We have a new hand dug water well. It is eleven meters deep and was dug at the end of the dry season. During the rainy season much of the soil surrounding the wells brick casing was washed away. At the end of the rainy season the inside of the well looked fine and had clear water. About 3 weeks later we checked the well and it was more than half filled with dirt. What could have caused this and how can we correct the problem?