•Shoreline change rates vary spatiotemporally.•Accretion rate is continuing but decreasing.•A close relationship exists between shoreline change and sediment discharge.•Contrasting temporal patterns ...of shoreline change exist between the eastern and northern segments.•Different shoreline segments respond differently to decreasing sediment supply.
Chongming Dongtan, located in the center of the Yangtze estuary, is a Ramsar Wetland of International Importance and National Nature Reserve. The dramatic decrease in river sediment load has attracted considerable scientific interest to this area, but few studies have paid attention to the shoreline dynamics. This study uses Landsat images spanning from 1987 to 2010 and an orthogonal transect method, which was previously developed by the authors, to model the spatial and temporal characteristics of shoreline change and explore its relationship to reduced river sediment load by use of regression analysis on three different spatial scales. Results show a general decrease in the average rates of shoreline change throughout the entire study period. The maximum average shoreline change rate of +115.5m/year occurred in the 1987–1990 interval and the minimum rate of +20.4m/year occurred from 2006 to 2008. Based on average rates of shoreline change, the coast of Dongtan was divided into three segments: the erosion segment, eastern accretion segment, and northern accretion segment. The temporal pattern of the northern accretion segment is almost completely opposite to that of the eastern accretion segment. The strongest-correlation transects are located on the northern side of the eastern tip of Dongtan and the next strongest transects are located on the south side. Other transects have a very low correlation. Transect 19 near the easternmost tip of Dongtan has a near zero correlation (r2=0.0045) but has the fastest accretion rate, and in general an increase in the shoreline change rate. The average rate of shoreline change and the net accretion area in Dongtan as a whole are significantly associated with sediment discharge at Datong Station (r2=0.69 and 0.75, respectively). This implies that shoreline accretion in Dongtan will probably slow down gradually, if the river sediment load continues to decrease in the future. The shoreline change rates achieved using our approach are consistent with previous studies, but the relationship with the river sediment load is different from results in a previous study on intertidal wetland based on bathymetric maps. The results and methods may be helpful in coastal management and understanding the evolution of the entire delta from the perspective of shoreline change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
Lake flow is one of the common hydrological phenomena in nature. The water exchange of lakes and the circulation of natural water resources are realized by the water movement caused by ...various factors. Lake current is of great significance in the hydrological and ecological environment and it is one of the focuses of scholars’ research. This paper takes Poyang Lake as the research area, and uses three texture enhancement methods of Laws, Gabor, and LBP operators to enhance the texture features of images based on multi-source remote sensing data, and uses the Hough transform to extract the flow direction of the Poyang Lake area. The results show that the three texture enhancement methods combined with Hough transform can extract the flow direction, but the Gabor filter has the best flow direction effect and the highest extraction accuracy. Gabor filter is the most adaptable for texture enhancement of images with different resolutions.
Abstract
The hydrological situation of Poyang Lake has undergone changes due to the influence of climate change and human activities. Its typical throughput and seasonal variation characteristics ...have attracted much attention. Research on the long-term hydrological variation of Poyang Lake needs to be enriched. Using remote sensing images from 1986 to 2020 and combining them with the Normalized Difference Vegetation Index (NDVI), this study extracts the water area of Poyang Lake and analyzes its variation characteristics. The results show that the water area of Poyang Lake has a consistent periodic variation with meteorological factors. Both the water area and meteorological factors have a main period of 18 m (months). Water area change points occurred in 2003, 2010, and 2016. In different research periods, there is a significant correlation between the water area and meteorological factor changes. Furthermore, the correlation between water vapor pressure and precipitation with the water area change is the strongest.
