A new GIS-based routing scheme for hydrological models

The development and application of a new GIS-based routing scheme for hydrological models are presented in this paper. The new approach differs from previous methods in four aspects: (1) it computes the flow direction continuously from 0›¦ to 360›¦ and allows runoff to leave each grid from any angle between 0›¦ to 360›¦ rather than from only one of the eight directions (i.e., 0›¦, 45›¦, 90›¦, 135›¦, 180›¦, 225›¦, 270›¦ and 315›¦) which allows the new GIS-based routing scheme to be able to represent efficiently effects of different spatial and temporal resolutions of the digital elevation model (DEM) data on river network routing; 2) it considers impacts of land cover/use change on overland and river routing dynamically; (3) it advances the early routing methods by fully coupling it with a hydrological distributed model to consider runoff re-infiltration; and (4) it corrects the flow directions at the boundary grids of a watershed by taking the advantage of DEM data at a finer spatial resolution. The new routing scheme is being applied to the watersheds of the Blue River and Illinois River at Watts, Oklahoma, which represent two different watershed shapes, by fully coupling it with the Three-Layer Variable Infiltration Capacity (VIC-3L) model, and the simulated streamflow will be compared to the observed and those simulated by other routing methods. Uncertainties associated with the new routing scheme and a typical 8-direction routing scheme on streamflow simulations will be investigated. Although the routing scheme presented here is implemented into the VIC-3L model, it can be easily applied to other hydrological models at any space-time scales.