Water displacement by sewer infrastructure and its effect on the water quality in rivers

Water quality is affected by a complex combination of natural and anthropogenic factors. To assess watershed integrity on a larger scale and for an optimal, cost-effective integrated watershed management, defining linkages between upstream watershed land cover and riverine water quality is essential. A correct upstream area calculation is an absolute necessity to reach conclusive results, but remains problematic in human influenced catchments. Especially sewer infrastructures (including wastewater treatment plants) are difficult to incorporate. We developed a method that allows us to integrate the sewer system in the upstream calculations and applied it on the Nete catchment in Belgium. Our results show strong changes in results compared to standard runoff methods. We conclude that if sewer systems are not incorporated in upstream area calculation, the impact of human activities on the water quality at a catchment scale estimates will be severely biased. A thorough understanding of the evaluated catchment and a correct translation of the different hydrological flow paths in the upstream area calculation is absolutely necessary to gain reliable results.