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Flooding Types

Flooding types

Learn more about the different types of flooding from:

Surface Water
Ground Water
River Water
Sewer Water

Learn more about flooding from surface water

Surface water flooding is the main source of flooding in our catchment areas when rainwater does not soak into the land or enter a drain, pond, reservoir, lake or river.

It usually happens during heavy rainfall (regarded as more than 30mm per hour) and is made worse by blocked ditches and drains, very dry, compacted soils (after periods of drought) and or, perversely, waterlogged soil.

Our area is quite rural so one of the main sources of surface water flooding is from agricultural run-off. Unfortunately, there is no early warning system for surface water flooding and it is difficult to predict.  However, you can check the risk of flooding here.

Farmers are encouraged to manage their land in ways that reduce run-off.  As well as reducing flood risks, improved management techniques will reduce the loss of valuable top soil, which is particularly visible when full rivers reflect local soil colour.

Learn more about flooding from ground water

Groundwater flooding happens naturally when water levels in the ground rise above the surface. It is common after long periods of constant heavy rainfall and likely in low lying areas, those with natural springs where limestone (chalk) is the main bedrock.

It may appear as a wide area of flooding (across flat ground) or at a low point e.g. a spring.

Impacts include the flooding of:

  • basements, underground car parks and similar structures
  • land and property, damaging possessions/crops/stock
  • sewer systems, in some cases lifting manhole covers and flooding the area with sewage (causing pollution as well as a flood incident)
  • utilities sited underground (power lines/telecoms/drinking water supply) causing service failures. Groundwater flooding may last far longer compared to other types (from weeks to months).
  • If a property is found to be at risk of this type of flooding, options are limited, both because of the volume of water typically involved and the difficulties in containing or channelling it. Some general measures to limit the impact include:
    • Moving services (electrics, boilers, service meters) well above the likely flood level if possible
    • Using water resistant materials (such as lime plaster or cement render) rather than gypsum plaster on walls
    • Using plastic or steel units in the kitchen and ground floor bathroom (rather than the usual chipboard carcasses)
    • Using waterproof flooring such as tiles rather than carpets
    • ‘Tanking’ (waterproofing) of basements/cellars
    • Collecting water in a sump (a low point into which water can drain) under the floor or next to the property
    • Using pumps to dispose of small quantities of water, which can then be discharged into a stream, ditch or drain (after receiving appropriate permissions)
    • Fitting non-return valves to drainage systems
    • Protecting septic tanks/cess pits with a concrete surround.

Learn more about flooding from river water

River flooding happens when a stream or river cannot cope with the amount of water that is flowing into it from the surrounding land. Rivers are usually defined as larger water courses, in our case the Rivers Welland and Witham, but also some smaller streams that are important for drainage can contribute to a flooding event. Other watercourses – smaller rivers, streams or ditches – can flood independently and locally all the while adding to the volume of water that larger rivers have to then carry.

The maintenance of watercourses is important and plays a key role in flood risk management. Responsibility for the maintenance of watercourses, particularly in relation to roadside ditches, is often misunderstood.  The legal term for this is ‘Riparian Ownership’.

If you own land including or alongside a watercourse then you are responsible for ensuring the flow of water through that channel.  The answer is not always dredging as this often speeds the water onto neighbouring properties.  A watercourse needs to be kept in good order to prevent flooding. This includes maintenance of the bank and bed, as well as any trees and shrubs growing on the banks. Any debris must also be cleared by the owner of the section, even if it did not originate from their land.  There are many techniques to manage and slow water levels, including natural flood management schemes

Learn more about flooding from sewers

Sewer flooding happens either when pipes in the network become blocked or when there is heavy rainfall and the sewers cannot cope with the volume of water as they are often not designed to cope with heavy or prolonged rainfall, which is more prevalent as a consequence of climate change. The danger of this type of flooding is that water is often contaminated with raw sewage. There are three main types of public sewer:

  • PUBLIC FOUL SEWERS: waste water from toilets, bathrooms, kitchens, washing machines and industrial effluent
  • PUBLIC SURFACE WATER SEWERS: rainwater from roofs, driveways or car parking areas
  • PUBLIC COMBINED SEWERS: these carry both surface and foul water. Sewerage companies are responsible for cleaning public sewers and must also ensure that an area is well drained.
  • The upkeep of sewers in the Trust’s catchment areas are the responsibility of Anglian Water, Southern Trent Water and Thames Water.