Modelling river quality in an Alpine basin The Valle Camonica case

The importance of water quality control in rivers is growing in heavily populated areas, where water resources are shared between users with different and sometime conflicting needs and where, as an additional constraint, minimum conditions of river naturality must be guaranteed. In this paper we investigate the problem of monitoring the evolution of water quality along the 70 km long reach of Oglio river, in Valcamonica. This alpine reach is characterized by many inflow tributaries, by several water intakes for power generation plants and by the presence of important urban and industrial areas. Moreover, the river enters lake Iseo, where pollution and euthrophic processes are in act. These features underline the complexity of the current application, that demands a watershed-scale, distributed modelling approach, capable of integrating hydrologic, hydraulic, ecologic and sanitary expertises. The model must be able to provide the connectivity information that is needed for computing discharge and pollutants load variation and convection along the Oglio main reach and along its tributaries. To this purpose we propose to solve the Streeter-Phelps equation for BOD and dissolved oxigen, and pure dilution for the other pollutants, in the framework provided by the drainage structures that can be derived from a digital elevation model of the watershed, where most topographic, hydrologic and hydraulic quantities that are locally needed for the simulation can be easily linked to the topologic properties of the drainage network and where the other informations can be easily integrated, as already shown by Pilotti et al. (1997) and Pilotti & Bacchi (1998).