Suspended sediment balance in Selenga delta at the late XX–early XXI century: Simulation by LANDSAT satellite images

Adaptation of the technology of water turbidity simulation by satellite image data for the delta of the Selenga R., the largest Baikal tributary is given. The results of processing a series of 82 Landsat images are used to assess the seasonal variability of suspended sediment balance in the Selenga delta in period from 1989 up to the present time. It is shown that, at higher water discharges (>1500 m³/s), suspended material will accumulate in the delta (on the average 15% of the total sediment transport at the delta head), governed by material precipitation within inundated floodplain area and lakes in the lower part of the delta. At lower water discharges (<1500 m³/s), a longitudinal increase in suspended sediment transport may take place, caused by setups from Baikal side and channel erosion in the branches.     

Water Level Fluctuations in the Kuban River Delta over the Period of Many Years

Three areas with different trends in water level variations over the period of many years have been distinguished within the Kuban Delta. It was found that the eustatic level rise of the Sea of Azov and soil subsidence on the sea edge of the delta and in the lower reaches of the Protoka Branch were responsible for the noticeable rise in water levels. A considerable water level drop caused by the river runoff regulation and erosion of the lower pool of the Krasnodarskii Waterworks was recorded in the upper part of the delta; in the rest part of the delta, water levels dropped insignificantly, which was partially due to the impact of the tectonic uplift.     

Regularities in the Space and Time Flow Variations in the Near-Mouth Reach and Delta of the Lena R.

Lena flow showed considerable, mostly climate-induced, changes in the recent 30–40 years. The character of these changes at the river watershed–sea border somewhat differs from that in the basin outlet station because of flow transformations in the near-mouth reach and, especially, in the delta. The new stationary and occasional expedition observations were used to improve the estimates of the major characteristics of the discharges of water, suspended sediment, and heat in the Lena outlet section and to identify the features and causes of their long-term and seasonal variations. Another important result is the estimation of flow characteristic in the reach downstream of the basin outlet station, at delta head, and on its coastline. New data are given on the present-day distribution of water and suspended sediment discharges between the major delta branches, their long-term variations, and the character of inundation of the near-head delta area during spring floods.     

Channel deformations and runoff redistribution within the Terek River mouth reach after the catastrophic flood of 2002

Results of field studies conducted in the Terek delta in 2002–2004 are presented. Seasonal vertical deformations of the river bed in the lower course of the main branch (the Novyi Terek) are shown to vary within 0.5–1.3 m; intense development of the delta bar takes place. Regeneration of water streams that died away in the 1980s–1990s, and the formation of a new channel network in the lower part of Terek delta are recorded.     

Hydrological regime of the Rhône Delta and dynamics of its coastline

Specific features of the hydrological regime of the Rhône River and the nearshore zone of its mouth are discussed. The processes of seawater intrusion into the delta branches are described. The information on the history of the delta evolution and development is presented along with the reconstruction of the Holocene evolution of the Rhône Delta and analysis of formation peculiarities of the present-day delta. Channel processes in the Rhône Delta and the dynamics of the delta coastline are described; characteristics of the deep-water fan are discussed, and the data on sediment balance are given.     

Formation of a new delta-like object in the Kapchagai Reservoir on the Ili River

The formation processes of a new delta-like object with a hydromorphic landscape in the upper part of the Kapchagai Reservoir on the Ili R.—an internal delta—are considered. The quantitative characteristics of the development of this delta are evaluated using data of Landsat-2, 5, and 7 space images over period 1975–2012. These processes were found to accelerate considerably in the wet year of 2012, and intense under-flooding and salinization of nearby lands were revealed in the Chilikskii alluvial fan on the southern wing of the Kapchagai delta. A consequence of this accumulative process was found to be the development of planar channel deformations of the Ili R. 30 km upstream the Kapchagai delta.     

The time-dependent variation of hydrogeochemical characteristics, thermal regime, and biocenoses in the fresh and thermal waters of the Lake Karymskii basin following the catastrophic underwater eruption of 1996 in the Akademii Nauk Caldera, Kamchatka

The results of biohydrogeochemical monitoring are used to study time-dependent variations in the hydrogeochemical characteristics of the Lake Karymskii water mass, the state and characteristics of underwater discharge zones in the Tokarev crater (formed in 1996), hydrogeochemical characteristics of thermal springs around the lake, and the biota succession in the lake for the period 1996–2006 (2007). We detected a stratification in the chemical composition of water over depth and the presence of persistent zones of increased concentrations of dissolved oxygen. We found an alkalization of lake water and a decrease in its total salinity. The new thermal springs and underwater discharges of thermal water and gases were found to be continuing. The first data were obtained on the concentration of microelements in the thermal springs of the Karymskii basin. The biodiversity of algae in Lake Karymskii was largely increased by the species diversity of benthic Bacillariophyta. The plankton phytocomponent of the precatastrophic period was found to have been regenerated in the lake as of April 2007.     

