Regularities of hydrological processes in the Chesapeake Bay (USA): Case study of a classical estuary

The main regularities of hydrological and hydrological-environmental processes occurring within the complex estuary, the Chesapeake Bay and the mouths of its tributaries, are discussed. The peculiarities of the estuary morphological structure, including the structures of tidal and net currents, salinity and water turbidity fields and their variability, the environmental conditions, and their human-induced changes. Using the Chesapeake Bay as an example, it became possible to reveal the basic features of classical estuaries subject to a considerable impact of river runoff and featuring mixing of river and sea water and moderate stratification of the water mass. It is shown that the regularities of hydrological processes in the Chesapeake Bay are typical of many mouth water bodies of estuarine type (inlets, drowned river valleys, lagoons, and tidal estuaries proper).     

Long-term variations in river and sea factors responsible for the hydrological regime and morphological structure of the Thames River mouth area

General geographic features of the Thames River, its basin, and mouth area, consisting of the tidal mouth reach of the river, a large estuary, and an open nearshore zone of the river mouth (the North Sea coastal zone) are discussed. The peculiarities of river and sea hydrological factors responsible for the regime of the Thames River mouth area are described in detail. Characteristics of the river water runoff were specified and supplemented by the data on the river inundations in the area of London. Particular emphasis was placed on variations in the mean sea level in the area of the Thames River mouth as well as on specific features of tides and storm surges in the area of the sea inlet into the estuary. Main regularities in the estuary evolution during Holocene and present-day morphological processes in the Thames River mouth area were revealed.     

Hydrological and morphological processes in the mouth area of the Columbia River (United States) and their changes under the impact of large-scale hydroengineering works

The main hydrological and morphological features of the Columbia River mouth area, including its tidal estuary, are discussed. Close attention is given to the characteristics of large-scale hydraulic projects in the river basin as well as to dredging and channel training operations in the river mouth area and to the assessment of the impact of these operations on hydrological and morphological processes. Variations in the regime of river flow after its regulation, processes of dynamic interaction and mixing of river and sea water in the estuary are characterized. Changes of the mouth bar and sea coasts near the Columbia River mouth as a result of construction of stream-training jetties are discussed.     

Assessment of faecal contamination and the relationship between pathogens and faecal bacterial indicators in an estuarine environment (Seine, France)

The Seine estuary, one of the largest estuaries of the European northwest continental shelf, is subjected to numerous anthropogenic influences. Here we present an assessment of the microbial faecal contamination of the estuary water. The most vulnerable areas were defined on the basis of the fluxes of indicator organisms and the occurrence of Salmonella and Cryptosporidium sp. and Giardia sp. (oo)cysts. The microbial quality of the water changes from upstream to downstream: in the upstream area, contamination by faecal-indicator bacteria and Salmonella occurs during periods of high flow; in the urbanized area, mid-way between the uppermost areas of the estuary and its mouth, discharge from a wastewater treatment plant and a tributary degrade water quality; at the estuary mouth, the accumulation of microorganisms attached to particles in the maximum turbidity zone, particularly Clostridium perfringens spores and oocysts of Cryptosporidium, is accompanied by inputs of ThC and Escherichia coli from tributaries. In some areas, significant strong relations are observed between Salmonella, (oo)cysts of protozoan, and levels of faecal indicators.     

Hydrological and morphological processes in Senegal River mouth area

The main features of the structure and water regime of the mouth area of the Senegal River and their changes caused by river regulation in its upper reaches and within its delta area are considered. Data on water and sediment runoff of the Senegal River and their variations along the river are specified. River runoff was found to dramatically decrease in recent decades because of a drought. Zoning of river mouth area was carried out, and morphological processes in its estuary, in particular, the formation of a new outlet of the river into the ocean with the formation of a lagoon, are described.     

Mouths of world rivers in the atlas of space images

This article characterizes the atlas prepared at the Faculty of Geography, Moscow State University; 87 mouths of the largest world rivers are presented in space images. The atlas has 325 pages, 95 maps, 425 images and six printer’s sheets of explanatory text. The atlas is based on space images in the Internet galleries with data representation at different territorial levels (river mouth area-delta, estuary or their complex-typical delta reaches). The atlas shows specific features of river mouth areas, their hydrological and morphological structure, including estuaries and river deltas, their long-term and seasonal dynamics, landscapes and delta land use, hydraulic structures in deltas, ports, cultural and historical monuments, as well as recreation objects.     

