Experimental Study On The Relationship Between River Structure And Restore The Water Quality At Plain River Network Area

With the rapid development of urbanization, the natural structure of rivers has beenchanged, and the pollution has also caused self-purification capacity of river descended.Therefore, the ecological restoration of rivers has already become task of top priority. It isreally important to supervise the construction of city ecological river network andrehabilitating ecological structure and function of river by research on river patterns,especially the relationship between river structure and water body self-purification,environmental capacity & nutrition cycle.This article analyzes factors like speed of flow, the width/depth ratios, the bendingcoefficient and active photosynthesis radiation to the changes of river self-purificationcapacity, and we obtained following important conclusion:The speed of flow has an important effect on the contents of organic matters andphosphorus in water and bottom sludge. When the speed of flow blows 0.5 m/h,contaminations in the river were mainly in the form of deposit. When the speed of flowexceeds 1.5 m/h, the hydrodynamics condition was propitious to the degradation of organicmatters in the river, but it promoted the release of phosphorus of sediment from the bottomof river and caused the rise of nutrient. The course of phosphorus cycling was controlledby alkaline phosphatase and hydrodynamic diffusion effect. Alkaline phosphatase playedimportant role in phosphorus cycling in current speed river. When the speed of flow below0.5 m/h, the phosphorus was cycling in-situ; when the speed of flow exceeds 2.5 m/h, thecontent of phosphorus significantly increased.Under the same hydrodynamic conditions, the width/depth ratios of river broughtobvious infection to the degradation of organic matters in water body, and phosphorus cycle and exchange at the interface of water body and bottom sludge. It was veryconducive to the degradation of organic matters when the width/depth ratios of river at 3.0.When the width/depth ratios of river below 2.0 or exceeds 3.0, the content of phosphorusin water body were high. So, we can achieved the maximal degradation of organic mattersand minimum release of phosphorus by design and construct the width/depth ratios of riverscientifically.Augmented the bending coefficient of rivers could also advantageous to thedecontamination of contaminations in the water body and bottom sludge. But the bendingcoefficient too big could increase the contacted area between water and bottom sludge,which would affect the water quality by the pollutants in the bottom sludge diffuse to thewater body. The experiment result indicated that it would most beneficial to the organicmatters degradation and phosphorus fixation in water body when the bending coefficient ofriver was 1.6.Another effect of urbanized development to the river was the big building intenselyreduced the active photosynthesis radiation of the river ecosystem. The change ofillumination intensity would affect the structure and productivity of critter community inwater body, as well as pollutant conversion process. The experiment discovered that, thecontent of organic matters in water body which under straight sunshine was obviouslylower above 12% than in the water body away from direct sunlight, so was the phosphorus.Therefore, this should cause highly recognition in the city planning and construction of cityecological river network.We should pay attention to the influence of supply water quality to the city slow flowriver in the aspect of management and control of River pollution. Sludge dredging in urbanriver also wants to adapt to place and time. The bottom sludge is the sources and sinks ofthe phosphorus and organic matters in river. The experiment discovered that, when theriver bottom sludge temperature exceeds 15℃, the content of organic matters in riverwater were the highest, which is also the river most prone to be black and smelly, whichcan be in line with the urban replacement of water projects, increase water quantity and input water-quality management; and in order to gain better effect, sludge dredging shouldperform during winter when bottom sludge temperature below 5℃.