Near-bottom stratified currents and sediment transport in reservoirs and lakes

Near-bottom density current during selective draw-off from the upper pool of the Istra Reservoir

“…These profiles are of interest for the development of methods of selective draw-off [1], and may be used, moreover, as standards for confirmation of mathematical models of stratified flows. Correspondence is observed between the U(z) profiles and the theoretical profile constructed on the basis of models from [5,10] when z < z u , and from [11] when z ³ z u . The averaged scales of the density current -height z u = 8 m, maximum velocity U m = 13 cm/sec, and density difference Äñ = 10 -3 g/cm 3 -are typical for these flows in reservoirs, lakes, and seas [10].…”

“…The specific content of suspended matter above the density current also diminished, but two times slower. The solid curve corresponds to the theoretical distribution S(t), as determined from the transport model, which is presented in detail in [5]. The minimum flow velocity of particles of suspended matter in the density current in the Istranskoye Reservoir ùf = 8´10 -4 cm/sec in similar periods [5] was used in the S(t) calculations.…”

“…The solid curve corresponds to the theoretical distribution S(t), as determined from the transport model, which is presented in detail in [5]. The minimum flow velocity of particles of suspended matter in the density current in the Istranskoye Reservoir ùf = 8´10 -4 cm/sec in similar periods [5] was used in the S(t) calculations. A decrease in wf to zero has virtually no effect on this model distribution of S(t), i.e., the buoyancy of the suspended matter was close to neutral.…”

“…2d -f) (1), as computed from formula (2) (2), and from model outlined in [3,4] (3); differences between densities of liquids in and above flow Äñ (4) and wind speed U w (5); b) thicknesses of density current determined from measured profiles of its velocity (6) and as computed from expression (5) -solid curve; c) integral Richardson numbers Ri u for density current (7), for entire stratum of water (over entire depth) Ri* (8), and for near-bottom section of flow Ria (9); d) concentration S of suspended matter in density current (averaged over its thickness), according to measurement data (10), and as computed from model outlined in [5] solid curve; differences in concentrations of dissolved salts ÄC dil in and above density current (11). Intervals in Fig.…”

“…The set of equipment that was employed included a device for synchronous recording of flow velocity U by rotometers at six horizons in a 3-m-thick layer, a turbidity meter, sensors of the temperature T and electrical conductivity C cn of the water, an anemometer to measure wind speed U w at a height of 2 m above the water, a positioning system (GPS), and an echo sounder [5]. Calibration of the turbidity meter with respect to the concentration S of suspended matter was accomplished from results of analysis of water samples.…”