Abstract
Previous studies mostly focus on an individual delta, or deltas at a global scale, to explore dam effects on deltaic hydrological alteration and morphological evolution, while comparative studies on selected similar deltas remain scarce. In this study, we compare the alteration of river discharge and sediment load, as well as the associated deltaic area and shoreline, of two deltas, namely, the Volta River Delta in Ghana and the Yellow River Delta in China, which are subject to similar forcings and mainstem dam influences. The results show that the sediment loads of the Volta River Delta and Yellow River Delta have decreased abruptly and gradually, respectively, to ~10% of the pre-dam level, presumably due to differences in reservoir capacity and upstream dam location. Sediment decline has led to a decrease of the fluvial dominance ratio, which has also been affected by the river mouth location and shoreline orientation. As a consequence, the area of the Volta River Delta has shifted to a new quasi-equilibrium, whereas the Yellow River Delta has kept prograding. This comparative study provides references for understanding the future evolution of similar deltas around the world.
Highlights
Deltas are of critical socioeconomic and ecological importance, and are inhabited by about half a billion of the world’s population [1]
Given the continuously increasing coastal erosion and degradation of deltaic ecosystems in this rapidly changing environment of the Anthropocene [3,9,10,11,12], understanding effects of dam regulation that lead to the hydrological alteration and morphological evolution of the world’s deltas is an imperative task
The results showed that the average annual river discharge and sediment load in the Volta River Delta were significantly different in phase I than in phase II, while those in phase II and III were similar (Figure 4a, p < 0.05), which confirms that the Akosombo Dam played a more important role in the hydrological alteration of the Volta River than the Kpong Dam [19,69].9 of
Summary
Deltas are of critical socioeconomic and ecological importance, and are inhabited by about half a billion of the world’s population [1]. Located at the interface between land and sea, deltas are significantly affected by climate change and intensive anthropogenic activities, such as sea-level increases, storm surges and upstream dam regulation [1,2,3]. It is well-recognized that dam regulation causes hydrological alteration [4,5,6] and morphological evolution of the world’s deltas [7,8]. Besset et al (2019) [10] analyzed the shoreline mobility and area change of 54 global deltas over 30 years, to quantify their vulnerability under changing sediment loads, showing that a decrease of sediment load due to dam regulation could further reduce the resilience of river deltas under sea-level rise and climate change
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