Types of flooding

The information below is a guide to the different types of flooding, their causes and the organisations responsible for managing them.

Surface runoff

The Flood and Water Management Act 2010 (FWMA) defines surface runoff as; rainwater (including snow and other precipitation) which (a) is on the surface of the ground (whether or not it is moving), and (b) has not entered a watercourse, drainage system or public sewer.

In addition, Planning Policy Statement 25 (PPS25) states that; intense rainfall, often of short duration, that is unable to soak into the ground or enter drainage systems can run quickly off land and result in local flooding.

There are several stakeholders identified by the FWMA who have a role in the management of surface runoff flooding, these are; Lead Local Flood Authorities, Local Planning Authorities, Water Utilities Companies, Highways Authorities, Riparian Owners.

Ordinary Watercourses

Ordinary Watercourses are defined as; every river, stream, ditch, drain, cut, dyke, sluice, sewer (other than a public sewer) and passage through which water flows and which does not form part of a main river.

In the County of Norfolk there are approximately 7,178 km of mapped ordinary watercourses that are included in the Environment Agency’s Detailed River Network dataset. This is undoubtedly a conservative figure as many ordinary watercourses in Norfolk remain unmapped.

In terms of local flood risk management, these watercourses are still largely influenced by the Land Drainage Act 1991. This Act identifies three key stakeholders in the management of ordinary watercourses, these are; Internal Drainage Boards, Local District Authorities and Riparian Owners.

Groundwater

The Flood and Water Management Act 2010 defines groundwater as; water below the surface of the ground and in direct contact with the ground or subsoil.

It is worth noting that this definition does not include water in buried pipes or other containers.

The UK Groundwater Forum describes groundwater flooding as a result of water rising up from the underlying rocks or from water flowing from abnormal springs.

Flooding from groundwater is classed as a Local Flood Risk and as such is the responsibility of the Lead Local Flood Authority which in Norfolk is Norfolk County Council.

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