Algorithms for pesticides transport distributed modelling

In order to build up distributed models which require a proper evaluation of the different hydrological, sedimentological and chemical variables, various algorithms developed and based on results obtained in former experiences are here presented. A digital model which divides the catchment with a square grid to obtain a set of cells, called rasters, is adopted and all quantities playing a role in the model are represented according to this methodology. They are geographic (elevation, watersheds, channels network, exposure, flowing index, etc.), geological and pedological (gravitational and capillary water storage, erodibility, etc.), climatic (rainfalls, temperature, humidity, etc.) and anthropic (land use, agricultural nonpoint pollution, etc.). A limited set of parameters that regulates the dynamics of water, sediments and pollutants are common for the whole basin. Grid dimensions and balance time-step are not fixed in advance, but they depend on information accuracy.