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.     

Tidal impact on the division of river discharge over distributary channels in the Mahakam Delta

Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels. A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations. The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper the discharge division that would occur in the case without tides.     

Effects of riverbed incision on the hydrology of the Vietnamese Mekong Delta

The hydrogeomorphology of the Vietnamese Mekong Delta (VMD) has been significantly altered by natural and anthropogenic drivers. In this study, the spatiotemporal changes of the flow regime were examined by analysing the long-term daily, monthly, annual and extreme discharges and water levels from 1980 to 2018, supported by further investigation of the long-term annual sediment load (from the 1960s to 2015), river bathymetric data (in 1998, 2014 and 2017) and daily salinity concentration (from the 1990s to 2015) using various statistical methods and a coupled numerical model. Then, the effects of riverbed incision on the hydrology were investigated. The results show that the dry season discharge (i.e., in March–June) of the Tien River increased by up to 23% from the predam period (1980–1992) to the postdam period (1993–2018) but that the dry season water level at My Thuan decreased by up to −46%. The annual mean and monthly water levels in June at Tan Chau and in January and June–October at My Thuan in the Tien River decreased statistically, even though the respective discharges increased significantly. These decreased water levels instead of the increased discharges were attributed to the accelerated riverbed incision upstream from My Thuan, which increased by more than three times, from a mean rate of −0.16 m/year (−16.7 Mm³/year) in 1998–2014 to −0.5 m/year (−52.5 Mm³/year) in 2014–2017. This accelerated riverbed incision was likely caused by the reduction in the sediment load of the VMD (from 166.7 Mt/year in the predam period to 57.6 Mt/year in the postdam period) and increase in sand mining (from 3.9 Mm³ in 2012 to 13.43 Mm³ in 2018). Collectively, the decreased dry season water level in the Tien River is likely one of the main causes of the enhanced salinity intrusion.     

Processes of delta formation in the mouth area of the Ganges and Brahmaputra rivers

The evolution of the Ganges and Brahmaputra river delta during the Holocene period is discussed. Particular attention is given to the processes of delta formation, the dynamics of the delta hydrographic systems, the channel processes in river branches, as well as to the dynamics of the delta coastline and nearshore zone bed over the last 150–200 years. The calculation of sediment budget in the mouth area of these rivers is presented.     

Dynamics of the Yenisei and Pur River Deltas

Variations in the mouth areas of the Yenisei and Pur rivers over the period of 50 years were revealed on the basis of comparison of topographic maps prepared in the 1950s and space images made from the Landsat satellite in 1973 (MSS System) and 1999, 2000 (ETM System). Maps of the drainage network dynamics were compiled; they show that, over a period of many years, mouth areas of northern rivers undergo slow but steady changes, which are indicative of the continuing protrusion of deltas into bays at a rate up to 20 m/year, the increment in mouth areas reaching 0.05–0.07% a year. As noted, secondary water streams die off under the condition of flow concentration in main branches, and small islands get integrated. It was found that, over the period under study, natural variations in the level of the receiving water body and human-induced changes in river basins (construction of a chain of reservoirs) did not have considerable impact on dynamic processes occurring in deltas.     

Mathematical modeling of the formation and progradation of a river mouth bar into a sea: Case study of Danube Delta branches

The effect of sediment yield of a stream and the energy of sea waves on the formation of bars and their dynamics at nontidal river mouths is demonstrated. Data on variations in the hydrological regime of the Potapovskii and Bystryi branches in the Danube Delta and the morphodynamics of their bars are given. Major problems of mathematical modeling of the formation and progradation of mouth bars into the sea are discussed. An analytical expression is obtained for the shape of the foreset slope of a bar, which moves over a constant-slope seabed. The results of simulation were checked against data on the Potapovskii and Bystryi branches in the Danube Delta.     

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.     

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.     

