Experimental Study On Fountain Reoxygenation Of Secondary River In Mountainous City Stagnant Zone

As the particular geographical conditions of rivers in mountainous city, stagnant regions existed before the channel and artificial dam lead to a lower velocity and a longer retention time. As a result, there are consumption of dissolved oxygen, accumulation of pollutants and the eutrophication happened in the river. Most of the traditional artificial aeration facilities are equipped in the middle of the river, for it will affect the draining flood and traffic if applied in the channel. The study was concentrated on reoxygenation in the stagnant regions of channel, an integrated fountain combined of reoxygenation and landscape was given based on the model of two-dimensional flow in stagnant regions simulated by CFD software, which made a demonstrative study about reoxygenation of fountain and provided the availability of application in the future. The main results are as following:Water quality in representative stagnant regions of Fu Niu Creek: In space, the pollution index such as CODMn and NH4+-N showed a decrease and then an increase, for TN and TP, there was no obvious changes, which was an evidence for self – purification in Fu Niu Creek upstream and midstream. In the middle and lower reaches of Fu Niu Creek, water quality was deteriorated and more stagnant regions existed which was affected by increased curves and hydraulic buildings. In time, water quality in dry season was worse than rain season and common season, but not significantly. It had greater effect on water quality in channel upstream than in the middle and lower reaches of Fu Niu Creek. It showed a significant positive correlation between rainfall and CODMn and a negative correlation with the other pollution index.Variation of DO in representative stagnant regions of Fu Niu Creek: In space, the DO concentration showed a decrease along the channel, and it was significantly higher in the surface water then the bottom. In time, the DO concentration in the dry season was higher than that in the rain season and common season upstream. In the middle and lower reaches of Fu Niu Creek, little difference could be seen in the different seasons which was due to more stagnant regions and increased depth. As a result, the main difference of DO concentration was between surface and bottom of the water.Simulator investigation of hydrodynamics of representative stagnant regions of Fu Niu Creek: Natural stagnant regions were formed in the curves of the Creek, in which the current velocity was low. The low velocity zone existed in the curves of natural channel facing the incoming flow. The whirlpool was not obvious in the whole flow distribution, which the course was the same with the Fu Niu Creek. Retention time was proper. An obvious artificial stagnant region was formed under the Railway Bridge downstream the river, which was affected by the two artificial dam. The flow direction was not very clear but the retention time was significantly prolonged due to low-velocity whirlpool resulted from the effect of piers in the middle of stagnate region.Simulator investigation of optimization for hydrodynamics in representative stagnant regions of Fu Niu Creek: Both of the two types of installation could destroy the low-velocity whirlpool resulted from the effect of artificial works. However, for the installation of whirlpool opposite to the incoming flow, new stagnant region and whirlpool would be formed and made it difficult to discharge in the stagnant regions no matter how the fountain velocity was. For the installation of whirlpool facing the incoming flow, low-velocity whirlpool was destroyed under a high velocity, which accelerated the flow and benefit the discharge of water in stagnant region.Single-factor test of fountain reoxygenation technology: Vertical fountain nozzle has a better mixing effect on the water at close range but a weak performance for far area. On the contrary, horizontal fountain nozzle has a better mixing effect on far water but a weak performance for close area. The optimal ratio of flow and water body capacity is 1:100 hourly which leads to a better reoxygenation performance and a lower energy consumption.Demonstration Research on fountain reoxygenation technology of Railway Bridge: Fountain has a significant effect on reoxygenation, the difference of DO concentration between the surface and bottom decreased, which is an evidence of uniform mixing of surface water and bottom water as the great influence of fountain agitation. DO concentration could basically meet the surface water quality standard of class III. With the operation of fountain, concentration of algae, NH4+-N and CODMn decreased relatively which could meet the surface water quality standard of class IV, the removal of TP and TN were not obvious which was classified as class V.According to the research of fountain reoxygenation on stagnant regions of Railway Bridge, a series of fountain reoxygenation technology were given which applies to rivers in mountainous city. It provides theory evidence to fountain reoxygenation technology of stagnant regions by integrated investigation of artificial reoxygenation performance of stagnant regions in the river and improvement of water quality.