Open Channel Flow Guide - Solartron Mobrey

process measurement solutions

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The Guide for implementing dependable & accurate open channel flow measurement

THE GUIDE For implementing dependable and accurate open channel flow measurement 1.0 The Importance of Dependable Flow Measurement 1.1 Environment Agency Requirements 1.2 The Benefits of Open Channel Devices 1.3 BS3680

2.0 A Turnkey Solution from Solartron Mobrey 2.1 Flow Audit Surveys 2.2 Installation 2.3 Certification 2.4 Health and Safety

3.0 Document Examples 3.1 Survey Forms 3.2 Survey Report 3.3 Certificate of Conformity 3.4 Calibration Data and Performance Curves 3.5 Survey Method Statement

4.0 Reference Documents 4.1 Selecting a Flow Specialist 4.2 Reference List – Discharge Flow Compliance Works

5.0 Published Articles 5.1 A benchmark for flow measurement accuracy 5.2 Implementing effluent flow monitoring regulations and guidelines 5.3 Logistics of effluent flow measurement problem solved.

1.0 The Importance of Dependable Flow Measurement Unreliable flow data can result in inefficient plant operation and unnecessary investment in plant upgrades. This is particularly true in the case of measurement of industrial and sewage effluents, yet it is frequently given the least priority and attention. Flow data obtained from a dependable source, enable plants to be operated in an efficient manner. By optimising treatment processes, operators can ensure that maximum treatment capacities are achieved, before additional investment is made. Where it is necessary to replace or upgrade plant equipment, operating capacities can be specified with confidence.

1.1 Environment Agency Requirements In addition to providing the plant operator with important information, it is now a legislative requirement that dischargers maintain accurate flow measurement records. The Environment Agency is currently implementing a programme, directed at Continuous Sewage and Trade Dischargers, to ensure accurate flow monitoring is in place, by specific time scales. The following are extracts from the Environment Agency document, “Procedure for Flow Measurement of Discharges” (version 4.2 Sept 2000) “The Aims and Objectives of Flow Measurement The limits in discharge consents are based on the maximum quantity, or load, of pollutants that can be allowed in the receiving water. To control load, consents specify limits for flow and pollutant concentration. Even where the discharge meets the quality limits, the river may be downgraded by excessive load because the discharge exceeds the consented maximum flow. It is thus necessary to monitor both the quantity and quality of discharges. The Agency requires reliable discharge flow data in order to regulate effectively discharges and receiving water quality. In addition, the Agency requires up to date flow information to plan for future growth of discharges. The Water Resources Act 1991 (as amended by the Environment Act 1995) Schedule 10, paragraphs 3(4) (e) to (g) specifically provides for conditions in consents requiring the installation, maintenance and testing of meters to measure and record the volume and rate of discharges. It also allows the Agency to require the discharger to keep records and make returns. Many existing consents place requirements on the discharger to obtain and provide such information, as do the standard national consent conditions. The policy requires the Agency to undertake a programme to insert conditions in consents to enforce the requirement for self monitoring of flows and reporting results to the Agency in accordance with a specified timetable. The Agency will also audit the installations and make provision for checking returns against consent limits and archiving returns for planning and other purposes. Where necessary the Agency will use Enforcement Notices to carry out this policy. Continuous Trade Discharges On all new and revised consents for trade discharges, the provision and maintenance of installations to measure and record the rate of flow and cumulative daily volume is essential. When pollutant concentration limits are imposed by a consent and monitored then it is equally important to measure effluent flows. Where the maximum daily volume of trade effluent exceeds 50m3/day and the consent is subject to numeric quality and flow limits, the discharger will normally be required to install and maintain a permanent flow monitoring installation and make regular returns to the Agency. If the volume limit is 5 to 50m3/day flumes, v-notch weirs or other agreed means should be provided to allow the use of flow measurement equipment

when required. The Agency may, exceptionally, require flow measurement structures for trade flows less than 5 m3/d. In this case the Agency will justify the need.

