Integrated Flood Risk Assessment System Based on the Set Pair Analysis and Variable Fuzzy Sets for Cascade Dams

Flood-caused dam break is an important dam safety problem. Dam flood risk assessment based on an appropriate assessing method is hence essential for reducing dam-break flood damages and losses. In this research, a comprehensive flood risk assessment system for cascade dams was developed by combining the set pair analysis (SPA) and variable fuzzy sets (VFS) theory (namely SPA-VFS for short), and expressing the flood risk as a product of hazard and vulnerability, which were quantified by selected indicators. In the case study of the Dadu river basin, reservoir capacity, dam height, dam age, gross domestic product (GDP) density, population density, and predicted damage were selected as the evaluation indicators, and the evaluation results derived the flood risk classes of each studied dam. The study indicates that the proposed SPA-VFS-based flood risk assessment model is simple and feasible, which enables its further application in flood risk analysis and evaluation, and its extension in the risk assessment of other natural disasters.

Influence of Hydrologic Alteration on Sediment, Dissolved Load and Nutrient Downstream Transfer Continuity in a River: Example Lower Brda River Cascade Dams (Poland)

Hydrologic alternation of river systems is an essential factor of human activity. Cascade-dammed waters are characterized by the disturbed outflow of material from the catchment. Changes in sediment, dissolved load and nutrient balance are among the base indicators of water resource monitoring. This research was based on the use of hydrological and water quality data (1984–2017) and the Indicators of Hydrologic Alteration (IHA) method to determine the influence of river regime changes on downstream transfer continuity of sediments and nutrients in the example of the Lower Brda river cascade dams (Poland). Two types of regimes were used: hydropeaking (1984–2000) and run–of–river (2001–2017). Using the IHA method and water quality data, a qualitative and quantitative relationship were demonstrated between changes of regime operation and sediment and nutrient balance. The use of sites above and below the cascade made it possible to determine sediment, dissolved load, and nutrient trapping and removing processes. Studies have shown that changes in operation regime influenced the supply chain and continuity of sediment and nutrient transport in cascade-dammed rivers. The conducted research showed that sustainable management of sediment and nutrient in the alternated catchment helps achieve good ecological status of the water.

Bacterial community structure upstream and downstream of cascade dams along the Lancang River in southwestern China

Extensive construction of dams by humans has caused alterations in flow regimes and concomitant alterations in river ecosystems. Even so, bacterioplankton diversity in large rivers influenced by cascade dams has been largely ignored. In this study, bacterial community diversity and profiles of seven cascade dams along the720 km of the Lancang River were studied using Illumina sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. Spatiotemporal variations of bacterial communities in sediment and water of the Gongguoqiao hydroelectric dam and factors affecting these variations were also examined. Microbial diversity and richness in surface water increased slightly from upstream toward downstream along the river. A significant positive correlation between spatial distance and dissimilarities in bacterial community structure was confirmed (Mantel test, r = 0.4826, p = 0.001). At the Gongguoqiao hydroelectric dam, temporal differences in water overwhelmed spatial variability in bacterial communities. Temperature, precipitation, and nutrient levels were major drivers of seasonal microbial changes. Most functional groups associated with carbon cycling in sediment samples decreased from winter to summer. Our findings improve our understanding of associations, compositions, and predicted functional profiles of microbial communities in a large riverine ecosystem influenced by multiple cascade dams.