Groundwater Flow Model to Simulate Drawdown Due to Leakage into Planned Rock Caverns at the Centre of Helsinki

A groundwater flow model was compiled to simulate drawdown due to groundwater leakage into planned rock caverns under the city area of Helsinki. Numerical model was applied to complete standard groundwater management plan. <br>The main features to be described in the model were hydrostratigraphic units forming a system of an unconfined and a confined aquifer, leakage of the groundwater into existing underground facilities, e.g. metro tunnels at the northern boundary, and the sea water intrusion depending on the sea level. Both aquifers carry out a risk from the point of view decreasing groundwater head, condition of wooden piles in the unconfined aquifer and subsidence of the clay layer above the confined aquifer. <br>Groundwater leakage to planned maintenance tunnel at two possible locations was simulated. As a steady-state result, leakage at Kluuvi crushed zone is not as critical as leakage at the western boundary of the model. Compensatory sea water can intrude along the crushed zone, but based on the present concept, there is no such hydraulic connection from the sea to the western boundary. Therefore at the western area recharge wells may be needed to maintain groundwater table and hydraulic head. <br>