Continuous Sewage Discharges Where pollutant concentration limits are imposed by a consent and monitored then it is equally important to measure effluent flows in order to provide quantitative estimates of the amount of pollutant materials discharged. All new and revised consents for continuous sewage discharges exceeding 5m3/day will require the provision and maintenance of a structure, such as a flume or v-notch weir, where the rate of flow and cumulative daily volume can be measured and recorded. At sewage discharges above 5 m3/d, which either have descriptive consent conditions or have a consented DWF less than 50m3/day, the discharger will provide a flow measuring location. However, the flow will only need to be monitored by the discharger when requested by the Agency, or the Agency may install portable flow monitoring equipment when required. If the Agency's information needs for a discharge in this size range will be satisfied by a simpler arrangement, then the Agency may allow the use of a simple physical measuring device, such as a level board and V notch. Here Agency staff on sampling visits will record the flow and the discharger may be required to keep records. Where an existing STW in this flow range has no provision for flow monitoring it will not be necessary to modify it solely for that purpose, unless the Agency specifically requires flow measurement at that site. Flow monitoring should be provided when the STW is next modified. At discharges above 250 population equivalent, or have a DWF equal to or greater than 50 m3/day the Agency will normally require the discharger to install and maintain equipment to measure and record instantaneous and cumulative daily flows. Flow measurement will be a continuing requirement for all these sites. For those discharges below the population equivalent thresholds for the Urban Wastewater Treatment Directive, where the controlled water quality is not significantly affected by the discharge and previous flow measurement has shown that the daily volume measurement is less than 80% of the consent limit then, at the discretion of the Agency, a reduced frequency of flow monitoring may be allowed. The reduced frequency will require flow measurement by the discharger only during one year in every two or three. The minimum frequency for flow monitoring will be one year in five. This reduces monitoring effort for satisfactory discharges, while allowing changes in flow to be monitored. If the circumstances change then the Agency may require an increased frequency or continuous monitoring. Intermittent Discharges For storm sewage overflows at STWs, the Agency needs to be able to confirm that the flow at which the storm overflow begins to operate is as required by the consent. As a minimum, where the overflow is fixed and flows cannot be adjusted, spot checks for consent compliance may be adequate, subject to Agency agreement. Once confirmed they should be rechecked from time to time, or when the flows to the works may have changed. Where the overflow setting can be adjusted, for instance by an adjustable weir plate, a penstock or by varying pump operation, then ensuring that pass forward flows meet consent requirements can only be achieved by continuous recording during operation of the overflow. Flow Meter Specification The flow measurement and recording systems should be installed to British Standards (e.g. BS3680) They must be calibrated within predetermined levels of accuracy and the consent should require a programme of maintenance and checking by the discharger. Continuous recording devices should have a digital display and a logging capability.

Implementation Timetable The Agency will monitor implementation of the flow monitoring programme. All sewage works above UWWTD population equivalent thresholds and all sewage works and other discharges below those limits that have been identified by the Agency as a priority, should have flow measurement in place as soon as is practicable. All eligible discharges should have flow measurement in place by April 2005. For trade effluents and non-utility STW discharges the Agency will establish a prioritised programme to require the provision of flow measuring facilities at each discharge. The Agency’s requirements will be explained to each discharger and an appropriate target date will be discussed. If the discharger does not agree a target date acceptable to the Agency then the Agency will set a date and modify the consent accordingly. If the discharger does not undertake the measures voluntarily then the Agency will require them to do so by an Enforcement Notice (in accordance with the Agency’s Enforcement Policy).”

Quality Assurance Flow monitoring should be supported by evidence that the uncertainty of the flow metering device(s) is no greater than 8% of total daily flow. However, it is recognised that in a few situations, the flow may fall below the minimum recommended for the device and an uncertainty of >8% (at 25% of maximum design flow) may be unavoidable.

Implementation Requirements The Discharger will be responsible for meeting the consent requirements according to the specifications set by the Agency. The Agency will give advice to Dischargers at their request. Following completion of the installation, the Discharger will be required to have the site audited and certified for accuracy by an independent expert. The reports will be returned to the Agency. The Discharger will prepare a Quality Control Manual for site maintenance, data collection, validation and supply to the Agency. They will be required to operate in accordance with the Manual. The Agency will carry out an ongoing programme of inspection and audit of sites and audit of compliance with the Manual. The Agency has produced an R&D report that provides requirements for flow measurement installations for dischargers and audit proposals (R&D Technical Report P150. “Flow Monitoring of Discharges: An Audit Manual”). This will initially provide the Agency’s specification for the construction and performance of flow monitoring installations.”

