Radiometric Method for Investigating the Permeability of Reservoir Beds

To locate isolated leaks over large areas of a reservoir or canal bed, the development has been undertaken of a method based on the use of radioactive solutions and radiometry. The method consists in introducing a homogeneous cloud of radioactive solution (having a higher density than the surrounding water) above the bottom of the reservoir, on which it settles after a few minutes. In places where there is an increased seepage rate (leakage of water) there is always a slight suction, which draws the radioactive solution out of the cloud on the bottom into the crevices and pores in the ground and thus causes a decrease in the radioactivity of the surrounding medium in the immediate vicinity. Repeated monitoring of the distribution of the radioactivity on the reservoir bottom then permits location of the leaking areas and the determination of their approximate extent. If, at the same time, the radioactivity of the outflowing water is measured at various points in the area under investigation and in the surrounding medium the hydrodynamic link can be established between the water seepage observed and the corresponding area of the reservoir bed. In order to locate the position of a particular leak more precisely when applying a cloud to a large bed area we divide the cloud into zones, injecting a different isotope into each zone. The paper discusses the underlying principle, the types of radioisotope used for the main and local solutions, and the level of radioactivity used. Descriptions are given of the method of injecting the radioactive solution, the equipment employed, and the measurement technique. An example is given of the practical application of the method in a reservoir (at Pszeczica), where the leaks occurring were in time causing damage to some parts of the anti-seepage layer and then to the dam itself. Investigations using the method described allowed precise determination of the location and extent of the leaking areas of the bed, showed the hydraulic link between these areas and the corresponding escape of water in the medium surrounding the dam, permitted determination of the leakage in the anti-seepage layer and, an extremely important point, confirmed that under the clay anti-seepage layer there are areas of considerable infiltration, which were the direct cause of the damage. The results of field experiments illustrate the considerable water-management possibilities of the method discussed. It allows the location of leaks in the bottom of natural and artificial reservoirs in rocky or sandy terrain, and leaks in canals discharging water or industrial effluent, which could pollute drinking water supplies. It also permits an assessment of the condition and location of damaged places in the anti-seepage barriers around hydraulic engineering structures. (author)