Flood Risk Assessment, Hydraulic Modelling, The Lane, Wyboston
Oct 4, 2016

Hydraulic Modelling and a Flood Risk Assessment has been completed by RAB Consultants in the proposal of the erection of new residential units at the site with associated access roads, gardens, paved areas, driveways, etc.

A large portion of the development is located in Flood Zone 3 in accordance with the Environment Agency. The main source of the flooding, Begwary Brook, which runs through the north part of the site, is therefore fluvial. There is no modelled data for the Begwary Brook and consequently a hydraulic model was developed, integrating all available geometrical information (topographic survey and LiDAR) while a hydrological assessment identified the appropriate flows for a range of return periods. By using Flood Modeller, 1D and 2D nodes were created in order to model the depth of flooding at this site.

The site is at risk of fluvial flooding during the 1% AEP (plus an allowance for climate change), however, replacing the culvert at Morris Walk would contain the water in Begwary Brook without overtopping.

Our assessment in order to meet the requirements of the National Planning Policy Framework involved:

  • Data collection, including hydraulic modelling of Begwary Brook
  • Liaison with the Environment Agency
  • An assessment of the risk of flooding from a number of sources including fluvial, groundwater and surface water, in accordance with Strategic Flood Risk Assessment for Bedford Borough Council

Updating the culvert was proposed in order for safe access and egress to be obtained. If the client decided not to update the culvert, development could not proceed in the 1% + 65% CC flood outline and therefore should only take place in Flood Zone 1. An access bridge would connect the north of the site with the south part of the site being placed at least 600mm about the 1% + 65% CC level.