River sedimentation and channel adjustment of the lower Yellow River as influenced by low discharges and seasonal channel dry-ups

Fluvial sedimentation can be classified as one of the three types in terms of different morphological units, i.e., vertical overbank deposition, vertical deposition on the riverbed and lateral deposition on the riverbank. With the example of the lower Yellow River, the three types of sedimentation have been studied in relation to channel adjustment. Since 1986, the lower Yellow River has entered a new period that is characterized by small discharges with seasonal desiccations (dry-ups), and strong sedimentation has occurred. Based on the measurement of 36 cross-sections along the lower Yellow River, the rates of the three types of deposition have been calculated and are reported in this study. Multiple regression has been used to express the relationship between the three rates of deposition and the channel shape adjustment index. Influenced by the difference in channel sediment and by downstream variations in water discharge and sediment load, the indices of channel deposition rate show a clear trend of downstream variation. Controlled by this, the manner of channel adjustment also shows clear trends downstream. Under the hydrological regime dominated by small discharges, the tendencies of adjustment of riverbed slope and bankfull slope are inverse, i.e., the channel slope tends to decrease but the slope at bankfull stage to increase. At present, the former tendency is dominant; thus, the sediment carrying capacity of the lower Yellow River tends to decrease, which intensifies channel sedimentation. (C) 2002 Elsevier Science B.V. All rights reserved