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HYDRAULIC CHARACTERISTICS OF SEWER SEDIMENT GATE FLUSHING TANKS: LABORATORY FLUME STUDIES
Citation:
Fan*, C, R Field*, Q. Guo, AND S. Liao. HYDRAULIC CHARACTERISTICS OF SEWER SEDIMENT GATE FLUSHING TANKS: LABORATORY FLUME STUDIES. Presented at ASCE, World Water and Environmental Resources Congress, Orlando, FL, 5/20-24/01.
Description:
The objective of this study was to test the performance of gate flushing tanks, simulated in a laboratory flume, to remove sediments from combined sewers and storage tanks. A significant amount of sediment/debris/sludge may accumulate at the bottom of a sewer during dry weather or small storms. Accumulated sewer sediment, if not flushed to a designated collector beforehand, may be washed directly to receiving waters during times of high-storm flow. A large fraction of the sediment may be biodegradable solids and numerous contaminants may be adsorbed onto the sediment. The direct discharge of this sediment to receiving waters will cause serious water quality problems. A gate flushing tank was installed at the head of a laboratory hydraulic flume. Tests were conducted under 40 flushing conditions, including combinations of various initial water depths in the flushing tank, flushing-gate opening heights, initial thicknesses of a sediment layer in the flume, and initial water depths in the flume, Noncohesive sediments of similar size to that of sewer sediments were used in the tests. Total weight and spatial distribution of flushed sediments were measured. The speed and height of the flushing surge were also measured using video imaging. Up to 50% of the sediment originally in the flume was flushed away under the testing conditions. These lab test results will be used to compare performance with ohter types of flushing devices and sewer sediments. A simplified hydraulic surge model was developed that compared well with laboratory results. The most appropriate sediment flushing/transport model was also identified from the laboratory results. The hydraulic and sediment transport models, after improvements in spatial and temporal variations, will be used to guide the design and placement of sewer sediment flushing devices.