Leonardo performs remarkable analyses of the behavior of running water encountering obstacles, which he defines as “objects.” With vivid drawings, he shows how such obstacles can deviate waters from their natural course, and he illustrates their effects on river banks and beds according to their various forms and positions. His insistence on the “great usefulness” of the science that studies the changes in flow generated by obstacles immersed in water is based on his belief that they can be used to protect river banks from erosion.