FLOOD RISK AND FLOOD LINE DETERMINATION
Flood risk and flood line determination are an important part of development planning for a wide range of potential developments. For commercial, housing and mining developments, no development may occur within areas that are potentially prone to becoming inundated with water, as a result of floods.
The need for flood line determination is frequently legislated or included in regulations. Typical examples would be regulations contained in:
General Notice 704 of the South African National Water Act (Act 36 of 1998), which stipulate that no mining activities may take place within, or below a defined 1:100-year flood line; or
Section 144 of the South African National Water Act (Act 36 of 1998) to ensure no person may establish a township unless the layout plan shows, in a form acceptable to the local authority concerned, lines indicating the maximum level likely to be reached by floodwaters on average once in every 100 years.
Flood risk and flood line determination form part of most hydrological investigations carried out by GCS. GCS can apply both statistical and deterministic methods can be used to determine design floods and flood hydrographs using industry accepted methodologies and approaches.
Flow rates through streams and rivers are modelled using state-of-the-art available hydrodynamic model packages (1D or 2D). Flood depths are calculated for a series of cross- sections across the river section. Calculated water levels can be mapped, using GIS or CAD, to indicate the areas that are likely to be flooded.
The GCS Hydrology Unit can assist a variety of clients to determine flood risk and flood lines for various planning purposes and engineering designs.