The terrestrial ecosystem hydrology model (TEHM) combines mechanistic models for climatic and hydrologic processes with vegetation properties to explicitly simulate interception and throughfall; infiltration; root zone evaporation, transpiration, and drainage; plant and soil water potential; unsaturated and saturated subsurface flow; surface runoff; and open channel flow. It is also possible to use the TEHM with models for forest stand biomass dynamics and chemistry and exchange of heavy metals to study the transport and fate of trace contaminants at a watershed scale. Walker Branch Watershed has been used as an example to illustrate development of the required input parameters and variables that are necessary to execute the TEHM. In all cases, emphasis has been placed on objective, physically based methods. When simulations of interception loss, soil moisture content, and base flow and storm flow are compared with observation, the overall adequacy of the model may be assessed. For user convenience, the documentation includes a complete discussion of input formats, example data input sets, output summaries, and a microfiche listing of the complete source deck and program output. As presented, the TEHM provides an operational tool and a model structure and data management capabilities that will be useful for future hydrologic simulationmore » work. From that viewpoint, the TEHM represents an important step forward in establishment of an objective framework for the study of terrestrial ecosystems.« less