The design and application are described of HYDRA, a new package of computer programs designed for the detailed modeling of the routing of water in converging channel networks. Geometric characteristics of intricate systems consisting of arbitrarily large numbers of channel segments can be considered. Accounted for in the simulation model are the relationships of the channel segments to each other, to surrounding areas, and to the rainfall variations and/or movement of storms. Storms are described as regions enclosed by boundaries approximated by any arbitrary number of polygon sides. The degree of detail with which either the network or storm patterns are defined may be chosen by the user. Results from this modeling package include, for finite storm events, the runoff rate and accumulated rainfall at any specified point on the network. (Modified author abstract)