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.

Comparison of Riverbed Changes between Sediment Budget Analysis with Measured Data and River Survey: Case Application to Part of Geumgang

Sediment measurement data are utilized as basic data for various river plans and research. The aim of this study is to compare between sediment budget analysis and riverbed monitoring results. The spatial range was from the Gongju-si (Gemganggyo) station to the Buyeo-gun (Baekjegyo) station in Geumgang, and the temporal range in this study was from 2011 to 2016. The estimated change in riverbed amount using the sediment budget analysis was 2,430,243 tons for sediments loaded over six years in the section. The analyzed riverbed changes sedimentation using the riverbed monitoring method were 2,165,146 tons based on the low level and 3,055,489 tons based on the flood level. Based on the riverbed monitoring performance, the relative errors in the sediment budget analysis results through sediment measurements were 10.9% and -25.7% for the low water and flood levels, respectively.

A Mass Balance Approach in Sediment Budgeting of Large Alluvial Rivers with special emphasis on the Brahmaputra in Assam

Morphology of an alluvial river channel is the consequence of erosion, sediment transport and sedimentation in a river. Sediment budget accounts for the sources, sinks and redistribution pathways of sediments, solutes and nutrients in a unit region over unit time. Human activities are the most important factors that affect the variation in the pattern of river sediment load. This paper discusses sediment budget of a few large rivers by review of literature and estimation of sediment budget of Brahmaputra River in Assam using mass balance approach. An attempt has also been made to discuss human and climatic impact on sediment load of major rivers of the world. Total sediment load in the Brahmaputra River at downstream location (India-Bangladesh border) was estimated to be 814×106 t/year. Considering 10% of sediment load of the Brahmaputra as bed load, suspended sediment load at downstream was estimated to be 733×106 t/year. Tributaries, bank erosion and scouring of river bed were found to contribute 52%, 27% and 21% respectively to sediment load of Brahmaputra at downstream locations. In spite of limitations of the dependable data, future complexity due to climate change impact and hydropower dam initiative in upstream of the River, the study is a simplified approach in sediment budgeting of the Brahmaputra.

Impact of River Dams on Littoral Cells Located Adjacent to the River Mouth

Terrestrial sediment is a major source of sediment to all coasts. Suspended sediment is carried away by the rivers and supplied to the coast to maintain sediment budget. The construction of dams across the rivers arrest sediment behind it and affect the sediment budget of littoral cells along the coast. Reduction in sediment supply induces ecological as well as geomorphological changes along the shoreline. Coastal erosion may accelerate due to reduced sediment influx. With the growing number of cross-river dams and water diversion projects, it has become a major concern before the scientific community to measure, understand and find solutions to multi-fold geo-environmental problems that are arising out of river damming. The present study aims to find out the impact of dams on the coast. It examines how the changes in the suspended sediment supply of an Indian river impact the coast in terms of loss of area due to erosion. Temporal analysis of geomorphological changes along the shoreline in relation to sediment influx holds immense importance to coastal management essential for the sustainable life and livelihood of coastal communities. Scientific investigation into the impact of river dams on the coastal environment is likely to provide a strong ground to reconsider the way present basin development projects function. Areal changes in littoral sediment cells adjacent to the river mouth have been quantified and correlated with changes in sediment influx. Changes along the shorelines have been detected through multispectral satellite images of Landsat belonging to different dates. Image processing and quantification of changes have been performed in QGIS 3.14 “Pi” platform. Virtual raster, raster calculator, field calculator and other required tools in QGIS were used during image processing.

Implication of Shoreline and Nearshore Morphological Changes on Sediment Budget of Wave-Dominated Chennai Beach, India

The study examines the shoreline (1990-2019) and nearshore morphological changes (seasonal) to understand the littoral drift and sediment budget variability. Shoreline change rate depicts erosion (-0.06 m/yr) in the northern sector and accretion (+0.12 m/yr) in the southern sector. Seasonal nearshore morphological changes from non-monsoon to monsoon period signifies net erosion (-1.8x10^4 m^3 ) in northern sector and net accretion (+2.5x10^4 m^3) in the southern sector. Although the lost sediment during monsoon is regained in non-monsoon period, the quantity of sediment gain is reduced in areas with human interventions. The results of the investigation depict the dominance of littoral drift towards north from February to October, when wave approach from east-southeast to south-southeast direction and southwards from November to January when the wave direction was from east-northeast to east-southeast. The net longshore sediment transport rate estimated during the study period was 2.6x10^5 m^3/year in the northern sector and 1.5x10^5 m^3/year in the southern sector with higher rate attributed to monsoon than the non-monsoon. Sediment budget results in deciphering the causes of erosion (-1.27×10^4 m^3/yr) in northern sector and accretion (3.91×10^4 m^3/yr) in southern sector in the wave-dominated Chennai beach.

Subaqueous geomorphology and delta dynamics of Lake Brienz (Switzerland): implications for the sediment budget in the alpine realm

Non-invasive techniques such as seismic investigations and high-resolution multibeam sonars immensely improved our understanding of the geomorphology and sediment regimes in both the lacustrine and the marine domain. However, only few studies provide quantifications of basin wide-sediment budgets in lakes. Here, we use the combination of high-resolution bathymetric mapping and seismic reflection data to quantify the sediment budget in an alpine lake. The new bathymetric data of Lake Brienz reveal three distinct geomorphological areas: slopes with intercalated terraces, a flat basin plain, and delta areas with subaquatic channel systems. Quasi-4D seismic reflection data allow sediment budgeting of the lake with a total sediment input of 5.54 × 106 t sediment over 15 years of which three-quarter were deposited in the basin plain. Lake Brienz yields extraordinarily high sedimentation rates of 3.0 cm/yr in the basin plain, much more than in other Swiss lakes. This can be explained by (i) its role as first sedimentary sink in a high-alpine catchment, and by (ii) its morphology with subaquatic channel-complexes allowing an efficient sediment transfer from proximal to distal areas of the lake.

Sediment Transport and Associated Long-term Bathymetric Changes due to Tidal Currents in The Seto Inland Sea, Japan

The topography of the seafloor is essential for determining physical phenomena such as ocean currents, favorable habitats for marine organisms, optimal vessel navigation, and so on. Prevailing currents and waves, as well as associated shear stresses acting on the ocean floor, are responsible for the formation of typical topographic features including sea caldrons and sandbanks through erosion of bedrock and sediments and their deposition processes. In the Seto Inland Sea (SIS), the most extensive semi-enclosed estuary in Japan, tidal currents affect pronouncedly the formation of seafloor topographic features; however, they have not been fully studied, particularly from a hydrodynamic viewpoint. This study aims to understand bathymetric formation under the predominance of tidal currents in the SIS. A 3-D high-resolution SIS circulation model based on the JCOPE2-ROMS system in a triple-nested configuration was utilized to examine the detailed hydrodynamic processes for the topography formations. A high correlation between the bottom shear stress and the scour depth of the erosive areas was observed, demonstrating that local tidal forcing has continuously been exerted on the seafloor to erode. A diagnostic sediment budget analysis was then conducted for sediments typical of the SIS, that is, gravel, sand, and clay, using the modeled circulation field. The horizontal divergence of the residual flows indicates consistency between divergence (convergence) and erosion (deposition). The sediment budget model also shows that these sediments are generally transported from deep to shallow areas in eroded terrains to form deposited terrains fringing the eroded terrains, whereas sedimentation tendency differs largely from location to location.