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Definitions 1

A Flood - is an overflow of a large amount of water beyond its normal limits, especially over what is normally dry land. 2 Flooding is a complex issue that can have numerous causes and usually arises from many different sources.

Source - the origin of flood water.3

Pathway - a route or means by which a receptor can be affected by flooding.4

Receptor - something that can be adversely affected by flooding.5

Intensity - The total rainfall depth (mm) divided by the total storm duration (hr).

Lag time - The time between the peak of the river flow and the centre of the rainfall.

Catchment - An area that serves a river with rainwater. Every part of land where the rainfall drains to a single watercourse is in the same catchment.

Rapid response catchment –This is a catchment that responds rapidly to rainfall.

Lead time – The time between a flood warning and an expected flooding event.

Flood alert – Issued to inform people that flooding is possible in a particular area, and thus that preparations should be made just in case as well as monitoring of the situation.

Flood warning – Issued to inform people that flooding is expected in a particular area, and thus that flood plans should be put into action, such as moving family, pets and valuables into a safe place.

Property Level Protection (PLP) 6 - A two year Defra pilot scheme, looking at the opportunity and benefits that improved property-level resistance and/or resilience measures might offer over sandbags or indeed no defences at all. Defra made £500,000 available for the scheme and a funding limit of £5,000 per property

Examples of the measures:

  • alleyway flood gates
  • door guards
  • air brick covers
  • sealing of apertures for pipes, cables, vents, etc.
  • the prevention of water entry through house drainage (WCs, drains, washing machine discharge pipes, etc.)
  • modified electrical systems – raised plugs and meters

Groundwater - Water which is below the surface of the ground and in direct contact with the ground or subsoil.

Main river- Large watercourses for which the Environment Agency has responsibilities and powers.

Ordinary watercourses - All watercourses that are not designated Main Rivers, and which are the responsibility of Local Authorities.

Fluvial flooding - occurs when rivers overflow and burst their banks, due to high or intense rainfall which flows into them.

Pluvial flooding - occurs when an extremely heavy downpour of rain saturates the urban drainage system and the excess water cannot be absorbed

Flooding from sewerage systems - occurs when the capacity of the drainage network is exceeded. This can be due to blockage, failure of equipment or overloading of sewers due to rainfall.7

Local flood risk - Flood risk from sources other than main rivers, the sea, and reservoirs, principally meaning surface runoff, groundwater and ordinary watercourses.

Wet Spots – are the name often given to key flooding locations, places where recent and relevant flood incident data indicates there is a high risk of future flooding.8

A Surface Water Management Plan is a study to understand the flood risk that arises from local flooding, which is defined by the Flood and Water Management Act 2010 as flooding from surface runoff, groundwater, and Ordinary Watercourses.  Therefore, the main aim of the SWMP is to produce a long term, area wide high level Action Plan to manage local sources of flooding within the Bath and North East Somerset area.9

Local flood risks that are the responsibility of the council: 10 11

  • Groundwater flooding - caused when the water levels in the ground rise above the surface level mainly as a result of prolonged rainfall causing the ground to become saturated. This may happen, for example, where there are underlying gravels, or porous or fractured rocks, allowing water to pass through. Flooding from natural springs would be classed as a form of groundwater flooding. Slow response means that groundwater flooding can occur a long time after prolonged or heavy rainfall and can last for a long time (often several weeks or months).
  • Surface water (rainfall) flooding - when water flowing over surfaces that cannot easily absorb water, such as roads and roofs, overwhelms the drainage network and accumulates on the surface. It is also referred to as pluvial flooding or flash flooding. This type of flooding often occurs quickly during, or shortly after, a high intensity storm.
  • Ordinary watercourses flooding - when any watercourse which is not classed as a main river such as a culvert or stream, cannot cope with large volumes of water during or after heavy rain and so the water overtops the banks. This can occur because there is more water draining into the channel than it can hold, or because it is blocked. Flooding from Main Rivers, (as defined by the Environment Agency) is not classed as ‘local’ flooding.

Local flood risks that are the responsibility of other Risk Management Authorities12

Bath & North East Somerset includes a number of Main Rivers* including the River Avon, Cam Brook, and the River Chew (as shown in Figure 1), which may present a flood risk to people living near to these. The operational management of flood risk from Main Rivers is undertaken by the Environment Agency who have developed plans and projects in partnership with other organistations.

The Environment Agency has created a Bristol Avon Flood Management Plan that includes details about flood risk in the city of Bath and other locations within Bath & North East Somerset. Wherever the Environment Agency develops plans or projects to manage flood risk on Main Rivers, the Council works with them as appropriate.

Figure 1: Ordinary watercourses and main rivers in Bath and North East Somerset 13

Main flood risk management responsibilities of the Council14

The main responsibilities of the Council associated with flood risk management are as the:

  • Lead Local Flood Authority
  • Local Highways Authority
  • Local Planning Authority
  • Emergency Planning Authority

As the Lead Local Flood Authority the Council is responsible for:

  • development, maintenance, application and monitoring of the B&NES Local Flood Risk Management Strategy;
  • recording flood incidents, investigating and publishing reports on flooding incidents as appropriate;
  • managing an Asset Register of structures or features which have a significant effect on flood risk in the region;
  • Ordinary Watercourse consenting and enforcement;
  • designation of assets (structures and features) that affect flooding, and;
  • statutory consultee for major planning applications with surface water implications.

As the Local Highways Authority the Council is responsible for:

  • maintaining adopted highways within the Bath & North East Somerset area,
  • ensuring highways are not dangerous for traffic.

As the Local Planning Authority the Council is responsible for:

  • preparing a Local Plan for development;
  • considering flood risk assessments submitted in support of applications;
  • determination of planning applications, giving consideration for flood risk within the region, and;
  • working closely with the Lead Local Flood Authority to ensure that planning
  • applications take adequate account of drainage requirements.

As the Emergency Planning Authority the Council has responsibility for:

  • planning for and responding to flood emergencies as a Category 1 responder under the Civil Contingencies Act 2004, and;
  • working closely with the Bristol & Avon Fire and Rescue Service and the Police Service to do this.