URBANIZATION EFFECTS ON HYDROGEOLOGICAL SYSTEMS

Humans are, perhaps, the main geological agent on the surface of the Earth, especially where populations concentrate. Cities and urban populations are growing at fast pace, yet groundwater remains an underutilized and poorly managed resource in most urban areas. Urbanization does increase flood intensity and is commonly been assumed to increase stream flows because of the inevitable increase in “impervious cover.” Groundwater recharge, however, is demonstrated to increase in general because of leaky utility systems, urban irrigation, and artificial recharge. In addition, even a cursory glance at most roads, sidewalks, or parking lots reveals that, far from being impervious, there are abundant fractures that may provide avenues for infiltration. The permeability of these surfaces is now quantified. These alterations to the hydrological cycle can maintain urban stream flows during summers or droughts. The permeability of the subsurface is altered so that determination of flow parameters is very difficult and remediation of contaminated sites difficult, but riparian buffer zones are effective in protecting water quality. If accompanied by pumping or drains to maintain urban infrastructure, springs and other groundwater dependent ecosystems can be greatly affected. Finally, the urban heat island effect is well documented – it can actually change the local climate. Most major cities rely on surface waters and groundwater is often an underutilized resource that may be utilized to address future needs. The effects of urbanization on hydrogeological systems are predictable and should be considered in planning for developing and existing major urban centers.