| River mouth areas, located in the "river-sea" contact zones, are complex natural objects which an abrupt restructuring occurs from the river-type hydrological regime to the regime of a receiving water body. The most characteristic feature is attenuation of the river jet (reduction of flow velocities) as it proceeds into the receiving water body. This process is accompanied by rapid deposition of suspended sediments of the river runoff. Such transformation occurs within the limits of very short distance equal averagely to 10 widths of the river channel in the mouth gauge. Measurements are made, using multiple methods, in the mouths of the Jordan River flowing into Lake Kinneret, and Kura River flowing into the Caspian Sea.; The results of field measurements as well as theoretical analysis, have led to revealing a number of special features of mouth currents. Using both theoretical analyses based on the equations of motion of a free turbulent jet with a variable mass and the results of measurements, it was shown that velocity attenuation follows the exponential law. Accordingly, the volume of suspended material carried by the river jet is decreasing. The longitudinal dimensions of turbulent eddies get smaller with the distance from the mouth gauge, while their orientation is changing from the predominantly vertical-longitudinal rotation with a horizontal axis to the predominantly horizontal-transversal rotation with a vertical axis. In the zone of mixing river and sea waters, the energy spectra become more narrow-band, their ordinates lowering as the river jet moves forward from the mouth, while the maximum spectral density shifts to the area of lower frequencies. The farther from the mouth, in the spectra of the river jet current there appear frequency intervals that can be described not by the Kohnogorov's "-5/3" law but by the "-7/3" law. As the river jet moves beyond the mouth bar, another frequency interval appears in the energy spectra; described by the "-3" law. This is attributed to the consumption of energy by the river jet flow for overcoming the ascending forces when the process of vertical mixing of river and sea water masses is going on beyond the bar. |