Hyperspectral image data provides new ideas and methods for the fine classification of wetland. Research on wetland spectral characteristics lays the foundation for wetland classification and ...improves classification accuracy. Based on "Zhuhai-1" hyperspectral image data, combined with the Pure Pixel Index (PPI), this paper extracted the average spectral curves of 11 typical ground objects in Poyang Lake wetland. Two mathematical transformation methods, namely, the continuum removal and the first derivative, were used to analyze the spectral characteristics of the ground objects before and after transformation, in combination with spectral characteristic parameters. The method of combining the mean distance of ground objects with the range of data error was used to select characteristic wavelengths before and after spectral transformation. Finally, the Mahalanobis distance method was used to verify the recognition effect. The results demonstrate that: (1) Spectral transformation can effectively amplify the differences between ground objects. The continuum removal led to an increase in the characteristic bands of four types of vegetation and the emergence of characteristic bands of four types of other ground objects. The first derivative method extended the characteristic bands of four vegetation from red-edge to near-infrared. (2) The method of combining the mean distance and the data error range can effectively screened out the spectral characteristic bands of typical ground objects in Poyang Lake wetland, resulting in hyperspectral dimensionality reduction. (3) The Mahalanobis distance method validates the recognition effect of the characteristic bands. In the screened characteristic bands, the Mahalanobis distance between different ground objects is larger than that between the same ground object, except between shoaly land and road. This study offers valuable insights into spectral recognition and classification of freshwater lake wetlands, and also demonstrates the potential of "Zhuhai-1" hyperspectral image data in wetland research.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Muddy coasts are widely distributed around the world, especially adjacent to large estuaries. These regions are highly susceptible to coastal erosion with its dense population, developed economy and ...low-lying land. Due to immense natural and human pressures, there is an urgent need for a more comprehensive understanding of coastal erosion risk in such areas. Various models have been established, but most of them focused on sandy coasts and physical factors that influence coastal erosion while socioeconomic factors were usually ignored. Accordingly, this study presents a GIS-based risk assessment of coastal erosion for muddy coasts by combining both the physical and socioeconomic aspects of erosion. The method is used to assess coastal erosion risk in the Yangtze Delta. Based on the DPSIR (Driving forces, Pressure, State, Impact, and Response) framework, 10 vulnerability indicators and 3 impact indicators corresponding to physical and socioeconomic aspects, respectively, are identified to constitute an indicator system. These indicators are weighted using the Analytic Hierarchy Process (AHP) technique, and then are combined into a Vulnerability Index and a Hazard Index, which then are merged into a Risk Index. Then, these indexes are normalized to 0%–100%. Finally, the normalized values are ranked into 5 levels: very low (<20%), low (20% ≤ Is<40%), moderate (40% ≤ Is<60%), high (60% ≤ Is<80%) or very high (≥80%). This study is the first to comprehensively assess coastal erosion risk in the Yangtze Delta by integrating physical and socioeconomic factors at a detailed spatial scale. The results provide a clear picture of the current coastal erosion risk in the study area, despite of some limitations. The study also reveals key gaps in data gathering and coastal management practices that need to be addressed in order to develop more effective long-term coastal management.
•The study presents a GIS-based erosion risk assessment method for muddy coasts.•Physical and socioeconomic influences are integrated into the methodology.•Results provide a clear understanding of coastal erosion risk in the study area.•Key gaps in data gathering and coastal management practices are explained.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Due to river runoff flow and tidal flow, coastal waters are often characteristic of high concentration of suspended sediment. In this paper, by using MODIS images of 250 m resolution and hydrodynamic ...model and in site observation, the author analyze the distribution characteristics of suspended sediment and hydrodynamics mechanism. Relatively high Suspended sediment concentration distribute in the alongshore and south and north of Nanhui neareshore. During the flood tide period, distribution range of high suspended sediment concentration is northward moved. During ebb tide period, the zone of turbidity maximum is shown near the south of Nanhui nearshore. Based on terrain data analyses in 1999, 2003 and 2008, altitude value of underwater terrain in most area of Nanhui nearshore is increase. Most area of Nanhui nearshore is depositing. Momaosha mudflat in the north of Nanhui nearshore is extending southeastward. South of the Nanhui subaqueous beach is extending slowly southeastward and southward.
Coastal erosion is an issue of widespread concern and the Yangtze Delta is one of the most important economic regions in China, has been showing a trend towards such erosion. Possible influences are ...global warming in the form of sea level rise and the increasing human activities in the catchment and its estuary. Most Current studies on coastal erosion in this region have focused on the causes and types of erosion. This paper presents a Decision Support Framework (DSF) to estimate the likelihood and possible degree of coastal erosion in the coastal zone of the Yangtze Delta. The framework also enables consideration of the potential management problems and economic development challenges. It has four major components: an integrated database, GIS-based risk assessment models, scenario generator and a visualization toolkit. Specific focus is on the development of a GIS-based risk assessment model for the muddy coasts of the Yangtze Delta. An Analytic Hierarchy Process (AHP) method was used to weight the variables of the model, such as coastal elevation, coastal slope, et al. The assessment results show the validity of the approach. The DSF will make relevant specialized data and information more accessible to managers, and has an extensive capability to facilitate communication and subsequent synergetic work between man and computers.
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