Constant velocity kinematic analysis of an infiltrating microcatchment hydrograph

A watershed of about 200 m² is used in many arid zones to provide the irrigation needs of a single tree. The objectives of this study were to develop and test a physical model to predict the hydrodynamic processes on a natural microcatchment of this size. A rectangular area of 125 m² was selected on loessial soil with a fairly uniform grade of approximately 1%. Rainfall was applied uniformly over the catchment at intensities of 60, 40, 20, and 10 mm/h. Inspection of all the hydrographs indicated that the nature of the recession part was very similar for all intensities. Recession appeared as a set of parallel lines which decreased rapidly the moment that the rain stopped. At all intensities the recession lasted about the same time (10.4 ± 2.3 minutes) and was independent of the surface detention. It was then suggested that a good approximation is obtained when velocity of water flow on the surface is assumed to be constant, independent of time or position along the catchment. These qualitative results simplify the analytical solution of the continuity equation and provide a new insight into the problem of flow over an infiltrating surface. In addition, the analytical solution developed for this case is much easier to utilize than large‐scale computer simulations.