The Spatio-Temporal Evolution of River Island Based on Landsat Satellite Imagery, Hydrodynamic Numerical Simulation and Observed Data

Abstract

A river island is a shaped sediment accumulation body with its top above the water’s surface in crooked or branching streams. In this paper, four river islands in Yangzhong City in the lower reaches of the Yangtze River were studied. The spatio-temporal evolution information of the islands was quantitatively extracted using the threshold value method, binarization model, and cluster analysis, based on Thematic Mapper (TM) and Enhanced Thematic Mapper+ (ETM+) images of the Landsat satellite series from 1985 to 2015. The variation mechanism and influencing factors were analyzed using an unstructured-grid, Finite-Volume Coastal Ocean Model (FVCOM) hydrodynamic numerical simulation, as well as the water-sediment data measured by hydrological stations. The annual average total area of these islands was 251,224.46 m2 during 1985–2015, and the total area first increased during 1985–2000 and decreased later during 2000–2015. Generally, the total area increased during these 30 years. Taipingzhou island had the largest area and the biggest changing rate, Xishadao island had the smallest area, and Zhongxinsha island had the smallest changing rate. The river islands’ area change was influenced by river runoff, sediment discharge, and precipitation, and sediment discharge proved to be the most significant natural factor in island evolution. River island evolution was also found to be affected by both runoff and oceanic tide. The difference in flow-field caused silting up in the Leigongdao Island and the head of Taipingzhou Island, and a serious reduction in the middle and tail of Taipingzhou Island. The method used in this paper has good applicability to river islands in other rivers around the world.

Design and Numerical Simulation of the Headworks in the Shizuishan Section of the Yellow River

“…Fish mouths impede the flow of streamflow to some extent [26][27][28][29], and there are significant differences in the hydrodynamic elements of the inner and outer rivers of the canal. This is due to the fact that the fish mouth causes the outer riverbed of the canal to sink, while the inner river rises.…”

Decadal evolution of fluvial islands and its controlling factors along the lower Yangtze River

“…Hudson et al (2019) reported that sedimentary deposition directly prompted the formation of fluvial islands. Shi et al (2018) showed that the key natural factor that influences island formation in the lower Yangtze River was sediment discharge. In addition, Gao C. et al (2013) stated that there were no significant relationships between changes in the island area and natural factors, such as annual runoff and precipitation, and speculated that the construction of many large reservoirs could be the primary factor of change.…”

Evolution characteristics of mid‐channel bars with a typical high/low bank structure in the Middle Yangtze River

“…Many scholars investigated the evolution processes of MCBs based on the data of river topography or remote sensing images (Lou et al, 2018; Smith & Winkley, 1996; Wang & Xu, 2018; Wang, Dai, et al, 2018; Wang, Li, & Cai, 2018). These studies at the early stage mainly focused on the investigation of causes and required conditions for the MCB formation (Ashworth et al, 2000; Słowik, 2018) or the numerical simulation methods for the adjustment processes of sandbars (Luchi et al, 2010; Nicholas et al, 2013; Repetto et al, 2002; Shi et al, 2018). Then increasing attention was progressively paid to study the evolution characteristics of MCBs downstream of a dam.…”