EXPERIMENT OF CHANNELIZATION DUE TO SEEPAGE EROSION

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.