Changes in stream channel morphology at tributary junctions, Lower Hunter Valley, New South Wales

Abstract

Many empirically derived models of downstream changes in channel form are based on the concept of hydraulic geometry, whereby changes in channel morphological variables are related by a continuous power function to increasing discharge or its surrogate. However, changes in discharge throughout a drainage basin are normally concentrated at the junctions of stream channels. At junctions, the relationship between discharge and channel morphology is discontinuous. Some Lower Hunter Valley stream channels were surveyed upstream and downstream of tributary junctions. While significant regional downstream relationships were established, consistent trends at tributary junctions were not apparent from the data. It is possible that considerable scatter evident in ratios of change on either side of each junction was due to local within‐site variability. In addition, the relative timing of discharge inputs and the nature of introduced sediment loads could be important in determining the magnitude and direction of channel change at tributary junctions. Interrelated changes in cross‐sectional, profile and planform variables may be expected below junctions. The resultant channel morphology, in terms of these variables, might not be wholly determinate.