永定河流域(北京段)不同生态护岸形式坡面侵蚀及面源污染特征

Characteristics of slope erosion and non-point source pollution in different ecological revetment in Yongding River Basin(Beijing section)

永定河是北京市的防洪安全屏障和供水河道,河道生态系统修复问题亟待解决。选择河北省廊坊市永定河沙质河道,建立13个野外标准径流小区,设置2个岸坡坡比,选取5种材料复合得9种护岸配置形式,研究3个放水流量下不同护岸形式的减流减沙效果以及对于总氮(TN)、总磷(TP)、氨氮(NH^(+)_(4)-N)、化学需氧量(COD)、生化需氧量(BOD_(5))5个面源污染指标的影响。结果表明:1)5种材料中减流减沙效果最好的是生态袋,平均减流31.57%,平均减沙70.70%;2)生态袋复合型护岸相对单一生态袋护岸对径流的削减效果提高22.63%以上,泥沙的削减效果提高3.25%以上;3)护岸的布置增加了水流的紊动性,使径流雷诺数增大,但均<500,仍处于层流范围,弗劳德数相对于空白对照小区降低,均>1属于急流流态;4)1∶1坡比下生态袋护岸对径流的削减效果不如石笼护岸,但泥沙的削减效果优于石笼护岸,随着坡度增加,生态袋护岸的减流效果变差,石笼护岸的减沙作用降低。

[Background]The Yongding River is the mother river of Beijing.It has bred a deep cultural heritage for the city of Beijing,and It is also the city's flood protection barrier,water supply channel and water source protection area.Due to the dry climate,the amount of incoming water has been declining,which has caused the river in the lower reaches of the Yongding River to be cut off for many years.Vegetation is difficult to grow and vegetation coverage was low,and the ecological environment of the river has been severely damaged.It is urgent to restore the Yongding River ecosystem.[Methods]This study used runoff plot to conduct water scouring experiments and organically combines the research of ecological bank protection and slope protection.Five types of revetment materials(geogrid,nature stone,ecological bag,gabion,and pine wood pile)were used to obtain 9 types of arrangements.Two revetment slope ratios were experimentally set up,and a total of 13 standard runoff plots were established in the field.Runoff and sediment in different runoff areas and the reduction rates of five non-point source pollution indicators,including total nitrogen(TN),total phosphorus(TP),ammonia nitrogen(NH^(+)_(4)-N),chemical oxygen demand(COD),and biological oxygen demand(BOD_(5))were measured.Based on this,the ecological protection effects of different forms of ecological revetments in the Yongding River Basin(Beijing Section)were studied.[Results]The ecological bag caused an average runoff reduction effect of 31.57%and an average sediment reduction effect of 70.70%.Compared with the single eco-bag revetment,the ecological bag composite revetment had an effect of reducing runoff by more than 22.63%,and the effect of reducing sediment by more than 3.25%.The arrangement of the revetment increased the turbulence of the water flow so that the runoff Reynolds number increased,but all were<500,which was still in the laminar range.The Froude number was lower than that of the blank control area,and all were greater than 1,belonging to the rapid flow state.The reduction of runoff by eco-bag revetment was not as good as that of gabion revetment under a slope ratio of 1∶1,but the reduction effect of sediment was better than that of gabion revetment.[Conclusions]The ecological bag demonstrates the best effect on reducing runoff sediment among the five shore protection materials,at the same time,the effect is significant on TP,TN,NH+4-N,COD,and BOD5.Compared with the single revetment form,the composite revetment form presents a better effect on reducing runoff sediment,and at the same time,it has better control effect on non-point source pollution.Runoff Reynolds number and Froude number increase with the increase of discharge flow.With the increase of the slope,the runoff reduction effect of eco-bag revetment gradually is reduced,the sediment reduction effect of gabion revetment is reduced.