Final answer:
The term that describes the building of a retaining wall to divert flood water away from a town is mitigation. This refers to taking proactive measures to reduce the impact of a potential natural disaster. Therefore, the correct option is a.
Step-by-step explanation:
The term that describes the building of a retaining wall to divert flood water away from a town is mitigation.
When a riverfront community builds a retaining wall to divert flood water, they are taking proactive measures to reduce the impact of a potential natural disaster. By constructing the wall, they are mitigating or reducing the risk of damage and loss that could occur during a flood event.
Examples of other mitigation strategies include building levees, constructing flood channels, and implementing zoning regulations to prevent development in high-risk flood areas.