Aerial views of semi-circular structures near wells in Vijayawada, AP :Information about their uses

My friend , Shri Vasudeva Adamaru sent me this interesting information. He was travelling near Vijayawada in a plane. From the plane, he could see Krishna river belt where paddy is grown extensively. Says he : "It seems these fields are irrigated using well water and the wells are surrounded by semi circular structures.It seems it is a interesting water use/harvest structure for study."

Are these water bodies wells?What are those semi-circular structures? Are they harvesting the run-off with these structures? Could anybody more throw light on these?

Aerial Images:

Image 1

Image 2

Shree Padre