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.     

Analysis of the Impact of Hydrotechnical Construction on the Amur River near Blagoveshchensk and Heihe Cities Using a Two-Dimensional Hydrodynamic Model

Water flow and sediment transport under the effect of hydrotechnical constructions on the Amur River near Blagoveshchensk and Heihe cities was analyzed based on two-dimensional hydrodynamic modeling using STREAM_2D software (the authors V. Belikov et al., Russia). Three modeling scenarios were considered: without constructions, with the embankment of Blagoveshchensk, with the embankment of Blagoveshchensk and a system of dams near the Chinese island of Big Heihe. Modeling results have shown that the embankment has only a local effect on the part of the Amur R. upstream from confluence with the Zeya R. The construction of dams in the side channels near the island of Big Heihe can lead to significant flow redistribution, providing the flow concentration in the main river channel and reduction of the water flow, entering the island system. An increase in erosion in the main channel downstream of the confluence near the left bank and a simultaneous increase in accumulation near the right bank of the Amur R. below the island system can take place as the result of side channels shutting by dams from the right bank.     

The structure of ice and ice cover in lower Amur reaches with branched channel

The study is focused on the specific features of ice regime in Amur lower reaches and the structure of ice surface in branches of different size and dynamic state. The main features of ice stratigraphy in different parts of the river have been identified, and ice cover characteristics have been found to show considerable heterogeneity across the channel. Quantitative data on the concentration of terrigenous material in the ice and its distribution within the ice mass have been collected. The amount of terrigenous material was estimated in the ice in Amur lower reaches, from where it is largely exported into the Sea of Okhotsk during spring ice drift.     

Regularities in sea level rise impact on the hydrological regime and morphological structure of river deltas

The problem of assessment of sea level rise impact on the hydrological regime and morphological structure of river deltas is discussed. Studies of the response of river deltas, which are among the most vulnerable natural objects, to the sea level rise has become urgent because of the global climate warming and the associated acceleration of the World Ocean level rise. Methods are described that can be used for the analysis, calculation, and prediction of sea level rise impact on submergence of deltas, propagation of backwater from the sea tides, surges, and salt seawater intrusion. Special emphasis is given to channel processes in delta branches, which accompany sea level rise, as well as to delta coastline erosion and flow redistribution among branches. In the course of research, due consideration was taken of the experience gained in studying the response of river deltas on the Caspian Sea coasts to the recent considerable level rise in this water body.     

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.     

Hydrochemical characteristics of the Chita River basin

Human-induced factors responsible for the formation of the Chita River hydrochemical regime in the Amur River basin are discussed. An environmental map of the Chita River basin is compiled. The available results of hydrochemical observations over surface water and groundwater discharged from reclaimed lands of Chita region are generalized. The main factors affecting the hydrochemical regime of the Chita River are specified.     

Changes in streamflow regimes and their responses to different soil and water conservation measures in the Loess Plateau watersheds,China

Investigating the changes in streamflow regimes in response to various influencing factors contributes to our understanding of the mechanisms of hydrological processes in different watersheds and to water resource management strategies. This study examined streamflow regime changes by applying the indicators of hydrologic alteration method and eco-flow metrics to daily runoff data (1965–2016) from the Sandu, Hulu and Dali Rivers on the Chinese Loess Plateau, and then determined their responses to terracing, afforestation and damming. The Budyko water balance equation and the double mass curve method were used to separate the impacts of climate change and human activities on the mean discharge changes. The results showed that the terraced and dammed watersheds exhibited significant decreases in annual runoff. All hydrologic metrics indicated that the highest degree of hydrologic alteration was in the Sandu River watershed (terraced), where the monthly and extreme flows reduced significantly. In contrast, the annual eco-deficit increased significantly, indicating the highest reduction in streamflow among the three watersheds. The regulation of dams and reservoirs in the Dali River watershed has altered the flow regime, and obvious decreases in the maximum flow and slight increases in the minimum flow and baseflow indices were observed. In the Hulu River watershed (afforested), the monthly flow and extreme flows decreased slightly and were categorized as low-degree alteration, indicating that the long-term delayed effects of afforestation on hydrological processes. The magnitude of the eco-flow metrics varied with the alteration of annual precipitation. Climate change contributed 67.47% to the runoff reduction in the Hulu River watershed, while human activities played predominant roles in reducing runoff in the Sandu and Dali River watersheds. The findings revealed distinct patterns and causes of streamflow regime alteration due to different conservation measures, emphasizing the need to optimize the spatial allocation of measures to control soil erosion and utilize water resources on the Loess Plateau.     

