Hydraulic studies of bottom regulatory devices

Introduction. Accidents at underwater pipeline crossings lead to serious environmental consequences. The choice of the location of the pipeline junction made without accounting the general dynamics of the channel process, use of improper construction technology of underwater trenches and pipeline laying often result in their destruction, which are caused by erosion and pipe sagging. Existing methods for protecting the pipeline by soil or crushed stone filling, exposure embedding with sandbags, strengthening with flexible concrete mats and other materials are not always effective and, as a rule, are expensive. Materials and methods. The article considers a method of protection of the main pipeline against erosion by means of through bottom devices of various types to determine their efficiency. Velocities of the flow are measured behind the bottom obstacles at the flow axis at several points in depth using the microcomputer flowmeter/velocimeter. The measuring sections are located at distances of 1 to 10 of flow depths from the bottom obstacles. The near-bottom velocities at the height of the roughness protrusions are calculated according to the dependences suggested by V.N. Goncharov. Results. The article shows results of laboratory hydraulic investigations of a tray flow around four types of bottom obstacle models: solid flat wall, slotted flat wall, volumetric round-section obstacle of fixed synthetic strings and volumetric soft structure. All the studied design models cause a rearrangement of the velocity diagrams and a decrease of near-bottom velocities. However, only through-passing structures are suitable for sediment deposition behind the barriers. If the bottom velocities are reduced to values less than sediment-washing ones, sediments will be deposited behind the barriers at a certain relative distance determined in the work. Conclusions. The investigated models of through bottom structures showed themselves to be quite effective in reducing the near-bottom speed and depositing sediments at a certain distance behind them. The most effective is the “volumetric” construction, since it gives the greatest reduction in relative velocities at a certain relative distance.