The mismatch between long-term monitoring data and modelling of solids wash-off to gully pots

Abstract

Urban runoff remobilises solids and their associated pollutants from urban-built environments and transports them to drainage systems via gully pots. This study presents an extensive monitoring campaign on the solids loading to drainage systems, including 104 gully pots as sampling locations and lasting 2 years. The solids loading is modelled with Build-Up and Wash-Off (BUWO) models and a Regression Tree (RT). The performance of the RT is substantially better than the performance of the BUWO models, such that it is not recommended to use a single BUWO model to predict the loading of a set of gully pots/catchments. It is discussed whether the generally observed mismatch between monitoring data and wash-off models, both in this study and in literature, points to a fundamental misunderstanding of the underlying processes. Finally, the results show that an increased street sweeping frequency does not significantly reduce the solids loading to drainage systems.