ABSTRACT:We have investigated channelization due to seepage erosion using two sizes of coarse sand (d50 = 0.86 and 0.56 mm), two chamber slopes (S = 0 and 3%) and three upstream water depths (H = 15, 17 and 19 cm). Water was fed at the far upstream end of a sand layer, and a small incipient channel was made at the center of the downstream scarp. Thus, groundwater flow converged into the central channel, promoted erosion and caused the development in both width and length. At the beginning, the retreat rates of channel heads were rapid but decreased after a while. A higher H induced a faster retreat and a larger size of the center channel. In the experiments with S = 0%, channel head bifurcation was always observed for d50 = 0.86 mm but not d50 = 0.56 mm. Thus, not only the characteristics of groundwater flow field soil properties but the sediment properties also affect the shapes of evolving channels. For S = 3%, however, bifurcation was only found in the experiment with d50 = 0.86 mm and H = 15 cm. It implies that H also controls bifurcation. In addition, new channels were initiated at the downstream scarp when S = 3%. An increase in the streamwise discharge due to a steeper slope may weaken the convergence of the groundwater flow into the center channel. Using the concept of network circularity, we can divide the channel development of our experiments into the initiation and extension phases.

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