Aeration is a mass transfer process between the atmosphere and water. Aeration is used for water quality enhancement in sewage treatment plants and in polluted rivers and lakes. This can be enhanced by creating turbulence in the water. Plunging overfall jets from weirs are a particular instance of producing such turbulence. In this paper, two intelligent models are realized to predict the air entrainment rate and aeration efficiency of weirs. Least square support vector machine (LS-SVM) is used as intelligent tool. Threefold cross validation test method is used to evaluate the performance of LS-SVM models. The correlation between predicted and measured values is found 0.99 for air entrainment rate and 0.98 for aeration efficiency. The test results indicate that the LS-SVM can be used successfully in predicting the air entrainment rate and aeration efficiency of weirs. Moreover, the performances of the LS-SVM models are compared with multi nonlinear and linear regression models.

Application of least square support vector machines in the prediction of aeration performance of plunging overfall jets from weirs

This comprehensive handbook on the hydraulic design of labyrinth spillways—from theory to current practice—presents a state-of-the-art method for the effective design of labyrinth weirs. The book provides a fundamental understanding of the theory of labyrinth weirs and continues with detailed sections on significant factors that affect the discharge characteristics of labyrinth weirs, such as crest shape, weir height, and sidewall angle. The most common design curves are discussed, and from these a recommendation is developed for only one design curve to be used in future designs. But because site conditions often vary so much from ideal conditions described in this book, a section on site-specific modeling criteria is included for making accurate predictions of prototype performance. In its review of past studies, the book closely examines many long-held concepts, especially concerning the idea of interference, nappe oscillation, and the definition of which head to use in design computations, and revises them in an effort to advance current thinking based on the latest research.

Hydraulic Design of Labyrinth Weirs

A new approach to improve the discharging capacity of sharp-crested triangular plan form weirs

Various structural measures have been advocated for river restoration and habitat improvement schemes. The W-weir is one such structure that can be used in mobile bed alluvial rivers to diversify habitat and provide grade control. Laboratory studies have been carried out in a large-scale meandering channel with a mobile bed to investigate their effects on flow and sediment transport processes. A W-weir placed immediately downstream of a riffle section created a strongly three-dimensional flow pattern and high-turbulence zones. Two adjacent scour holes of different depths and substrate are formed under clearwater and live bed conditions. The continuity of sediment transport along the channel was not interrupted by the structure and the upstream afflux is minimal. Overbank flow significantly influenced the action of the weir and the scour hole was shifted closer to the structure. In a relatively tight bend followed by a short crossover reach, the weir may affect bed load transport pathways in the downstream bend. Finally, the study provides insights to guide their design for restoration projects.

Hydraulic Evaluation of W-Weir for River Restoration

Options for managing hypoxic blackwater events in river systems: a review.

A high level of dissolved oxygen is vital for the maintenance of healthy streams and rivers. Structures in rivers can increase dissolved oxygen levels by creating turbulent conditions where small air bubbles are carried into the bulk of the flow. Plunging overfall jets from weirs are a particular instance of this, and the aeration properties of such structures have been studied widely in the laboratory and field over a number of years. On the other hand, labyrinth weirs, where the weir sill is cranked in planform thus increasing their length, have received little or no attention in this context. They have a proven hydraulic advantage over straight weirs of increased discharge at the same head for design conditions. However, they also serve to modify the combined overfall jet as individual jets from adjacent sections of the weir collide. This paper describes an experimental investigation into the nature of these jets and how they affect the aeration performance of a triangular plan labyrinth weir. It is demonstrated that the aeration efficiency of these labyrinth weirs generally is better than their equivalent-length linear weir and that this advantage becomes more pronounced as the weir included angle becomes smaller and also at lower overfall drop heights and higher discharges. These results point to the possible advantage of these type of weir in situations where both hydraulic and aeration performance needs to be optimized.

Chau Chiu Tsang

Papers

Aeration performance of rectangular planform labyrinth weirs