Runoff hydrograph simulation based on time variable isochrone technique

A new method based on an extension to time–area (TA) concept is proposed for rainfall–runoff transformation in watersheds. The method uses time variable isochrones, such that the runoff hydrograph responds well to temporal changes in excess rainfall intensity. The method employs a kinematic-based travel time scheme, which improves existing isochrone extraction techniques. A raster-based approach deals with spatial domain discretization and supports rainfall–runoff simulations in a modular distributed model. The model uses digital elevation model (DEM) data, ground slope, flow direction, and flow accumulation maps to characterize the watershed terrain. The time series of travel time (or isochrones) maps constitute the basis for incremental and total runoff hydrograph computations. The model was calibrated and validated on a small catchment. The methods and modeling algorithms extend the original TA routing method to a distributed terrain-driven, hydraulic-based, and GIS-compatible technique where isochrones vary as the storm intensity and infiltration rate develop.