Flow rate measurement is important in estimating other hydraulic flow parameters such as discharge and sedimentation. In recent decades, estimating flow velocity in open channels has attracted the attention of many researchers. Since flow velocity measurement methods in open channels are practically expensive and rarely used, in this study, by designing inexpensive GPS vessels with different sizes in cylindrical shapes and Spherical, velocity flow in open channels was investigated. GPS, stopwatch, and tape measure were used to measure the velocity, and comparing the results of these tools with each other showed a slight difference between the devices in estimating the velocity value. These vessels were used for open channels with several minutes to several hours intervals. The results of two field measurements of GPS vessels were analyzed, one in the water channel located in Agha Seyed Sharif Shaft and the other in a natural stream located in Fouman. The cost of construction of these vessels was much cheaper than other flow velocity measuring instruments and they had good accuracy.