What is a floodline?

A floodline is a line drawn on a contour plan showing the edge of the water level of a river during flood condition. For instance, the 50-year floodline shows the top width of a river to be expected during a 50-year flood.

Why have floodlines?

Local authorities (e.g. municipalities, environmental protection agencies), in special cases also State Departments (e.g. Water Affairs, Environmental Affairs) request a floodline investigation report for all riverine developments, as the erection of buildings near or below the floodline is not allowed.

Which floodline must be considered?

Local authorities will determine against which flood (20-, 50-, and/or 100-year flood) a specific property or development must be protected. Usually a housing development will be protected against a 50-year flood. A 20-year flood might be considered for single, non-permanently occupied houses and fairways on golf courses, and a 100-year flood for high-value or strategic important structures. For a development, downstream of a major dam, even a dam-break flood investigation may be requested.