A mathematical model of river hydrodynamics with cascade reservoirs and pollutant has been established and verified by using analytic solutions of partial differential equation for transportation and diffusion. Ten dispatch schedules of single or multi- reservoirs have been set up and executed according to that a pollution accident occurred upstream or downstream to a reservoir. It shows that which dispatch schedule should be selected was decided by sensitive factors of a target river segment downstream. A dispatch model of large flux with short time duration by utilizing a reservoir nearest to the segment was more appropriate for which was more sensitive to concentration than other factors, while a model of appropriate flux discharge with long time duration was more suitable for those being more sensitive to extra concentration retention of pollutants. Compared with a single reservoir dispatch, multi-reservoirs have larger effective storage capacity to reduce the loss by a sudden water pollution accident better by supplement water step by step from upstream to downstream.
Tidal prism is a rather sensitive factor of the estuarine ecological environment. The historical evolution of the Lingdingyang water area and its shoreline were analyzed. By using remote sensing data, the evolution of the water area of the bay was also calculated in the past 30 years. Due to reclamation, the water area was greatly decreased during that period, and the most serious decrease occurred between 1988 and 1995. Through establishing the two-dimensional mathematical model of the Pearl River estuary, the tidal prism of the Lingdingyang bay has been calculated and analyzed. The hybrid finite analytic method of fully implicit scheme was adopted in the mathematical model's dispersion and calculation. The results were verified though the method of combining the field hydrographic data and empirical formula calculation. The results showed that the main tidal entrance of the bay is the Lingdingyang entrance, which accounts for about 87.7% of the total tidal prism, while Hong Kong's Anshidun waterway accounts for only 12.3% or so. Combining the numerical simulations and the historical evolution analysis of the water area and tidal prism, and compared with that in 1978, it showed that the tidal prism of the bay was greatly decreased, and the reduced area was mainly the inner Lingdingyang bay, which accounted for 88.4% of the whole shrunken areas. As weakening trends of the tidal powers of the medium and neap tides are obvious, the tidal prism is decreased during the medium and neap is larger than that during the spring.
Abstract:A three-dimensional eddy model considering buoyancy was established to simulate vertical buoyant flow from a square orifice in static ambient. The hybrid finite analytic method with stagged grid was used to solve this model. Experiments were made to confirm the efficiency and validity of the model, and concentration on the axis under different experimental conditions was obtained. Conclusions showed that axial concentration from a square orifice coincided well with those from a circular one after a little distance from the jet mouth. The shapes of temperature distribution on different height cross-sections tallied well with those from a circular orifice. The existence of self-similar area of temperature was confirmed also.
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