Mapping Subsurface Conditions and Detecting Seepage Channels for an Embankment Dam Using Geophysical Methods: A Case Study of the Kinion Lake Dam

Abstract

Capacitively-Coupled Resistivity (CCR), Electrical Resistivity Tomography (ERT), and seismic surface wave testing using Love and Rayleigh waves were performed on Kinion Lake Dam, an embankment dam that has historically experienced significant seepage and internal erosion issues. The goal of this study is to detect seepage locations in the embankment dam for remediation purposes and map bedrock location across the area using nondestructive geophysical measurements. Surveys were completed along the crest and downstream toe of the dam to map subsurface conditions with a focus on seepage detection. The seismic surface wave data were analyzed using two different methods: Multichannel Analysis of Surface Waves (MASW) and Full Waveform Inversion (FWI). Both MASW and FWI methods were shown to be capable of resolving the bedrock layer below the dam, but the FWI method, provided a higher resolution image of the subsurface conditions compared to MASW method. However, the MASW and FWI provided little guidance regarding the seepage path through the dam. The CCR and ERT surveys, on the other hand, were shown to be very valuable for seepage detection. The seepage paths of the embankment dam were detected by comparing the resistivity measurements acquired in a wet winter and a dry summer. These seepage regions correspond well with previous sinkholes observed in the pool area following a drought. Additionally, new drilling in the two regions which showed differences in resistivity indicated the areas contained highly fractured limestone with evidence of solution cavities. It seems that the highly fractured limestone becomes fully saturated during the wet season causing very low resistivity values for these layers in wet seasons, but it quickly loses the water during the dry season leading to a highly resistive material in dry seasons. Therefore, seasonal resistivity measurements can be considered as a useful method for locating potential weak zones of earthen hydraulic structures in a cost-effective and timely manner.