Application of 2D-Ert In Feasibility Study of Hydropower Projects In Nepal

In Nepal seismic refraction is the traditional method of subsurface exploration for geotechnical<br>applications. Until the mid-90s seismic refraction was routinely used to investigate proposed sites for<br>hydropower projects of Nepal. These areas lie in the mountain and are inaccessible for vehicular<br>transportation. Very high heterogeneity of surface material creates poor energy coupling for both source<br>and receiver. Because of the high-energy content and easy transportability, explosives were the preferred<br>source for the generation of seismic waves. <br>Due to the rebel activities in the recent years, however, the government has tightened regulations<br>on transporting and using explosives. This situation has forced the hydropower projects to search for<br>alternative geophysical methods in place of seismic refraction. Electrical resistivity tomography (ERT)<br>was selected as a possible replacement method. In the initial stage of the application of ERT, various<br>electrode arrays and data acquisition approaches were evaluated for data quality and subsurface<br>resolution. Experience in different projects reveals that the pole-dipole electrode arrangement with data<br>levels at different electrode spacing is suitable for better resolution of the subsurface material.<br>Furthermore, manual acquisition, although less productive than automatic acquisition, seems to secure<br>higher quality data. With these systems of data acquisition ERT was able to fulfill most of the objectives<br>of the subsurface investigation at hydropower projects.