Asian Research Journal of Agriculture

One of the common methods to prevent the erosion of the furrows’ bed is to enter the water flow with a discharge less than the maximum of eroding discharge. Accordingly, it is important to determine the threshold velocity of the bed particle motion. In the current study, the average diameter of particles in each soil class was determined using 12 available classes in the soil texture triangle and then in an irrigation furrow with a fixed bed and triangular cross section, the threshold velocities were calculated using the equations provided by El-Zaemey, Novak, Nalluri and Charles Heinz Bong and compared them with proposed values of Walker et al and the US Department of Soil Conservation. The results were also compared with the Shields graph by determining the Shields parameter and boundary layer Reynolds number in the slope range of 0.5% to 1% for each soil texture class. A graph was presented based on all the above mentioned methods to simplify the use of the results. In addition to specifying the difference in velocity values predicted ​​by different methods, the graph can be also used to determine the maximum permissible velocity in furrows.