Foundamental Studies on Oxygen Reaeration at Hydraulic Structures in Nature-Oriented River Work

在过去，人们已经认识到水工建筑物通过空气夹带对改善河流中氧气不足的潜在贡献，并且有几篇论文报告了跌水堰的氧气吸收。本文通过对三个堰和两个铺石鱼坡的现场观测，研究了相对复杂的水工建筑物和简单的渣堰的氧传递特性。其中两个堰由上游和下游两端都有落差的斜坡组成。其余的堰是一个卵石铺成的倾斜堰。从这些堰得到的结果，它的结论是，在流动过程中的曝气性能的斜坡上是小于在下降，但它会更多，如果斜坡铺设天然卵石。这是由于底部不平整产生的水跃、飞溅和湍流，促进了氧气通过气-水界面的传递。在两个铺有巨石的鱼坡进行了实地观察。结果表明，在相同落差条件下，鱼坡的复氧性能大于落差条件。此外，还明确了氧传递效率取决于漂石间距与射流出现点之间的流动距离之间的关系。如果漂石间距大于亚临界流向超临界流转变的距离，则必然发生水跃。水跃对复氧的贡献很大，特别是在流量不大的情况下。

The potential contribution of hydraulic structures through air entrainment to the improvement of oxygen deficiencies in rivers has been recognized in the past and several papers reporting oxygen uptake at drop weirs. However it has not been clear that predictive equations proposed in those papers are applicable to a variety of design situations.The objective of the research is to evaluate the oxygen transfer at relatively complicated hydraulic structures through comparing to simple drog weirs.The field observations were done at three weirs and two boulder-paved fish slopes. Two of the weirs consist of slope with drops at both upstream and downstream ends. The remaining of the weirs is a boulder-paved sloping weir. From the results obtained at these weirs, it is concluded that aeration performance during flowing on the slop is less than at the drop but it would be more if slop was paved by natural boulders. This is due to the hydraulic jump, splash and turbulence generated by bottom unevenness, which improve oxygen transfer through air water interface.To confirm the above results., field observations were carried out at two boulder-paved fish slopes. The results showed that the reaeration performance at the fish slopes were greater than those at drop which has same drop height of the fish slopes. Moreover it was cleared that the oxygen transfer efficiency depends on the relashionship between the interval of boulders and flow distance up to the point where jet flow emerges. If the interval between boulders is greater than the distance in which subcritical flow changes into supercritical flow, hydraulic jump surely occurs. Hydraulic jump greatly contributes oxygen reaeration especially when discharge is not so large.