The Yangtze River Estuary (YRE) is the largest estuary in China, with three-order bifurcations and four outlets into the sea. In recent years, issues of saltwater intrusions have received increased attention due to the increased levels and frequencies of the intrusions. The saltwater intrusions into the YRE resulting from river discharges were investigated in this study based on river discharge levels at the Datong station. A hydrodynamic and salinity transport model (MIKE21) was used to quantify the influences of the river discharges on the saltwater intrusions in the YRE. The model was effectively validated through observational data of the tidal and salinity levels. The 25%, 50% and 70% frequencies of the river discharges during the dry seasons were determined to be 18,112, 16,331 and 14,832 m³/s, respectively. A multi-year averaged river discharge of 27,856 m³/s was used to simulate the salinity level changes resulting from the different river discharges. The results revealed the following: (1) the salinity of the South Branch (SB) was distributed as “high–low–high”; and the changes in the salinity levels were greatly affected by the river discharges. A strong correlation was found between the salinity and flow in the North Branch (NB) and SB of between 0.917 and 1; (2) the changes in the river discharges had major impacts on the changes in the salinity levels in the SB. When the runoff was 27,856 m³/s, the salinity excessive area rate (the ratio between salinity excessive area (>0.45‰) and the SB area) less than 10%. However, when the river discharges were reduced to 16,331 m³/s, the salinity excessive area rate is more than 50%; (3) As the river discharges decreased, the amplification line (0.2‰) also rapidly decreased, and the amplification lines (0.45‰, 2‰) increased. At points far from the river’s entrance, the effects of the runoff were observed to be weakened, such as the amplification lines gradually becoming reduced; (4) the changes in the river discharges were observed to have significant impacts on the freshwater reservoir water withdrawal. When the river discharges were maintained at 27,856 m³/s, the salinity of the Baogang, Chenhang, and Qingcaosha Reservoirs remained below 0.45‰. The salinity levels of the four reservoir locations examined in this study were found to exceed the Chinese drinking water standard (0.45‰) for more than 23 days in the 14,832 m³/s river discharge scenario, which negatively affected the drinking water of the population living near the YRE.

More attention has been paid to saltwater-intrusion-related problems in recent years. In this research study, a saltwater intrusion function in the Yangtze River Estuary (YRE) was constructed based on the theory of the interactions between energy accumulation and impedance. A MIKE21 model was used to simulate the hydrodynamics of the YRE. Then, through the analysis of the relationships between the river discharge conditions, tidal ranges, and saltwater intrusion, it was determined that, under certain river discharge conditions, the tidal ranges and salinity levels at the stations in the southern branch (SB) of the YRE conformed to S-shaped curve characteristics. Also, the tidal ranges and salinity excessive area rate (SEAR) displayed similar characteristics. Furthermore, the river discharge conditions were also found to match the S-curve characteristics between the two aforementioned relationship features. Therefore, the saltwater intrusion function of the YRE was constructed based on the previously mentioned development rules. Also, the applied quantification methods were elaborated, and the values of the parameters were determined. As a result, the critical river discharge (more than 10,000 m³/s) was obtained, which could withstand large-scale saltwater intrusions. When the river discharge was greater than 30,000 m³/s, the area was considered to be basically without salt water intrusions, and the estuarine ecology was in an optimal state. The saltwater intrusion losses from 2005 to 2015 are also calculated. These findings have important reference value for water dispatching of the YRE in the dry season.

Evaluating the hydrological application of reanalysis datasets is of practical importance for the design of water resources management and flood controlling facilities in regions with sparse meteorological data. This paper compared a new reanalysis dataset named CMADS with gauge observations and investigated the performance of the hydrological application of CMADS on daily streamflow, evapotranspiration, and soil moisture content simulations. The results show that: CMADS can represent meteorological elements including precipitation, temperature, relative humidity, and wind speed reasonably for both daily and monthly temporal scales while underestimates precipitation compared with gauge observations slightly (<15%). The hydrological model using CMADS dataset as meteorological inputs can capture the daily streamflow chracteristics well overall (with a NS value of 0.56 during calibration period and 0.61 during validation period) but underestimates streamflow obviously (with a BIAS of $-42.42$ % during calibration period and a BIAS of $-33.29$ % during validation period). The underestimation of streamflow simulated with CMADS dataset is more seriously in dry seasons ( $-48.40$ %) than that in wet seasons ( $-39.41$ %) for calibration period. The model driven by CMADS estimates evapotranspiration and soil moisture content well compared with the model driven by gauge observations.

Due to the lack of comprehensive and continuous tracking, the international water resources and its development and utilization data is difficult to meet the actual needs of the development of water resources development and management to provide accurate positioning of the status quo. This paper analyzes the achievements of hydropower resources development and water storage facilities in major countries, especially in developed countries, and analyzes the degree of hydropower development and utilization in China from an international perspective. Research shows that China is rich in hydropower resources, ranking first in the world, hydropower power generation is also ranked the forefront of the world. But the Hydropower economic development degree in 2013 is 52%,lower than the major developed countries which is more than 70% level. Chinas hydropower resources development and utilization is lower than the he average level of the countries which the human development index between 0.7 to 0.8. Some gross indexes of hydropower resouerces in China which ranked in the forefront of the world, but compared with developed countries, the gap about the level of development and utilization and the level of socio-economic development still exists.