Estimation of flow velocity during ice drift and ice jams breaking at the river mouths of cryosphere

Subject: in this paper we discuss a method of calculation of the increase in mean water discharge during spring debacle of water streams in cryosphere. The main features of the debacle of water streams of river mouth zones in cryosphere are considered: ice drift, regular formation and destruction of ice jams, catastrophic floodings and washout holes. We discuss the methods of forecast of ice jams based on the estimate of the water discharge upstream of the potential cross-section of ice accumulation. Research objectives: theoretical investigation of flow velocity distribution over the depth of the stream during the ice breakup and its application for estimation of the stream velocity during the ice breakup. Materials and methods: the results of papers that describe the remote methods of estimating the speed of ice on the surface of water are analyzed. The aerophotography and satellite imagery methods, which enable us to estimate the stream velocity and water discharge during the ice breakup, are analyzed. These methods permit us to calculate current velocity profile and water discharge during breakup. Possibility of using logarithmic and power laws for description of flow velocity profile over the depth is investigated. The advantages of estimation of stream resistance with the help of Darcy-Weisbach coefficient in comparison with Manning’s roughness coefficient are discussed. Results: we consider application of power law for distribution of velocity over the depth to calculate the specific discharge of the water stream with ice floes on the surface. By integrating the specific discharge values through the width of a stream with the use of independently measured depth and water levels, one obtains water discharge of the stream. The method assumes that the ice run is not highly dense, and the stream velocity profile is not considerably different from that of an open stream due to the quick motion of ice on the water surface. Calculated magnitude of specific water discharge includes the water discharge moving along with the ice and the water discharge inside the permeable ice layer. The magnitudes of porosity of permeable ice layer during the ice breakup in rivers are presented. Conclusions: the research shows that application of power law velocity profile for estimation of stream discharge during the ice breakup has some advantages as compared with the logarithmic one. In particular, it becomes unnecessary to define the roughness coefficient during the ice drift, which is not a less difficult task than the estimation of water discharge. The improved method based on the power law velocity profile, developed in this paper, enables one to reduce the error of the method, as compared with the method based on logarithmic law velocity profile.