ABSTRACT
Runoff and erosion are the overland processes that transport phosphorus. The processes and equations describing the processes have been described in many references. The purpose of this chapter is to present the common approaches used for modeling runoff and erosion processes in models that simulate phosphorus transport and to illustrate similarities and differences in implementation among selected phosphorus models. Implementation of the processes varies among the phosphorus models, depending on model characteristics such as spatial representation of the drainage area (e.g., lumped or distributed), spatial scale (e.g., field or watershed), purpose of the model (e.g., event prediction or average annual predictions for management), computational time step (e.g., daily vs. shorter time steps during rainfall or runoff events), and land uses and conditions represented (e.g., agricultural, urban, forested land uses, frozen soils).
