KARST-RELATED FLOODING IN THE ONONDAGA FORMATION; WESTERN NY

Karst-related flooding occurs between Leroy and Caledonia in an area where water tables exhibit dynamic seasonal variation. This peculiar groundwater environment resulted from the history of deglaciation which has eroded much of the unconsolidated glacial sediments, leaving behind thin immature soils overlying fractured, karstic, carbonate bedrock. Stream incision and highlands to the south have resulted in high potentiometric gradients and groundwater flowpaths that respond to individual meterologic events. This peculiar hydrogeologic regime poses a challenge to current watershed management because of the dynamic nature of subsurface flowpaths and their potential to carry pollution. This ongoing study seeks to understand the groundwater system and how it contributes to flooding, much of which occurs along Rt. 5 between the Villages of Leroy and Caledonia. Surveys were conducted in spring 2007 to map flooded areas. Water levels were monitored in three sinkholes and discharge measurements were taken in Oatka Creek to document water losses to the Onondaga FM. The loci of several flooding events occur near the contact of the Onondaga and Marcellus Formations. Several sinkholes flood occasionally when water tables rise above the surrounding landscape. We interpret the flooding to be caused by the presence of high elevation recharge areas to the south, a release of confining conditions at the Onondaga / Marcellus contact, a piezometric surface that is close to the ground elevation, and seasonal rainfall/snow melt events. Flooding may also occur where spatial heterogeneities in fractures cause recharge to temporarily exceed the conveyance capacity of the bedrock. Groundwater intercepted by the Onondaga FM ultimately moves eastward along open fractures to a system of springs located in Caledonia.