Influence of the Hanjiang River's Inlet Sediment Decrease on Modern Sedimentation in the Underwater Delta  
[PERSON]  
1 Haikou Marine Geological Survey Center, China Geological Survey, Haikou 570100, China; [EMAIL_ADDRESS] (Y:W.); [EMAIL_ADDRESS] (X.W. ); k\(\_\)learn6126.com (C.H. ); [EMAIL_ADDRESS] (Y.Z.) [PERSON]  
that would otherwise enter the sea. Thus, the sediment supplies of deltas have decreased, and the deposition rates have been significantly affected. The changes in underwater delta deposition are mainly reflected in the transformation of underwater delta erosion and deposition, changes in the deposition rate, and changes in the sediment particle size. The key factor affecting the erosion crises of large river deltas is the sharp reduction in the sediment flux into the sea [2; 10]. In previous studies, it was found that the significant reduction in the sediment flux from rivers into the sea had an important impact on the evolution of the underwater delta topography, and this impact reduced the deposition rate of the underwater deltas or changed the delta from a depositional state to an erosional/alluvial deposition equilibrium state. [PERSON] et al. (2019) calculated the deposition rates of six columnar samples (collected in 2014-2015) from the Yangtze underwater delta based on \({}^{210}\)Pb dating and found that the Yangtze underwater delta experienced a transition from rapid deposition to slow deposition [11]. In recent years, the changes in the sediments delivered by the Hanjiang River into the sea and the sedimentation pattern of the Hanjiang underwater delta have gradually attracted the attention of scholars. [PERSON] et al. (2017) analyzed the hydrological data of Chao'an Station from 1955 to 2012 and concluded that since 2000, the construction of many hydropower stations and the increase in land vegetation coverage have led to a significant decrease in sediment discharge from the Hanjiang River to the sea. Moreover, the main reason for the reduction in sand flux was investigated [12]. [PERSON] (2019) used the MK test to analyze water and sediment data from 1955 to 2016, and the results showed that the sediment load changed abruptly in 1998 [13]. [PERSON] (2016), based on the analysis of the various characteristics of the sediment load at Chao'an Station from 1951 to 2011, concluded that the sudden change point was in 2001, and the main reason for the sudden change was that after the 1990s, the construction of multiple upstream cascade power stations, reservoirs, and junctions intercepted some sediment [14]. From the 1950s to the 1980s, several small hydropower stations were built in the upper reaches of the Hanjiang River, and since the 1990s, large hydropower stations have been built. The Qingxi Hydropower Station, completed in 1997, has a total installed capacity of 144 MW and a total storage capacity of 75 million m\({}^{3}\). The Mianbuatan Hydropower Station, constructed from 1998 to 2003, has a total installed capacity of 600 MW and a total storage capacity of 2.035 billion m\({}^{3}\). [PERSON] (2022) studied the changes in the sediment flux entering the sea from the Hanjiang River and its impact on the adjacent sea areas over the past 60 years. The results of the study showed that there was no significant change in the runoff of the Hanjiang River into the sea, whereas the sediment flux into the sea showed a significant decreasing trend [15]. The large-scale hydropower stations (Qingxi and Mianhuatan hydropower stations) in the Hanjiang River Basin are the main factors causing the significant reduction in the sediment flux into the sea. The years in which notable changes occurred identified by the above studies are not very different, and the difference may be caused by the inconsistencies in the starting and ending years of the hydrological data.