LINKING HYDRODYNAMIC AND WATER-QUALITY MODELS WITH DIFFERENT SCALES

Procedures have been developed to allow linkages between finite-differ ence hydrodynamic and water quality models having different temporal a nd spatial scales by defining appropriate values for the mean flow and dispersion coefficients. These procedures account for numerical dispe rsion, based on model formulation and solution parameters, as well as temporal and spatial averaging between different model scales, which i ntroduce additional dispersion effects. Temporal averaging of velocity generates an equivalent dispersivity, which is estimated from the roo t-mean-square velocity fluctuation, evaluated over the averaging perio d. Dispersivity due to lateral and longitudinal averaging depends on t he distributions of velocity and dispersion over the areas being avera ged. The calculations are based on preservation of predicted mass dist ributions when different modeling scales ate used, and results from a specific case study are used to confirm the validity of these procedur es.