Numerical modeling of groundwater flooding in urban area: The case of polustrovo (st. petersburg, russia)

The present paper describes the implementation of a numerical model to simulate groundwater flooding in the Polustrovo urban area of St. Petersburg (Russia), characterized by a moraine aquifer system. The main purposes are to determine the causes of groundwater flooding and to simulate some examples of engineering solutions. The study concerns (a) data collection and processing also by means of geostatistical analysis, (b) conceptual model elaboration and (c) implementation of a 3D groundwater flow model (design, execution and calibration) using MODFLOW code. Results point out a shallow flow system governed by topography and by groundwater-surface water interaction. All surface water bodies collect water from the shallow aquifer. Flow direction is mainly W/E in the northern part of the area and N/S in the southern part. Hydraulic gradient of shallow aquifer (average of 0.4%) varies depending on lithology distribution, whereas in the deep aquifer the gradient has a constant value of 0.3%. In the southern part of the area, deep aquifer has artesian condition. Flooding results in the southern zone of study area, according to field observation. Likely cause of flooding is the quick decrease of hydraulic conductivity along flow direction in the shallow aquifer, in addition to the decrease of soil surface elevation. The rising of deep groundwater under artesian condition in the zones where the aquitard is eroded can increase the intensity of flooding. Finally, the modeling indicates that a passive drainage system or a hydraulic barrier (pumping wells) could represent some engineering solutions of the flooding problem.