Hydrology

We are an independent planning and environmental consultancy delivering a wide range of hydrological solutions to clients across the UK.

We work to develop a client–based relationship based on trust, and place emphasis on adding value, innovation and professionalism to achieve deliverable outcomes; meeting expectations, budgets and timescales. Our comprehensive understanding of policy and procedures and our director-led multidisciplinary approach ensures we bring to bear the right mix of skills and experience to provide creative solutions for the most hydrologically challenging and complex projects.

A simple guide to flood risk assessments

A flood risk assessment is required for any development over one hectare, or which sits within the flood zones as defined by the Environment Agency, SEPA, or Natural Resources Wales. They are designed to make sure development is guided to the lowest flood risk areas, thereby protecting property and people from the dangers of flooding. They are often a requirement for validation of a planning application or to better inform owners/prospective purchasers of the flood risk to their land and buildings.

What is a flood risk assessment?

A flood risk assessment is a technical document looking at detailed flood risk written by a Chartered professional, e.g. CIWEM, ICE. It examines all the flood risks from all sources of flooding, e.g. (fluvial, pluvial and groundwater), and looks at Sustainable Drainage measures to reduce surface water flood risk areas. It may involve flood modelling to determine a flood event by risk assessment, or to redefine flood zones. It is a technical document which compares spatial data from a variety of sources, e.g topographic survey, river flood levels, tidal flood levels, bringing it together into a comprehensive analysis document to understand the flood risk of an area or region of land.

Why do I need a flood risk assessment?

Flood Risk Assessments are required for planning applications/planning permission based on guidance within the national planning policy framework, or from recommendations made within strategic flood risk assessments or the agency flood map. Local planning authorities will advise of the requirement for a Flood Risk Assessment within their planning application validation requirements. They may also request a sequential test. Development sites within critical drainage areas also require assessment. The assessment will identify if the property is at risk of flooding, and may recommend a flood warning and evacuation plan. Flood Risk Assessments can also be required for COMAH installations, where the risk of flooding and potential release of pollutants is a risk. Insurance disputes can also require assessments to determine if an activity is increasing flooding or causing nuisance to another property.

What should a flood risk assessment report include?

Enzygo’s flood risk assessments have been tried and tested at numerous planning appeals and are, therefore, regarded as very robust. Many of our clients regard the Enzygo report as a gold standard in the assessment of flood risk due to its thoroughness and deliverability when undertaken for development site proposals. The typical content of a Flood Risk Assessment is as follows: Executive Summary; this provides a summary of the report on one side of A4 so readers can quickly understand the content of the report and the results/recommendations of the assessment.

Flood Risk Assessment

introduction

Provides background on the report, sets out its objectives and aims, alongside the legislation relevant to the assessment.

source of information

This section identifies the information relied upon by the report, listing each source and where it can be found in the reports appendices, it also highlights any consultations with statutory regulators such as the water companies, local councils, lead local flood authorities and environment agency. Details of the site walkover are also included alongside any water features on site.

site location & description

Here the report looks at the site location, land use, topographic information, soils and geology alongside hydro-geology sewerage and drainage assets details.

flood risk assessment

The potential sources of flooding are reviewed alongside sewer flooding and flooding from infrastructure failure.

Flood risk mitigation measures

Mitigation measures are proposed for the development if required and the flood risk is summarised and guidance on the sequential and exception tests provided.

site drainage

The existing surface water drainage regime is explored, greenfield runoff rates calculated, suds options explored alongside a surface water management strategy being developed. Exceedance routes are understood, should the drainage fail, and a foul drainage strategy is developed.

summary & conclusion

Reviews the flood risk, mitigation measures and flood guidance detailing the sites drainage and an overall conclusion to the overall assessment.

How much does a flood risk assessment cost?

Flood Risk Assessments for Planning and Environmental flood risk assessments can vary in price, this mainly depends upon the size of the site and complexity of flooding sources. A very basic flood risk assessment can start from as little as £1,500 ex VAT, depending upon what is required and the sources of flooding. More complex flood risk assessments for planning applications are typically £3,000 to £8,000, these often include soakaway testing, drainage design and purchases of complex data sources. Where flood modelling is required, this can mean the addition of thousands of pounds, depending on the size of river modelled. It is important to remember that just because you submit a flood risk assessment, it doesn’t guarantee a success, and additional work can be required.