Other potential causes of flooding

Preliminary historical data should be collected at this stage about landslides, avalanches, volcanoes and the modification of the river channel. 

After the site selection phase, if it is established that there is a potential for flooding or for serious erosion at a site, a detailed study should be undertaken to detect the reference mechanism for site flooding and, therefore, to define the relevant design basis flood for the plant. A similar study should be carried out within the framework of a safety assessment of the plant. In this latter option, the data from the site monitoring system which has been in operation since the preliminary phase of site evaluation should have the highest priority. 

Hydrological data to be collected include the following data  

Relevant bodies of water are aU streams, rivers, artificial or natural lakes, ravines, marshes, drainage systems and sewerage systems that may produce or affect flooding on or adjacent to the nuclear power plant site. Bodies of water that are outside the watershed in which the plant is located, but that may, by overflowing the watershed divide, produce or affect flooding of the plant site, are also considered relevant bodies of water. 

For bathymetric surveys a base level should be established. For a fixed base level, if not already available, a system of benchmarks should be arrayed and correlated with the national system of benchmarks. 

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