A distributed continuous simulation model to identify critical source areas of phosphorus at the catchment scale: model description

Abstract. This paper presents CAMEL (Chemicals from Agricultural Management and Erosion Losses), a distributed continuous simulation model to simulate daily phosphorus (P) transformations and transport at the catchment scale. CAMEL is a process-oriented mass-balance model that is based on both analytical and numerical approaches. In the model, a catchment is represented using a network of square grid cells each of which is comprised of various storages of water, sediment and P. Most of hydrological processes, soil erosion, sediment transport, and P transformations and transport are described using process-based equations. The P transformations between five P storages (active organic, stable organic, labile, active inorganic, and stable organic) are described using first-order kinetic equations. A comprehensive cascade routing scheme is used to simulate P retention and transport along the channel system. Dissolved P is also transported by groundwater flows, described using a two-dimensional Boussinesq equation. CAMEL simulates both surface and subsurface processes explicitly and therefore is suitable for catchment-scale applications. The distributed, process-oriented structure of CAMEL enables the model to be used for identifying critical source areas of P at the catchment-scale. CAMEL is also computationally efficient, allowing for long-term scale applications.