The given diagram explains how to build flood-resistant houses in areas that are prone to flooding.
In total, two different methods are described here. The first method is adopted in areas where there is already a stopbank present to prevent the river water from entering the ground level. The stopbank itself is built taller than the 100 year flood level. It has a floodgate to drain the internal ponding that occurs due to runoff resulting from precipitation. In such areas, the house is built on tall pillars to successfully safeguard it from the flood waters.
The second method is suitable for places without a stopbank. Here, the house is built on even taller pillars compared to the house in the previous condition. In this case, the house floor level is raised at least 300 millimeters above the 100 year flood level to prevent it from getting damaged by the flood.
Overall both methods ensure safety to houses from flood water. The only difference is in the elevation of the houses which is determined by the presence or absence of an external barrier.