Estimation of snowdrift filling of sections of earth canals

Abstract

The practice of operating existing hydraulic engineering complexes the year-round under conditions of a harsh climate has revealed a number of difficulties in delivering water along open earth canals in the winter [1 ]. Snowdrifts in the channel of canals are the cause of some difficulties [2]. They are produced f rom snow being transported by blizzards and form on elements of the canal cross section (slopes, berms, surface of the ice) in different volumes. The parameters of snowdrifts and their role in creating emergency situations on operating cascades depend on the physiographic conditions of the region and design characteristics of the hydraulic structures. The sections of canals and their individual elements (embankments, spoil banks) project as poorly streamlined bodies for a perpendicularly directed snow--wind flow. The wind flow leaves behind them a region of recirculating air, which is closed in this region of the flow. Visual observations of the process of formation of snow deposits in the channel conducted on the Irtysh--Karaganda canal in 1974-1979 indicate a regularity of the deposition of snow within the area of recirculation of the flow (eddy zone). It was established from the results of statistical analysis of the data of field measurements of snowdrift filling of sections of canals that the surface of the snow drifts coincides with the line of the axial component of the zero speed of the snow--wind flow, which regardless of the size and shape of the section runs at an angle of 80 ~ -+ 95" to the vertical at the point of separation of the air flow. The line of zero speeds is the boundary of snow accumulation in the channel. Maximum snowdrift filling of canal sections will be observed when the area of the eddy zone is filled to the line of the zero speeds. The characteristics of the limits of snowdrift filling of canal sections obtained made it possible to develop relations for calculating the main parameters of snow deposits. The formula for calculating the maximum volume of snow in a trapezoidal channel has the form Vsd = H 2 (5,673--cig tp)/2, ( 1 )