The provided pictures illustrate two distinct designs for flood defense for houses in prone flooding areas.
Overall, it is evident that the key difference in the two methods is the stopbank. Additionally, it is also noticeable that the house is built higher than the ground in both circumstances.
Looking at the information in more detail, in the first diagram, there is a stopbank constructed higher than the measured flood level. Additionally, there is also a floodgate in the right area of the stopbank, which helps to drain off water from internal ponding such as the runningoff of rain, straight to the river below the berm. The house is built on stilts with its floor equal to the freeboard which is about 300mm higher than the 100 year ponding level.
Where there is no stopbank, as shown in the second diagram, there is also no berm and floodgate and the flood will then not be stopped. In this case, the solution is to construct the building on stilts. The measurement called “freeboard” helps to evaluate the height of the floor level of the house, which is 300mm higher than that of the flood.