PREDICTION OF WATER-QUALITY IN LAKES AND RESERVOIRS .1. MODEL DESCRIPTION

A one-dimensional water quality model (DYRESM Water Quality) is descri bed which combines a process based hydrodynamic model (DYRESM) with nu merical descriptions of phytoplankton production, nutrient cycling, th e oxygen budget and particle dynamics. The hydrodynamic component is f ree from calibration, which ensures that it is readily transferable to other lakes and reservoirs. This improves water quality predictions d erived for different hydrodynamic forcing events. It also allows for i dentification of the specific hydrodynamic processes that influence wa ter quality, The water quality component consists of 13 state variable s which may include up to three algal groups, BOD, dissolved oxygen an d four components of the dissolved oxygen budget (inflows, biochemical processes, surface aeration and oxygen present in the reservoir at th e start of a simulation), nutrients (PO4-P, NO3-N, NH4-N, TP and TN) a nd inorganic particles. The particle model simulates settling and floc culation/deflocculation of up to seven different size classes of parti cles. The hydrodynamic, water quality and particle models interact on a sub-daily time step. Forcing data for the model are entered as daily -averaged values. The ecological component requires calibration for ea ch new application through adjustment of several different biological and chemical parameters. Literature ranges for these parameters are wi de, but provided the process description is correct, many of the param eters can be validated with measured data. (C) 1997 Elsevier Science B .V.