Development of a coupled pathogen-hydrologic catchment model

Large numbers of pathogens can be mobilised from drinking water catchments during wet weather causing serious problems in management of water treatment plants. This paper presents an attempt to model pathogen discharges from large catchments. Two conceptual continuous pathogen models have been developed and evaluated using E. coli as a pathogen indicator. The first model, the EG model, describes surface and subsurface pathogen transport processes by means of wash-off and loss equations. It is coupled to an existing hydrologic model (SimHyd) that predicts flows. The second model, named ASP, takes into account only surface pathogen transport processes. It is coupled to a stormflow-baseflow separation model, and therefore is simpler than EG. The models have been tested against baseflow and storm event E. coli concentrations measured at three dissimilar catchments from southern Australia. The prediction of pathogen peak concentrations by the EG model was reasonably good; the coefficient of correlation between the measured and modelled pathogen peaks for all three catchments was r2 = 0.93. However, the ASP model was not able to model the peaks well (r2 = 0.54). The prediction of pathogen loads was significantly better with r2 = 0.95 for the EG model and r2 = 0.89 for the ASP model. It was concluded that a slightly more complex EG model was performing better than the oversimplified ASP model.