An integrated hydrological modeling approach based on the discretization of a watershed into spatial units called representative elementary watersheds (REWs) has been introduced in earlier publications. Global balance laws were formulated at the spatial scale of a REW by integrating the point-scale conservation equations over particular control volumes. The choice of the control volumes is subject to the specific flow behavior to be described and is dependent on the hydrological characteristics of the spatial regions. These include the unsaturated subsurface flow, groundwater flow, and overland and channel flow. The REW-scale balance laws constitute generally valid governing equations for environmental flows encountered in hydrological systems and are applicable, in contrast to point-scale equations, independently from the chosen spatial and temporal scale of representation. This paper presents a first application of the REW approach to a complex hydrological system and shows how a theory that has so far only been used for synthetic cases is applicable to real-world situations. In this context the most challenging research effort remains the formulation of appropriate closure schemes for mass and momentum (and energy) fluxes at the REW scale. It is recognized that the schemes proposed for the closure of the fluxes in this paper are subject to limitations but are sufficient to expose the philosophy and the essential working principles. The advantages of the particular spatial discretization and the current limitations of the closure schemes are highlighted. In this context it is pointed out which way future research should go to consolidate the REW approach as a more general and scale-independent modeling philosophy for hydrological systems.