Fingal East Meath Flood Risk Assessment and Management Study

Topographical Survey

The topographical survey involves a number of different surveying activities. Information on each of these activities is detailed below.

Channel and structure cross sectional survey

The channel and structure cross sectional survey involves a land survey by teams of surveying specialists. The survey teams use specialised surveying equipment to gather detailed measurements of the shape of the river channel and any structures located in the river channel such as bridges or weirs. This information is gathered at regular intervals along the river channels in the form of cross sections.

The watercourses that are understood to give rise to the existing or potential future flood risk within the catchment (such areas include existing towns and villages subject to flooding, and other areas understood to be prone to flooding and for which significant development is anticipated) are defined as High Priority Watercourses (HPWs). For HPWs cross sections have been surveyed at approximately 50 to 100 metres along the river channel. For other areas of the catchment where flood risk is considered to be moderate, the watercourses which flow through these areas are defined as Medium Priority Watercourses (MPWs). Cross sections have been spaced at approximately 750 to 1000 metres for these MPWs. The information gathered as part of this survey has been used to develop hydraulic computer models of the watercourses in the study area. A map showing the HPW and MPW watercourses can be downloaded at the following link.

DigiTech 3D were appointed as the survey contractor to carry out the survey works which took place between Winter 2008 and Winter 2009.

Flood defence geometric survey

A geometric survey of the flood defence assets surveyed as part of the flood defence asset survey has been completed. The survey was carried out by DigiTech 3D, who gathered information on the shape and height of flood defence assets in the study area. This information has been added to the Flood Defence Asset Database (FDAD) and used to develop the hydraulic computer models of the study area.

LiDAR survey

LiDAR (Light Detection and Ranging) involves using an aeroplane with a special measuring device to provide detailed information on the shape and height of the ground. LiDAR data has been captured along the river corridors and the coastline in the FEM FRAM Study area. The LiDAR data has been used to develop a high resolution Digital Terrain Model (DTM) of the river catchments.

The DTM has been used in a number of the project activities including hydraulic computer modelling and flood mapping. The DTM has also be used to estimate property threshold levels to allow us to determine the depth to which properties are likely to be flooded. This information is used to assess the economic damage occurring as a result of flooding.