1.2 The Benefits of Open Channel Devices. Historically, the preferred method of measuring gravity fed effluent flowrates is via an open channel flow structure, installed in conjunction with a suitable gauged head measurement device. This still remains the case. Over the years the methods of obtaining gauged head measurements have changed as technology has advanced, but the primary structures are essentially unchanged. Consequently the characteristics of this type of device are well documented and readily verified by competent personnel. The type of flow structure used is dependent upon many factors, including the fluid conditions, site hydraulics and the operating flowrates. In the case of a sewage treatment works, a flume is normally to be found on the works inlet, whilst either a flume or weir is normally used to monitor final effluent flows. Reasons why this type of measurement is generally preferred over more sophisticated and sometimes less expensive methods are: • The overall simplicity of the devices • The technology is established and well documented. • The operation and measurement value can easily be verified • The ease and hence low cost of maintenance. Because of these factors the overall cost of ownership becomes comparable with systems that initially appear less expensive.

1.3 BS3680 When an open channel structure conforms to the requirements of the relevant section BS 3680 Part 4, then its performance can be predicted. If the geometry or operating parameters fall outside of those laid down in the standard, its’ characteristics cannot be verified without conducting exhaustive tests. Since it is imperative that both site operator and the regulative authorities are provided with valid data, the only acceptable solution is to ensure that structures substantially comply with the appropriate standard. Despite its’ importance, recent studies undertaken by several water companies, have concluded that the majority of their open channel flow structures, used to monitor flow to treatment and effluent discharges, at waste water treatment works, fail to meet the requirements of BS3680. There were a variety of reasons why the structures failed to comply with the standard. These included: • Structure sizing incompatible with actual flowrates • Damaged or bowed flumes and weir plates • Uneven channel beds • Poor upstream / downstream conditions • Instruments calibrated incorrectly • Sensors located in incorrect positions

2.0 A Turnkey Solution from Solartron Mobrey Solartron Mobrey are able to provide a complete turnkey service relating to flow measurement structures. This service can include: • Flow audit survey and report on the condition and suitability of existing installations • Survey and report to recommend the most suitable method of providing a new flow measurement installation. • Cost estimates for both new and remedial works. • All aspects of construction and installation associated with the provision of new structures or remedial works on existing installations. • Instrument calibration and commissioning. • Certification of completed installations to verify compliance. Solartron Mobrey ultrasonic instruments are widely used within the water industry, but we recognise that some companies may wish to utilise alternative suppliers; although disappointing, this is not a problem to our engineers, who are well versed in the installation and calibration of instruments produced by all current major manufacturers.

2.1 Flow Audit Surveys A survey consists of three main activities: 1. A visual inspection – which includes: obtaining an understanding of the process, assessing the operating conditions and effects of any adjacent equipment or pipework, taking note of ‘scum’ marks which could indicate problematic operating conditions and noting the overall condition of the structure. 2. An inspection of all critical dimensions – including, all dimensions associated with the primary structure, structure levels and the position of the gauged head measurement sensor. 3. An inspection of the head measurement system – including, verification of all programmed parameters, a calibration check and noting the overall condition of the system. Survey findings are recorded on forms, which have been developed to suit the type of structure. Following the survey, calculations are carried out to verify geometric compliance and produce measurement uncertainty curves. The results are reviewed and are combined with the physical findings of the survey to produce a summarised report. The equipment use by Solartron Mobrey engineers, whilst carrying out flow audit surveys, includes the following: • Calibrated surveyors level, tripod and measuring staff • Spirit levels • Purpose made internal callipers • steel rules and measuring tapes • Digital camera • Certified multimeter • Portable computer • Personal protection equipment • Cleaning and sterilisation materials • Mobile telephone

2.2 Installation Solartron Mobrey are able to undertake every aspect associated with the construction of open channel structures and the installation of associated instrumentation, cabling etc. Activities include: • Supply of GRP / GRC / PVC flumes and stainless steel weir plates. • Supply of all instrumentation, calibration reference plates, enclosures, cabling etc. • All works associated with structure construction / repairs. • All works associated with instrument installation. • All works associated with over-pumping, in order to obtain access to the structure.

