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 2
0 0 K F < 5 would be fulfilled.