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Water 2019, 11(4), 773; https://doi.org/10.3390/w11040773

Optimised Triangular Weir Design for Assessing the Full-Scale Performance of Green Infrastructure

1
Department of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, UK
2
Thames Water Utilities Limited, Reading RG2 0RP, UK
*
Author to whom correspondence should be addressed.
Received: 12 March 2019 / Revised: 10 April 2019 / Accepted: 12 April 2019 / Published: 14 April 2019
(This article belongs to the Section Urban Water Management)
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Abstract

Conventional triangular weirs have been originally developed to measure, divert, and control surface water. However, a special application of these weirs, such as for low flow measurements in full-scale monitoring of Green Infrastructure (GI), is not well investigated. Available head-discharge relationships for triangular sharp-crested weirs are only valid under a free-flow regime. Literature focusing on the V-notch weir usage for GI assessment suggests that it is necessary to calibrate the head-discharge relationship before its use. This study focuses on understanding the effects of site constraints on the measurement performance of a V-notch weir at low flow rates, and the validity of equations derived for similar applications that can be found in the literature. The variation of discharge coefficient in various flow regimes was investigated experimentally based on calibration runs covering flow rates between 0.054 l/s and 7 l/s. The results show that for 30° and 45° V-notch weirs, three flow regimes can be identified. It was observed that literature equations to calculate the discharge coefficient are valid for partially-contracted triangular weirs only at heads greater than vertex distance from the channel. However, for low flows that are expected to occur when estimating the full-scale performance of GI, the equations available from the literature for similar site conditions underestimated the flow rate between 85% and 17%. This emphasises the need for accurate calibration of a V-notch device under the site conditions to achieve the necessary level of accuracy in GI performance estimation. The procedure outlined in this work can be easily replicated to determine the optimal monitoring system configuration. Alternatively, if the site conditions would match those described in this study, the computed discharge using the proposed relations, in combination with the general V-notch weir equation, provides a significant improvement in the accuracy of measurements, expands the head applicability range of V-notch weirs, and enables better understanding of GI performance at the full scale. View Full-Text
Keywords: green infrastructure; full-scale performance; triangular weir; V-notch weir; head-discharge relationship; low flow rate; urban drainage green infrastructure; full-scale performance; triangular weir; V-notch weir; head-discharge relationship; low flow rate; urban drainage
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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El Hattab, M.H.; Mijic, A.; Vernon, D. Optimised Triangular Weir Design for Assessing the Full-Scale Performance of Green Infrastructure. Water 2019, 11, 773.

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