Analytical and numerical analysis of tides and salinities in estuaries; part II: salinity distributions in prismatic and convergent tidal channels

Estuaries, commonly, are densely populated areas serving the needs of the inhabitants in multiple ways. Often the interests are conflicting and decisions need to be made by the local managers. Intake of fresh water for consumption, agricultural purposes or use by industries may take place within a region not far landward of the limit of salt intrusion. Human interventions (e.g. deepening of the navigation channels) or climate changes (sea level rise, reduction of the river discharge) can bring these intake locations within the reach of saline or brackish water and consequently endanger their function. To support policy and managerial decisions, a profound knowledge of processes associated with the salinity structure in estuaries is required. Although nowadays advanced numerical three-dimensional models are available that are able to cope with the complexity of the physics there is still a need for relatively simple tools for quick-scan actions in a pre-phase of a project or for instructive purposes. The analytical model described in this paper may serve these needs. It computes the maximum salinity distribution using the dispersion coefficient in the mouth as the only model parameter. The model has been calibrated using observational data in a large number of estuaries and experimental data in a tidal flume. The dispersion coefficient was successfully related to geometric and hydrodynamic parameters resulting in an expression that can be used for convergent estuaries as well as prismatic channels, see Eqs. 25a and 25b. Application of the model in a predictive mode showed its promising capabilities. Comparison with three-dimensional numerical models indicates that the channel geometry in the estuary mouth largely influences dispersive processes. The analytical model for salt intrusion may be used in combination with the analytical model for tidal propagation in convergent estuaries and tidal channels by Van Rijn (part I). In this way, input is obtained on the tidal velocity amplitude and the Chézy roughness following calibration of this model on tidal amplitudes along the estuary.     

Hypersalinization of river estuaries in West Africa

Regularities in processes of seawater intrusion into the rivers of Senegal, Saloum, Gambia, and Casamance in West Africa are analyzed. The seawater intrusion during the low-flow period, which is a common phenomenon for the lower reaches of these rivers, has taken on extreme features in the course of the severe drought that occurred in West Africa in the 1970s–1980s. The processes of progressing water salinization in estuaries under the impact of drastic reduction of atmospheric precipitation and river runoff, considerable evaporation water losses, and tides are described. Due consideration is given to the unique hydrological phenomenon, i.e., the so-called reverse estuary. The Senegal River mouth is taken as a case study of cyclic variations in runoff, water salinity, and distance of saltwater penetration into the river. Certain environmental consequences of water salinization are discussed using the Casamance River estuary as an example. Methods used in Africa to prevent seawater intrusion and salinization of estuaries harmful for the environment and economy are described in this article.     

Tidal straining effect on the suspended sediment transport in the Huanghe (Yellow River) Estuary, China

Tidal straining effect on sediment transport dynamics in the Huanghe (Yellow River) estuary was studied by field observations and numerical simulations. The measurement of salinity, suspended sediment concentration, and current velocity was conducted during a flood season in 1995 at the Huanghe river mouth with six fishing boats moored at six stations for 25-h hourly time series observations. Based on the measurements, the intra-tidal variations of sediment transport in the highly turbid river mouth was observed and the tidal straining effect occurred. Our study showed that tidal straining of longitudinal sediment concentration gradients can contribute to intra-tidal variability in sediment stratification and to asymmetries in sediment distribution within a tidal cycle. In particular, the tidal straining effect in the Huanghe River estuary strengthened the sediment-induced stratification at the flood tide, thus producing a higher bottom sediment concentration than that during the ebb. A sediment transport model that is capable of simulating sediment-induced stratification effect on the hydrodynamics in the bottom boundary layers and associated density currents was applied to an idealized estuary to demonstrate the processes and to discuss the mechanism. The model-predicted sediment processes resembled the observed characteristics in the Huanghe River estuary. We concluded that tidal straining effect is an important but poorly understood mechanism in the transport dynamics of cohesive sediments in turbid estuaries and coastal seas.     

