Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Some considerations of straightness in channel form relating to the estuary of the Maclennan river, South Otago (New Zealand) Journal Paper

Jenks, W.N.
Journal / Source
Journal of Hydrology
Patterns of regular deviation about a mean downstream vector characterize many natural waterways. Straight channels are distinctive in that they do not deviate, and occur relatively infrequently. The basic objectives of this paper are, firstly, to examine a specific instance of straightness occurring within the estuary of the Maclennan river, and secondly, to present from this examination some new concepts which may lead to a wider understanding of the general case. Specifically, 19 morphometric and 2 hydraulic variables are measured and analysed through 37 channel cross-sections representing the entire tidal system. A subset of 10 cross-sections represents the straight reach. A model is developed to describe change occurring through space, and by implication through time, within these 21 sets of variates. Stochastic processes are found to replace least probable normal distributions with most probable log-normal frequencies. In the latter situation, minimum variance and quasi-equilibrium conditions prevail. At a wider level of reference, a study of tidal meanders occurring at the extremities of the tidal system is made. From this, the conclusion is reached that channel processes operating within these areas through the Late Holocene have expended fluvial and tidal energies, input at the ends of the system, in such a manner as to inhibit change within the straight reach. Finally, the hydraulic exponents associated with the rate of discharge at half-ebb are considered as potential indices of channel stability. In its general conclusions, the paper supports the contemporary hydraulic theories of least work, minimum variance, and most probable channel form.