EA to step up enforcement of flow regulations

According to Alasdair Ward of Meggitt Mobrey, the EA is to step up enforcement of discharge consents with specific reference to flow, in an attempt to achieve water quality objectives set following the Environment Act (1995).

As part of its wider duty to protect the environment, the EA requires dischargers to measure and record their effluent flows. This requirement is included in most discharge consents granted by the EA.

Under a new policy, the EA will soon start to implement a new programme designed to ensure compliance with European directives, under the Water Resources Act (1991) and the Environment Act (1995).

Where consents already include flow measurement conditions, these will be enforced ­ where they do not, appropriate conditions will now be added. 98% of STWs in the UK have open channel flows, and for many it is also the preferred type of channel for discharge.

As one of the first steps in its programme to ensure compliance, in January the EA published Technical Report P150: Flow Monitoring of Discharges; An Audit Manual.

The report summarises the essential relevant information from the European directives, and from the British Standard BS 3680. Methods of measurement of liquid flow in open channels are described, beginning with the design and use of primary flow structures, such as flumes and weirs.

Based on existing documentation and experimental data, the EA report has identified a maximum tolerance of 8% for discharge flow monitoring. Work by Mobrey¹s flow audit team indicates that about 90% of all open channel flow structures in the UK do not meet this level of accuracy. According to the EA, many sites are inadvertently sub-standard, and operators may not even be aware that there is a problem. Typical problems include design inaccuracies, build-up of deposits over time, inappropriate up or down-stream flow conditions and incorrectly calibrated secondary instrumentation.

Technical report P150, which will now be used by EA personnel surveying sites, sets out guidelines for the flow audit procedure. It is also available for companies which carry out their own flow audits.

The EA will require that dischargers install flow monitoring to the required specification and have the installation certified by an external body. A number of installations will be audited by the EA each year.

There is no doubt that technical report P150 is a useful, and much needed document; the widespread use of which is to be encouraged throughout the industry. However, there do appear to be a number of discrepancies between it and other standards which need to be resolved, if confusion is to be avoided. These include:

  • In section 2.2.2.7 (Construction of the Primary Device), P150 quotes the BS3680 tolerance for flume construction. In fact, these tolerances are almost universally unachievable in practice and most flow engineers tend to employ more practical guidelines to ensure accuracy of the flume. Meggitt understands that implementation is currently being discussed within the EA, but it seems likely that, as long as the overall accuracy of the installation can be shown to be within 8%, the BS tolerance details will probably not be enforced.
  • In section 2.2.3 (Installation Effects), the technical report quotes BS3680, saying that the distance that should be allowed upstream of a weir is Œ10 times the maximum width of the nappe, plus five times the maximum head.
The report omits to say that this distance is only required by the BSI if the approach velocity is negligible. If there is no disturbance to the water, then the upstream distances are not necessary for accurate measurement.

To comply with the legislation on effluent discharge, water companies must complete a full flow audit, correct any errors and implement a maintenance programme to ensure that accuracy is maintained. Notably, they must document all these procedures in a manner suitable for inspection by the EA, in order to prove compliance.

Mobrey offers flow auditing and consultancy for compliance with these new regulations. A certificate of compliance for inspection by the EA is issued when work has been completed to the required standard.

However, as the EA does not operate an accreditation scheme for bodies carrying out this work, there is still a serious risk of inexperienced operators offering sub-standard compliance audits, despite publication of the P150 report.

Meggitt would welcome an accreditation scheme for companies offering consultancy and contract civil work, such as the Œcompetent body' scheme, which authorises test laboratories to certify electromagnetic products used in the electronics industry.

Such a scheme would set minimum levels of quality and give the industry a practical means of ensuring compliance with the EA's regulations.


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