Human activities that could cause erosion by water would be agriculture and construction because in these activities, they move around the soil and dirt which causes damage to the land and higher chances of erosion.
These human activities cause erosions because when the soil gets moved around too much, there will be no more soil left to absorb the water if flooding occurs. With heavy forces of water, like floods, landscapes that lack soil will most likely have an erosion. When there isn't enough soil, the floods will be harder to get rid of and it will cause more damage to the land. Floods are likely remove all the soil material on the land overall.
To prevent erosion by water due to the human activities, they can use vegetation. With the help of plants, they will create deep root systems that will protect the soil from water. In addition to that, they can also use 'coir' mats which is a natural coconut fiber that is going to protect the soil while the plants grow. Other ways to prevent erosion would be using mulch. Mulch helps reduce water evaporation and enriches the soil which means when it absorbs the rainwater, the mulch will reduce the chances of an erosion and protect the land.