Dimensional analysis of current ripples in recent and ancient depositional environments

Abstract

The aim of this thesis is to better understand the dynamics of small-scale ripples through experimental and field-based studies. For that purpose a firm database is established which allows to evaluate relationships between flow strength, time-lag and ripple morphology in sandy depositional environments. Several series of flume experiments were performed with the following objectives: l. to develop empirical models for the time-lag in the development of ripples from flat bed conditions; 2. to study the equilibrium ripple dimensions for different grain sizes and flow conditions; 3. to compare the results with other flume studies; and 4. to apply the experimentally obtained results to natural ripples in modem and ancient sedimentary environments. TIle methods used in the flume experiments are described in Chapter 2. TIle results of steady flow experiments with very fine sand (D50=O.095 mm) and fine sand (D50=0.238 mm) are discussed in Chapters 3 and 4, respectively. The flume models, derived from the steady flow experiments, are compared with the results of other flume studies in Chapter 5. Chapter 6 discusses the dimensions and plan form of ripples formed in tidal environments, based on the results of a series of theoretical calculations and flume experiments simulating unsteady flow in tidal enVironments, and applies the results to examples from recent tidal environments. Next, the applicability of the flume models to natural environments is further examined with special reference to deep marine environments (Olapters 7 and 8). 11le criteria required for the quantification of time-lag and flow parameters from natural ripple dimensions are discussed in Chapter 9, and finally, the main conclusions are summarized in Chapter 10.