CLIMATE AND EPHEMERAL-STREAM PROCESSES: TWENTIETH-CENTURY GEOMORPHOLOGY AND ALLUVIAL STRATIGRAPHY OF THE LITTLE COLORADO RIVER, ARIZONA.

Abstract

During the first 40 years of the twentieth century, erosion was the dominant geomorphic process affecting the morphology of the Little Colorado River channel. The discharge regimen was one of frequent large floods and high annual discharge that created a wide sandy channel free of vegetation. In the 1940s and early 1950s, average annual discharge to about 57% of that of the preceding period as well as reducing the frequency of large floods. The channel adjusted to the new hydrologic regimen by reducing its width. Events of 1980 suggest that the flood plain has ceased to accrete, although climate has not fluctuated. The flood plain has probably reached a critical height above the channel, beyond which further accretion is unlikely under the existing discharge regimen. The recent history of the Little Colorado broadly suggests that flood-plain development was initiated by climatically induced hydrologic fluctuations. Floor-plain deposits in the stratigraphic column of such ephemeral streams may record repeated adjustments to altered hydrologic conditions. Refs.