393 / 2024-03-11 16:16:52

Geyser Regimes in Covered Manhole of Urban Stormwater Systems

Air release; Covered manhole; Cover ventilation; Geyser prediction; Stormwater system

Subtheme 1: Water-related Hazard and Risk Reduction > Topic 2: Simulation and Forecast of Water Hazard

Urban geysers are explosive eruptions of air-water mixtures from stormwater system manholes during heavy rainstorms, garner significant attention due to their potential impacts on public safety. Typically, these phenomena arise when trapped air pockets within stormwater tunnels are released, transitioning from open channel flow to pressurized flow conditions. Our study experimentally examines the air-water flow characteristics associated with air pocket release in covered stormwater system manholes.



Four distinct geyser regimes were identified: no-geyser, single air-release geyser, single rapid-filling geyser, and multi-geysers. The air-release geyser is characterized by a distinctively rising upper surface of the water column and an air-water interface, which culminates in elevated pressure beneath the manhole cover. Conversely, the rapid-filling geyser is triggered by an enlarged pressure difference between the manhole and the external head following the air-release geyser. This regime gives rise to a rapidly ascending air-water mixture within the manhole. The corresponding air-water movements and pressure evolutions during geyser were studied.



Various influencing factors on geyser regimes were investigated, including manhole diameter, cover ventilation area, external head, and air pocket volume. Notably, the manhole diameter and cover ventilation area emerged as the most critical factors determining geyser occurrences. As the manhole diameter increases or the cover ventilation area decreases, the maximum heights of both air-release and rapid-filling geysers decrease significantly, thereby reducing the likelihood of geyser occurrences. Conversely, increasing the external head and air pocket size can elevate the maximum geyser heights, and their impact on geyser occurrences intensifies as the manhole diameter decreases or the cover ventilation area increases.



Empirical equations to predict the maximum heights of the geysers are obtained. These predictions provide a safe assessment of geyser occurrences when compared to the manhole height. Our findings can facilitate early warnings of geyser occurrences when combined with information on stormwater system structures and real-time monitoring of operational conditions. Additionally, they offer a foundation for the safe design and operation of stormwater systems