Study of Internal Water Exchange in Lake Balkhash

摘要

The terminal lake Balkhash is located in arid zone in south-east of the Republic of Kazakhstan. Lake Balkhash is fed mainly by the Hi River, which provides 80 % of the drain. The distance of the lake from west to east (the length of about 600 km, thewidth of about 30 km), uneven distribution of inflow of water and salt (more than 80 % of drain is supplied to the west part) along the length, intensive evaporation stipulate quasi-stationary water-balance flow and transfer of salt from east to west. Lake Balkhash consists nominally of two parts subdivided by the Strait Uzunaral: the west and the east parts. Salinity distribution along the length of the lake depends on its subdivision into reaches. With distance from the west extreme end the water mineralization increases step-wise in each of the reaches, thus creating peculiar hydrochemical districts. Despite numerous previous studies of the lake the aspects of water and salt exchange in the lake interior are not clarified up till now. This study isaimed at development of a new method of estimation of internal water exchange between the west and the east parts of the lake with consideration for hydrometeorological factors. The research procedure is based on two-dimensional numerical solution of differential equations of unsteady slowly varying water flow in free channel (Saint Venant equation). Parameterization of the equations is based on the generalized results of hydrochemical survey of the lake and measurements in the Strait Uzunaral, performed in 1983-1987. The number of water exchange cycles at the boundaries of hydrochemical districts varies from 89 to 259. The most frequent variations of the flow are in West Balkhash. This can be attributed, probably, to higher surface area and lower depth in comparison with East Balkhash. The higher is the surface area and the lower is the depth, the more intensive is the response of water body to variation of wind direction. Cumulative volume of influent water eastwards within overall ice-free period via the boundaries of hydrochemical districts varies from 24.8 km3 to 76.7 km3, and from 22.7 km3 to 71.0 km3 westwards. It should mentioned that the difference between them in each boundary in terms of direction and quantity equals to water-balance flow.For instance, the eastward flow via the Strait Uzunaral (boundary IV-V) within ice-free period amounted to 27.9 km3, and 24.7 km3 westwards, the difference of 3.2 km~3, is the water-balance overflow within the same period via the strait, eastwards. In East Balkhash, including the Strait Uzunaral, in the boundaries between IV-V, V-VI, and VI-VII hydrochemical districts the average time of continuous flows is twice as much as in the other boundaries. The maximum duration of flow in one direction for theeast phase varies from 27.7 to 105.2 h with the volume of water overflow up to 2.33 km3, for the west phase these properties are 35.5 h, 116.3 h, and 2.30 km~3, respectively. The highest time of water flow in one direction is in the Strait Uzunaral bothfor the east and for the west phase.