Study On Ecological Reconstruction Of Rain-source Urban Inland Rivers By Bypass Channel

Due to the straightening and hardening of the inland rivers.,and the hydrodynamics in the dry season are insufficient,in the rainy season are steeply rising in the rain-sourced city rivers,which makes ther ecosystems of the rain-sourced citie rivers seriously damaged,and the self-purification capacity is reduced.The traditional ecological restoration methods are difficult to implement.In order to solve this problem,this study proposes to preserve the original river channel,construct a natural bypass river system along the original river channel,and intercept the water into the bypass channel during the dry season;During the rainy season,floods are discharged into the original river.Under the premise of maintaining flood control capacity of rivers,we will ensure the hydrodynamics of rivers,provide suitable habitats for living organisms,and restore river ecosystem and self-purification capacity.In this study,four submerged plant assemblages(Combination 1:Vallisnerianatans(Lour.)Hara,Hydrilla verticillata,Potamogeton wrightii Morong;Combination 2:Vallisnerianatans(Lour.)Hara,Ceratophyllum demersum,Potamogeton wrightii Morong;Combination 3:Vallisnerianatans(Lour.)Hara,Hydrilla verticillata,Myriophyllum verticillatuml;Combination 4:Vallisnerianatans(Lour.)lHara,Ceratophyllum demersum,Myriophyllum verticillatumV)were screened from the flow rate and seasons,for rain-source urban inland rivers,and the ecosystems were constructed in the simulated rivers,the operation of the bypass river system was simulated,the operation was monitored,and the key factors affecting the self-purification capacity of the system were analyzed.On this basis,a rain-sourced city rivers is selected to construction a demonstration project and the operation is monitored,so as to provide reference for the ecological restoration of other rain source type city river.This study draws the following main conclusions:(1)By studying the effects of four different plant combinations on water purification capacity under different flow rates and seasonal conditions,it was found that the removal rate and flow rate of SS,COD,TN,TP and NH3-N were positive when the flow rate was 0-0.01 Om/s,.negative when the flow rate and flow rate was 0.010?0.025m/s.The combination of Vallisneria,Ceratophyllum,and Polamogeton,rightii Morong has good adaptability to water flow changes.(2)Different types of aquatic plants are planted in a simulated river channel to simulate the operation of the bypass river system.The average removal rates of NH3-N,TN,TP and COD in the simulated river system were 62.3%,55.0%,62.7%and 33.3%,respectively.The concentration of NH3-N and COD can be basically upgraded to the V category by the inferior V class in the<<Surface Water Environmental Quality Standard>>(GB3838-2002).TN and TP indicators sometimes exceed the standard,especially the TP indicator.(3)Sampling and analysis of the microorganisms in the three main parts of the system showed that the wood piles and submerged plant rhizosphere soil is more suitable for the growth of functional bacteria than the stone wall revetment,and the cyanobacteria which can fix nitrogen and cause"water bloom"in the sample of stone wall revetment is the dominant microorganism.It indicates that the habitat construction should avoid the use of cement material in a large area,and adopt the wooden pile material suitable for the growth of functional bacteria.The aerobic-anoxic-anaerobic environment forms in the rhizosphere soil of submerged plants,and the abundant aquatic environment is conducive to the growth of various microorganisms.(4)According to the operation of the demonstration project from September to February,the average removal rates of CODCr,BOD5,NH3-N,TN and TP in the bypass channel system are 51.95%,50.67%,84.65%,70.52%and 64.83%,respectively.The main assessment indicators have reached the class IV water standard of the<<Surface Water Environmental Quality Standard>>(GB3838-2002)from the worse than grade V water.The construction of the bypass river system not only ensures flooding during the rainy season,but also ensures that the river ecosystem is not destroyed by floods,effectively improving the self-purification capacity of rainwater-type rivers.The actual water quality indicators of the actual project treatment are better than the simulated channel river system,indicating that complex habitats are more conducive to improving the purification capacity of the river.