How does water enter the area marked with an a?

The water can enter the area marked with an A through rainfall that hits the Earth's surface and  a runoff flows across the surface, then most of this water soaks into the ground and seeps down to become groundwater and flow along until it will reach the river, lake or ocean.

after making a punnet square using bv bv bv bv you will find that the ratio will be 9: 7 or a 128.6% probability.

hope this