Basic requirements for water measuring and water accounting devices developed to fulfil static control of water distribution have not changed virtually in recent decades. It is due primarily to the use of water accounting and measuring instruments developed and used in conditions of steady uniform water flow when unique dependence on depth and water discharge on the rise and decline of the waterline levels is observed. Under operation of watercourses in the unsteady water flow regimen, the existing means of water measurement are not applicable. Simultaneous direct measurement of hydraulic parameters in controlled cross sections of waterways is complicated even under steady water flow regimen. Nowadays there is the lack of data to predict extreme values of discharges and water depth in downstreams of the waterworks due to the absence of tested and feasible methods of water depth and discharge measurement in calculated cross sections of waterways. With the application of the complete integral theory, a hydraulic calculation of the changes in the flow rate and the depth of flow in fixed sections of the downstream of the waterworks was performed. It is based on the analytical method of linearized system solution of one-dimensional differential equations in partial derivatives of Saint-Venant hyperbolic type.