ONE-DIMENSIONAL UNSTEADY-FLOW AND UNSTEADY PESTICIDE TRANSPORT IN A RESERVOIR

A one-dimensional unsteady contaminant transport model employing an un steady hydraulic transport field was used to model four pesticides (al achlor, atrazine, metolachlor, metribuzin) in Coralville Reservoir, Io wa, USA. Eulerian chemistry data were collected during April-July 1986 along three longitudinal points in the impoundment. The water quality model uses a split-operator format for solving the advective-dispersi ve-reactive equation, and is coupled with a fixed bed through particul ate settling and diffusive exchange. The velocity, reach volume and av erage depth were generated by an unsteady open channel code (CARIMA) a nd input to the water quality program. The time-step used in the water quality program was one day, and the space-step was 250 m. The Couran t number ranged up to 64 in the water quality model while avoiding sig nificant numerical dispersion. Longitudinal dispersion was held at a c onstant 0.5 m(2)/s. The upstream concentration boundary condition was reconstructed by reaching agreement between downstream data and model output. The frequency of data collection suggested that some high conc entration events could go unmeasured. Good model calibrations were rea ched for the modeled chemicals. The system was dominated by advective processes. Calibration of the water quality model was more sensitive t o transport parameters than to reaction kinetics.