Answer:
The best explanation for why tiny river has recently been experiencing increasing erosion of the sediment along its banks is increased runoff.
Step-by-step explanation:
The main agents of soil erosion are wind, climate change, ice and water circulation.
Runoff is caused by precipitation, which is capable of produce erosion on the banks of a river, with some negative consequences for the environment.
Runoff depends on the flow of water, coming from rainfall, which moves across the surface of the soil, with great capacity for infiltration and erosion. In this case, runoff is the only possible cause of soil erosion
With respect to the other options:
Decreased Slope , decreased rainfall and increased vegetation are not factors related to the erosion in the bank of a river.