ABSTRACT
In physics, we learn of conservation of several quantities: mass, energy, and momentum. In open channel flow, we make use of these conservation laws to analyze a flow. My general observation is that students find conservation of mass (i.e., the continuity equation) obvious; water can neither be
created nor destroyed. Conservation of energy and momentum require a bit more effort to accept, but it has been my observation that conservation of energy is more intuitive than conservation of momentum, perhaps because energy depends only on location; it is a scalar quantity. Conservation of momentum is a bit more challenging because of its directional nature; it is a vector quantity. Further confounding students is the fact that the units of momentum, as classically treated in open channel flow, appear similar to energy. As is the case in this book, momentum is generally introduced after conservation of energy. Students must reconcile these questions: “Why is energy conserved here but not momentum?” and its complement, “Why is momentum conserved here but not energy?”
