Final answer:
The most hazardous part of the coastal floodplain is the storm surge impact area, labeled as a High-risk flood Zone on maps. These regions are prone to the destructive forces of high tides and storms, especially in low-lying coastal areas where many populated cities are situated.
Step-by-step explanation:
The most hazardous part of the coastal floodplain is the storm surge impact area, which is shown on the map as a High-risk flood Zone. The storm surge impact area includes regions susceptible to the effects of exceptional increases in sea levels, such as sequences of high tides, hurricanes, or other storm-related phenomena. These areas, notably low-lying coastal zones, are at particular risk during such events. A clear example of this includes the intertidal zone, which extends between the high and low tide lines of a beach and experiences constant changes due to tidal ebb and flow. Notably, the foreshore is the zone between the low-tide line and high-tide line, often wet from the tides and highly susceptible to destruction from storm surges. Coastal communities in these zones are at risk of significant disruption and damage, especially when considering that many populated cities are located in low-lying coastal areas.