Hydrological-morphological processes in the mouth area of the Orinoco (Venezuela)

The peculiarities of the hydrological regime of the Orinoco River and the coastal zone of the Atlantic Ocean that affect the hydrological-morphological processes in the mouth area of the Orinoco River are considered. The major features of the delta water regime, including its inundation, runoff distribution over the delta branches, water and sediment balance, and the processes of river and sea water mixing are described. Special attention is paid to the morphological processes at the Orinoco mouth (delta evolution and modern processes at its coastline).     

Sediment regime and morphological processes in the Hong Ha (Red River) mouth area

Main features of sediment regime in the mouth area of the Hong Ha River (Red River), Vietnam, are discussed. As shown, the hydraulic engineering construction on the Da tributary resulted in a nearly two-fold decrease of river sediment yield. Sediment budget components at the river mouth were analyzed to establish that more than 90% of the sediment yield was detained in the delta branches and in the nearshore zone of the river mouth. Morphological processes in the Hong Ha River mouth area were characterized in detail including delta evolution during Holocene and the dynamics of its channel network, coastline, and mouth bars. Special attention was given to modern processes of delta progradation at the mouths of main branches and to wave erosion of other parts of the delta coastline. The causes for the intensification of this kind of erosion and change of the delta type in the late XX century are discussed.     

Hydrological processes in the mouth area of the Nemunas (Neman) River

The geographic characteristics of the Nemunas (Neman) River basin is presented with due consideration for the hydrological regime of this river and the Curonian Lagoon (Marios). The following geographic and hydrographic features of the Nemunas mouth area are described in detail: the landscape and climatic conditions, delta water balance, water flow distribution among branches, flow-induced changes in water levels, specific features of ice regime in the delta, storm surges, and floods.     

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.     

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.     

Specific features of hydrological and morphological processes in the mouth area of the Mekong River

The geographical and hydrological features of the Mekong River basin and the nearshore zone of the South China Sea, which influence the hydrological regime of the Mekong River mouth, are discussed. Detailed characteristics are provided for the drainage system of the Mekong River mouth area, water flow distribution among the delta branches, processes of the delta submergence during floods, as well as propagation of tidal, surge-induced level fluctuations and seawater intrusion into the river. Regularities of the Holocene evolution of the Mekong River mouth area and recent processes of delta formation are also discussed.     

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.     

The hydrological regime and the morphological structure of the Godavari River delta (India)

The major hydrological and geographic characteristics of the Godavari River and the coastal zone of the Bay of Bengal that have their effect on the hydrological regime and the morphological structure of the river delta are considered. The hydrographic, climatic, and environmental conditions in the Godavari delta are described. The specific features of hydrological processes in the delta are considered, including river and bay water mixing and the impact of tropic storms and hurricanes on the delta. The main features of morphological processes in the delta are revealed, including cyclic changes in the delta in Holocene and the dynamics of the channel network and delta coastline in the past 150 years. It is shown that the processes of erosion and retreat of the delta coastline became more active in the late XX century.     

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.     

Peculiarities of the hydrological regime of the Ganges and Brahmaputra river mouth area

The basic peculiarities of the hydrological regime of one of the largest mouth areas of the world, i.e., the common mouth of the rivers of Ganges and Brahmaputra, are discussed. The main features of natural conditions (including climatic) of the mouth of these rivers and the delta drainage system are characterized. The hydrological regime of the Ganges and Brahmaputra rivers, the largest rivers of South Asia, is studied in greater detail; the quantitative assessments of the water and sediment runoff of these rivers are specified. Provision is made for revealing the basic peculiarities of river flow distribution among numerous delta branches, annual floods during southwest monsoons, tidal phenomena in the maritime zone of the delta, and disastrous storm surges and inundations in the period of tropical cyclones. Flood control measures taken in Bangladesh to protect the population and lands are described.     

Hydrological and morphological features of the Upper Angara mouth area

The hydrological and morphological processes in the mouth area of the Upper Angara (which ranks second in terms of water abundance among Baikal Lake tributaries) are considered. The major external factors that determine those processes have been revealed. The main features of the delta??s water regime, including the effect of anthropogenic level rise in the lake, are described. Specific attention is paid to morphological processes in the delta and on the barrier bar, separating a large mouth lagoon from the lake.     

Hydrological–morphological processes in the mouth area of the Congo R. and the effect of submarine canyon on these processes

The general geographic, hydrographic, climatic, and hydrological characteristics of the Congo R. basin are considered. The major features of the riverine and marine factors that have their effect on the hydrological regime and morphology of the delta and estuary of the Congo R. are identified; the effect of a submarine canyon on the morphological features of the estuary is analyzed in detail; and changes in river delta structure in the XX century and currently are considered. The hydrological—morphological characteristics of the largest mouths of African rivers, the formation conditions of water and sediment runoff, and variations of their deltas are compared.     