2.3 Certification Upon completion of construction / remedial works, the structure is re-surveyed and assuming all aspects of the installation provide substantial compliance with BS3680, a certificate of compliance is issued in conjunction with calibration records, performance curves and tables.

2.4 Health and Safety All site personnel are experienced in the operation and hazards present on sewage and process plants, and are familiar with the health and hygiene requirements. The where applicable the site operators Heath & Safety procedure will be adopted. Where procedures are not available for the activities, Solartron Mobrey procedures will be adopted. All works are carried out in accordance with previously agreed Method Statements. Although no entries will be made without prior arrangement, at least one site operative will be confined space trained. This is considered necessary in order to recognise unidentified hazards.

Bestobell Service

Flow Survey - General Information Customer : Site Name: Survey by:

Site Code: Date:

Primary Device Duty: Material of construction (PVC, GRP etc) Visual condition of flume

Type: Rectangular flume

Visual condition of approach channel

Comment on approach velocity

Details of obstructions < 30 X hmax upstream of flume

Is there a standing wave present in the exit transition of the flume

Details of any obstructions downstream of the flume that could cause drowning

Details of any re-circulation flows being returned upstream of the flume and method of measurement

Survey Rect Flume (01_01_1).xls

Page 1 of 1 pages

Bestobell Service Flow Survey - dimensions Channel and Throat widths 'B' & 'b' (mm) A

2

1

5x'B'

3

4

5

B C D

6

5x'hmax'

Measurement 1

height

Channel width 'B' 2

3

4

Throat width 'b' 5

6

A B C D Flume Dimensions Approach 'L1'

Channel dimensions Height

Prismatic 'L'

Uninterrupted Approach

Scum Lines Normal Maximum

Exit 'L2'

Approach / flume offset

Roughness

Sensor Location Distance from flume

Overall Length Flume height Hump height

Height from datum

Channel and Flume survey staff readings (mm) 4A 1A

5x'B'

1

location

Channel levels 2

6A 7A

3A

2A

4B

Staff

5A

5B

6B

5x'hmax'

3

4

Flume levels 5

6

Exit 7

A B Comments

Survey Rect Flume (01_01_1).xls

Page 1 of 2 pages

Bestobell Service Flow Survey - Instrument details Manufacturer Level Sensor Model No Temp Sensor Model No Controller Model No MSP Par No Others Par No

Secondary Device Location:

Blanking distance

mm

EPROM No Original Value

Description

Calibrated Value

Type:

General Condition:

Survey Rect Flume (01_01_1).xls

Page 2 of 2 pages

A Water Company

ABC WWTW Flow Survey Report

Bestobell Service Lake View, Cooper Street, Hazel Grove, Stockport, Cheshire SK7 4LT Telephone 0161 483 0931

Example report (01_01_1).xls

Page1 of 6

Bestobell Service Flow Survey - General Information Customer : A Water Company Site Name: ABC WWTW Survey by: Paul Cherry / Shawn Mantle Primary Device Duty: Flow to Treatment Material of construction (PVC, GRP etc)

Site Code: Date: 22-Aug-00 Type: Rectangular Flume Concrete flume and channel

General Condition: The approach velocity is smooth and tranquil, albeit the channel and flume are covered with slime. There is a 280mm high step in the channel, approx 2100mm upstream of the flume. The variance in flume throat width, exceeds both BS3680 and practical limits. This is largely due to the poor concrete finish at the entry to the throat, and could be rectified. The level variance in approach channel bed marginally exceed practical limits, whilst the variance in the flume bed is excessive. The flume discharges correctly with no signs of backing-up or drowning. This point of measuremnt does not capture storm return flows, which are returned downstream of the flume, into a common wet well. A separate flowmeter will need to be provided for this.

Consent Discharge Flow Monitoring can be achieved by summating the FTT and the storm return flow measurements. The storm event setting requires proving, but does not require a logging.

