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
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
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 184.108.40.206 (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
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
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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