The construction of underground subway facilities will introduce a barrier to the natural groundwater flow due to the presence of permanent structures buried in the ground. This will create a damming effect and cause a rise in the groundwater level in the vicinity of the subway structures. This paper presents an equilibration system that was adopted for the second avenue subway project in Manhattan, New York City to deal with the groundwater accumulation problem. The equilibration system consisted of a network of pipes and manholes that collects water built up on the upstream side of an underground structure to be transferred across and discharged into the ground on the downstream side. The design of the equilibration system was based on the principle of hydraulic flow under a potential energy difference. The system was designed to be self-sustaining and maintenance free.
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