Prediction of Shoreline Change for the Calculation of the Integrated Littoral Sediment Budget

The severe coastal erosions are being accelerated along the east coast of South Korea owing to the intermittent erosions and depositions caused by the imbalance between the effective sediment volume supplied from coasts and rivers and the sediment transport rate. Consequently, many studies are being conducted to develop coastal-erosion reduction measures. To accurately determine the cause of coastal erosion, the causes of the erosion and deposition should be accurately diagnosed, and a comprehensive evaluation system for the sediment transport mechanism in the watershed and sea while considering regional characteristics is required. In particular, realizing the evaluation of the effective sediment volume that flows from the river to the sea through observations is a highly challenging task, and various research and developments are required to realize it, as it is still in the basic research stage. The purpose of this study was to systematically analyze the comprehensive sediment budget for coastal areas. First, an analytical system was developed. Then, a shoreline model was constructed by considering the size of the mixed particles. The parameters required for developing the model were determined using the observation data to improve the shoreline model. A sediment runoff model was applied to evaluate the effective sediment volume supplied from the river to the sea, and the applicability of this model was evaluated by comparing it with the sediment supply volume according to the soil and water assessment tool model. The representative wave and the input parameters of the model were set using the observation data of several years. It was found that the prediction performance of the shoreline change model improved when the effective sediment volume was considered, and the particles of the sediment on the shore were assumed to comprise multiple sizes. In particular, the prediction performance improved when the balance of the sediment budget was adjusted by applying a groin having a structurally similar performance to take into consideration the geographic features of the Deokbongsan (island) in front of the river mouth bar. The model demonstrated a good performance in reproducing long-term shoreline changes when the characteristics of the sea waves and the effective sediment volume were considered.

Investigating Behavior of Six Methods for Sediment Transport Capacity Estimation of Spatial-Temporal Soil Erosion

Estimation of sediment transport capacity (STC) plays a crucial role in simulating soil erosion using any physics-based models. In this research, we aim to investigate the pros and cons of six popular STC methods (namely, Shear velocity, Kilinc-Richardson (KR), Effective stream power, Slope and unit discharge, Englund-Hansen (EH), and Unit stream power) for soil erosion/deposition simulation at watershed scales. An in-depth analysis was performed using the selected STC methods integrated into the Grid Surface Subsurface Hydrologic Analysis model for investigating the changes in morphology at spatial-temporal scales at the Cheoncheon watershed, South Korea, over three storm events. Conclusions were drawn as follows. (1) Due to the ability of the KR and EH methods to include an additional parameter (i.e., erodibility coefficient), they outperformed others by producing more accurate simulation results of sediment concentration predictions. The KR method also proved to be superior to the EH method when it showed a more suitable for sediment concentration simulations with a wide range of sediment size and forcing magnitude. (2) We further selected 2 STC methods among the 6 methods to deeply explore the spatial distribution of erosion/deposition. The overall results were more agreeable. For instance, the phenomenon of erosion mainly occurred upstream of watersheds with steep slopes and unbalanced initial sediment concentrations, whereas deposition typically appeared at locations with flat terrain (or along the mainstream). The EH method demonstrated the influence of topography (e.g., gradient slope) on accretionary erosion/deposition results more significantly than the KR method. The obtained results contribute a new understanding of rainfall-sediment-runoff processes and provide fundamental plans for soil conservation in watersheds.

Exomorpholithogenesis of the Selenga River delta at the present stage of the hydroclimatic cycle

The materials of complex interdisciplinary studies of the relief forming in different periods of water availability in the Selenga River delta are presented since the technogenic level rise of Lake Baikal. Four water and sediment runoff anomalies, synchronous with water level fluctuations in the Lake are identified. The current boundaries of the Selenga River mouth area (RMA), floodplain complex, flooding territories in the maximum water ability conditions are identified. The RMA covers the territory from the main channel bifurcation nod to Lake Baikal, includes subaerial and subaqueous parts of the protruding delta, the interaction zone fluvial processes and different-aged terraces deposits and adjacent lagoons Proval and Cherkalov Sor. Semi-empirical models and data on the water runoff and sediment yield are presented.

