Hydraulic and hydrologic routing

The movement of a floodwave is governed by the laws of fluid mechanics. The two equations for clear water flow are the conservation of mass, or the continuity equation, and the momentum equation. These two equations are referred to as the Saint-Venant equations. Traditional hydraulic routing involves a numerical solution to these equations as partial differential equations. Therefore, hydraulic routing is viewed as being more physically based than hydrologic routing.

Traditional hydrologic routing typically uses an algebraic solution to the continuity equation and a relationship between changes in storage in the reach and discharge at the outlet. Hydrologic routing is often based on analogies of stream channels and basins as a set of storage reservoirs with appropriate properties. In fact, hydrologic routing equations are often referred to as storage routing equations. As a result, hydrologic modeling is inherently empirically based. Typical hydrologic routing equations include the Muskingum routing and the Reservoir (Puls) routing procedures.