As a part of the modernization of the national hydrological network, a large number of ADCPs were delivered to the stream-gaging stations of the Roshydromet and, as a rule, used only during the open channel period. At the same time, the measurement of water discharge during the freeze-up period has always been a laborious, technically complex task, and using ADCPs during this period can optimize the measurement procedure. The article presents the issues of the features of ADCPs using on the national hydrological network of Roshydromet, the existing instrument and methodological base for measuring water discharge under the ice cover with ADCP. Either, the results of comparative field measurements of water discharge and velocities on the Ob, Neva and Oredezh rivers were considered. These rivers cover a wide range of hydrodynamic conditions: the Ob is a typical large river, with an average flow velocity is about 0.30 m/s, and a maximum depth about 20 m; the Neva is a unique large river, with a high average flow velocity value is about 0.8 m/s and a maximum depth not exceeding 11 m; the Oredezh river is a typical small river with mean flow velocity about 0.2 m/s and depths of not more than 1.5 m. In the experiments, ADCP Teledyne RiverRay and SonTek M9 were used, and comparative measurements were performed by the mechanical current meter and electromagnetic flow velocity device “Poseidon-1”. On the basis of these experiments first conclusions were drawn about the features of the ADCP application during the freeze-up period. Thus, the authors found that it is most effective to use ADCPs on medium and large rivers - labor and time costs are significantly lower than using conventional methods for measuring water flow, and the measurement accuracy is comparable. At the same time, the article notes a number of significant weak points, most of which boil down to the thesis that the measurement of water discharges using ADCP under ice involves the use of a large number of technically complex and expensive equipment, and the failure of at least one element leads to the inability to complete the measurement. Special attention is paid to the main technical aspects of working with devices, as well as with specialized software. Therefore, it is always recommended to have a spare standard measuring instrument in extra. The main technical aspects of working with devices as well as with specialized software are also discussed in more detail in the body of the article.

The use of non-contact doppler flow radars to determine water discharge is a widespread trend in hydrometeorological surveying and monitoring. However, is it reasonable to consider such an instrument as one of the most suitable and perspective for the hydrological observation network? In-situ testing have been carrying out by authors of this article and the analysis performed in scientific papers cannot provide a single-valued positive conclusion on this issue. Obvious advantage of these radars as independent safe mode of operation seems to overweight their obvious weak points. Many "undercurrents" do not allow this method to be recognized as reliable, such as the problem of transition from surface to medium flow velocities, which consists in the data processing apparatus, reliable positioning of the device, blanking distance task and etc. All in all, this article discusses the main advantages and "vulnerabilities" of the use of such an instrument as non-contact doppler radars to determine water discharge from a scientific and practical points of view.

Technological progress could not but affect the sphere of hydrometric measurements. New instruments have been implemented to add to such traditional measuring instruments as mechanical current meters or to replace them. Over the past 20 years, the number of different types measuring instruments has increased dramatically. That is why the analytical review and classification of these devices are needed to help with making appropriate management decisions in the field of streamflow monitoring and surveys. The article presents the multivariable classification of measuring instruments, based on such factors as: morphology scaling (channel width and depth), measuring conditions (open, weed or ice-covered channel), logistical factor (mobile or stationary) and required accuracy. Characteristics of each type of measuring instruments were also considered and the limitations of their applicability were described. The results presented in the paper are expected to expand the horizons of approaches used for estimation of water discharge.