ve experienced
• Check your insurance policy, or talk to your insurance broker or insurance provider about basement flood coverage
• Avoid pouring fats, oils and grease down household drains
• Keep storm sewer grates clear
• Seal cracks in foundation walls and basement floor
• Considerations for overland flood entry-points
• Reduce home water use during heavy rainfall events
• Maintain eavestroughs and downspouts
• Avoid storing items directly on the basement floor
• Downspout disconnection, extension and splash pads
• Lot grading, backfilling and swales
• Weeping tiles, sump-pits and sump-pumps
• Mainline, normally open backwater valve
• Maintain sewer laterals
• Severance of storm sewer lateral
• Considerations for reverse sloped driveways
• Window wells and window well covers
• Avoid remodelling or finishing basements

Homes that do not have a weeping tile, where the weeping tile has not been maintained, or where there is poor lot drainage also have a greater chance of suffering from infiltration flooding.

Sanitary sewage is generated by the use of toilets, sinks, drains and other home water uses. Because this type of sewage contains a high degree of contaminants and can pose a significant risk to human health and the environment, it requires treatment at sewage treatment facilities before it is released back into the environment. Sanitary sewage is collected through sanitary sewer laterals, which connect homes and buildings to underground sanitary sewer pipes. Storm sewage consists of excess surface water, resulting from rainfall or snowmelt that has collected in streets, sidewalks, roofs and parking lots in urban areas. Various methods are used to channel this water to underground storm sewer pipes, including swales and catch basins. Although storm sewage is significantly cleaner than sanitary sewage, it can be contaminated with pet waste, salt and other contaminants picked up from city streets and other urban surfaces. In most cases, your neighbourhood is serviced by underground sewage pipes that are either combined, separated or partially separated. These pipes carry either sanitary sewage, storm sewage, or a combination of both to sanitary sewage treatment facilities and nearby lakes, streams and rivers. Combined sewer systems convey a combination of sanitary sewage and storm sewage, which is conveyed to sewage treatment facilities before being released into local surface water, including lakes, streams and rivers. Combined sewers are designed to automatically bypass treatment facilities and re-route excess sewage to local surface water bodies when they become overwhelmed. This automatic bypass is called a combined sewer overflow (CSO), and it helps to protect sewage treatment facilities from damage and also helps to reduce the chances of sewer backup in buildings. However, as CSOs result in the release of raw, untreated sewage, they can have a significant negative impact on local surface water quality. Reduced water quality can have a negative impact on aquatic life, and can also reduce the recreational qualities of lakes and rivers. As homeowners’ weeping tile and downspout connections can contribute a substantial amount of water to the combined sewer, they can increase the chances that CSOs will occur. Separated sewer systems have two individual pipes that are designed to convey only sanitary sewage and only storm sewage. The separation of the different types of sewage allows municipal engineers to direct sanitary sewage to treatment facilities, while storm sewage is allowed to flow into nearby lakes, streams and rivers with less intensive treatment. In some cases, neighbourhoods are serviced by partially separated sewers, which include sections that are combined and sections that are separated. Sewer backup can happen when municipal sanitary, combined, or storm sewer systems receive more water than they can handle. Excess water can cause the sewers to "surcharge," and push water backwards through home sewer laterals and cause sewage to backup into the home through basement floor drains, toilets and sinks. Excessive surcharge in the municipal sewer can create high pressures around basement floors and the foundation, which can cause structural damage to the home. For example, excess pressure in pipes beneath the home can result in heaving of basement floors, especially when improper backwater valves are used. When weeping tiles are connected to the municipal system through sanitary sewer laterals or storm sewer laterals, sewage can be forced back into the weeping tiles, resulting in possible structural damage to the home.

