Abstract
On November 2014, the Municipality of Grandate, near Lake Como, had to deal with a great emergency that was caused by the flooding of factory undergrounds. The authors realized a hydrogeological study to understand the causes of groundwater flooding and to prepare a pre-feasibility study concerning possible actions for groundwater control. The hydrogeological structure is rather complex and required time-consuming reconstruction of the conceptual site model. A transient numerical model was developed to analyse the system behaviour in different scenarios. The flow model was calibrated in a steady and unsteady-state using the automatic calibration code Model-Independent Parameter Estimation (PEST). The study demonstrated that the reason for floods was mainly due to the concurrence of three causes: (1) the hydrogeological structure of the area was recognized as a stagnation zone, (2) groundwater rising, and (3) extremely heavy rainfall in 2014. Through the PEST RandPar function, 100 random rainfall scenarios were generated starting from rainfall data for the last 20 years. The model was used to run 100 1-year long simulations considering the probability distribution of recharge related to the 100 randomly generated rainfall scenarios. Through collecting the piezometric heads that resulted from the simulations, monthly probability curves of groundwater exceeding a threshold level were obtained. The results provided an occurrence probability of groundwater level exceeding the underground structures level between 12% and 15%.
Highlights
The development of industry in several major cities in Europe caused groundwater levels to drawdown until they were tens of meters below ground level
Regardless, the current paper demonstrates that a hydrogeological analysis coupled with mathematical modelling and stochastic analysis can provide satisfying approximate forecasting of the behavior of the piezometric levels and can be a useful tool for the assessment of risk related to groundwater flooding
The mathematical model, which was calibrated in an unsteady state as well as using the levels that were registered in the piezometer that was located in the flooded area since March 2016, was used that were registered in the piezometer that was located in the flooded area since March 2016, was to forecast the system behavior in three different scenarios: used to forecast the system behavior in three different scenarios: Scenario 1 (Business As Usual: 2014 rainfall, no interventions are simulated)—Starting from the Scenario 1 (Business As Usual: 2014 rainfall, no interventions are simulated)—Starting from the calibrated situation, the recharge values of 2014 were set in the model and the year was simulated
Summary
The development of industry in several major cities in Europe caused groundwater levels to drawdown until they were tens of meters below ground level. Since the end of the last century, many European cities have been affected by the groundwater rising phenomenon that is the result in many causes, such as the deindustrialization process, urbanization, and the variation of the aquifers recharge rate because of climate change. These different conditions have led to local rises of the water table, ranging from 3 m to 30–40 m with different consequences [5], with the flooding of underground structures among them. On November 2014, the Municipality of Grandate, located 10 km southward of Lake Como, had to deal with a great emergency that was caused by the flooding of numerous undergrounds of buildings and factories that
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