Flood Risk management

Legislation

Two pieces of new legislation that impact upon flood risk management and local authorities were created recently. These are the Flood Risk Regulations 2009 which came into force on December 10 2009, and the Flood & Water Management Act (FWMA) which gained Royal Assent on April 8l 2010.

The Flood Risk Regulations 2009 was created to transpose the EU Floods Directive (Directive 2007/60/EC) into domestic law in England and Wales. The Floods Directive provides a framework to assess and manage flood risks in order to reduce adverse consequences for human health, the environment (including cultural heritage) and economic activity.

The Flood and Water Management Act 2010 makes specific provision for the recommendations provided by Sir Michael Pitt in his independent review of the flooding experienced across much of England and Wales in 2007.

Under these pieces of legislation, LB Tower Hamlets, as a Unitary Authority has been designated a ‘Local Lead Flood Authority’ (LLFA) and has formally been allocated a number of key responsibilities with respect to local flood risk management.

Preliminary Flood Risk Assessment

Under the Flood Risk Regulations 2009, LB Tower Hamlets was required to carry out a Preliminary Flood Risk Assessment (PFRA) This is a high level screening exercise to identify areas of significant flood risk within a given study area. The flooding could be caused by surface water, groundwater, ordinary water courses or canals. The PFRA involved collecting information on past and future (potential) floods, assembling the information into a Preliminary Flood Risk Assessment report, and identifying Flood Risk Areas.

The PFRA report for LB of Tower Hamlets provides a high level summary of significant flood risk, based on available and readily derivable information, describing both the probability and harmful consequences of past and future flooding. This information is used as the basis for action to prevent future flooding or to mitigate its impact.

Surface Water Management Plan

LB Tower Hamlets, as LLFA, is required to produce a Surface Water Management Plan under the FWMA. Direct rainfall modelling was carried out across the borough for a number of scenarios that were likely to create flooding. It’s the same raw data that was used in the PFRA. The results of this modelling were then developed to identify Local Flood Risk Zones (LFRZs) where flooding affects houses, businesses and/or infrastructure. Those areas identified to be at more significant risk have been delineated into Critical Drainage Areas (CDAs) representing one or more LFRZs as well as the contributing catchment area. These are all described in the SWMP

Having identified the potential risk, the SWMP turns to focus on what action the borough as LLFA should take or lead on to reduce flooding in LFRZs specifically and elsewhere and/or mitigate its harmful effects. This is summarised in the SWMP Action Plan.

Strategic Flood Risk Assessment (Level 2)

LB Tower Hamlets, as Planning Authority, is required to produce a Level 2 Strategic Flood Risk Assessment (SFRA) in support of its Local Development Framework. It builds upon the Level 1 SFRA completed in August 2008 and was produced in response to the guidance in Planning Policy Statement 25- Development and Flood Risk (now withdrawn). The Level 2 SFRA has been able to incorporate the information on and risk posed by surface water flooding that was identified in the PFRA and then SWMP.

Volume 1 of the SFRA contains a general assessment of the risk from all sources of flooding across the whole borough. This is followed in Volume 2 with a detailed analysis of where flood risk is a significant issue in 31 individual key development sites. It describes the potential sources of flooding and provides relevant guidance for both planners and developers alike.

Local Flood Risk Management Strategy

The Tower Hamlets Local Flood Risk Management Strategy (LFRMS) is designed to provide guidance and information for residents, businesses and developers regarding Tower Hamlets strategy for dealing with flooding within the borough.

It contains an explanation of the work to assess the potential risk of flooding with a description of our work to investigate this through more detailed borough-wide modelling. Surface water is tracked through a composite model containing rainfall, land topography, gullies and sewerage so as to identify the nature, extent and location of predicted flooding.

The strategy outlines the ways in which, the impact of flooding may be mitigated. It covers the essential role gullies play as the first line of defence and continues with an explanation of the measures that we are taking to protect property. This is followed by an overview of the valuable contribution that SuDS can make to prevent flooding, together with a link to our SuDS Guidance document.

SuDS guidance document

SuDS absorb excess surface water and reduce the pressure on the standard drainage system. They are either placed in the street or in developments. The drivers for LBTH to introduce SuDS are European directives and London planning guidance which have fed through to Council planning policies. More recently the Flood & Water Management Act has reinforced the need by Lead Local Flood Authorities to promote and install SuDS.

The LBTH SuDS guidance is aimed at developers, council officers and other bodies within the borough who would install SuDS. It begins with a description of the legislative and policy background and then explains the nature, purpose and attenuation requirements of SuDS in Tower Hamlets.