Dissolved and suspended organic mater in the Amur and Songhua River water

Results of studying the concentration of total, dissolved, and suspended organic matter in the water of the Amur and its main tributaries (the rivers of Bureya, Songhua, etc.) in 2005–2006 are presented. A high concentration of organic matter of anthropogenic origin was recorded in the water of the Songhua River, which has a significant effect on the Amur water quality. The export of organic matter with the Amur River water into the Amur Liman was accessed.     

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.     

Sediment mobility and bed armoring in the St Clair River: insights from hydrodynamic modeling

The lake levels in Lake Michigan‐Huron have recently fallen to near historical lows, as has the elevation difference between Lake Michigan‐Huron compared to Lake Erie. This decline in lake levels has the potential to cause detrimental impacts on the lake ecosystems, together with social and economic impacts on communities in the entire Great Lakes region. Results from past work suggest that morphological changes in the St Clair River, which is the only natural outlet for Lake Michigan‐Huron, could be an appreciable factor in the recent trends of lake level decline. A key research question is whether bed erosion within the river has caused an increase in water conveyance, therefore, contributed to the falling lake level. In this paper, a numerical modeling approach with field data is used to investigate the possibility of sediment movement in the St Clair River and assess the likelihood of morphological change under the current flow regime. A two‐dimensional numerical model was used to study flow structure, bed shear stress, and sediment mobility/armoring over a range of flow discharges. Boundary conditions for the numerical model were provided by detailed field measurements that included high‐resolution bathymetry and three‐dimensional flow velocities. The results indicate that, without considering other effects, under the current range of flow conditions, the shear stresses produced by the river flow are too low to transport most of the coarse bed sediment within the reach and are too low to cause substantial bed erosion or bed scour. However, the detailed maps of the bed show mobile bedforms in the upper St Clair River that are indicative of sediment transport. Relatively high shear stresses near a constriction at the upstream end of the river and at channel bends could cause local scour and deposition. Ship‐induced propeller wake erosion also is a likely cause of sediment movement in the entire reach. Other factors that may promote sediment movement, such as ice cover and dredging in the lower river, require further investigation. Copyright © 2012 John Wiley & Sons, Ltd.     

Organic matter in the water of lakes near the Lower Amur floodplain

The concentration and dynamics of organic matter in the Lower Amur water and near-floodplain lakes in the period of spring-summer flood and summer high low-flow period are described on the basis of hydrochemical and hydrological studies carried out in 2004–2005. The contribution of lakes to the organic component of Amur water is shown to vary within wide limits and depend on allochthonous and autochthonous processes as well as on the phase of Amur water regime.     

Limited modification of mid-latitude landscapes by ice sheets: The case of northeast Scotland

The paper uses a case study in Scotland to examine the amount and processes of landscape modification by Quaternary ice sheets. There is an inverse correlation between the distribution of landforms of glacial erosion and pre-glacial landscape remnants in northeast Scotland. The implication is that in places ice sheets can preserve a pre-glacial landscape unscathed, while elsewhere they remove the pre-glacial weathered rock. The location of glacial protection or erosion is strongly influenced by the topography and its influence on former ice sheet flow and basal thermal regime. The classic glacially eroded landscape of areal scouring can be produced by the removal of only 10–50 m of weathered rock. Furthermore rock basins, often regarded as the hallmark of glacial erosion, may be directly inherited from the pre-glacial pattern of deep weathering.     

