Prediction of Geyser Occurrences in Covered Manholes of Urban Stormwater Systems

Abstract

Storm geysers are air–water eruptions from stormwater manholes during intense rainfalls, which raise public safety concerns. They arise from entrapped air release in stormwater tunnels as flow transitions from open to pressurized. This paper experimentally investigated air–water flow characteristics during air pocket release in covered manholes. Four geyser regimes were identified: no geyser, single air-release geyser, single rapid-filling geyser, and multigeysers. The air-release geyser and rapid-filling geyser refer to ejections of water column and air–water mixture induced by distinct mechanisms. Impacts of manhole diameter, cover ventilation area, system pressure head, and initial air pocket volume on geyser regimes were analyzed. As manhole diameter increases or cover ventilation area decreases, maximum geyser heights decrease, subsequently decreasing the likelihood of geyser occurrence. Higher system pressure head and larger initial air pocket volume increase the maximum geyser heights. Equations were derived to predict the maximum geyser heights, and prediction accuracies exceeded 87%, providing safe predictions of geyser occurrences relative to the manhole height. The findings can help provide advance warning of geysers when combined with information of stormwater system structures and real-time monitoring of operating conditions.