URBANIZATION-INDUCED INCREASES IN AQUIFER RECHARGE AND SPRINGFLOWS

Historical trends and worldwide data show significant changes in aquifer recharge caused by urbanization. With urbanization, it is documented that “impervious” cover increases, which both decreases direct recharge and increases flooding. However, leakage from utility systems (water, sewage, and storm sewer), irrigation return flow, leakage of surface runoff, storm water detention systems, and infiltration from losing streams generally increase recharge. Leakage rates range from 6 to over 50% in water and sewage lines. Storm sewer leakage rates are inferred to be similar. The area between Austin and San Antonio, Texas, is undergoing intensive urbanization and our data demonstrate significant groundwater recharge from these new urban sources. This is shown by water budgets and the fact that, at low flows, some urban streams mostly consist of water from these sources, which is demonstrated by isotope studies. We find that impervious surfaces are not impervious; secondary permeability in pavements, curbs, and gutters can be significant in promoting recharge. Analysis of springflow data from the karstic Edwards Aquifer normalized versus precipitation data for 50 to 80 years demonstrate increasing springflows that correlate with urbanization for Barton and San Marcos springs. Comal Springs, without a significant local recharge input, have not. In most cases, significant water quality degradation has not been documented.