Mapping borehole-accessed karst solutional features and culvert conduits using remote sensor technology

Abstract

Prior papers have described prototype sensors that were developed to autonomously map pathway, flow velocity, and dimensions as they flow through karst conduits. The prototype sensors are equipped with sonar and magnetometers to measure conduit morphology and orientation. The sensors are developed to be approximately neutrally buoyant but have been equipped with a propulsion system to enable the sensors to negotiate around impediments in the flow channel and avoid stalling at the walls of the conduit or cave. Data collected during an excursion are downloaded from the sensor upon completion of the survey mission. An autonomous sensor was successfully used to characterize a segment in Honey Creek Cave, a wet cave in south-central Texas. Sonar proved to be effective in measuring the cave dimensions and the velocity of flow. A magnetometer was used to orient the pathway taken by the sensor. Together, these data provided a representative reproduction of the oriented morphology of the wet cave. Two variations of the initial generation of sensors have been developed to meet the requirements of projects funded by the United States Army Corps of Engineers for mapping borehole-accessed karst solution cavities and by the Federal Highway Administration for mapping, monitoring, and diagnosing damage to roadway culverts. The first variation is tethered to map karst voids intersected by a drill hole but where discharge to a spring is not anticipated. The second features an enhanced sonar scheme to overcome the extreme multipath environments found inside a partially filled metal culvert and to provide localization information in a magnetically shielded environment.