Secondary Device Location: In control room

Type: Warren Jones WJ460

General Condition: The control unit is in reasonable condition and uses both channels - CH1 = Inlet to works, CH2 = FTT. The calibrated range of 120l/s is acceptable for the operating conditions, although several programmed parameters are incorrect. The gauged head sensor is too close to the flume for BS3680 compliance, and could be lowered to improve measurement accuracy. A calibration reference plate is not fitted.

Summary

FTT Flume

This structure does not comply with BS3680 For substantial compliance with BS3680, it is recommended that the FTT flume throat be refurbished to reduce width variance, and the bed levelled to acceptable limits. The gauged head sensor requires re-positioning and lowering for improved accuracy, and a calibration reference plate installed. The control unit requires re-programming with the correct parameters. In order to record the total treated flow, we recommend that an electromagnetic flowmeter be installed in the 150mm storm return pipeline. The flowrates derived from both this and the FTT structure should then be summated. Work required: * Refurbish flume cheeks / level bed * Fit calibration reference plate and re-position sensor * Re-programme control unit * Install storm return magmeter and chamber * Verify the storm event flowrate * Certify the measurement system

Photo Here

Storm Return pipeline

Example report (01_01_1).xls

Page 2 of 6 pages

Bestobell Service Flow Survey - dimensions Channel and Throat widths 'B' & 'b' (mm) A

2

1

3

4

5

6 B

5x'B'

5x'hmax'

Measurement

Channel width 'B' 2

1

height

3

Max Scum

C

Norm scum

D

Base

Throat width 'b' 5

4

6

A

603

602

605

311

310

302

B

604

604

605

311

310

302

C

606

604

606

309

309

302

D

606

606

608

309

309

302

Flume Dimensions Approach 'L1'

Channel dimensions Height

Prismatic 'L'

400 1200

Uninterrupted Approach

Exit 'L2'

1100

Approach / flume offset

Overall Length Flume height

2700

Hump height

Sensor Location Distance from flume

1640 0

Height from datum

Scum Lines 1640 Normal 6000 Maximum

240 350

0 Roughness

0.6

Blank Dist

300

670 1570

Channel and Flume survey staff readings (mm) 4A 1A

5x'B'

1

location A B

3845

Channel levels 2 3842

6A 7A

3A

2A

4B

Staff

5A

5B

6B

5x'hmax'

3

Flume levels 5

4 3845

3846 3846

3843 3843

Exit 7

6 3833 3834

3687

Comments

Example report (01_01_1).xls

Page 3 of 6 pages

Bestobell Service Flow Survey - Instrument details Manufacturer Warren Jones Level Sensor Model No Temp Sensor Model No Controller Model No WJ460 MSP Par No Others Par No

Blanking distance

300 mm

EPROM No

Description Displayed value 'b' L 'B' ks Q max h max Pulse Units Interval Average

Original Value

Calibrated Value

300 1200 602 1 120 387 0 Lit/sec 5 180

Example report (01_01_1).xls

Page 4 of 6 pages

Bestobell Service Flow Survey - Conformance / Uncertainty Data BS3680 Conformance (Limits) minimum "b" shall be > 100mm hmax/b shall be < 3

302 1.26



hmax/L shall be < 0.67

0.32



bhmax/B(hmax+p) shall be < 0.7

0.51



* Width < 3.07 * Transv < 1.00 Approach level varn. < 1.94 Sensor location at 3 to 4 hmax (mm)

4.50 0.50 2.00 670



Uninterupted approach (mm)

6000



Throat Variations

* Longt < 1.20

6.50



* The maximum acceptable dimensional variance is indicative of practical limits, and exceeds the variance limits stated within paragraph 6.3.3 of BS3680 Part 4C

Calculation data 605 307 1200 0 1640 1183

Error in Flow calculation % Uncertainty in zero datum (mm) Uncertainty @ Qmax

(mm)

1570

Uncertainty @ 25 % of Qmax

Maximum head "h" (mm)

387

Estimate of Normal Flowrate (l/s)

