Font Size: a A A

Distributed Non-point Sources Pollution Modeling And Its Application In Xiangxi Watershed

Posted on:2009-08-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:C ZhangFull Text:PDF
GTID:1101360272991725Subject:Hydraulic engineering
Abstract/Summary:PDF Full Text Request
China is now faced with a nation wide water quality crisis, as eutrophication keeps invading and suffocating an increasing number of lakes and reservoirs. The Three Gorges reservoir, for example, has seen eutrophication occurrences in tributaries of the upper Yangtze due to point and non-point source pollution. With point source pollution being gradually put under control, the non-point source (NPS) pollution (nitrogen and phosphorus) stands as the major issue that needs to be addressed to help prevent or combat possible large scale eutrophication in the reservoir.A distributed NPS pollution model is developed to quantify sediment erosion, pollutants transportation, as well as to study changing law of pollutant loads. Based on the main frame of the distributed hydrology model, this model incorporates a sub-model for calculating runoff in the slope under various land cover, with a second sub-model for flow routing in river networks. Soil erosion/sediment transportation and pollutants transportation sub-models are also added to the above mentioned 2 sub-models, composing the integral distributed NPS pollution model. New advance in construction of the overall frame has been achieved.Systematic research is made on the supportive techniques for developing NPS pollution model. Starting from the multiple tree theory, a new algorithm for automatic topology among the sub-basins is put forward; parallel routing based on the automatic hierarchical organization of river networks, namely the Plus One ranking, is achieved. Additionally, the automatic joint usage of diffusive/dynamic wave method for rooting is implemented.An integrated application DWHEMT is developed with Visual C++, supported by GIS, database, multi-thread parallel calculation techniques. The application has basic and expanded functions of common model systems, including pre-processing of raw data, model calculation and post-processing of results. With much attention being paid to the organization and cooperation among the modules of function, the adaptability and expansibility of the application are enhanced further. The application has enhanced automatic data extraction and preparation capabilities. It supports both database and file based data exchange modes, and is also compatible with many popular database formats such as Access, Oracle etc. The multi-thread parallel calculation mechanism is adopted by slope unit calculation, which can exert the capacity of a multi-core PC to its full content.The Xiangxi River watershed is chosen as the case area. After the collection and preprocessing of DEM, image materials of remote sensing of land use and land cover, categorized distribution map of soil, hydrology data, meteorological data etc, a simulation of dynamic hydrological process is carried out and an example in Xingshan Hydrologic Station is served. On the basis of hydrology simulation, the variation processes and changing laws of sediment and total nitrogen and phosphorus within the Xiangxi River Watershed is studied. The results show that the soil erosion in Xiangxi River watershed has the positive correlated to the rainfall intensity in short-term; there are obvious positive correlation between monthly average total nitrogen concentration and rainfall, while the monthly average total phosphorous concentration is more deeply affected by human; the enhanced deposition and dilution effect, caused by the impoundment of Three-gorge Reservoir, are temporary. As the accumulation of pollution goes on in the gulf, the water quality there would probably continue deteriorating.
Keywords/Search Tags:NPS, Distributed simulation, Soil erosion, Pollutant loads
PDF Full Text Request
Related items