Search

Ecological water was stolen by industrial and domestic water consumption in the Weihe River, which led to a disquieting decline in riverine ecologic functioning. Based on river regionalization and typical years of hydrologic frequency analysis, a variable eco-environmental water demand (EEWD) calculation method was put forward with a monthly runoff process against its traditional fixed volume. The main stream of the Weihe River in Shaanxi Province was regionalized into seven zones in accordance with the location of gauging stations, boundary of administrative districts, and desirable target of water qualities by water function regionalization; typical years with hydrologic frequencies of 25, 50, 75, and 95% were introduced to take annual variation into account, so as to meet the hydrologic characteristics of the river. In addition, the monthly process was suggested to reflect the seasonal change of EEWD. In this study, EEWD was divided into three parts: water demand for sediment transport, diluting and self-cleaning, and basic ecological water demand according to the major problems with the Weihe River. The results showed that EEWD had obvious annual and seasonal variation at time scale, while it tended to increase from upstream to downstream, with the maximum value being . The EEWD showed a strong relationship with runoff, sewage discharge, and sediment erosion and deposition status. The method used herein provided a credible scientific basis for estimating EEWD on the river with serious annual and seasonal hydrologic variation and with great changes along the river, which proposed a significant reference to rivers with similar situations to the Weihe. [ABSTRACT FROM AUTHOR]

The major obstacles to simulating flood flow in the Yellow River are its high sediment concentration, complex compound cross section, and rapid change in channel planform. This paper presents an improved one-dimensional numerical model that takes into account the effect of sediment concentration and bed change on mass and momentum conservation of flood flow in the Yellow River. The model is calibrated and then validated by simulating three individual flood events. Results show that an increase in sediment concentration leads to a reduction in flood wave celerity and peak discharge. The generalized likelihood uncertainty estimation (GLUE) method is used to evaluate the uncertainty of modeling results. A sensitivity index, analogous to the Nash-Sutcliffe efficiency factor, is adopted to quantify the sensitivity of calibration parameters. The modeling results are sensitive to the choice of Manning's roughness coefficient and the empirical recovery coefficient for suspended sediment transport at reaches of transitional channel planform. [ABSTRACT FROM AUTHOR]

This paper presents a two-dimensional morphological model for unsteady flow and both suspended-load and bed-load transport of multiple grain size to simulate transport of graded sediments downstream from the Three Gorges Reservoir. The model system includes a hydrodynamic module and a sediment module. The hydrodynamic module is based on the depth-averaged shallow water equations in orthogonal curvilinear coordinates. The sediment module describing nonuniform sediment transport is developed to include nonequilibrium transport processes, bed deformation, and bed material sorting. The model was calibrated using field observations through application to a 63-km-long alluvial river channel on the middle Yangtze River in China. A total of 16 size groups and a loose layer method of three sublayers were considered for the transport of the nonuniform bed materials in a long-term simulation. Predictions are compared with preliminary results of field observations and factors affecting the reliability of the simulated results are discussed. The results may be helpful to the development of more accurate simulation models in the future. [ABSTRACT FROM AUTHOR]

The formation and geomorphic evolution of the Jiuduansha Shoal are investigated over the past 50 years in this paper. The sedimentary processes, formation, and geomorphic evolution of the Jiuduansha Shoal in the Yangtze River Estuary, eastern China, are analyzed based on digitized sea maps from 1945 to 2001, satellite images from 1975 to 2001, and field survey data in the spring-neap tidal cycle in the dry and flood seasons in 2003. The suspended sediment concentration and hydrodynamics of the North Passage and South Passage during the dry and flood seasons in the spring-neap tidal cycle in 2003 were investigated, and relations between the North Passage and South Passage of the Jiuduansha Shoal are analyzed. Results show that seasonal and spring-neap tidal cycle variations in sediment and water discharge from the drainage basin correspond to erosion and deposition on the Jiuduansha Shoal. The results and data can provide useful information for the management of the Yangtze River Estuary and restoration of the estuarine tidal flat ecology. [ABSTRACT FROM AUTHOR]