Flood risk assessment and hydraulic modelling

Planning applications and managing flood risk

The Environment Agency estimates that year on year flooding in the UK poses a huge risk to people and property. The increase in frequency of extreme weather events is evidence that this is becoming a reality we have to live with, here in the UK and globally.

UK government policies for minimising flood risk to property and the environment are set out as follows;

  • National Planning Policy Framework (NPPF)
  • Scottish Planning Policy [Sections 196 – 211] / Flood Risk Management (Scotland) Act 2009
  • Northern Ireland Strategy Planning Policy Statement (SPPS)
  • Wales Technical Advice Note 15 (TAN 15)

Local authorities, in accordance with the guidance, ensure that flood risk is a consideration in the planning process for all new developments to lessen the risk of the damage caused by flooding, so it is essential to have full understanding of any flood risks and evidence of this to be provided as part of the planning process

Workers at a work site, the ground has been dug up

The FRA will accompany the planning application, as the document outlines the threat of flooding and the measures by which the risk can be mitigated or avoided.

A Flood Risk Assessment is determined by the scale and location of a development; therefore, we will ask the right questions to ensure we provide the correct advice in relation to the scope and detail of a project.

In conjunction with the above, we will identify the potential source(s) of flooding, review flooding history, obtain critical water levels and determine the influences on river hydraulics. The FRA will consider flooding from tidal, fluvial, groundwater, sewer, highway and on-site drainage sources. The assessment can cover a number of other factors such as loss of floodplain storage, washland modelling, flood plans, access and egress, sequential testing, exception testing and surface water drainage issues.

Through a series of alleviation measures and engineering options, we will determine the most cost effective and practical solutions to completely avoid or mitigate, within acceptable limits, the risk of flooding on-site or elsewhere.

EPG has hydraulic modelling capabilities that ensure we can undertake compliant Strategic Flood Risk Assessments (SFRAs) and Flood and Coastal Erosion Risk Management (FCERM) appraisal projects.

Do I need a drainage impact assessment (DIA)?

A Drainage Impact Assessment (DIA), which often complements the FRA, provides a preliminary review of the potential options for drainage design that may be developed in avoidance or mitigation of flood risks. It also considers the physical changes that the proposed drainage measures may cause to the development and the off-site area drainage efficiency beyond the proposed development. The DIA is supplemented with Microdrainage, Causeway Flow or InfoDrainage calculations to prove the existing runoff rates from site (brownfield or greenfield) and to determine the betterment of the proposed drainage system.

The DIA invariably offers an outline design for an appropriate sustainable drainage system that will consider benefits in comparison with the existing flood protection measures.

Flowing water

Hydraulic modelling

Hydraulic modelling is a technique which involves creating a computer model that mimics the hydraulic characteristics of rivers, streams, floodplains, drainage systems and sewers and coastal areas. These models predict the volumes, flow pathways and velocity of water as it moves through an identified area.

EPG uses hydraulic modelling for SuDS and NFM designs, and also for FRAs sFRAs and FCREM projects.

We use the latest fully integrated one-dimensional (1D) and two-dimensional (2D) industry accepted software.

A 1D (one-dimensional) hydraulic model is used when the primary focus is on simulating and analysing the flow of water in a single dimension, typically along the length of a channel or a pipeline. It is suitable for the modelling of open channel flows, rivers and streams modelling, sewer and urban stormwater drainage and pipeline systems.

A 2D model solves the equations across a 2D mesh for a represented area showing the flow patterns in a horizontal and vertical dimension. It is suitable for direct rainfall modelling, floodplain and coastal mapping, urban flooding, and dam and breech analysis.

A 1D/2D hydraulic model combines elements of both one-dimensional (1D) and two-dimensional (2D) hydraulic modelling to provide a more comprehensive representation of water flow in a hydraulic system. The hydraulic system is divided into components where 1D elements (typically representing the main channel or pipes) are combined with 2D elements (representing floodplains, overland flow, or other areas with lateral spreading). It is suitable for main channel flow where it floods onto a flood plain, urban drainage with urban flooding and direct rainfall, hydraulic structure analysis.

EPG primarily uses TUFLOW and ESTRY as its hydraulic modelling software which is an EA approved software for use on FCERM projects.

To talk to us about your project please fill in the form below, email us on enquiries@epg-ltd.co.uk or talk to us on 01925 652983.   

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