Levees and dams are beneficial to farmlands mostly because of two reasons:
1. Watering
- they manage to accumulate water, huge amounts of it when there's more rain, so in the periods where there's little to no rain the water is used for watering of the plants on the farmlands and allowing them to continue growing and the farmers to have benefit.
2. Flood prevention
- they also prevent floodings, maybe not always, but the success rate of preventing the floods is very big, and it is extremely beneficial for the farmers because it is protecting the farmlands from getting overrun by water and be destroyed.