Gully pots are one of the most ubiquitous urban drainage infrastructures in the urban catchment. Installed at the inlets to the sewer pipe network, they reduce the risk of sediment-induced blockages in the subsequent pipe connections and decrease the pollutants load on recipients by proportionally retaining the input solids. A well-functioning gully pot system requires proper maintenance frequencies which however in reality are more dependent on e.g. the budget availability and catchment vulnerability and less dependent on the gully pots’ actual performance.
Despite the long and extensive use of gully pots, the knowledge on their actual field performance and the impact of various factors on the performance is still lacking. Therefore, this licentiate thesis aims at contributing to the understanding of sediment scour behaviour under varying rainfall conditions as well as to identifying the temporal changes to physicochemical properties of gully pot sediments due to varying anthropogenic practices in the urban catchment.
The findings of this work highlighted the considerable temporal changes in the concentrations of sediment PAHs where an over 300-fold decrease of PAH-L led to a switch from a PAH-L dominated profile approximately 20 years ago to a PAH-H dominated profile nowadays. The upgraded atmospheric emission controls by the local industries and improved vehicle technology were hypothesized as contributors to such changes. With regards to the metals, the temporal decrease of Pb was attributed to the implementation of the EU End of Life vehicle Directive whereas the temporal increase of Cu, Zn, Co, Cr and V in especially the fine fractions of solids was related to the winter road maintenance operations. The winter road maintenance operations (e.g. traction grits and studded tyres) may also have contributed to the high solids accumulation rates (0.176 - 0.819 kg·m-2·year-1) in gully pots of the road catchment.
The gully pots in this work were emptied with an eductor truck and the pollutant load in both the dredged water and sediment phases were characterised. The results suggested approximately 90 % of metals were retained in the sediments and 9 % were associated with suspended matters in the dredged water with < 1 % of metals presented in dissolved fractions.