An experimental study on the dynamics of wave blocking and breaking on opposing currents

A detailed experimental study has been carried out in a laboratory to study the strong wave-current interactions that are observed at the mouth of river inlets. The aim of this work was twofold. Firstly, to study the dynamics of wave blocking under different wave climates and, secondly, to develop empirical formulae that quantify energy dissipation due to current-limited wave breaking. These formulae can then be used in numerical models simulating wave-current interactions.; The experiments were conducted in a 30 m long recirculating flume. A channel with a varying width was placed in the middle part of the flume to simulate an inlet. The experiments were designed such that wave blocking occurred close to the narrow part of the channel where the currents were maximum. All the experiments were conducted in a constant water depth of 0.5 m. The experiments were broadly divided into 3 parts: the monochromatic wave tests, the narrow-banded spectral tests, and the random wave tests.; The monochromatic tests were further subdivided into two subgroups: the wave reflection tests and the wave breaking tests. The wave reflection tests were small amplitude tests in which the waves were reflected from the blocking point with very little breaking. The measured amplitude envelope for the smallest amplitudes was an Airy function and confirmed the linear theory predictions. In the breaking wave tests there was very little to no reflection and all the blocking was accompanied by wave breaking. The blocking phenomenon was found to depend strongly on non-linearity. An empirical dissipation formula based on a modified bore model approach was developed and tested with the data.; The narrow-banded spectral tests were also divided into two subgroups: the wave group tests and the wave packet tests. The aim was to see if a moving blocking point could generate long waves upstream of the blocking region. In the wave group tests, the individual components of the spectra were blocked separately at their respective blocking points. No long wave motion was observed in any of the tests.; A weakly non-linear narrow-banded amplitude envelope numerical model has been developed for a varying channel. The model accounts for wave blocking by allowing the phase to be complex. The model uses a linear dispersion relation. Comparisons with data show that though the model can handle wave blocking, it is unable to predict the correct blocking position as that depends strongly on amplitude dispersion effects. Also, the model blocks the waves at the carrier frequency of the modulating wave train, whereas observations have shown that the actual blocking occurs at the separate blocking points of the respective spectral components.; Finally, random wave tests were also conducted to compliment the monochromatic wave tests. The random wave tests consisted of TMA spectra of varying energy and peak frequency. The tests varied from most of the spectrum getting blocked, to very little blocking. Using an empirical probability of breaking based on the data, a bulk dissipation formula for energy loss due to current-limited breaking in random waves has been proposed and tested with the data using both a bulk wave action conservation model and a spectral model. The energy dissipation formula is based on a wave slope formulation, and other formulae based on a wave slope formulation also compared well with the data.