Discharge Calculation of Side Weirs with Several Weir Fields Considering the Undisturbed Normal Flow Depth in the Channel

Adrian Lindermuth,Bernhard Gems,Markus Aufleger,Théo St Pierre Ostrander,Stefan Achleitner

doi:10.3390/w13131717

Abstract

Discharge behavior at side weirs is significantly influenced by the water surface profile along the weir crest. In the past century, different approaches were developed to describe this profile and the associated discharge coefficients. However, the application of these methods to practical problems poses a particular challenge, as a complex three-dimensional funnel is formed due to the discharge reduction, leading to significant uncertainties in determining the relevant flow depth. For this reason, a new approach for the determination of the discharge coefficient of side weirs was developed that refers to the undisturbed normal flow depth in the main channel. Based on a comprehensive parametric study utilizing 3D-numerical simulations, the influence of the weir and channel characteristics on the discharge behavior at the side weir was analyzed. A revised formula for estimating the discharge coefficient for side weirs with multiple weir fields was derived using multiple regression analyses. Validation of the numerical simulations was carried out by applying a physical scale model, showing good agreement between the results.

Highlights

The discharge behavior is mainly influenced by prevailing flow depth, weir crest length, and a specific discharge coefficient [2]
For a controlled weir with multiple weir fields regulated by sluice gates, weir discharge can be adjusted by the number of open gates, representing the effective weir length
In order to control and adjust this system, reliable flow depth and discharge measurements are required that reflect current flood conditions, but they are unaffected by the impact of discharge reduction on the water surface

Summary

Introduction

In the context of flooding, side weirs are used in rivers where effective flood mitigation requires discharge diversion into an attached channel or retention basin. Early or unnecessary discharge reductions can reduce mitigative retention capacity of the basin, hindering the efficacy of the system [1]. To exploit the full retention capacity of the mitigation system, weir discharge regulation is crucial. Due to the typically lateral arrangement of these basins to the river, inlet structures need to be aligned parallel to the main flow direction in the channel and represent a lateral weir. In order to control and adjust this system, reliable flow depth and discharge measurements are required that reflect current flood conditions, but they are unaffected by the impact of discharge reduction on the water surface

Methods

Results

Conclusion