"Hydrodynamics is the study of water flow. It helps us to understand how water behaves when it flows in pipes and channels and to answer such questions as – what diameter of pipe is needed to supply a village or a town with water? How wide and deep must a channel be to carry water from a dam to an irrigation scheme? What kind of pumps may be required and how big must they be? These are the practical problems of hydrodynamics.
Hydrodynamics is more complex than hydrostatics because it must take account of more factors, particularly the direction and velocity in which the water is flowing and the influence of viscosity."
(p. 51 em KAY, Melvin (2008). Practical Hydraulics. Taylor & Francis, 2 nd ed., 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN, ISBN 0-203-96077-7 Master e-book ISBN.)