Following flooding in September 2013, several areas along Lakewood Road and Lake Road in northern Eddy County, New Mexico, were damaged by multiple sinkhole collapses. Pettigrew & Associates contracted NCKRI to conduct electrical resistivity (ER) surveys for cavities to guide road repairs. NCKRI agreed to conduct this research to assist in solving a threat to public safety in addition to collecting additional geophysical data, to include in its database for future detailed studies of ER data collection methods and analyses.
The sinkholes in the study area, cover collapse sinkholes, form by the piping of soil and alluvium into underlying karstic cavities. Their position along the two roads is the result of drainage channels along either side of each road, which have promoted groundwater recharge in these linear areas for many years. The piping of the unconsolidated materials created cavities in the alluvium that slowly stoped up toward the surface and into the soil. The flood of September 2013 focused substantially greater flow down into the soil in the channels until the cavities became sufficiently large and unstable to collapse and breach the surface. A visual survey of the area by Pettigrew and NCKRI personnel on 12 February 2014 supported this hypothesis, finding that collapse and related features appeared to diminish with distance from the roads (Figure 1). Subsequent interviews with Lakewood residents revealed additional karstic fissures and sinkholes occurring several tens of meters from the roads, but still indicating the majority were concentrated along the drainage channels.