Changing weather patterns in the UK have led to increased flood risks for low lying properties and periodic rises in the water table in many areas. The Met Office states
"Evidence of heavy rainfall events may have become more frequent over time; what in the 1960s and 1970s might have been a 1 in a 125-day event is now more likely to be a 1 in an 85-day event."This ties in with the Met Office records, which shows that since 1910 record-breaking rainfall months or seasons have occurred 17 times, 9 of which have occurred since the turn of the millennia. A cause for concern for many basement owners, but what are the practical implications of this, and how does it affect your property? According to the Environment Agency, over 5 million properties in the UK are at risk of flooding. That’s approximately one in five homes. In the Yorkshire area, the main risks of flooding come from surface water and, riverside and floodplain locations (e.g. Knottingly and Hull). Many of the ‘flash floods’ occurring in the UK over the last decade have come from surface water flooding. Surface water flooding occurs when excessive precipitation falls over a short period of time, meaning rivers burst their banks and infrastructure such as drainage systems and flood management systems cannot cope with the sudden deluge. By design, Basements are inherently the part of a property the most prone to flooding. They are the lowest level of a building, typically built partly or entirely below ground level. But how does basement flooding occur? Basement flooding in extreme weather occurrences can be caused in a number of ways: 1. Surface inflow, or overland flooding During heavy rain or snowfall any excess water, which the ground cannot absorb collects as surface water. This surface water may pool around the house or accumulate in hard surface depressions such as ditches and driveways. The settlement of lot grading around a building and downspouts discharging roof run-off water too close to your house can add to the volume of surface water. This water can then flow into your home via cracks and defects in the construction. 2. Seepage. After heavy precipitation, the ground absorbs water. Some of the water is directly absorbed by the soil. The remaining water works its way down through the ground and collects at a certain level. The level at which water accumulates is dependant upon previous precipitation and the local geology, but is known as the ‘water table’. If the water table rises, water can enter the basement via cracks, holes and other unintended flow paths. Regardless of the condition of the drainage materials and pipework around the foundation, if water can enter the foundation floor or walls via cracks and holes or other defects, it likely will do so during heavy rains, ground-thaw or snow-melt periods, when there’s lots of water in the ground. 3. Foundation drainage failure. Homes usually have some form of a drainage system built around them. This safeguard promotes the movement of water away from the basement and blocks the entry of water into the building. Over time sediment can build up in the drainage system, or cracks can form in pipes leading to additional water accumulating around your foundations. So as Home-owners what precautionary measures can you take to minimize flood damage to your basement? 1. Regular maintenance and servicing of your drainage infrastructure. Gutters and downspouts must be cleaned to ensure fast drainage and discharge of precipitation away from the walls of your property. Good drainage infrastructure ensures that roof runoff is removed efficiently. With poorly maintained drainage water can collect and stagnate near the foundations, which can lead to seepage. 2. Sump pump installation and maintenance. A sump pump and sump pit can provide piece of mind knowing that any water will accumulate in the pit and be discharged swiftly to avoid basement flooding or damage to foundations. Regular servicing of the sump pump will ensure performance is optimized. 3. Proper grading of the property Land grading is the art of sculpting the soil in the landscape to promote proper water drainage. The consensus seems to be that a good slope to aim for when grading land extending out from a house foundation is about 6 inches for the first 10 feet this translates to a "slope" of 5 percent. 4. Flood insurance While the above precautionary measures will minimize your risk of basement flooding, if you live in a flood prone area you will need specialist flood insurance on top of your home insurance. If you are unsure if your home is lies within a flood-prone area the Environment Agency’s Flood Map For Planning will show the likelihood of flooding based on your postcode. For more information about the type of flooding which could occur in your area the Environment Agency’s Flood Risk Tool provides a colored overlay map distinguishing flooding from rivers, surface water, and reservoirs.