Academic literature on the topic 'Estuaries Coast changes Hydrodynamics Dissertations'

Abstract. Assessing the impacts of both natural (e.g. tidal forcing from the ocean) and human-induced changes (e.g. dredging for navigation and land reclamation) on estuarine morphology is particularly important for the protection and management of the estuarine environment. In this study, a novel analytical approach is proposed for the assessment of estuarine morphological evolution in terms of tidally averaged depth on the basis of the observed water levels along the estuary. The key lies in deriving a relationship between wave celerity and tidal damping or amplification. For given observed water levels at two gauging stations, it is possible to have a first estimation of both wave celerity (distance divided by tidal travelling time) and tidal damping or amplification rate (tidal range difference divided by distance), which can then be used to predict the morphological changes via an inverse analytical model for tidal hydrodynamics. The proposed method is applied to the Lingdingyang Bay of the Pearl River Estuary, located on the southern coast of China, to analyse the historical development of the tidal hydrodynamics and morphological evolution. The analytical results show surprisingly good correspondence with observed water depth and volume in this system. The merit of the proposed method is that it provides a simple approach for understanding the decadal evolution of the estuarine morphology through the use of observed water levels, which are usually available and can be easily measured.

Abstract This synthesis of the morphological and stratigraphical evolutions of the Marennes-Oléron Bay (west coast of France) combines bathymetric data (1824 and 2003) and very high-resolution seismic profiling groundtruthed by vibracore samples. The Marennes-Oléron Bay is characterised by a very high sedimentation rate and appears to be an ideal place to investigate the sedimentary record of the major environmental changes that occurred since the last several millennia. The sediment budget of the Marennes-Oléron Bay, between 1824 and 2003, is clearly positive. The flood-dominated northern Marennes-Oléron Bay displays sediment gain in both intertidal and subtidal areas whereas the ebb-dominated southern Marennes-Oléron Bay displays sediment gain restricted to the intertidal area and deepening of subtidal channels. In addition, human influences such as oyster farming may play a role in the sediment gain of the bay. The sediment-fill of the northern Marennes-Oléron Bay consists of five main phases: (1) lenticular units and flooded intertidal flats recording lower sea level periods before 7500 yr B.P.; (2) tidal channel-fills recording changes in tidal drainage pattern from 7500 to 5000 yr B.P.; (3) a subtidal unit which constitutes the main phase of sediment fill in the northern part of the bay from 5000 to 1500 yr B.P.; (4) a major channelized erosional surface related to huge coastline changes from 1500 to 1000 yr B.P.; and (5) a mud drape emplaced during the last millennia and potentially recording historical human impact (deforestation and land reclamation). The sediment fill of the southern Marennes-Oléron consists of sandbanks, mixed sand-and-mud flats and tidal channels, mainly emplaced under wave-and-tide processes since the last centuries. Despite its relatively thin (20 m at the maximum), recent and rapid sediment fill, the stratigraphic organization and morphological evolution of the Marennes-Oléron Bay is very complex and spatially variable. Like in many other estuaries, sediment fill of the Marennes-Oléron Bay was successively controlled by relative sea level changes, and then by sediment supply driven by hydrodynamic changes related to huge coastline migrations, and finally by human activities. Moreover, this kind of “rocky coast” estuary, where the sediment-fill is very thin and discontinuous, is characterised by a bedrock control at each phases of the sediment fill both in terms of preservation in topographic lows and in terms of control on hydrodynamics and related sediment input.