The use of sonar data for mapping the muddy bottom of water reservoir

The goal of the work was to find a method to determine the structure of the subsurface of the bottom of a water reservoir with relatively soft ooze-muddy sediments using the recorded parameters of the first and second sonar echoes. This would allow avoiding the use of expensive devices such as sub-bottom profilers. Sonar measurements were taken on the entire lake commencing from the depth accessible to the measuring boat with outboard transducers. The sonar screen image and the first and second echo parameters were recorded and used according to the RoxAnn method. In order to verify and extend the scope of the sonar data, measurements of the bottom depth and hardness were made using a pole at 40 control points located along five cross sections. Finally achieved numerical models of sediment structures under the bottom surface of the water reservoir for three reference surfaces: depths for initial top surface of the colloidal state (ooze) layer, top surface of dense muddy bottom and surface of solid bottom under muddy layer. Each of them was obtained by two independent methods, in which the input data was the depth measured by the sonar for the initial top surface of the colloidal state layer or roughness of the first echo. The volume between the numerical surfaces for the colloidal state layer, which is important for environmental protection purposes, was calculated using three different methods. The results were very similar. The difference of volume was within 1.7–5.7%. Each of the method of measuring any layer volume using a single beam echo sounder / sonar can be used to assess the scope of work and the costs of required restoration measures or water reservoir by removal of colloid suspension layer. The advantage of the developed method is the possibility of performing the work using a single beam echo sounder/sonar instead of an expensive sub-bottom profiler.