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.     

Modeling of ice phenomena in the mouth of the Vistula River

The mouth of the Vistula River, which is a river outlet located in tideless area, is analyzed. The Vistula River mouth is a man-made, artificial channel which was built in the 19th century in order to prevent the formation of ice jams in the natural river delta. Since the artificial river outlet was constructed, no severe ice-related flood risk situations have ever occurred. However, periodic ice-related phenomena still have an impact on the river operation. In the paper, ice processes in the natural river delta are presented first to refer to the historical jams observed in the Vistula delta. Next, the calibrated mathematical model was applied to perform a series of simulations in the Vistula River mouth for winter storm condition to determine the effects of ice on the water level in the Vistula River and ice jam potential of the river outlet.     

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.     

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.     

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.     

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.     

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.     

Specific Features of Development of the Modern Sulak River Delta

The development of the Sulak River Delta in the 19th and 20th centuries is discussed. It is shown that a drastic reduction in sediment runoff after the establishment of river flow regulation, anthropogenic restructuring of the river channel system in the delta area, and large-scale variations in the Caspian Sea level had an impact on the delta evolution. The processes of delta degradation over the period of the recent sea level rise are analyzed. The dynamics of the Sulak Delta in recent decades is studied using space photographs.     

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.     

Delta formation processes at the Mississippi River mouth

Specific processes of delta formation at the Mississippi River mouth are discussed. In the last 7000–8000 years, a series of large deltaic lobes was formed in succession at the Mississippi River mouth under the condition of high river sediment runoff and stabilization of the ocean level after its sudden postglacial rise. In the mid-XX century, the formation of a new deltaic lobe began at the Atchafalaya Branch mouth. Over the last centuries, the processes of delta formation at the Mississippi River mouth slowed down as a result of the river sediment runoff decrease after flow regulation of the Missouri and Arkansas tributaries; in some parts of the deltaic plain, these processes gave way to degradation of marshes and seashore erosion under the impact of intense land subsidence. The current processes of delta formation are under the great influence of local economic activities.     

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).     

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.     

Channel morphology and sediment movement in a tidal river,pitt river,British Columbia

The Pitt River is a meandering river channel linking the Fraser River estuary and Pitt Lake. The lake acts as a temporary reservoir for tidally diverted Fraser River flow. Stage level can fluctuate 2 m in Pitt River and as much as 1.2 m in Pitt Lake on a tidal cycle. Stage data from three locations in the system, used in conjunction with velocity measurements (profiles and tethered meter), revealed large tidal and seasonal variations in discharge. Calculations indicate that during the flood, basal shear stress peaks earlier in the cycle and reaches higher values than during the ebb. Thus, sediment moves farther forward on a flood flow than it moves back on the succeeding ebb. An upstream movement of sediment in Pitt River from the Fraser River is indicated by: (1) the identical mineralogy of the two rivers, (2) a decrease in median grain size from the Fraser to Pitt Lake, and (3) a predominance of flood-oriented bedforms in the river channel. A delta, 12 km² area, has accumulated at the lower (draining) end of the lake. Studies of the river channel using hydrographic charts revealed regular meanders (λM = 6100 m) and evenly spaced riffles and pools which appear to be scaled to the strongest flow, winter flood current (2400 m³/s). The winter flood is thus considered to be the effective discharge. Meander point bars are accreting on the ‘upstream’ side indicating deposition by the flood-oriented flow. The three dimensional geometry of the large-scale bedforms which cover the sandy thalweg of both river and delta channel was determined by echo sounding and side-scan sonar. Three distinct sizes (height/spacing = 0.8 m/10–15 m; 1.5 m/25–30m; 3m/50–60 m) of large-scale bedforms (sand waves) were found; their linear relationship of height vs. spacing on a log-log plot suggests a common genesis. Their occurrence by size does not appear to be related to depth of flow but rather to their position in the channel with respect to large scale features which alter flow.     

