| Abstract: | Previous studies in Japanese mountains have shown that drainage density (D) correlates negatively with relief (R) and the erosion rate (E), whereas elsewhere both R and E correlate positively with D. To investigate the inconsistency, this paper compares two types of D–R relations for eight mountain river basins in central Japan. R is computed from a digital elevation model for 1109 morphometric samples of area 0·5 km × 0·5 km. Drainage networks in these cells were first constructed by map criteria applied previously in Japan — deeply notched V-shaped contours with an angle <53°. The resulting D correlates negatively with R, confirming preceding studies. When drainage lines along shallower hollows were added, however, the calculated D essentially constant. These relations arise from active landsliding in high-relief terrains, which has eroded steep channel banks into gentle ones. The decline of channel banks with increasing R is accelerated in terrains underlain by soft rocks, because of rapid erosion. The constant D for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains. Because the D–R and D–E relations for Japan reflect a uniquely Japanese physiographic setting characterized by frequent landsliding, they differ from those relations for other regions where channelization by gullying predominates. © 1997 by John Wiley & Sons, Ltd. |
