Although DC electrical resistivity imaging is widely applied to dike investigation, either rapid 2D or high-resolution 3D approaches fail to address actual needs. An intermediate electrical resistivity imaging approach referred to as ?3D-? is introduced in this paper. The methodology is based on existing tools, and it offers useful and sufficiently reliable 3D images of the investigated structure within a cost-effective and flexible procedure. The survey design, the model discretisation, and the thorough integration of a priori information are the main phases of this procedure. To demonstrate the benefits and limitations of this approach, it is applied to an existing stretch of embankment levee along the Loire River. A numerical study was carried out both on synthetic and real data to assess the 3D imaging capability of the approach and the influence of prior information on the inversion outputs. The important role of a priori information is shown to be even more essential here. The results demonstrate the efficiency and versatility of the 3D- approach for reliable and cost-effective investigations of long dikes.