Abstract
In Japanese mountains, erosive force markedly increased after the Pleistocene-Holocene transition because of increased heavy rainfall, resulting in channel incision along hillslope hollows and tributaries. This paper investigates the process of channel incision in the Matsumoto Region of central Japan based on morphometry. Attention is directed toward the effects of headward erosion and channel widening on channel expansion. Channel length and area occupied by channels were measured for more than eight hundred 500×500m morpho-. metric samples taken from eight watersheds. Analyses of channel length and channel area based on location-for-time substitutions have revealed that channels develop through two stages. At the early stage, the channel length-channel area relation is expressed by a power function. The function indicates that headward erosion contributes to about 80 percent of the channel-area increase whereas channel widening contributes to about 20 percent. At the late stage, channel length tends to be unchanged owing to the stabilization of channel heads, and channel widening solely accounts for the channel-area increase. The stabilization of channel heads occurs when channel length has reached about 80 percent of total valley length. The ratio of 80 percent most likely represents a limit of channel elongation determined by the geomorphological and hydrological threshold of erosion.
