EPG Clear UK - Flood Risk Assessments

In accordance with Planning Policy Guidance Note 25 (PPG25), local planning authorities must ensure that flood risk is taken into account as part of the planning process for all new developments so as to reduce the risk of flooding and the damage it causes.

Flooding is a natural process that poses a risk to people and property, and the experience of recent years suggests that the incidence and frequency of flooding may be escalating.

Flood Risk Assessments are required to accompany planning proposals to identify the threat of flooding for the proposed development and the measures by which the risk can be minimised or avoided. PPG25 sets out Government policy on minimising the flood risk to property and the environment, outlining specific issues that should be addressed.

EPG Clear is able to provide clients with appropriate and expert advice regarding the scope and detail of works required for a Flood Risk Assessment that is determined by the scale and location of the development.
The key components of a Flood Risk Assessment are identifying the source of flooding, reviewing the flood history, deriving critical water levels and identifying any influences on river hydraulics. Projects must assess flooding from tidal, fluvial, groundwater, and on-site drainage sources individually and in combination. River modelling may be required where sufficient flood risk data does not already exist.
In addition to evaluating the direct risk of flooding the Flood Risk Assessment covers a number of other factors such as loss of floodplain storage and surface water drainage issues.

Development often imposes new land uses on an area, which in turn can increase the surface water runoff during a storm event. Drainage calculations establish storm runoff from the site, and assess the risk of flooding should the drainage system become restricted.

Having assessed the flood risk to a site, a series of alleviation measures and engineering options such as Sustainable Urban Drainage Systems (SUDS), on-site storage and compensation storage can be evaluated by which the risk can be avoided completely or mitigated within acceptable limits to avoid flooding on-site or elsewhere.

EPG Clear has a team of engineers and specialists in hydraulics based around the country capable of providing clients with expert technical advice on flood risk assessments for small and large developments. We can produce comprehensive reports addressing the issues raised in PPG25 to meet the requirements of the Environment Agency and local planning authorities.

It is important to take account of any flood risks early in the development process as planning policy and EA advice can become significant constraints on the potential use of available land packages.

EPG Clear provides the following capabilities to support the completion of flood risk assessments

		Desktop investigations to utilise existing and historic data

		Site Surveys and topographical surveys

		Hydrological studies

		Hydraulic modelling using InfoWorks and HydroWorks

		River modeling using ISIS and HEC-RAS

		Postcode mapping

		Drainage assessments

The most important elements of flood risk assessments are the discussions with the Environment Agency to establish the site specific requirements and to confirm the level of detail that is required. Adequate information relating to the proposed development and the affected flood plain can then be collected.

River modelling may be required if justified by the size and complexity of the development. River models can be used to represent the associated watercourses and flood plain and provides an understanding of how the level of flood risk may change. River modelling can be tailored to suit the requirements of each development and to suit the available data.

The information is then used to prepare an assessment report, in which a recommended approach to achieving the required development with a minimum level of flood risk impact will be presented.

EPG Clear is also experienced in the design and management of SUDS and has designed schemes for a diverse range of projects. The implementation of SUDS is implicit in the requirements of PPG25.

A case study for a recent Flood Risk Assessment can be found below

Holmfirth Flood Risk Assessment (PDF File)

Intro	Sustainable Drain Design	Flood Risk Assessments

Drainage Assessment and Modelling		Contact Details