AN EXPERIMENTAL-STUDY ON THE BURROWING ACTIVITY OF RIVER CRABS ON SUBSURFACE WATER-MOVEMENT AND PIPING EROSION

The effects of the burrowing activity of river crabs on subsurface wat er movement and piping erosion were studied through a flume experiment . Cohesive field soil was used and constant fluvial head was applied. During the experiments with river crabs, burrows were excavated downwa rds under the groundwater level. At the outlet of each burrow, the cra bs excavated pellets of soil and stacked them in piles, in the form of cone mounds. These mounds acted as effective dams for subsurface outf low, but they sometimes collapsed. The roofs of the burrows also caved in occasionally, whereby the crabs would excavate new burrows. The bu rrowing activity of the crabs led to marked erosion. In contrast, no m arked erosion was observed in experiments without crabs, indicating th at piping erosion occurs through the assistance of burrowing activity. It was observed that burrowing activity and piping erosion was pronou nced when the hydraulic head was not significantly high (0.21-0.25). A nalysis of the potential distribution of the soil mass indicated that the head loss close to the burrow was small in the case of experiments with crabs. This suggests that the burrow enhances rapid discharge of subsurface water. Consequently, burrowing activity was found to play an important role in piping erosion and rapid discharge of subsurface water. (C) 1997 Elsevier Science B.V.