Many-year variations in river delta structures

Data on several river deltas are used to analyze the regularities in their dynamics in the context of variations of water and sediment runoff, sea level, and hydroengineering activities in delta areas. The basis for this analysis includes the results of many-year studies of river deltas in Russia and the world. The specific features of the evolution of the structure and morphometry of bayhead deltas, forming in bays, lagoons, and estuaries are shown in the case of the Alikazgan delta in the Terek mouth area and the deltas of two watercourses in the Mississippi mouth area. Data on many-year variations of the morphometric characteristics of modern protruding deltas in open coastal zones are systematized, and the factors that have an effect on these changes are analyzed. The types of delta formation processes and the types of deltas are considered with regard to the factors involved. The majority of modern river deltas are found to slow down their progradation into seas under the effect of anthropogenic runoff decline; moreover, some deltas have started retreating and degrading.     

Water circulation, sediment dynamics, erosional and accumulative processes in the Gironde Estuary (France)

The basic features of the hydrological regime and morphodynamics of the mouth area of the Garonne and Dordogne rivers and its part, i.e., the Gironde Estuary, are discussed. The main attention is given to the analysis of water circulation and sediment dynamics in the Gironde Estuary under the joint impact of seasonal river flow and tidal fluctuations. In addition to this, the estuary evolution during the Holocene period and regularities of present-day erosional and accumulative processes are characterized.     

Water and sediment dynamics at Saint Lawrence River mouth

The main features of the hydrological regime and morphological structure of the estuarine-type mouth area of the Saint Lawrence River are considered. Data on the structure of water masses, thermal and ice regimes in the Gulf of Saint Lawrence, which has a significant effect on the estuary, are given. The major attention is paid to water mixing processes, water and sediment dynamics in the estuary under the joint effect of river runoff and tides, and as a function of bed topography. The parameter determining the type of water stratification and circulation is discussed. The effect of the Coriolis force on the stratified flow in the estuary and formation of the geostrophic current is discussed.     

A field study of estuarine pollution in Madras,India

A field study has been made of the quality of water in three estuaries in Madras, India, receiving a variety of human and industrial wastes. Among the three estuaries, the Buckingham canal is grossly polluted with no surface flow. The Cooum estuary, though grossly polluted, because of the flow and flushing into the sea may be recovered if precautions are taken. The Ennore estuary, with a large volume of water flowing, has a peculiar problem at the mouth due to continuous formation of a sand bar due to long-shore currents. This sand bar prevents the flushing of the estuarine water. As a result, the pollutants discharged either in the estuary or in the sea accumulate at the mouth. This pollution, together with impaired self-purification of the estuary, resulted in a decrease in fish production.     

Water and sediment dynamics in the estuary and mouth area of the Seine River

The principal features of the hydrological regime of the Seine River mouth area are discussed. Attention is focused on studying the dynamics of water and sediments in the estuary of the Seine River and in its tidal mouth area under the combined effect of seasonal variations in river runoff and tides. The history of development and improvement of the estuary is described.     

Estuarine modification of nutrient and sediment exports to the Great Barrier Reef Marine Park from the Daintree and Annan River catchments

Nutrient and suspended sediment concentrations were measured in the dry season and during the rising and falling stages of flood events in the Annan and Daintree rivers to estimate catchment exports. These flood events were also sampled along the salinity gradient in the estuary and nearshore shelf to quantify the modification of terrestrial sediment and nutrient loads as they pass through estuaries into the Great Barrier Reef lagoon. In the Daintree River TSS concentrations were found to increase between the catchment and the estuary plume. The source of TSS may have been scour of the estuarine channel or from land use in the catchment of the lower estuary. In the dry season nitrogen enters the Annan and Daintree estuaries predominantly in the form of PON and DON in roughly equal proportions. Nitrogen exports to the GBR are mostly in the form of DON. In the wet season the majority of nitrogen enters the estuaries as DON and leaves as PON. Nitrogen removal in the estuaries and plumes appears to be biologically mediated once suspended sediment concentrations decrease to a point where phytoplankton growth is not light limited. In the dry season phosphorus enters and leaves the estuaries primarily in organic form. PIP is the dominant form of phosphorus in river water, but leaves the estuary more evenly distributed between all forms. These estuarine processes result in less nitrogen and phosphorus being delivered to the GBR lagoon than is exported from the catchment. The differences between these estuaries highlights the need for further work to explore modifications in estuaries that drain into the Great Barrier Reef lagoon.     

