Estimation of Travel Time in Overland Flow via Diffusive Wave Approximation

Different analytical methods such as kinematic wave (KW) and diffusive wave (DW) approximation can be used to investigate the overland flow mechanism. In this article, for the first time, the results of these two methods are compared in calculating the travel time of flow over a rectangular plane. Positions of isochrones and the effect of bed slope on travel time are also investigated. It is elaborated that travel time of the rectangular plane in diffusion wave approximation is greater than that of the kinematic wave approximation. For example, by decreasing bed slope from 0.01 to 0.001 the travel time will increase by 99% in kinematic wave approximation and 130% in diffusive wave approximation. Also, the relative difference of the two methods will increase by 14%. It is also deduced that by decreasing the bed slope, the difference between the two subsequent isochrone distances will become greater in diffusion wave approximation than that of the kinematic wave approximation. On the other hand, with 10% of relative difference between kinematic and diffusive waves the criterion of < 5 would be fulfilled.