Our Location
Leonards Road, Ivybridge
Devon, PL21 0RU

Flood Risk Assessment, SUDs & Sewerage Design

JGP’s engineers and scientists have considerable expertise in a wide range of water-related disciplines including Flood Risk Assessment (FRA); hydraulic modelling, river and coastal engineering, surface and foul water drainage design and catchment and water resources studies.

Our engineers can provide guidance on all aspects of drainage and flood alleviation schemes including project initiation, feasibility studies, detailed design, planning and statutory approvals, tendering and contract supervision. We also undertake site investigations for soakaway and percolation tests; as well as site appraisals of existing infrastructure.

Flood Risk Assessments

All forms of flooding and their impact on the natural and built environment are material planning considerations and flood risk can be an important issue for developers. JGP is able to guide developers through the planning process, National Planning Policy Framework (NPPF), and can provide a Flood Risk Assessment (FRA) tailored to suit the location, scale and type of development. Liaising with the regulatory bodies enables us to ensure regulatory compliance and reach appropriate, cost-effective and pragmatic solutions for our clients. A FRA is required to accompany a planning application where a development site is located within Environment Agency indicative Flood Zones 2 or 3; is larger than 1 hectare; is located within an Environment Agency-designated ‘Critical Drainage Area’; or is likely to affect a watercourse, such as the culverting of an open-channel. New developments need to be safe to use over their intended lifetime and must not result in an increase in flood risk elsewhere.

Depending on the proposed development and flooding scenario, our FRAs can range from simple factual statements to detailed flood modelling with hydraulic analysis and interpretation. Our Flood Risk Assessment services include:

  • Catchment hydrology and flood flow estimation using the Flood Estimation Handbook
  • Procurement of flood data from the Environment Agency
  • Hydraulic flood modelling (1-D and 2-D) to determine flood levels, extents and hazard
  • Extreme tidal flood and wave action, including wave overtopping analysis
  • Consultation with Environment Agency and Local Authority Officers
  • Advice and design for flood risk mitigation measures to make development safe
  • Collation and assessment of the evidence required by the Local Authority for Sequential and Exception Tests
  • Residual uncertainty analysis to EA guidance
  • Code for Sustainable Homes (CfSH) Design Documentation for Flood Risk (SUR2)

River and Coastal Engineering

Our Engineers are experienced in hydraulic and structural design of:

  • River and coastal structures such as channels, culverts, weirs and fish passes;
  • Flow controls devices;
  • Flood defence, including sea walls;
  • Erosion protection; and
  • Cliff and coastal slope stabilisation.

We can carry out hydraulic modelling and wave overtopping calculations to achieve appropriate design standards and performance. We also prepare applications for statutory consents including Marine Licences, Flood Defence Consent and Abstraction Licences.

Hydrology and hydrogeology

JGP offers a comprehensive range of hydrological and hydrogeological services including:

  • Determination of catchment characteristics, both by on-site observation and desk-based resources including the flood estimation handbook;
  • Determination of rainfall intensities by using a variety of methods:
  • Calculation of Greenfield run-off rates using variety of methods, including Revitalised Flood Hydrology 2 (ReFH2) models;
  • Ground infiltration testing to BRE 365;
  • Consideration of ground stability and contamination in relation to infiltration;
  • Groundwater monitoring and flow path assessments.

Surface Water Drainage, including SuDS

JGP has considerable experience in the design of cost-effective surface water drainage and attenuation systems to satisfy the Environment Agency and planning authorities.  Our engineers have extensive expertise in the design of Sustainable urban Drainage Systems (SuDS), which are an integral element of surface water drainage schemes for property developments of all scales.  We can provide comprehensive advice and design for any scale of development, including:

  • Surface water drainage design
  • Sustainable Drainage Systems (SUDS) strategy and implementation;
  • Surface water soakaway and attenuation systems;
  • Rainwater harvesting;
  • Drainage strategies to address Planning Consent Conditions; and
  • Code for Sustainable Homes (CfSH) Design Documentation for Surface Water Management and Run-off (SUR1)


Our ground investigation engineers carry out site investigations with infiltration tests to inform drainage design.  Where slow infiltration rates are encountered, our engineers can employ continuous water level monitoring equipment to enable tests to be carried out cost-effectively over several days:

Soakage Tests – carried out in accordance with BRE 365, provide infiltration rates for soakaway design for surface water drainage.  The test includes an assessment of the geology on-site and potential flow paths to ensure that drainage will not affect down-slope properties.

Percolation tests – conducted in accordance with BS: 6927, within smaller hand-dug trial pits.  These tests ptovide infiltration rates for the design of foul drainage.

Our engineers can also provide site appraisals of existing drainage infrastructure.

Foul and Wastewater design

JGP offers a high-quality design service for foul water and wastewater disposal. Our expertise includes private or mains drainage for developments of any size from residential to commercial/industrial sites.

We can also provide designs and project management services for wastewater treatment plants and pumping stations.