River water quality model no. 1 (RWQM1): I. Modelling approach

Successful river water quality modelling requires the specification of an a ppropriate model structure and process formulation. Both must be related to the compartment structure of running water ecosystems including their long itudinal, vertical, and lateral zonation patterns. Furthermore, the tempora l variability of abiotic boundary conditions may be important and must be i ncorporated by an appropriate choice of model parameters. A six-step decisi on procedure is proposed to achieve these objectives. The steps address the determination of the following model features: (1) temporal representation (dynamic or steady-state); (2) model dimensionality; (3) mixing; (4) advec tion; (5) reaction terms; and (6) boundary conditions. Numerical criteria b ased on process time constants and length scales provide a basis for these decisions.