River channel deformations in the area of damless water intake

Abstract

A mathematical model of the unsteady uneven movement of the river flow in the area of the damless water intake, flowing in deformable channels, was developed and numerically implemented. In the developed model of the deformation of the river channel, flowing on easily eroded beds, adapted formulas of the transporting ability of the flow are used, the hydrodynamic equations of motion and continuity of the flow, deformation of the channel, and sediment balance. To close the system of differential equations, we use the adapted formula of the conveying ability of the flow–Benold. In the calculations, the non-erosion speed was taken according to the formula C.E. Mirtschulava, taking into account standard values of adaptive coefficients. It is suitable for describing deformation processes, taking into account the drift of dredging slots. The model contains the minimum number of equations and empirical constants. In the present work, a numerical model is proposed for predicting channel processes in river beds in the area of damless water intakes and is verified on the results of experimental studies. The figures show sequential deformations of the channel, arising due to natural causes, as well as due to channel adjustment and treatment works (discharge of soil from the supply channel into the river). As can be seen from these figures, the channel from multi-sleeve is gradually turning into one-sleeve. It has been established that after 1 year of observation at low water, as a result of discharge of sediment from the sewage treatment works, the river ducts die off. These ducts are observed only in the flood. Note that below the Karshi main channel (KMCh), the left bank eroded by about 150 m. After a 10-year course, the low-water course turned into a one-arm riverbed. As a result of the erosion of the left-bank islands, it turned into the river itself. During the flood, there are also no pronounced sleeves, a significant erosion of the left bank is noted, up to 700 m. After that, this bank was strengthened. In the future, the channel process did not undergo significant changes. Towards the end of the 10th year of observation, the channel broadened somewhat, and the flood depth decreased in the flood. Comparison of the results of field and numerical studies shows that the developed model gives good results. For low-water conditions, coincidence is better than for flood conditions. During the flood, under natural conditions, somewhat greater depths are observed on the floodplain than in the calculations. It should be noted that both in calculations and in kind:

- there was a significant erosion of the left bank below the KMCh;

- the channel of the Amudarya river in the considered section from multi-sleeve turned into practically one-sleeve.