Channel Width "B" (mm) Throat Width "b" (mm) Throat Length "L" (mm) Hump Height "p" (mm) Flume Depth "H" (mm) Range to target (mm) Sensor height

Roughness "k" (mm) Mean fluid temp (oC) ∆r (measurement error ) %

0.6 15 0.5 0.3 1.0 4.33%

Estimated uncertainties assuming substantial compliance with BS3680 Head

Flow

Flow

eh

(Lit/sec)

Flow (M3/hr)

(mm)

(ML/D)

(mm)

0.0 19.4 38.7 58.1 77.4 96.8 116.1 135.5 154.8 174.2 193.5 212.9 232.2 251.6 270.9 290.3 309.6 329.0 348.3 367.7 387.0

0.00 1.07 3.55 6.68 10.49 14.88 19.76 25.11 30.89 37.05 43.58 50.44 57.64 65.14 72.94 81.03 89.40 98.05 106.97 116.15 125.57

0.00 3.86 12.78 24.06 37.75 53.55 71.15 90.40 111.20 133.39 156.88 181.60 207.49 234.50 262.59 291.70 321.83 353.00 385.10 418.12 452.04

0.00 0.09 0.31 0.58 0.91 1.29 1.71 2.17 2.67 3.20 3.77 4.36 4.98 5.63 6.30 7.00 7.72 8.47 9.24 10.03 10.85

7.75 7.66 7.56 7.46 7.37 7.27 7.17 7.08 6.98 6.88 6.79 6.69 6.59 6.50 6.40 6.30 6.21 6.11 6.01 5.92

CD

0.7309 0.8482 0.8679 0.8834 0.8959 0.9047 0.9117 0.9175 0.9220 0.9256 0.9285 0.9308 0.9329 0.9345 0.9360 0.9373 0.9386 0.9397 0.9407 0.9417

CV

1.0404 1.0503 1.0519 1.0532 1.0542 1.0550 1.0556 1.0561 1.0565 1.0568 1.0571 1.0573 1.0575 1.0576 1.0577 1.0578 1.0579 1.0581 1.0581 1.0582

Example report (01_01_1).xls

% of

Error X

Flow

% +/-

0.9% 2.8% 5.3% 8.4% 11.8% 15.7% 20.0% 24.6% 29.5% 34.7% 40.2% 45.9% 51.9% 58.1% 64.5% 71.2% 78.1% 85.2% 92.5% 100.0%

61.04% 30.39% 20.31% 15.31% 12.35% 10.40% 9.03% 8.03% 7.26% 6.67% 6.19% 5.81% 5.50% 5.24% 5.02% 4.84% 4.68% 4.55% 4.43% 4.33%

Page 5 of 6 pages

Bestobell Service Discharge / Uncertainty Curves Stage Discharge Curve 450

Gauged Head (mm)

400 350 300 250 200 150 100 50 0 0

20

40

60

80

100

120

140

Flow (litres/sec) Uncertainty Curve 70%

+/- % Uncertainty

60% 50% 40% 30% 20% 10% 0% 0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Flow rate (%)

Example report (01_01_1).xls

Page 6 of 6 pages

BESTOBELL SERVICE Lake View Cooper Street Hazel Grove Stockport Cheshire SK7 4LT 0161 483 0931

CERTIFICATE OF CONFORMITY Customer name: A Water Company Site name: ABC WWTW Site asset code: Duty: Flow to Treatment Type of primary device: Concrete Rectangular Flume Type of secondary device: Warren Jones 460 (Channel 2) Calibrated range (hmax / flow rate / uncertainty): 380 mm / 120 l/s / 3.50 % 25% calibrated range (h / flowrate / uncertainty): 153.4 mm / 30 l/s / 5.17 %

We hereby certify that on the date of inspection, the above installation substantially conformed to the appropriate section of BS3680 part 4, subject to the exclusions / comments below. Exclusions/comments:

Maintenance: In order to maintain compliance, the operation of head sensing instrumentation must be checked at regular intervals. The structure must be regularly inspected and kept clear of silt, debris and biological growth. (Changes in operating conditions, unauthorised modifications to structures or adjustments to instrument calibration will invalidate this certificate).

