Reservoir assessment using non-invasive geophysical techniques

Abstract

This paper describes the use of three geophysical techniques to detect potential seepage that could jeopardise the integrity of reservoir embankments, could induce partial or total collapse and pose a risk to the population nearby. A fast-scanning geophysical technique using two dipole electromagnetic (EM) profile apparatus GEM2 provided the first step to detect the weakest points on the selected dams in order to proceed to a more detailed analysis and visualisation of the soil erosion (fissuring or piping) using electrical resistivity tomography (ERT). Finally, self-potential surveys were carried out to relate to the EM and ERT anomalies that could be pathways for seepage and changes of the water displacement inside the embankment. The three geophysical techniques used were evaluated in one case study of reservoir in a location relevant to flooding issues in Czech Republic. A risk approach based on the geophysical results was undertaken for the reservoir embankment. The three techniques together were compared for the same problematic section and confirmed seepage by showing similar results. Conclusions were also drawn on the efficiency of using these three techniques as a package to give a comprehensive non-invasive assessment to be used as common practice by local authorities and environment agencies whereby remedial action could be recommended to protect assets and civilians.

Geophysical Methods and their Applications in Dam Safety Monitoring

“…Other similar cases may be cited from the Kaffrein Dam (Jordan) [69], riverbanks dikes and embankments for a group of reclamation and irrigation channels located between Malalbergo and Barricella, Bologna (Italy) [70], Oba earthfill dam (Nigeria), [71], and the Røsvatn field test dam in Norway [72] and many others. Detection of seepage within foundations of embankment dams was also performed for many earthfill dams using geophysical methods such as: the Vitineves reservoir Dam (Czech Republic) [73], Success Dam, California, (USA) [74], Beaver Dam, Arkansas (USA) [75], an unnamed homogeneous earth-fill dam located at the base of the Rocky Mountain foothills in Jefferson County, Colorado (USA) [76], Wadi Megenin Dam (Libya) [77], Krousovitis Dam (Greece) [78], Mill Creek Dam, Walla Walla, Washington (USA) [79], Coursier Lake Dam, British Columbia, Canada [80], Wolf Creek Dam, Russell County, Kentucky, (USA) [81]. In all these cases, one or combination of many geophysical techniques were used to get valuable knowledge on the behavior of the earthfill dams and dikes under consideration.…”

“…The primary field induces a secondary field in the ground whose intensity depends on the conductivity (resistivity) of the medium surrounding the transmitting coil. Therefore, water ingress can be detected [32]. EM profiling's fast and simple field implementation leads to a high acquisition speed, which combined with the simplicity of the data processing results in a very low cost, thus lending itself as an ideal method for initial, overall and complementary tool.…”

Subsurface condition assessment of critical dam infrastructure with non-invasive geophysical sensing

“…The depth to obtain the information on the conductivity of the medium depends on the frequency of the primary electromagnetic field or on the length of the transmitter coils. Instruments based on EM signals can provide a rapid, cost effective and contactless method to assess earth-fill structures (Sentenac et al, 2018). The CMD-2 from the company GF instruments (Czech Republic) that was used for the surveys, generates a fringing field between two electrodes at a constant frequency range, penetrating the external medium which depends on the electrical and magnetic properties of soils (Michalis et al, 2015).…”

Characterization of a river embankment using a non‐destructive direct current electrical survey

“…Geophysical methods have previously been applied to river embankments and earth dams. The methods and objectives of previous studies were as follows: fracture detection using electrical surveys and frequency domain electromagnetic (FDEM) methods (e.g., Sentenac et al ., 2013; Nthaba et al ., 2020); animal burrow detection using electrical surveys, FDEM and ground penetrating radar methods (e.g., Borgatti et al ., 2017); leakage and internal erosion detection using time‐lapse electrical surveys (e.g., Sjödahl et al ., 2008); seepage and leakage detection using electrical surveys, FDEM and self‐potential methods (e.g., Sentenac et al ., 2018); embankment and foundation soil property estimation using electrical surveys and multi‐channel analysis of surface waves (MASW) (e.g., Hayashi et al ., 2013; Rahimi et al ., 2018); and soil moisture and water saturation monitoring using electrical surveys (e.g., Jodry et al ., 2019; Tresoldi et al ., 2019). Although electrical surveys are commonly used, most of them are 2D and time‐lapse 2D surveys.…”