An online diffusion-wave open-book overland flow model was developed using the Muskingum-Cunge routing method with lateral inflow, together with the scripting language PHP embedded into HTML. The open-book configuration consists of two planes draining into a channel in the middle. A unique feature of the model is its grid independence, which enables it to produce the same peak flow and outflow hydrograph, regardless of the grid specification. Grid independence is attained by matching the physical diffusivity of Hayami with the numerical diffusivity of Cunge. Modeling accuracy is assured by requiring the input of the time interval Δt and allowing the model to internally calculate the space interval Δx to keep the Courant number close to 1. Moreover, the model is capable of incorporating the dynamic component of wave propagation by specifying the hydraulic diffusivity as a function of the Vedernikov number. The model was tested for grid independence and overall accuracy by varying selected physical and numerical parameters. Results show that the model is grid independent and capable of conserving volume. The calculated hydrographs depict the variability in a predictable manner; thus, making the model numerically stable, consistent, and accurate.
