It is shown experimentally that upon a rapid draining of water within a basin, the Froude number quickly reaches its maximum and then remains virtually constant. Stationary long three-dimensional waves that arise on the water’s surface form bottom ridges, the distance between which is equal to the length of the waves. It is established that ridges on the shores of the northern part of the Caspian Sea (Baer’s Mounds) could have been formed by three-dimensional waves upon a sudden drop in the level of the Caspian Sea.

The results of experimental studies of the interaction between the horseshoe vortices formed in nonuniform water flows and a sand surface are presented. The central part of the initial cylindrical vortex ascends, driven by the Kutta—Joukowski force. The vortex tails submerged into sand approach each other, grabbing the sand by their ends. Sharp bends are formed at the axes of the vortex tails. If the bends occlude, a ring vortex is formed above the bends. The ring approaches the surface at an angle of 40° and moves along the flow: the angle decreases, and the radius of the ring increases. When the whole vortex reaches the water surface, it breaks, loses the entrapped sand, and forms a ridge on the bottom.

The conditions for the formation and destruction of an annular vortex are obtained along with the parameters of horseshoe-shaped vortices during their deformation in a flow with a shift in velocity. The results are presented from an experimental study of the interaction between horseshoe-shaped vortices and an eroding underlying surface. The vortex traps sand through the ends of supports. An annular vortex carries the sand after the supports are destroyed. The trapped sand precipitates as an annular vortex breaks down, forming a mound on the bottom.

The conditions of the resonant excitation of waves on a liquid surface by a horizontal air flow that has a decreasing velocity in the direction of motion were established, such that steady waves occurred when the period of the escape of a chain of eddies that is generated in a viscous layer of an air flow coincided with the period of natural oscillations, which is determined by the dispersion relationship for a group of waves. The dependence of the lengths of steady waves on the air-flow velocity over the surface of clean water and water with a light oil film was obtained. The resulting model was tested experimentally.

A technique for calculating viscous drift on the slopes of waves in the zone of their generation is proposed. Viscous stress is calculated for the wave’s front slope and the water-air interface. The calculations are performed with allowance for the eddies that form in the expanding viscous layer of wind flow and the deforming of the water’s surface. The technique is validated on the basis of experimental data.

This paper suggests a physical model that explains the origin of the main front of a three-meter wave that moved along the bed of the Adagum River through the town of Krymsk on July 7, 2012 at the time of flooding during rain showers that caused catastrophic destruction and casualties. It has been proven that the cause of the wave origin was a sudden change of water flow intensity resulting from the construction of an unregulated water outlet. The construction was erected without taking changes in climate into consideration and it caused an extreme increase of the volume of rainfall run-off. First, it was experimentally proven that the sudden change of water-flow intensity was associated with the change of the runoff regime through a water outlet pipe that occurred without human involvement.

A drift current was experimentally studied on the slopes of wind waves in an amplification zone. It was found that the drift decreases proportionally to the wave steepness at the front wave slope. We tested a hypothesis that relates the decrease in the drift velocity at the front wave slope with the formation of vortices in a viscous air layer. A physical model of the event and a method for the calculation of the drift decrease at the front wave slope in an amplification zone are suggested. The model calculations agree well with experimental data within the measurement error, which is less than 10% of the measured value.