Assessing the effect of urbanization on the water quality of the river Rhine : estimation of the natural baseline quality

The natural baseline quality of the Rhine is estimated by discriminating a baseflow and a surface flow component in the river discharge. The quality of the baseflow and the surface flow is estimated in two ways, along with the load by industrial and domestic discharges. A multiple linear regression estimation proved to be valuable for a first estimation, but was unable to handle weekly, seasonal and discontinuous changes in the parameters. Therefore an adaptive parameter estimation technique was applied. A random walk type of temporal change was allowed in the parameter values, which were estimated by a Kalman filter. The concentration in the baseflow is rather low for most constituents. The quality of the interflow and surface runoff seems somewhat influenced by human activity, e.g. for nitrate and phosphorus. The actual concentration of the constituents in Rhine water is considerably higher than in the baseflow and surface flow, due to the discharges induced by urbanization.