Analysis of the drainage density of experimental and modelled tidal networks

摘要

Based on controlled laboratory experiments, we numerically simulate theinitiation and long-term evolution of back-barrier tidal networks inmicro-tidal and meso-tidal conditions. The simulated pattern formation iscomparable to the morphological growth observed in the laboratory, which ischaracterised by relatively rapid initiation and slower adjustment towardsan equilibrium state. The simulated velocity field is in agreement withnatural reference systems such as the micro-tidal Venice Lagoon and themeso-tidal Wadden Sea. Special attention is given to the concept of drainagedensity, which is measured on the basis of the exceedance probabilitydistribution of the unchannelled flow lengths. Model results indicate thatthe exceedance probability distribution is characterised by an approximatelyexponential trend, similar to the results of laboratory experiments andobservations in natural systems. The drainage density increases greatlyduring the initial phase of tidal network development, while it slows downwhen the system approaches equilibrium. Due to the larger tidal prism, thetidal basin has a larger drainage density for the meso-tidal condition(after the same amount of time) than the micro-tidal case. In bothmicro-tidal and meso-tidal simulations, it is found that there is an initialrapid increase of the tidal prism which soon reaches a relatively steadyvalue (after approximately 40 yr), while the drainage density adjusts moreslowly. In agreement with the laboratory experiments, the initial bottomperturbations play an important role in determining the morphologicaldevelopment and hence the exceedance probability distribution of theunchannelled flow lengths. Overall, our study indicates an agreement of thegeometric characteristics between the numerical and experimental tidalnetworks.