The steady-state concept is hard to reconcile with the reality of flow in ephemeral channels. The interaction of flow and hydraulic geometry is usually considered at various states of time dependency, whereas channel slope is thought to be subject to change only over considerable periods of time.
The results of field work in two ephemeral channels cut in the Pliocene-Pleistocene clays of the Basento Valley, southern Italy, indicate that in this particular environment, hydraulic geometry is subject to rapid change both in space and time. In particular, channel slope is shown to have been subject to dramatic change within a period of two years. On the basis of field evidence, it is suspected that lagged disturbances are dominant in the channels such that the hydraulic geometry is continually adjusting to changed circumstances. It is suggested that in the case of these channels, the random influences are more easily identified and modeled than the deterministic ones.