The critical shear stress τc (the intercept of the
regression of equation 3 along the x-axis) varied
considerably (table 3 and fig. 4). Apparently, τc increased
with root density, as shown by the fitted line in figure 4.
However, regression analysis showed no significant trend
between RD and τc in this study, indicating that the critical
shear stress fitted with equation 3 may likely be inde