happy to slip beyond the control of the stern banks , the danube here wanders about at will among the intricate network of channels intersecting the islands everywhere with broad avenues down which the waters pour with a shouting sound ; making whirlpools , eddies , and foaming rapids ; tearing at the sandy banks ; carrying away masses of shore and willow-clumps ; and forming new islands innumerably which shift daily in size and shape and possess at best an impermanent life , since the flood-time obliterates their very existence .