Date of Award
geophysics, resistivity, conductivity, heterogeneous sediment, electrical imaging
The area near the inlet of Spuyten Duyvil Creek in Inwood Hill Park in New York City exhibits complex hydrological processes. The inlet is a tidal flat, which contains brackish water; a mixture of saltwater and freshwater. The area was modified by man, built on a shell bed and contains heterogeneous sediment. One field adjacent to the inlet contains several small sinkholes. Electrical resistivity and ground conductivity techniques were used in order to get an understanding of the hydrological processes of this field. It was hypothesized that the formation of the sinkholes is due to the tidal forcing of the water table. The measurements collected at the study site show evidence that tides do have an effect on the water table. The ground conductivity surveys showed variable conductivity around the sinkholes however the greatest change in conductivity occurred laterally in the field. The conductivity increased going towards a patch of vegetation located in the southeast corner of the field. Higher conductivity near the patch of vegetation in the southeast corner of field was probably due to overwash of brackish water. Infiltration of freshwater in topographically low areas was also observed in the conductivity contour maps. The resistivity surveys showed the water table increase and then decrease after high tide. There was evidence of piping where one of the sinkholes was located. This particular sinkhole was observed in 2002 however, this sinkhole was filled during lawn work conducted by the New York City Parks Department. It can be concluded that the formation of sinkholes in the field is not instantaneous and is a long process. This is the reason why there is little variation with respect to time in conductivity around the sinkholes. Given enough time, the sinkhole originally seen in 2002 could reappear.
Khaleda, Rea A., "Electrical Conductivity and Resistivity Study of Heterogeneous Sediment in Inwood Hill Park, Manhattan, NY" (2019). CUNY Academic Works.