Channel Sequence Development in Aggradational Streams with Example from South Canadian River, Texas: ABSTRACT

Abstract

At least 8 channel sequences of varying relative age have been observed in the floodplain of the South Canadian River. These sequences initially identified by vegetational differences on aerial photographs probably represent deposition during major flood events. Surface features on the most recent channel sequences include longitudinal bars, elongate scour marks, and extensive ripple-marked areas near bars. Within an individual sequence the only sedimentary structure types observed are plane bed, trough cross-stratification, and ripple cross-stratification. Channel sequences, or small divisions within them, are punctuated by mud or silt-mud layers. These layers or clay drapes are deposited as the result of the settling out of fine sediment during waning flood conditions. Channel sequences older than the most recent 2 or 3 flood events are heavily vegetated and commonly discontinuous downstream. Moving correlation coefficient (r) analysis indicates that the sinuosity and position within the floodplain of channel sequences or remnants of all ages are controlled by the confinement of the South Canadian River valley and location within the valley of earlier sequences. This shows that major floods with a strong aggradational effect are probably a valley-wide phenomenon within this depositional system. Daily discharge data show that floods, with a discharge of greater than 10,000 cu ft/sec, occur less than 1% of the time in the South Canadian River. These floods are catastrophic events which cause major changes in the configuration of the river floodplain. End_of_Article - Last_Page 632------------