Assessment of urbanization-related groundwater flooding process via Visual MODFLOW modeling: A case study for the northern part of Almaty city, Kazakhstan

Groundwater flooding might be triggered by disregarding hydrogeological processes during urban area development. Such flooding might result in public disruption, engineering infrastructure destruction, and general damage to natural and human environments, as in the northern part of Almaty city. A MODFLOW groundwater flow model was used to simulate and quantitatively assess the changes in hydrogeological conditions affecting the groundwater flooding process. A field study of the Akbulak micro-district research site showed that groundwater flooding occurred in its center owing to a water table hillock with a total area of 0.07 km² and groundwater levels ranging from 1.2 to 0.25 m below the ground surface. The MODFLOW simulation suggested that this water table hillock developed from runoff, which, owing to a decrease in natural infiltration across an urbanized area, accumulated in low-elevation areas and infiltrated. This runoff accumulation effect may be up to eight times the annual average precipitation amount. Once in local sub-basins, larger runoff volume infiltrates into an underlying aquifer water table that is already high, might cause groundwater flooding in populated areas. The Almaty scenario simulation confirmed the field observations, suggesting that the clogging of the Karasu-type stream has concentrated runoff to low-elevation areas and is the leading cause of flooding.