Hydrology, Flood Risk and Drainage

Hydrology, Flood Risk & Drainage

Hydraulic Modelling

We are able to produce models of fluvial, tidal and surface water systems to assess the risk and hazard created by a flood event, through the use of industry standard hydrodynamic software packages including MicroDrainage, Flood Modeller Pro and HEC-RAS.  The models enable us to predict a range of statistics including flooding depths, velocities and inundation rates.

For existing or proposed reservoirs we are able to undertake Reservoir Inundation Modelling to produce flood inundation mapping to assess the impact of a breach to a reservoir.

Assessment of Flood Risk

We have extensive experience in producing Flood Risk Assessment (FRA) reports for sites at risk of fluvial (river), tidal, pluvial (surface water) and groundwater flooding or alternatively exceeding 1 hectare.  The FRA will review potential sources of flooding to the site, which may involve obtaining flood data from the Environment Agency or undertaking in house hydraulic modelling.  The report will identify the risks associated with flooding and if required, we will recommend appropriate mitigation measures (flood resilient/resistant construction techniques). 

As part of the FRA we will produce a preliminary assessment of the existing and proposed surface water drainage system, however if required the report can be upgraded to a Flood Risk Assessment & Surface Water Drainage Strategy which will incorporate a schematic surface water drainage design.

The typical scope of the Flood Risk Assessment & Surface Water Drainage Strategy includes the following;

• Where necessary obtaining Environment Agency flood level data, details on historic flooding and flood defences within the vicinity of the site
• Establishing the likelihood of the development flooding;
• Establishing the risk to the future site users;
• Establishing the need for flood mitigation methods to be utilised.
• An assessment of suitability for infiltration based on soil types and geology
• Review of groundwater sensitivity and groundwater levels
• Preparation of a schematic surface water drainage scheme for the proposal including Micro Drainage Design Simulations and drainage plan
• Calculations showing the pre and post development peak runoff flow rate for the critical rainfall event
• Preparation of a surface water maintenance schedule
• Details on how the drainage design satisfies SuDS techniques in terms of water quality, attenuation and discharge for the lifetime of the development

If you are concerned that your development may not be viable due to the risk of flooding we offer flood risk feasibility services that provides guidance on the best way to move development forward in more challenging areas.

We provide Flood Warning and Evacuation Plans for existing and proposed developments to support Flood Risk Assessments where development occurs in Flood Zone 2 and 3 or to address planning conditions.

Surface & Foul Water Drainage

With the introduction of the Lead Local Flood Authority (LLFA), planning authorities are requesting that sustainable drainage schemes (SuDS) be prepared at earlier stages in the planning process.  Plandescil are able to undertake Surface Water Drainage Strategy reports that incorporate the requirements of the Local Authorities Checklist for full or outline applications.

The typical scope of the Surface Water Drainage Strategy includes the following;

• An assessment of suitability for infiltration based on soil types and geology
• Review of groundwater sensitivity and groundwater levels
• Preparation of a schematic surface water drainage scheme for the proposal including Micro Drainage Design Simulations and drainage plan
• Calculations showing the pre and post development peak runoff flow rate for the critical rainfall event
• Preparation of a surface water maintenance schedule
• Details on how the drainage design satisfies SuDS techniques in terms of water quality, attenuation and discharge for the lifetime of the development

We design foul and surface water drainage systems for private and adoptable situations, obtaining the necessary statutory approvals (i.e. Section 104 and 106).

Our engineers have extensive experience in water management, flood alleviation, river engineering, drainage and irrigation schemes. Whenever possible we design sustainable drainage systems and are keen to promote efficient use of resources. We look for innovative ways to provide cost effective solutions to site conditions.