Which factor influencing erosion rates can a contractor most effectively control?

Ground cover is a significant factor influencing erosion rates that contractors can effectively manage. The presence of vegetation, mulch, or other types of ground cover can stabilize the soil and reduce the impact of rainfall on the ground. By implementing practices such as planting grass, using erosion control blankets, or applying straw mulch, contractors create a protective layer that helps prevent the soil from being washed away. This proactive approach can significantly minimize erosion and improve the stability of the site.

In contrast, factors like weather conditions, proximity to water sources, and soil type are largely beyond a contractor's control. Weather conditions, for instance, vary unpredictably and can dramatically influence erosion through heavy rainfall or wind. Proximity to water sources affects drainage and can exacerbate erosion, but is a situational constraint that can't be modified. Soil type influences erosion susceptibility based on its texture and composition, yet this is also a natural characteristic that cannot be changed. Therefore, focusing on ground cover is the most effective strategy contractors have at their disposal to control erosion rates.