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.     

Fluvial thermal erosion investigations along a rapidly eroding river bank: application to the Lena River (central Siberia)

In Central Yakutia, frozen river banks are affected by a combination of thermal and mechanical erosion. Exceptional bank retreat of up to 40 m per year is observed. This results from ground thawing produced by heat transfer from the ?ow of water through the frozen ground, followed by mechanical transport of the thawed sediments. A one‐dimensional model is proposed to estimate the thermal erosion ef?ciency. A test of this model is a comparison of results obtained from experiments carried out in a cold room. A hydraulic channel allows measurements of the thaw front propagation, as well as the thermal erosion rate, in simulated ground ice that is subjected to warm water ?ow. Various laboratory simulations demonstrate the validity of the mathematical model for the range of laboratory conditions. A hierarchy of parameters (Reynolds number, water and ground ice temperatures) is proposed to explain the present ef?ciency of thermal erosion along the Siberian rivers. From the characteristics of the Lena River (geometry, temperature and discharge) during the ?ood season, the erosion of banks with different ice content predicted by the model is in agreement with ?eld observations. Copyright © 2003 John Wiley & Sons, Ltd.     

River ice cover influence on sediment transportation at present and under projected hydroclimatic conditions

A large number of rivers are frozen annually, and the river ice cover has an influence on the geomorphological processes. These processes in cohesive sediment rivers are not fully understood. Therefore, this paper demonstrates the impact of river ice cover on sediment transport, i.e. turbidity, suspended sediment loads and erosion potential, compared with a river with ice‐free flow conditions. The present sediment transportation conditions during the annual cycle are analysed, and the implications of climate change on wintertime geomorphological processes are estimated. A one‐dimensional hydrodynamic model has been applied to the Kokemäenjoki River in Southwest Finland. The shear stress forces directed to the river bed are simulated with present and projected hydroclimatic conditions. The results of shear stress simulations indicate that a thermally formed smooth ice cover diminishes river bed erosion, compared with an ice‐free river with similar discharges. Based on long‐term field data, the river ice cover reduces turbidity statistically significantly. Furthermore, suspended sediment concentrations measured in ice‐free and ice‐covered river water reveal a diminishing effect of ice cover on riverine sediment load. The hydrodynamic simulations suggest that the influence of rippled ice cover on shear stress is varying. Climate change is projected to increase the winter discharges by 27–77% on average by 2070–2099. Thus, the increasing winter discharges and possible diminishing ice cover periods both increase the erosion potential of the river bed. Hence, the wintertime sediment load of the river is expected to become larger in the future. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrological processes in the mouth area of the Hong Ha (Red River)

The main features of hydrological processes taking place in the mouth area of the Hong Ha River in Vietnam are considered. The geographic and hydrological conditions in the Hong Ha River basin and in its receiving water body—the Gulf of Tonkin, South China Sea—are briefly characterized. The main features of the mouth area of the Hong Ha River as a specific geographic object are identified. The hydrological regime of the delta and the nearshore zone of the Hong Ha River are described in detail. Water balance of the delta, runoff water levels and delta inundation, water and sediment runoff distributions over delta branches, and the effect of tides, typhoons, and storm surges on delta regime are considered. Present-day problems of the use and protection of natural resources at the Hong Ha River mouth are briefly discussed.     

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).     

Calculating basal temperatures in ice sheets: an Excel spreadsheet method

The flow of ice sheets and their geomorphological impact is greatly influenced by their basal thermal regime. Calculations of basal temperatures in ice sheets are therefore fundamental in evaluating glacier dynamics and in determining the spatial distribution of zones of erosion and deposition beneath ice masses. Calculations of basal temperatures are not frequently attempted, however, primarily because of the techniques required to solve the heat conduction equation between the ice surface and the base. This paper describes a new Excel spreadsheet method of solving this equation that can readily be applied to both former and contemporary ice sheets. The application of the spreadsheet is illustrated with two examples. The first provides a calculation of basal thermal regime beneath the north eastern part of the Scottish ice sheet during the last glacial maximum; the second shows how basal ice temperatures can be calculated beneath the modern Antarctic ice sheet. Copyright © 2002 John Wiley & Sons, Ltd.     

