Sea Cave Study
Recently, we were asked to conduct a high resolution resistivity survey to evaluate for the presence of voids caused by sea caves at a proposed water filtration plant expansion. In order to acquire the necessary data, a sting survey was conducted along several profiles oriented parallel to the coast line. The sting survey method utilizes the placement of 56 electrodes for each spread for a total of 3 spreads. The data collected was later processed to reveal electrical contrasts in the subsurface which represent changes in geologic structure and the presence of voids.
Survey was conducted in varied terrain, including areas of asphalt and high brush. It was necessary to core through the asphalt to achieve electrical contact with the soil. One large profile was conducted by conducting multiple spreads with the role-a-long method. As you can see, two highly resistive (yellow and red areas) were detected and interpreted to be possible void areas associated with potential sea caves.
Some benefits to consider:
- These surveys can be conducted in endangered habitat sensitive areas.
- No permitting is required for conducting these surveys, and therefore, can be scheduled ahead of drilling.
- When conducted in conjunction with exploratory borings or test pits, it can increase the overall extent of subsurface information as well as aid in boring and test pit location.
Southwest Geophysics has used Resistivity Surveys to:
- Map Faults
- Map fracture zones for water well sighting
- Map large karst voids and sea caves
- Find depth to groundwater, in certain specific situations
- Generally characterize subsurface geology.
- Aid environmental contamination flow projects when used to evaluate locations of paleo stream channels or fault zones.
- Find buried bedrock valleys, which can be an important source of groundwater in unconfined aquifers.
- Vertical joints or cracks, which can indicate subsidence features.