The extent to which a property is at risk of flooding is linked to the location of the property – that seems straight forward, don’t buy a house near a river or on the coast if you do not want to be at risk of flooding – simple – or is it? The straight answer is no. Although a property next to a river or the coast is more likely to be at a high risk of flooding, similarly a property that is nowhere near a river or the coast may also be at risk of flooding.
To understand flood risk, we need to consider the main causes of flooding:
Surface Water flooding (‘ Pluvial Flooding’)
In their publication ‘ A clear guide to Flooding for Property Owners’ the Royal Institution of Chartered Surveyors (RICs) state that there are estimated to be nearly 4m properties in the UK at risk of surface water flooding. To be affected by surface water flooding the property does not have to be anywhere near a river or the coast.
Surface water flooding is caused by the effect of prolonged and exceptionally heavy rainfall which causes the existing drains and sewers to overflow. Although more of a threat to low lying areas, and properties at the foot of a slope, surface water flooding can effect properties on higher land.
Surface water flooding is most common in urban areas due to the fact that most of the land is covered by impermeable surfaces such as tarmac and concrete. This is because the water flows off the land rather than being absorbed and soaking into the ground. Another cause is where there are new developments in the area and the sewers are not upgraded sufficiently to deal with the additional use.
Surface water flooding can be consigned to one or two individual properties at a time aswell as to whole streets and estates.
Ground Water Flooding
Similar to Surface Water flooding , this is caused through heavy rainfall and the reduced capacity of the existing drains and sewers to take the water away.
Unlike surface water flooding, which can occur very suddenly, Ground Water flooding builds up over time. In instances where there are prolonged periods of rainfall, the continued soaking of the ground raises the level of the water table until it is raised to above ground level. Areas which are most at risk of ground water flooding are those in low lying areas with porous soil and built on or around rock, or where the water table in the area is naturally high.
A risk to Ground Water flooding is not always immediately obvious, as the water table level is not visible. Ground water flooding is an increasing threat to properties with basements and cellars.
River Flooding (‘Fluvial’)
River flooding played a major part in the flooding that has occurred almost annually since 2007.
River flooding occurs when the rivers and streams are unable to carry away the water flowing within them. Increased water flow into the river may be caused by increased tidal pressure ( in tidal rivers) , surface water flooding ( water from the drains and sewers flowing into the river) and ground water flooding or a combination of some or all of these.The flood risk posed by river flooding is extenuated by poor maintenance of the rivers and streams by the agencies that are responsible for them.This can be by simply failing to dredge the river beds regularly or by not clearing the weed and reed growth both of which leave less room for the water to flow within the river.
River flooding is often extensive and longer- lasting than either surface water flooding or ground water flooding. The flooding caused by river flooding is often deep and fast moving. River flooding is also often widespread covering whole towns, farms and estates.
Tidal or Coastal Flooding
Tidal flooding is caused by high tides often combined with a storm which raises the level of the sea and defeats the existing sea defences. Associated mainly with the flooding of coastal towns, Tidal flooding may cause flooding in areas near tidal river basins which are some distance from the coast as the increased pressure from the sea tides forces flood water up the tidal reaches of the rivers and estuaries.Tidal flooding was very prominent this year in coastal town . Areas such as the Somerset levels which is in close proximity to the River Parrett ( a tidal river) was effected by a combination of both tidal and river flooding. It is widely believed that the incidences of tidal flooding are likely to increase as the sea levels rise due to global warming.
A review of the causes of flooding shows that whether or not a property is at risk of flooding is not an open or shut case. A property may have a very low risk of flooding at the outset, however changes in the area, such as an increase in new developments on flood plains may mean that the property becomes at risk of flooding.
Environment Agency Flood Risk Maps and Flood Risk Reports
The first check that a property owner or potential buyer can make is on the Environment Agency website where they have flood maps showing which areas are at a risk of flooding. The information provided by the Environment Agency flood maps is fairly general and not specific to individual properties.The Flood Maps show areas at risk and whether or not there are adequate defences against flooding in place.Until recently, the Environment Agency flood maps did not take account of surface water flooding which accounts for around 50% of flooding in the UK.
The Environment agency flood maps will also grades areas by post code depending on the risk of flooding. The Grades or bands used are low, moderate or significant.
For a more accurate assessment of the risk of flooding it is necessary to obtain a flood risk report from one of the many specialist search providers. A flood risk report will provide you with a detailed account of the flood risk for a specific property and will also break the detail of the flood risk down to risks from the different types of flooding. If the usual conveyancing searches undertaken in the Conveyancing process reveal a flood risk, the mortgage provider will usually insist on a specialist flood risk report.