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The Qingjiang River is the second largest tributary of the Yangtze River in Hubei Province and is also a typical karst catchment. Eighty-two important groundwater samples were collected during the high and low water periods of 2019. The results show the following. (1) The major hydrochemical types are Ca + Mg-HCO3 and Ca-HCO3, indicating that carbonate weathering is the main factor controlling the groundwater chemistry. (2) The results of inverse hydrochemical modeling reveal two kinds of groundwater–carbonate rock interactions. One is the codissolution of calcite and dolomite, and the other is dedolomitization, which is widespread in the dolomite aquifers. Furthermore, gypsum has a tendency to dissolve in each aquifer, and the common ion effect of Ca2+ caused by gypsum dissolution promotes dedolomitization. The modeling results suggest that major elements can be effectively used to trace the material source of the groundwater. (3) The chemical weathering of carbonate rock is mainly affected by carbonic acid, sulfuric acid, and nitric acid. After accounting for the impacts of evaporites and atmospheric input, the calculations show that the contribution of carbonic acid involved in carbonate weathering is 70.9% in the high water period and 70.0% in the low water period. Statistical analysis of karst spring discharge and the contributions of the acids involved in carbonate weathering reveals that the two are positively related. This result reflects the behaviors of sulfuric acid and nitric acid under the hydrodynamic conditions in different seasons. Therefore, carbonate weathering should be carefully evaluated in karst areas with abundant groundwater, and the role of groundwater in carbonate weathering is worthy of further study. [ABSTRACT FROM AUTHOR]

An efficient reservoir operation technique plays a very important role in improving the water resources and energy efficiency of reservoirs. In order to effectively avoid or alleviate the "curse of dimensionality" of Multi-dimensional Dynamic Programming (MDP) in the application of cascade reservoirs operation optimization (CROO) and keep a global convergence at the same time, two dimension reduction methods are proposed in this paper. One is a hybrid algorithm of MDP and a Progressive Optimality Algorithm (POA), named MDP-POA, which combines the global convergence of MDP and the strong local search ability of POA. MDP-POA first takes the global optimal trajectory of MDP in a low discrete degree as the initial trajectory of the POA, and then implements further optimization to the obtained initial trajectory by the POA with a high discrete degree, so as to avoid the "curse of dimensionality" of MDP in high discrete degree and the dependency of the POA for the initial trajectory. The other is an improved MDP (IMDP), which first constructs a corridor by the optimal trajectory of MDP in a lower discrete degree, and then implements further optimization in the corridor by MDP with a relatively high discrete degree, so as to avoid a large number of unnecessary calculations, and shorten the run-time effectively. In a case study, the results of MDP-POA, IMDP, and MDP are compared and analyzed from the aspects of power generation and run-time. The analysis indicates that the proposed MDP-POA and IMDP both have a good application effect and are worthy of further promotion. [ABSTRACT FROM AUTHOR]

Hydrological data on the Upper Qingjiang River from 1960 to 2012 document trends of runoff caused by hydropower engineering projects and long-term changes in rainfall. Annual runoff correlates strongly with annual precipitation, but is significantly reduced after reservoir construction compared to earlier values. Comparisons of intense, pre- and post-construction rainfall events suggest that the Chebahe and Dalongtan reservoir projects respectively clips the magnitude of the flood peaks and delays runoff delivery. [ABSTRACT FROM AUTHOR]

In order to assess the health risks of heavy metals in surface water of Qingjiang River, surface water samples were taken at designed cross-sections of the river and analyzed for Cr, Cu, Zn, Pb, Cd, As, and Mn. Health risks from these heavy metals for adults and children in wet and dry seasons were compared by water environmental health risk assessment model of the USEPA. It found that the main excessive element is Mn, concentrating in the Danshui, Yantouxi, and Pingluoxi, the slightly excessive element is As, the concentration of Mn was above national standard, and it mainly distributed in Danshui, Yantouxi, and Pingluoxi, As was slightiy over the standard, and it concentrated in Wujiahe, The content of heavy metals during wet season were all higher than those during dry season. Cr, Cu, Zn, and Cd are mainly originated from the nature, Pb and As are separately mainly originated from traffic and agriculture, Mn originated from mining mainly in the downstream, while it has natural source from upper to middle. The health risks of heavy metals in surface water to adults and children in wet season are higher than those in dry season. The main health risk area was the midstream. As was the highest health risk element and children were the most preventive group. Specially, people in towns who drink the water from midstream should pay more attention.