On the build-up of storm water solids in gully pots

A substantial part of urban surfaces is to some extent impermeable. Rainfall on these areas turns into runoff, which mobilises solids present on these surfaces. This runoff is removed from urban built areas by different type of drainage systems via gully pots. The objective of a gully pot is twofold, namely 1) to convey runoff to the drainage system with minimal hydraulic losses, while 2) to remove entrained solids to protect the downstream system. The continuous removal of suspended solids results in a growing sediment bed in the gully pot. This sediment bed can eventually reduce the hydraulic capacity of the gully pot and increase the probability of urban flooding due to rainfall. The increasing sediment bed also reduces the removal efficiency, which implies that more solids are transported to the downstream drainage system. Therefore, the objective of this study is to quantify the related processes, which are the build-up of solids on the street, the transport of solids to gully pots, and the removal of solids in gully pots. Which would assist the decision of the optimal cleaning interval of the sand trap. Four research questions have been formulated to meet the study objective:
1. What is the solids loading to gully pots in terms of mass and composition?
2. Does street sweeping reduce the solids loading to gully pots?
3. What is the removal efficiency of solids of a gully pot?
4. How do the in-gully-pot hydraulics influence the removal efficiency?