Calculation of mean velocity and discharge using water surface velocity in small streams

• Measurement of water surface velocity is simpler than that of mean velocity in small streams.
• There is a strong relationship between water surface and mean velocity.
• Using this relationship discharge of stream can be calculated easily.
• The constant which be determined in this study is smaller than in literature.

Calculation of mean velocity and discharge are very important for demands such as water management, water supply, irrigation and flood control. This paper presents to determine the mean velocity and discharge in small streams using based water surface velocity. For this purpose, flow measurements were carried out at four different cross-sections at eighteen field measurements in central Turkey. The mean velocities (Um) were calculated using velocity–area method. (Um) and water surface velocities (uws) at these stations exhibited a linear distribution as Um=0.552uws which has R2=0.99 determination coefficient. It was observed that this constant was smaller than the literature value 0.85. The advantage of this ratio is that it does not change in T/R (T; width of cross-section, R; hydraulic radius) and Froude numbers for the small streams. Using this constant, mean velocities (Umcal) and discharges (Qmcal) for all measurements can be calculated. The average relative error between measured and calculated discharges (Q−Qmcal) was found to be 4.08%. The results presented that this method can be utilized to determine the mean velocity and discharge in small streams successfully.