Misure di trasporto superficiale e iporeico in un corso d acqua naturale

Transport processes of substances that are present in natural water courses and solute longitudinal dispersion phenomena involve a large number of physical variables and, therefore, are difficult to analyse. Nevertheless, in the case of one-dimensional steady flow, convection due to mean water velocity and the longitudinal dispersion coefficient may be sufficient to characterise the behaviour of a stream. Studies effected in the last twenty years have shown the importance of another phenomenon: the solute exchange between the main channel and the lateral dead zones. Solutes experience a temporary storage, and then are released in the superficial water body. In the present work some experimental tests performed in the Surdo Torrent (Calabria, Italy) are described. The tests are relative to the measure of the conductivity variation of water due to the impulsive local injection of passive solute (sodium chloride). Results evidence the non negligible phenomena of hyporheic exchange and their influence on the superficial transport. The application of the software OTIS-P, which solves the equation governing the solute exchange with the storage zones, coupled with the advection-dispersion equation, permitted the assessment, for each river reach analysed, of the longitudinal dispersion coefficient and the Transient Storage Model parameters, concerning the hyporheic exchange.