The friction resists the flow of water just as friction between two solid surfaces resists the movement of the surface relative to each other. The principle of conservation of energy can be used to assess energy as water flows through pipelines and soils. The terms are similar to the terms we saw in the conservation equations for water and nitrogen. If we have a control volume such as a soil or pipe, then the principle of conservation of energy can be applied as follows. We can set up the conservation of energy equation in the same form as the conservation of mass equation.
Energy dissipation is similar to the generation term in the conservation of mass equation.
Change in internal energy is similar to the change of mass within the control volume. We can substitute the terms from the figure above into the boxes . If we multiply EV r , then we end up with units of energy, Joules. In irrigation and drainage, we often refer to the energy of water in units of length. The total energy of water, H, is often referred to in terms of length.