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

过去已经认识到水工结构通过空气夹带对改善河流缺氧的潜在贡献，并且有几篇论文报道了水滴堰的吸氧情况。然而，这些论文中提出的预测方程是否适用于各种设计情况还不清楚。本研究的目的是通过与简单的堰相比较来评价相对复杂水工结构的氧传递。实地观察是在三个堰和两个石铺鱼坡进行的。其中两个堰由斜坡组成，在上游和下游两端都有落点。堰的剩余部分是一个由巨石铺设的倾斜堰。从这些堰的试验结果可以看出，在坡面上流动时的掺气性能比在坡面上下降时要差，而在坡面上铺设天然巨石时掺气性能会更好。这是由于底部不均匀产生的水力跳跃、飞溅和湍流，从而改善了空气-水界面的氧气传递。确认以上结果。，在两个卵石铺成的鱼坡进行了实地观察。结果表明：鱼坡处的复氧效果优于与鱼坡高度相同的落点处的复氧效果。此外，氧气传递效率取决于岩石间距和流动距离之间的关系，直到射流出现。如果岩石之间的距离大于亚临界流转变为超临界流的距离，则必然会发生水力跳变。特别是在流量不太大的情况下，水跃对氧气再生有很大的贡献。

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.