Backwater valve (sometimes referred to as a backflow valve): A valve that is placed in the sewer lateral that helps to prevent water from backing up from the municipal sewer into the basement. Catch basin: Catch basins direct surface stormwater to the underground storm or combined sewer system. Cleanout port: Cleanout ports allow for access to the home’s sewer laterals for cleaning and maintenance purposes. Cleanout ports may be located either in the basement, close to where the sanitary sewer lateral enters the basement, or outside of the home, usually somewhere close to the foundation or between the home and the street. Combined sewer: A sewer that has been designed to convey both sanitary sewage and storm sewage. This type of sewer often services older areas of Canadian communities. Combined sewer overflow (CSO): Combined sewers are designed to automatically bypass treatment facilities and re-route excess, untreated sewage to local surface water bodies when they become overwhelmed with excess sanitary and storm sewage. This automatic bypassing is called a combined sewer overflow.

Exfiltrate: Exfiltration occurs when high pressure water or sewage is forced out of sewer pipes or sewer laterals through cracks or loose joints in the pipes.

Groundwater: Water that is contained within soil and between rocks below the earth’s surface. Infiltration and inflow: Infiltration occurs when groundwater infiltrates into the sanitary sewer system (for example, through cracks in pipes and loose pipe joints). Inflow occurs when excess stormwater enters the sanitary system directly, for example, through downspout connections, leaky manholes, and cross-connections where parts of the storm sewer system have been accidentally or illegally connected into the sanitary sewer system. Infiltration flooding: Flooding that enters the home through cracks in the basement floors and walls. This water "infiltrates" through the ground and into the basement. One in five year storm: A storm that has a 1 in 5 chance of occurring in any given year. One in one hundred year storm: A storm that has a 1 in 100 chance of occurring in any given year. One in two year storm: A storm that has a 1 in 2 chance of occurring in any given year. Overland flooding: Water that flows over the surface of public and private property, and can enter homes and buildings through doors, windows, vents, and other above-ground openings. Overland flow route: A pre-determined route that is designed to direct overland rainwater and snow-melt flow in a controlled manner. Overland flow routes may include streets with heightened curbs or ditches, and often direct flows to nearby lakes, streams or rivers or to underground storm sewer systems. Permeable and impermeable: Permeable surfaces, including grassy yards, have the ability to absorb a limited amount of rainfall. Impermeable surfaces, including paved driveways and roofs, have no ability to absorb rainwater. Soil may also be permeable or impermeable. For example, the backfill area around a home may be composed of more pervious soils, and undisturbed soils may be less pervious. Sanitary sewage: Sewage that is created by use of a building’s plumbing (for example, sinks, toilets, dishwashers, laundry machines) and is considered a highly contaminated health hazard. Sanitary sewer: An underground sewer-pipe that is designed to convey only sanitary sewage. Sanitary sewer lateral: An underground pipe that connects a home’s plumbing to the municipal sanitary or combined sewer system.

Sewer backup: Sewage that is forced back through storm and sanitary sewer laterals from sanitary, storm or combined sewers. Sewage flooding typically enters lower levels of a home through plumbing fixtures, including floor drains, sewer cleanouts and basement toilets, sinks and showers. Storm sewage: Storm sewage is created directly by rainfall and snowmelt. This water is cleaner than sanitary sewage, but can be contaminated with chemicals and debris. Storm sewer: An underground sewer-pipe that is designed to convey only stormwater flows. Storm sewer lateral: An underground pipe that connects a home to the underground, municipal storm sewer system. Stormwater management: The practice of managing overland and underground water flows created by rainfall and snow-melt. Stormwater management is commonly the responsibility of the municipal government. Sump-pit: A sump-pit collects water from the home’s weeping tiles. Sump-pump: A sump-pump is a device that is placed into the sump-pit to pump weeping tile discharge out of the basement. Surcharge: The technical term for water backup in a sewer pipe due to insufficient capacity from overloading or blockage. See "Sewer backup." Swale: A grassy, shallow ditch-like depression used to direct stormwater flows. Urban flooding: Urban flooding occurs in urban areas, where there is a high concentration of buildings and impermeable surfaces, such as roadways, parking lots and roofs. This type of flooding can result from heavy rainfall, snowmelt or surcharging sewer systems. Urban flooding can occur in areas that are not at risk of flooding from rivers or other natural surface water bodies. Weeping tile: A series of tiles or a perforated pipe located along the bottom of a building’s foundation that is used to collect and drain groundwater away from the building.