Abstract
Urban runoff (re)mobilises solids present on the street surface and transport them to urban drainage systems. The solids reduce the hydraulic capacity of the drainage system due to sedimentation and on the quality of receiving water bodies due to discharges via outfalls and combined sewer overflows (CSOs) of solids and associated pollutants. To reduce these impacts, gully pots, the entry points of the drainage system, are typically equipped with a sand trap, which acts as a small settling tank to remove suspended solids. This study presents data obtained using Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) measurements in a scale 1:1 gully to quantify the relation between parameters such as the gully pot geometry, discharge, sand trap depth, and sediment bed level on the flow field and subsequently the settling and erosion processes. The results show that the dynamics of the morphology of the sediment bed influences the flow pattern and the removal efficiency in a significant manner, prohibiting the conceptualization of a gully pot as a completely mixed reactor. Resuspension is initiated by the combination of both high turbulent fluctuations and high mean flow, which is present when a substantial bed level is present. In case of low bed levels, the overlaying water protects the sediment bed from erosion.
Highlights
IntroductionRunoff contains suspended solids, which are (re)mobilised from the street surface by raindrop impact [1]
Urban drainage systems are meant to remove runoff from urban areas
When the sediment bed gets close to the impinging jets, which originate from the gully pot inlet, the interaction between the sediment bed and the flow becomes apparent; particles can resuspend from the sediment bed and be transported out of the gully pot
Summary
Runoff contains suspended solids, which are (re)mobilised from the street surface by raindrop impact [1] Accumulation of these solids in urban drainage systems result in a reduction of the hydraulic capacity ([2,3]), as they contain pollutants, pose a risk for the water quality of receiving water bodies (e.g., [4,5,6]). To reduce these adverse effects gully pots, the entry points of the drainage system (Figure 1), are usually equipped with a sand trap that acts as such an interceptor. A gully pot can be seen as a small settling tank
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