The effects of discharge and slope on hyporheic flow in step‐pool morphologies

This paper focuses on surface–subsurface water exchange in a steep coarse‐bedded stream with a step‐pool morphology. We use both flume experiments and numerical modelling to investigate the influence of stream discharge, channel slope and sediment hydraulic conductivity on hyporheic exchange. The model step‐pool reach, whose topography is scaled from a natural river, consists of three step‐pool units with 0.1‐m step heights, discharges ranging between base and over‐bankfull flows (scaled values of 0.3–4.5 l/s) and slopes of 4% and 8%. Results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges. In contrast to findings in a pool‐riffle morphology, those in this study show that steep slopes cause deeper surface–subsurface exchanges than gentle slopes. Numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity. These experiments and numerical simulations emphasize the importance of topography, sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange. Our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool‐riffle bed forms. Copyright © 2014 John Wiley & Sons, Ltd.     

Geomorphic evolution of the Qingshuigou channel of the Yellow River Delta in response to changing water and sediment regimes and human interventions

Delta channels are important landforms at the interface of sediment transfer from terrestrial to oceanic realms and affect large, and often vulnerable, human populations. Understanding these dynamics is pressing because delta processes are sensitive to climate change and human activity via adjustments in, for example, mean sea level and water/sediment regimes. Data collected over a 40-year period along a 110-km distributary channel of the Yellow River Delta offer an ideal opportunity to investigate morphological responses to changing water and sediment regimes and intensive human activity. Complementary data from the delta front provide an opportunity to explore the interaction between delta channel geomorphology and delta-front erosion–accretion patterns. Cross-section dimensions and shape, longitudinal gradation and a sediment budget are used to quantify spatial and temporal morphological change along the Qingshuigou channel. Distinctive periods of channel change are identified, and analysis provides a detailed understanding of the temporal and spatial adjustments of the channel to specific human interventions, including two artificial channel diversions and changes in water and sediment supply driven by river management, and downstream delta-front development. Adjustments to the diversions included a short-lived period of erosion upstream and significant erosion in the newly activated channel, which progressed downstream. Channel geomorphology widened and deepened during periods when management increased water yield and decreased sediment supply, and narrowed and shallowed during periods when management reduced water yield and the sediment load. Changes along the channel are driven by both upstream and downstream forcing. Finally, there is some evidence that changing delta-front erosion–accretion patterns played an important role in the geomorphic evolution of the deltaic channel; an area that requires further investigation. © 2020 John Wiley & Sons, Ltd.     

Assessment of groundwater resources of Quaternary aquifer system in concordance with avoidable negative impact on geoenvironment,south-eastern part of Lithuania

This paper focuses upon south-eastern Lithuanian Quaternary aquifer system groundwater resources formation modelling. Groundwater model calibration has been performed for a pre-development and transient flow conditions. The results demonstrate that there is an intense interaction between groundwater and surface water bodies which form groundwater resources and runoff. For Quaternary cover the majority of unconfined groundwater outflows to surface water streams, the remaining part discharges through the confined interglacial/interstadial aquifers and lateral outflows across the boundaries. Groundwater prognostic exploitable resources can be obtained without a significant negative impact on the geoenvironment. The main sources of exploitable resources formation are increase in groundwater recharge and lateral inflow (40.7%), decreased outflow via streams and lateral boundaries (41.2%) and drawing up additional flow from the hydraulically connected streams (14.5%).     

A synthesis of dominant ecological processes in intensive shrimp ponds and adjacent coastal environments in NE Australia

One of the key environmental concerns about shrimp farming is the discharge of waters with high levels of nutrients and suspended solids into adjacent waterways. In this paper we synthesize the results of our multidisciplinary research linking ecological processes in intensive shrimp ponds with their downstream impacts in tidal, mangrove-lined creeks. The incorporation of process measurements and bioindicators, in addition to water quality measurements, improved our understanding of the effect of shrimp farm discharges on the ecological health of the receiving water bodies. Changes in water quality parameters were an oversimplification of the ecological effects of water discharges, and use of key measures including primary production rates, phytoplankton responses to nutrients, community shifts in zooplankton and delta15N ratios in marine plants have the potential to provide more integrated and robust measures. Ultimately, reduction in nutrient discharges is most likely to ensure the future sustainability of the industry.     

Hydrological and Morphological Processes in the Kura River Delta

Peculiarities of the development of the Kura Delta over the last 200 years are discussed. As shown, changes in the delta were greatly affected by the Caspian Sea level drop during 1929–1977 and its rise during 1978–1995 as well as by natural and human-induced variations in the water and sediment runoff of the river. It was noted that the delta area decreased by nearly 40% as a result of the sea level rise. The following significant changes in the Kura Delta were revealed in recent years using space images: river water rushed through the right mouth spit and, hence, the main Southeastern Branch was devoid of its flow and a new sea spit began its formation in the branch mouth using wave-cut products.