The Effect Of River Flow Regulating Measures On Repairing River Ecosystem

With the development and improvement of ecological restoration engineeringtechnology in near-nature river, the ecological benefits of it has aroused wide attention. Theregulating measures play an important role in ecological restoration engineering. This studymakes a research on ecological benefits of it based on controlling flood engineering.It takes the near-river flowing into the northwest of Shitoukoumen (a reservoir inChangchun) as the experimental section, and use engineering measures（ecological weir,riverbed pile engineering, rockfill engineering, artificial wetland）as object of this study. Itmakes a contrastive analysis on the ecological restoration of engineering measures and fourindexes including hydrological, water quality, physical habitat, vegetation. It aims to providescientific references and related theoretical foundation for river ecological restoration inmiddle or small-sized river in the future.(1) Ecological weir,riverbed pile engineering, rockfill engineering can both change theflow velocity, which falls after rising from head water to tail water. The normal flow velocityis5-23cm/s during the non-precipitation period. The peak velocity can reach36cm/s underthe disturbance of engineering measures. After the rain, the disturbance of engineeringmeasures is similar to that of non-precipitation period. The normal flow velocity is9-29cm/s,while the peak speed is44cm/s.(2) Ecological weir, riverbed pile engineering and rockfill engineering have someinfluences on the depth of the river to some extent. The depth of tail water of the riverbedpile engineering can reach86cm, and that of ecological weir and rockfill engineeringrespectively are41cm and29cm. But rockfill engineering can greatly change the depth ofriver at a large range. Riverbed pile engineering has great influence within the scope of5meters between the head water and the tail water. Ecological weir has little influence on thedepth of river.(3) Turbidity and dissolved oxygen index show positive transformation from the headwater to the tail water, and the ecological effectiveness has been improved. The pH value isin the scope of the pH value of the drinking water. But the variation of pH can be1.15withinthe scope of3km.(4) The flow velocity changes greatly in the curve and the engineering area. In thelong-term of erosion, transportation, deposition, the sandbar of the head water has beencontinuously deposited and that of the tail water declines. In the inner side of the river bend,the sandbar has been continuously deposited, and that of the outer side of the river benddeclines. (5) Measures of adjusting flow velocity obviously disturb the composition of plasmidsize of the bottom of river bed. The disturbance of ecological weir and rockfill engineeringon plasmid size of the bottom of river bed indicate that the big-size plasmid increase from thehead water to the tail water. Travel size of plasmid among the0.6mm-1.5mm increases withthe influence of the pile engineering.(6) It has large quantity of organic matter and various kinds of vegetation in the upperand middle sandbar of the experimental section. Between July and August, the cover rate isnearly100％in the west of bridge and Shijiancun section. It has little organic matter andgravel is the main kind in the sandbar and river bed of tail water. The kind and number ofvegetation decreases and it is mainly a simple community with dayflower being theconstructive species.There are various advantages and disadvantages for different engineering measures.Ecological weir has advantages in creating a landscape and heterogeneous substrate, but ithas a defect in hydrologic disturbance; riverbed pile engineering can change flow velocityand depth of water greatly, but it has a defect in improving dissolved oxygen; the riverbedriprap work can create the heterogeneous substrate, but it has a defect in changing the flowvelocity and depth of water and improving the dissolved oxygen; compared with the otherstretches of river, artificial wetland has a great change in hydrological conditions and create alandscape, but the water is turbid, and dissolved oxygen decreases.It makes a suggestionwhen it has an ecological restoration, it should adopt different engineering measures torestore it by considering the relevant factors.