Behaviors of the Yukon River Sediment Plume in the Bering Sea: Relations to Glacier-Melt Discharge and Sediment Load

Sediment plumes, released to the Bering Sea from the delta front of the Yukon River, Alaska, are initiated mainly by glacier-melt sediment runoffs in the glacierized regions of the Yukon River drainage basin. The surface sediment plumes are extended around the fan-shaped Yukon River delta, which is followed by the northwestward dispersion. During continuous measurements of the Yukon River discharge and sediment load, behaviors of the sediment plumes were explored by shipboard and coastal observations in the Bering Sea. At the high river sediment load of ca. 2500 kg/s, the plume partially plunged into the sea bottom layer. The plunging probably originated in the nepheloid-layer formation from the flocculation of river-suspended sediment, of which more than 90% wt. is silt and clay (grain size d < 63 μm). In order to numerically obtain the area of the surface sediment plumes, a satellite image analysis was performed by using three near-infrared bands in MODIS/Aqua or MODIS/Terra. The plume area was significantly correlated (R2 = 0.735, p < 0.01) to the sediment load averaged for the two days with time lags of 20 days and 21 days to the date of a certain satellite image. Hence, the dispersion of plume-suspended sediment appears to be controlled by the sediment runoff events in the Yukon River rather than the northward “Alaskan Coastal Water”.

Behaviors of the Yukon River Sediment Plume in the Bering Sea: Relations to Glacier-Melt Discharge and Sediment Load

Sediment plumes, released to the Bering Sea from the delta front of the Yukon River, Alaska, are initiated mainly by glacier-melt sediment runoffs in the glacierized regions of the Yukon River drainage basin. The surface sediment plumes are extended around the fan-shaped Yukon River delta, which is followed by the northwestward dispersion. During continuous measure-ments of the Yukon River discharge and sediment load, behaviors of the sediment plumes were explored by shipboard observations in the Bering Sea offshore from the Yukon delta. At the high river sediment load of ca. 3000 kg/s, the plume partially plunged into the sea bottom layer. The plunging probably originated in the nepheloid-layer formation from the flocculation of river-suspended sediment, of which more than 90 %wt. is silt and clay (grain size d &lt; 0.063 mm). In order to numerically obtain the area of the surface sediment plumes, a satellite image analy-sis was performed by using three near-infrared bands in MODIS/Aqua or MODIS/Terra. The plume area was significantly correlated (R2=0.735, p&lt;0.01) to the sediment load averaged for the two days with time lags of 20 days and 21 days to the date of a certain satellite image. Hence, the dispersion of plume-suspended sediment appears to be controlled by the sediment runoff events in the Yukon River rather than the northward “Alaskan Coastal Water”.

Retrieval and Spatio-Temporal Variations Analysis of Yangtze River Water Clarity from 2017 to 2020 Based on Sentinel-2 Images

The Yangtze River is the third longest river in the world. Monitoring and protecting its water quality are important for economic and social development. Water clarity (Secchi disk depth, SDD) is an important reference index for evaluating water quality. In this study, Sentinel-2 multispectral instrument (MSI) remote sensing images were utilized together with the Forel-Ule index (FUI) and hue angle α to construct an SDD retrieval model, which was applied to the Yangtze River from 2017 to 2020, which was used to describe color in the International Commission on Illumination (CIE) color space to construct an SDD retrieval model that was applied to the Yangtze River for the period 2017–2020. Further, the spatial distribution, seasonal variation, inter-annual variation, and driving factors of the observed SDD variations were analyzed. The spatial distribution pattern of the Yangtze River was high in the west and low in the east. The main driving factors affecting the Yangtze River SDD was sediment runoff, water level, and precipitation. The upstream and downstream Yangtze River SDD were negatively correlated with the change in water level and sediment runoff, whereas the midstream Yangtze River SDD was positively correlated with the change in water level and sediment runoff. The upper and lower reaches of the Yangtze River and overall SDD showed a weak downward trend, and the middle reaches of the Yangtze River remained almost unchanged.

Performance of Winter-Sown Cereal Catch Crops after Simulated Forage Crop Grazing in Southland, New Zealand