Sedimentation patterns in the Selenga River delta under changing hydroclimatic conditions

The Selenga River delta (Russia) is a large (>600 km²) fluvially dominated fresh water system that transfers water and sediment from an undammed drainage basin into Lake Baikal, a United Nations Educational, Scientific, and Cultural Organization World Heritage Site. Through sedimentation processes, the delta and its wetlands provide important environmental services, such as storage of sediment‐bound pollutants (e.g., metals), thereby reducing their input to Lake Baikal. However, in the Selenga River delta and many other deltas of the world, there is a lack of knowledge regarding impacts of potential shifts in the flow regime (e.g., due to climate change and other anthropogenic impacts) on sedimentation processes, including sediment exchanges between deltaic channels and adjacent wetlands. This study uses field measurements of water velocities and sediment characteristics in the Selenga River delta, investigating conditions of moderate discharge, which have become more frequent over the past decades (at the expense of peak flows, Q > 1,350 m³ s^?1). The aims are to determine if the river system under moderate flow conditions is capable of supporting sediment export from the main distributary channels of the delta to the adjacent wetlands. The results show that most of the deposited sediment outside of the deltaic channels is characterized by a large proportion of silt and clay material (i.e., <63 μm). For example, floodplain lakes function as sinks of very fine sediment (e.g., 97% of sediment by weight < 63 μm). Additionally, bed material sediment is found to be transported outside of the channel margins during conditions of moderate and high water discharge conditions (Q ≥ 1,000 m³ s^?1). Submerged banks and marshlands located in the backwater zone of the delta accumulate sediment during such discharges, supporting wetland development. Thus, these regions likely sequester various metals bound to Selenga River sediment.     

Mapping of ground motion amplifications for the Fraser River delta in Greater Vancouver,Canada

Earthquake Engineering and Engineering Vibration - The Fraser River delta in Greater Vancouver, Canada consists of deep soft deposits of silts and clays, and it is well known that the deep soil...     

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 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.     

Changes in the Lena River runoff during the Holocene

The spatial and temporal changes in the Lena River runoff over the last 9 thousand years are reconstructed through studying the freshwater microfossils in sediment cores obtained from the Laptev Sea inner shelf immediately adjacent to the Lena delta and subject to the freshening effect of river water inflowing the sea through the main arms of the delta (the Trofimovskaya, Bykovskaya, and Tumatskaya arms), the sediments having been thoroughly AMS ¹⁴C dated. The freshwater species of diatoms (predominantly the river ones) and green algae that enter the shelf with river water served as indicators of river runoff. The reconstruction of paleosalinity of the sea surface water in the regions under study is based on the relationships (established earlier) between the distribution of freshwater diatoms in the surface layers of sediments in the Arctic seas and the gradients of water salinity in summer. Data on variations in the composition of aquatic microfossil associations in sediments and the reconstructed paleosalinity in the regions of the eastern and western paleovalleys of the Lena River are used to determine the main paleohydrologic events that controlled the variations in the Lena runoff into the shelf zone of the Laptev Sea during the Holocene.     

Characterization of transboundary POP contamination in aquatic ecosystems of Pearl River delta

During the past two decades, the rapid development of the Pearl River delta leads to substantial accumulation of various toxic organic compounds. This study aims to give a preliminary characterization of the existing state of contamination in this region and to provide insight into the possible fate of persistent organic pollutants (POPs) in this estuary. The available data on POPs in water, river, estuarine sediments, soil, and marine organisms within the Pearl River delta are compiled. It is shown that it may lead to transboundary POP pollution problems at both Hong Kong and Macau Special Administration Regions located at the downstream end of the region. It is noted that the levels of DDTs and HCHs in various environmental media are at alerting levels and that fresh DDT might still be applied illegally within the region. A systematic research is required to determine both the temporal and spatial variations of all POPs in various carrying media of the Pearl River delta as a whole.     

Heavy Metals in the Water and Bottom Sediments of the Selenga River Delta

The overall concentration of Cu, Pb, Zn, Cr, Mn, and Fe are determined in the water and bottom sediments of the Selenga River delta. The concentration of Cu, Pb, and Zn is found to decrease in the lower course of the river, at the delta outlet. The concentration of Mn and Fe is found to decrease in the downstream direction from the river's upper course along the investigated delta arms, whereas the concentration of Zn and Cr in certain arms exceeds their concentration in the upper section of the delta.