Debris Accumulation at Trash Racks Upstream of Inverted Siphons

Abstract

Accumulation of debris, and subsequent clogging of trash racks upstream of inverted siphons and culverts can pose serious inundation risks. If the upstream water level continues to rise till the banks overflow due to the blockage of the inlet, it can lead to damages and potential casualties in case of floods. Therefore, a thorough understanding of debris accumulation processes and implementation of mitigation measures in design methods is essential, even though, this is not being a common practice currently. While existing research has focused primarily on experimental studies of debris accumulations or retrospective analyses of flood events, this study leveraged datasets from Waterschap Limburg, containing water level and discharge measurements collected on site. To obtain an enhanced understanding of debris accumulation processes at trash racks upstream of inverted siphons. This research analyzed stage-discharge measurements around inverted siphons throughout Limburg to identify debris-induced anomalies in the flow conditions that corresponded to debris extractions. This process served as a foundation for a targeted investigation of these anomalies in the water levels and water level differences across the trash rack at the inverted siphon at Tungelroysebeek. Detection methods were developed to identify instances of debris removal across the dataset. This enabled an analysis of seasonal influences on the frequency of debris accumulation and extractions, where an increased occurrence of removals was found in fall months. Furthermore, Extreme Value Analysis was employed to statistically model the extreme behavior of extraction events, estimating the return periods for days with significant extractions of debris accumulations. This study demonstrated that historical water level and discharge data can be used to detect debris accumulation through stage-discharge analysis and application of identification methods. Insights were acquired on seasonal influences on the debris accumulation process, and on the likelihood of extreme accumulation events. The obtained results are expected to be useful in flood-risk assessment and development of targeted debris management strategies, and can support engineers in decision making for design and mitigation processes.