Using GPR for assessing the volume of sediments from the largest natural dam lake of the Eastern Carpathians: Cuejdel Lake, Romania

Cuejdel Lake in the Eastern Carpathians (Romania) formed in 1991 following the damming of the Cuejdiu brook from torrential rainfall causing a massive landslide of natural deposits. In 2011, using a Bathy-500DF Dual Frequency Hydrographic Echo Sounder, the first detailed bathymetric model of the lacustrine cuvette was produced, using more than 45,000 depth readings. This was the first ever use of a Ground Penetrating Radar (GPR—a Malå Ramac X3M GPR with a 100 MHz antenna) in Romania for evaluating the rate of clogging of a dam lake. The thickness of the alluvial deposits and the rate of clogging were determined on the basis of the measurements taken in wintertime, when the ice cover was 30–45 cm. The data concerning the clogging were correlated with the solid transport from the level of the catchment basin developed in the flysch area, and with the sedimentation conditions of the lake (the analysis of the annual non-glacial varve, in situ biodegradation). The morphologic evolution of the lacustrine cuvette, determined on the basis of three DEMs, revealed a significant quantitative dynamics of the alluvial deposits (sediment accumulation rate 1–16 cm/year; volume of sediments across bathymetric levels 33.6–440.4 m³/an; total volume accumulated in 22 years 103,988.87 m³, which represents 8.5 % of the initial volume (1,223,001.33 m³); average annual clogging rate 4521.26 m³/year or 0.36 %/year). In 2004, Cuejdel Lake was declared a protected natural area; accordingly, no hydrotechnical works can be carried out in order to stop the erosion and, implicitly, the clogging.