The diagrams compare two different methods of defence for homes that are at risk of being flooded. Summarize the information by selecting and reporting the main features, and make comparisons where relevant.
The given diagrams illustrate two methods of protection; one way of defence is by having a stopbank and the other with no stopbank, of homes which are facing the problem of being flooded.
Overall, the defence mechanism with an introduction of a stopbank seems to be effective in reducing the problem of the drowning of the raised building than the other method for avoiding the risk of flooding.
Regarding the first case, where a stopbank has been set up beside a 100-year flood level in river/drain with a flood gate and berm at the ground level. Internal ponding is present underneath the raised building, all along with the ground level.
When rainfall occurs, the rainwater flows down the cliffs and pass through the internal ponding under the house until it reaches the stopbank consisting of 300mm freeboard. At that point, the water movement path is changed, and the water is directed towards the flood gate situated at the ground level. Consequently, the water level (100-year flood level) remained the same, avoiding flooding away of houses.
On the other hand, in the second diagram, due to the absence of the stopbank, the 100-year flood level has increased as the rainwater is flooded directly without any obstacle in between, which resulted in an increased water level under the building. Eventually, it leads to the risk of flooding of homes.
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