Redistribution and export of contaminated sediment within eastern Fukushima Prefecture due to typhoon flooding

Tropical cyclones expose river basins to heavy rainfall and flooding, and cause substantial soil erosion and sediment transport. There is heightened interest in the effects of typhoon floods on river basins in northeast Japan, as the migration of radiocaesium‐bearing soils contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident will affect future radiation levels. The five main catchments surrounding FDNPP are the Odaka, Ukedo, Maeda, Kuma and Tomioka basins, but little quantitative modelling has been undertaken to identify the sediment redistribution patterns and controlling processes across these basins. Here we address this issue and report catchment‐scale modelling of the five basins using the GETFLOWS simulation code. The three‐dimensional (3D) models of the basins incorporated details of the geology, soil type, land cover, and used data from meteorological records as inputs. The simulation results were checked against field monitoring data for water flow rates, suspended sediment concentrations and accumulated sediment erosion and deposition. The results show that the majority of annual sediment migration in the basins occurs over storm periods, thus making typhoons the main vectors for redistribution. The Ukedo and Tomioka basins are the most important basins in the region in terms of overall sediment transport, followed by the other three basins each with similar discharge amounts. Erosion is strongly correlated with the underlying geology and the surface topography in the study area. A low permeability Pliocene Dainenji formation in the coastal area causes high surface water flow rates and soil erosion. Conversely, erosion is lower in an area with high permeability granite basement rocks between the Hatagawa and Futaba faults in the centre of the study area. Land cover is also a factor controlling differences in erosion and transport rates between forested areas in the west of the study area and predominantly agricultural areas towards the east. The largest sediment depositions occur in the Ogaki and Takigawa Dams, at the confluence of the Takase and Ukedo Rivers, and at the Ukedo River mouth. Having clarified the sediment redistribution patterns and controlling processes, these results can assist the ongoing task of monitoring radioactive caesium redistribution within Fukushima Prefecture, and contribute to the design and implementation of measures to protect health and the environment. Copyright © 2016 John Wiley & Sons, Ltd.     

Recent changes in the sediment regime of the Pearl River (South China): Causes and implications for the Pearl River Delta

Riverine sediments have played an important role in the morphological evolution of river channels and river deltas. However, the sediment regime in the many world's rivers has been altered in the context of global changes. In this study, temporal changes in the sediment regime of the Pearl River were examined at different time scales, that is, annual, seasonal, and monthly time scales, using the Mann–Kendall test. The results revealed that precipitation variability was responsible for monthly and seasonal distribution patterns of the sediment regime and the long‐term changes in the water discharge; however, dam operation has smoothed the seasonal distribution of water discharge and resulted in decreasing trends in the annual, wet‐season, and dry‐season sediment load series since the 1950s. Due to the different regulation magnitudes of dam operation, differences were observed in sediment regime changes among the three tributaries. In addition, human activities have altered the hysteresis of seasonal rating curves and affected hysteresis differences between increasing and decreasing water discharge stages. Sediment supply is an important factor controlling river channel dynamics, affecting channel morphology. From the 1950s to the 1980s, siltation was dominant in river channels across the West River and North River deltas in response to the sediment increases; however, scouring occurred in the East River deltas due to sediment reduction. Significant erosion occurred in river channels in the 1990s, which was mostly due to downcutting of the river bed caused by sand excavations and partly because of the reduced sediment load from upstream. Although sand excavations have been banned and controlled by authority agencies since 2000, the erosion of cross sections was still observed in the 2000s because of reduced sediment caused by dam construction. Our study examines the different effects of human activities on the sediment regime and downstream channel morphology, which is of substantial scientific importance for river management.