A Geyser in a stormwater (SW) and combined sewer system (CSS) is an oscillatory and violent release of a mixture of air and water through vertical shafts. Violent geysers are highly destructive. In the case of combined sewer systems, many municipalities operate their systems at a fraction of their maximum capacity to avoid transients and geysers. Operating CSSs at a fraction of their capacity means that these systems are not fully utilized and hence, combined sewer overflows (CSOs) occur more often than they should. These overflows contain not only stormwater but also untreated human and industrial waste, toxic materials, and debris. The U.S. Environmental Protection Agency estimates that in 31 states and the District of Columbia, 772 combined sewer systems with more than 9,000 CSO outfalls annually discharge about 850 billion gallons of untreated wastewater and stormwater. Geysers have been studied numerically and experimentally for over three decades. Even though geysers were studied for a relatively long time, their violent behavior was neither reproduced experimentally nor numerically. The motivation of this thesis is to present the results of an experimental study that for the first time produced violent geysers (few consecutive eruptions with heights that may exceed 30m) that resemble those observed in the field. This experimental study also included tests of a retrofitting method for minimizing geyser intensity in terms of height and eruption velocity. The retrofitting consists of a simple diameter reduction (e.g., orifice) at the bottom of the dropshaft. The dimensionless eruption height and velocity were found to have a good fit with the power forms obtained in the dimensional analysis. The eruption height and velocity were found to increase with the dimensionless air mass flow rate and the ratio between dropshaft height and dropshaft diameter. Results indicate that the eruption height and velocity decrease with a decrease in orifice diameter (e.g., lower air mass flow rate). For the experimental conditions considered in the present study, the proposed retrofitting method was found to be an effective strategy for minimizing the intensity of violent geysers where a geyser eruption is nearly eliminated when the ratio between orifice diameter and dropshaft diameter is about 1/8.
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