In certain situations desk based information is not available or detailed enough to meet the requirements of a particular project brief. More detailed work is required to understand flood mechanisms and define flood risk. This may be the case when a site is located within Environment Agency Flood Zones 2 or 3, in a locality where detailed hydraulic modelling has not been undertaken.

Or, where a flood alleviation scheme is needed and a hydraulic model is required to define the level of flood risk and to develop an options appraisal.

A typical hydraulic modelling exercise would involve several key stages:

• Review of catchment hydrology using gauged data where available and/or standard methods of flood estimation
• Construction of a hydraulic model within a 1D model such as HEC-RAS or ISIS
• Analysis of results from the hydraulic model to define flood extent and water levels.