Hydrological Regime and Morphodynamics of the Yangtze River Mouth Area

The features of the hydrological regime, modern morphological structure, fluviomorphological processes, and the history of formation of the Yangtze River mouth area are discussed. The influence of the huge river water and sediment runoff and tides on the hydrological and morphological processes in the Yangtze River mouth is shown. The possible impact of construction of the large waterworks Three Gorges on the hydrological and morphological processes in the Yangtze River mouth is roughly evaluated.     

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.     

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.     

Hydrological processes at an Arctic river mouth: Case study of the Colville River, Alaska, USA

Data on the Colville River mouth (Alaska, USA) are used to discuss the regularities in hydrological processes taking place in river mouth areas, functioning under extreme arctic conditions. Seasons and periods are recognized in the annual cycle of the Colville river mouth hydrologic regime. A thick ice cover commonly forms in winter in the river, its delta distributaries, and the offshore zone. Water salinity in under-ice water in the distributaries and near-delta river reach appreciably increases in late winter. The spring flood is very short; in this period, snowmelt water propagates toward the ocean first over ice and next under it. A wedge of freshened waters forms in the nearshore zone above fast ice. River runoff abruptly drops in the summer-autumn low-water period. The morphological processes in the distributaries and some ecological conditions in the delta are also discussed.     

Variations of the hydrological regime,morphological structure,and landscapes of the Indus River delta (Pakistan) under the effect of large-scale water management measures

The hydrological regime, morphological structure, and landscapes of the Indus River delta are considered, and the significant changes that took place in them during the second half of the XX century because of the large-scale hydraulic engineering activity in the river’s basin, runoff regulation, and water withdrawal for irrigation are analyzed. It is shown that the abrupt decrease in water and sediment runoff in the Indus have affected the hydrological processes in the river’s lower reaches and caused delta degradation.     

The Hydrological Regime and the Peculiarities of Formation of the Po River Delta

The peculiarities of the hydrological regime of the delta and near-shore zone of the Po River are discussed. The intrusion of salt seawater into the delta is described. The history of the Po Delta formation has been restored on the basis of the analysis of historical, archeological, and cartographic data. As shown, the peculiarities of hydrological and morphological processes in the Po River mouth are associated with natural and specifically with human-induced variations in sediment runoff of the river, with levee construction along branches, subsidence of deltaic deposits, and eustatic rise of the sea level.     

Hydrological and morphological processes in the Chao Phraya Mouth Area (Thailand) and their anthropogenic changes

The hydrological and morphological features of the Chao Phraya Mouth Area (Thailand) are considered. The attention is focused on the assessment of the effect exerted on the hydrological and morphological processes in the delta and the nearshore of the Chao Phraya River by a considerable anthropogenic drop in water and sediment runoff of the river; land subsidence near Bangkok caused by groundwater withdrawal; sea level rise; and wave intensification.     

Changes in the long-term hydrological regimes and the impacts of human activities in the main Wei River,China

ABSTRACT

Under the combined influence of climate changes and human activities, the hydrological regime of the Wei River shows remarkable variations which have caused many issues in the Wei River in recent decades, such as a lack of freshwater, water pollution, disastrous flooding and channel sedimentation. Hence, hydrological regime changes and potential human-induced impacts have been drawing increasing attention from local government and hydrologists. This study investigates hydrological regime changes in the natural and measured runoff series at four hydrological stations on the main Wei River and quantifies features of their long-term change by analysing their historical annual and seasonal runoff data using several approaches, i.e., continuous wavelet transform, cross-wavelet, wavelet coherence, trend-free pre-whitening Mann-Kendall test and detrended fluctuation analysis. By contrasting two different analysis results between natural and measured river runoff series, the impacts of human activities on the long-term hydrological regime were investigated via the changes of spatio-temporal distribution in dominant periods, the trends and long-range memory of river runoff. The results show : (a) that periodic properties of the streamflow changes are the result of climate, referring to precipitation changes in particular, while human activities play a minor role; (b) a significant decreasing trend can be observed in the natural streamflow series along the entire main stream of the Wei River and the more serious decrease emerging in measured flow should result from human-induced influences in recent decades; and (c) continuous decreasing streamflow in the Wei River will trigger serious shortages of freshwater in the future, which may challenge the sustainability and safety of water resources development in the river basin, and should be paid great attention before 2020.

Editor Z.W. Kundzewicz; Associate editor K. Hamed