(1) Background: Winter grazing of livestock poses significant environmental risks of nitrogen (N) leaching and sediment runoff. (2) Methods: A field study tested the effects of sowing catch crops of oats (Avena sativa L.), ryecorn (Secale cereale L.) or triticale (Triticosecale) in June and August (winter) in Southland, New Zealand (NZ), on the risk of N leaching losses from simulated N loads left after winter forage grazing. (3) Results: Catch crops took up 141–191 kg N ha−1 by green-chop silage maturity (approximately Zadoks growth stage 52; November/December). Importantly, early-sown catch crops were able to capture more N during the key leaching period from winter to mid-spring (77–106 kg N ha−1 cf. 27–31 kg N ha−1 for June and August treatments, respectively). At this time, ryecorn and triticale crops sown in June captured 20–29 kg ha−1 more N than June-sown oats (77 kg N ha−1). In October, early-sown catch crops reduced mineral N in the soil profile (0–45 cm depth) by 69–141 kg N ha−1 through the process of plant uptake. At green-chop silage maturity, catch crop yields ranged from 6.6 to 14.6 t DM ha−1. Highest yields and crop quality profiles (e.g., metabolizable energy, crude protein, soluble sugars and starch) were achieved by the oats, irrespective of the sowing date, indicating that trade-offs likely exist between environmental and productive performances of the catch crop species tested. (4) Conclusion: The catch crop of choice by farmers will depend on the desired end use for the crop, its place in the crop rotation and its potential for an environmental benefit.

DYNAMICS OF TURBIDITY OF RIVER WATER ON THE LEFT-BANK TRIBUTARIES OF THE DNIEPER (ON THE EXAMPLE OF THE SUMY REGION)

The article is devoted to the study of sediment runoff, especially one of the characteristics that reflects erosion processes in the catchment area, water turbidity using the example of the rivers of the Sumy region. The main purpose of the article is the spatial and temporal analysis of the turbidity indicators of the rivers of the Sumy region (left-bank tributaries of the Dnieper). The article highlights information on the sediment runoff of the rivers in the region for the entire period of observations, describes modern own studies of the turbidity of river water and establishes the features of the formation of sediment runoff in the rivers of the region. It was found that the indicators of turbidity of river water grow in the direction from north to south of the study area, in the zone of mixed forests are minimal, and in the forest-steppe – maximum; high values of the average turbidity index characteristic of small rivers in the region, аmong the average rivers, the maximum values were recorded for the Sula and Vorskla rivers; during floods, turbidity values are maximum, and during low water periods, they are minimal; there is a tendency to an increase in the indicators of maximum and average turbidity of river water. Particular attention is paid to the influence of river regulation on turbidity indicators. It was found that the deceleration of water exchange is facilitated by the accumulation of sediments in the channel above the dam (high indicators of the thickness of the silt layer), and also below the dam (the creation of a channel island, probably due to the uneven throughput of the dam’s gate valves, which creates a different flow rate from the right and left banks). Decreased flow velocity, increased water turbidity and, as a consequence, siltation, deterioration of river water quality (appearance of swamp odor, decrease in transparency, color change) leads to changes in the species composition of aquatic organisms, extinction of river species and the appearance of atypical river species, overgrowth. In their conclusions, the authors argue that sediment runoff is formed mainly due to washout from the surface of the catchment area, high turbidity indicators in rivers whose basin is more prone to erosion, where the indicators of plowing of the basin surface are maximum, water protection zones and coastal protective belts are destroyed, but when studying the turbidity of river water it is necessary take into account additional factors.

THE RIVER’S SEDIMENT IN THE NORTH-WEST RUSSIAN FEDERATION

Large forested areas, small slopes of catchments, the presence of lakes and swamps, the karstification of the basin, and a large share of underground river feeding contribute to a decrease in the amount of sediment runoff in the rivers located in the North-West of Russia. The distribution of sediment runoff during the year is determined by the flow regime of the river. The maximum values of the monthly solid runoff modules of all the studied rivers are observed at high water in March – May, usually reaching the peak in April, which is typical for the north-western region. Moreover, the passage of the maximum for the northern rivers (Pasha, Oyat and Tikhvinka) mainly falls on April – May; for rivers flowing in the southern part of the region – on March – April. The minimum values of the annual runoff modulus in the low-water period are extremely insignificant, especially in winter, and for some years they are close to zero. This is quite understandable due to the significant contribution of soil erosion to the formation of solid runoff of watercourses, with the most intensive processes of soil erosion occurring during the period of active snowmelt and floods. A steady increase in air temperature and precipitation layers for the North-West of the Russian Federation in the last thirty years in comparison with the previous climatic period has led to an increase in the river runoff for the studied watercourses. At the same time, according to the observations for the selected climatic periods, there is a decrease in the annual solid runoff. This can be explained by socio-economic changes – a significant decrease in agricultural activity in the region. In addition, taking into account the increase in the water content of the rivers, the decrease in the solid runoff can be explained by the redistribution of the intra-annual course of meteorological values that occurred as a result of climatic changes.