Generation of odorous hydrogen sulfide in the anaerobic sediment of storm-drains has become a critical issue in low-lying coastal cities. The sulfate brought in by tides is reduced to sulfide within the anaerobic sediment phase inside the storm-drains. Mixing the sediment with ferric-based chemicals in granular form oxidizes the sulfide ions eliminating the odor problem but they need to be regenerated for a sustainable solution. A gate positioned at the location where the storm water is discharged into the sea, closed at low tide and opened at high tide is proposed to generate a dam-break flow into the storm-drain. The study investigates the use of dam-break generated flow as a means of regeneration by mixing and oxidizing the ferric-based granules and sediments in storm-drains....[ Read more ]

Generation of odorous hydrogen sulfide in the anaerobic sediment of storm-drains has become a critical issue in low-lying coastal cities. The sulfate brought in by tides is reduced to sulfide within the anaerobic sediment phase inside the storm-drains. Mixing the sediment with ferric-based chemicals in granular form oxidizes the sulfide ions eliminating the odor problem but they need to be regenerated for a sustainable solution. A gate positioned at the location where the storm water is discharged into the sea, closed at low tide and opened at high tide is proposed to generate a dam-break flow into the storm-drain. The study investigates the use of dam-break generated flow as a means of regeneration by mixing and oxidizing the ferric-based granules and sediments in storm-drains.

The study involved physical model tests and numerical simulations. A storm-drain model (6.6 m long, 0.3 m wide, 0.3 m high and slope 1:20) and a large reservoir (8.0 m long, 2.0 m wide), representing the sea, were built inside a towing tank and were separated by a gate that was raised quickly at a simulated high tide level. The physical setup was reproduced numerically in FLUENT, Navier-Stokes equations based state-of-art software that overcomes the limitations of using a shallow water equations based model. The Volume of Fluid method was used to model the three-dimensional, two-phase system consisting of two volumes, the storm-drain and the reservoir.

The experimental measurements were used to validate the results of the numerical model. Large eddy simulation (LES) model was selected as the most suitable viscous model to reproduce the system and it was used for detailed hydrodynamic studied. The importance of three-dimensional modeling due to the effects of cross-currents was highlighted. The deviations in hydrodynamics from general dam-break studies due to the presence of infinitely large reservoir such as different flow volumes during uprush and back wash phase and water-depth time-series were investigated. The Froude number scaling method was successful tested for prediction of bed shear stress in actual problematic sites.