The objective of the research was to analyze the accuracy of defining roughness coefficient. For this purpose two methods were used to determine water discharge by “slope-area” method: considering drop of free surface of water and excluding the drop. As a reference water discharge the discharge calculating by volume method was assumed. During the investigation experiments on defining the impact of flow depth and water discharge on roughness coefficient at the range of tray bottom slope 0.0002 to 0.0006 were carried out. To confirm reliability of data obtained, statistical treatment of values of roughness coefficient, calculated considering drop of free surface of water and excluding the drop, was done. In the first experiment variation coefficient was 0.82 % against 1.27 %, in the second one – 0.81% against 1.23 %, and in the third – 0.59 % against 1.64 %. Data obtained were analyzed in order to define the impact of free surface drop on the accuracy of determining water discharge. As a result of conducted calculations relative error in the first experiment was δQmax = 2.51 %, in the second – δQmax = 2.83 %, and in the third – δQmax = 3.24 %. Considering the drop of free surface relative error on discharge in the first experiment was δQmax = 1.67 %, in the second – δQmax = 1.84 %, and in the third – δQmax = 1.25 %. Based on the results obtained, the conclusion can be formulated that defining of roughness coefficient and water discharge according to proposed method should be done considering drop of free surface of water. While the method proposed allows determining and monitoring the value of water discharge in a continuous mode (on-line).
Keywords: roughness coefficient, slope-area method, water discharge, drop of free surface of water, Chezy coefficient.