Numerical modelling of morphodynamics—Vilaine Estuary

The main objective of this paper is to develop a method to simulate long-term morphodynamics of estuaries dominated by fine sediments, which are subject to both tidal flow and meteorologically induced variations in freshwater run-off and wave conditions. The method is tested on the Vilaine Estuary located in South Brittany, France. The estuary is subject to a meso–macrotidal regime. The semi-diurnal tidal range varies from around 2.5 to 5 m at neap and spring, respectively. The freshwater input is controlled by a dam located approximately 8 km from the mouth of the estuary. Sediments are characterised as mostly fines, but more sandy areas are also found. The morphology of the estuary is highly influenced by the dam. It is very dynamic and changes in a complicated manner with the run-off from the dam, the tide and the wave forcing at the mouth of the estuary. Extensive hydrodynamic and sediment field data have been collected in the past and provide a solid scientific basis for studying the estuary. Based on a conceptual understanding of the morphodynamics, a numerical morphological model with coupled hydrodynamic, surface wave and sediment transport models is formulated. The numerical models are calibrated to reproduce sediment concentrations, tidal flat altimetry and overall sediment fluxes. Scaling factors are applied to a reference year to form quasi-realistic hydrodynamic forcing and river run-off, which allow for the simulations to be extended to other years. The simulation results are compared with observed bathymetric changes in the estuary during the period 1998–2005. The models and scaling factors are applied to predict the morphological development over a time scale of up to 10 years. The influence of the initial conditions and the sequence of external hydrodynamic forcing, with respect to the morphodynamic response of the estuary, are discussed.     

Generation of overtides and compound tides in Amazon estuary

Tidal propagation in estuaries is affected by friction and fresh water discharge, besides changes in the depth and morphology of the channel. Main distortions imply variations in the mean water level and asymmetry. Tidal asymmetry can be important as a mechanism for sediment accumulation and turbidity maximum formation in estuaries, while mean water level changes can affect navigation depths. Data from several gauges stations from the Amazon estuary and the adjacent coast were analyzed and a 2DH hydrodynamic model was configured in a domain covering the continental shelf up to the last section of the river where the tidal signature is observed. Based on data, theoretical and numerical results, the various influences in the generation of estuarine harmonics are presented, including that of fresh water discharge. It is shown that the main overtide, M₄, derived from the most important astronomic component in the Amazon estuary, M₂, is responsible for the tidal wave asymmetry. This harmonic has its maximum amplitude at the mouth, where minimum depths are found, and then decreases while tide propagates inside the estuary. Also, the numerical results show that the discharge does not affect water level asymmetry; however, the Amazon river discharge plays an important role in the behavior of the horizontal tide. The main compound tide in Amazon estuary, Msf, generated from the combination of the M₂ and S₂, can be strong enough to provoke neap low waters lower than spring ones. The results show this component increasing while going upstream in the estuary, reaching a maximum and then slightly decaying.     

Description of Ecosystem of the Lower Odra and the Odra Estuary

Environmental conditions of the lower river Odra and its estuary show a high variability of chemical and biological parameters, related to the dynamics of the river, its mouth area, the Lake Dabie-Szczecin Lagoon system, and the Pomeranian Bay. Water chemistry, affected by the total sum of industrial, urban, and agricultural pollution discharged from the direct drainage area is discussed. This pollution load influences the composition and ecological structures of terrestrial, frequently unique, phytal communities associated with aquatic areas, phyto- and zooplankton, benthos, fish fauna, and avifauna. The current status of the terrestrial and aquatic ecosystems is described; elements of cultural infrastructure existing within the Lower Odra Valley in Western Pomerania are mentioned as well.     

Hydrological and morphological processes at the Zhujiang River mouth area, China

Hydrological and morphological processes in the Zhujiang River (Pearl River) mouth area of China are discussed. The hydrological regime of the Xijiang River, which is the largest river of South China and the main source of water inflow into the Zhujiang mouth area, is described. The basic features of the hydrological regime of the delta and the near-shore zone of the Zhujiang River mouth are characterized, much attention being given to the role of tides and mixing of river and sea water in the hydrological regime. Special emphasis is placed on morphodynamic processes at the mouth area and the history of the Zhujiang Delta evolution.