One-dimensional unsteady flow and unsteady pesticide transport in a reservoir

A one-dimensional unsteady contaminant transport model employing an unsteady hydraulic transport field was used to model four pesticides (alachlor, atrazine, metolachlor, metribuzin) in Coralville Reservoir, Iowa, USA. Eulerian chemistry data were collected during April–July 1986 along three longitudinal points in the impoundment. ter quality model uses a split-operator format for solving the advective-dispersive-reactive equation, and is coupled with a fixed bed through particulate settling and diffusive exchange. The velocity, reach volume and average depth were generated by an unsteady open channel code (CARIMA) and 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 Courant number ranged up to 64 in the water quality model while avoiding significant numerical dispersion. Longitudinal dispersion was held at a constant 0.5 m2/s. stream concentration boundary condition was reconstructed by reaching agreement between downstream data and model output. The frequency of data collection suggested that some high concentration events could go unmeasured. odel calibrations were reached for the modeled chemicals. The system was dominated by advective processes. Calibration of the water quality model was more sensitive to transport parameters than to reaction kinetics.