The diagrams illustrate two different methods for protecting buildings from flood damage in areas prone to heavy rainfall and rising water levels. One method involves the use of a stopbank, while the other shows an alternative approach in the absence of such a barrier.
In the first scenario, a stopbank is constructed parallel to a river or drain to prevent floodwaters from reaching residential areas. This embankment includes a berm and a floodgate, which help control the flow of water. A freeboard, or safety margin, is maintained above the 100-year flood level to further reduce flood risk. However, rainwater runoff from the land behind the stopbank can still cause internal ponding, so houses are built on raised platforms to prevent water from entering.
In contrast, the second diagram depicts a situation without a stopbank. Here, houses are elevated above the 100-year flood level by placing them on stilts or raised foundations. The floor level of the house includes a 300 mm freeboard above the predicted flood height to provide additional protection.
Overall, both methods aim to safeguard buildings from flooding, but the use of a stopbank provides a physical barrier against external floodwaters, whereas the raised building design relies solely on elevation to mitigate flood damage. The former is more infrastructure-intensive, while the latter is a practical solution in areas where constructing a stopbank is not feasible.