Date of Inspection : 19/12/00 By : S Mantle

A Water Company

ABC WWTW Flow Survey Report

Bestobell Service Lake View, Cooper Street, Hazel Grove, Stockport, Cheshire SK7 4LT Telephone 0161 483 0931

Example laminate (01_01_1).xls

Page1 of 5

Bestobell Service Flow Survey - dimensions Channel and Throat widths 'B' & 'b' (mm) A

2

1

3

4

5

6 B

5x'B'

5x'hmax'

Measurement

Channel width 'B' 2

1

height

3

Max Scum

C

Norm scum

D

Base

Throat width 'b' 5

4

6

A

603

602

605

305

304

302

B

604

604

605

304

303

302

C

606

604

606

304

302

302

D

606

606

608

303

302

302

Flume Dimensions Approach 'L1'

Channel dimensions Height

Prismatic 'L'

400 1200

Uninterrupted Approach

Exit 'L2'

1100

Approach / flume offset

Overall Length Flume height

2700

Hump height

Sensor Location Distance from flume

1640 0

Height from datum

Scum Lines 1640 Normal 6000 Maximum 0 Roughness

0.6

Blank Dist

250

1380 816

Channel and Flume survey staff readings (mm) 4A 1A

5x'B'

1

location A B

3837

Channel levels 2 3835

6A 7A

3A

2A

4B

Staff

5A

5B

6B

5x'hmax'

3

Flume levels 5

4 3836

3836 3836

3835 3835

Exit 7

6 3837 3836

3680

Comments

Example laminate (01_01_1).xls

Page 2 of 5 pages

Bestobell Service Flow Survey - Conformance / Uncertainty Data BS3680 Conformance (Limits) minimum "b" shall be > 100mm hmax/b shall be < 3

302 1.25



hmax/L shall be < 0.67

0.32



bhmax/B(hmax+p) shall be < 0.7

0.50



* Width < 3.03 * Transv < 1.00 Approach level varn. < 1.90 Sensor location at 3 to 4 hmax (mm)

1.50 0.50 0.50 1380



Uninterupted approach (mm)

6000



Throat Variations

* Longt < 1.20

1.00



* The maximum acceptable dimensional variance is indicative of practical limits, and exceeds the variance limits stated within paragraph 6.3.3 of BS3680 Part 4C

Calculation data 605 303 1200 0 1640 436

Error in Flow calculation % Uncertainty in zero datum (mm) Uncertainty @ Qmax

0.6 15 0.52 0.3 1.0 3.50%

(mm)

816

Uncertainty @ 25 % of Qmax

5.17%

Maximum head "h" (mm)

380

Estimate of Normal Flowrate (l/s)

Channel Width "B" (mm) Throat Width "b" (mm) Throat Length "L" (mm) Hump Height "p" (mm) Flume Depth "H" (mm) Range to target (mm) Sensor height

Roughness "k" (mm) Mean fluid temp (oC) ∆r (measurement error ) %

Calculated Uncertainties Head

Flow

Flow

eh

(Lit/sec)

Flow (M3/hr)

(mm)

(ML/D)

(mm)

0.0 19.0 38.0 57.0 76.0 95.0 114.0 133.0 152.0 171.0 190.0 209.0 228.0 247.0 266.0 285.0 304.0 323.0 342.0 361.0 380.0

0.00 1.02 3.40 6.40 10.04 14.24 18.92 24.04 29.58 35.48 41.73 48.31 55.20 62.39 69.86 77.61 85.63 93.92 102.46 111.25 120.28

0.00 3.66 12.24 23.04 36.13 51.27 68.11 86.56 106.47 127.73 150.23 173.92 198.73 224.61 251.51 279.41 308.26 338.11 368.87 400.51 433.00

0.00 0.09 0.29 0.55 0.87 1.23 1.63 2.08 2.56 3.07 3.61 4.17 4.77 5.39 6.04 6.71 7.40 8.11 8.85 9.61 10.39

4.14 4.05 3.95 3.85 3.75 3.65 3.55 3.45 3.35 3.26 3.16 3.06 2.96 2.86 2.76 2.66 2.56 2.46 2.37 2.27

CD

0.7238 0.8471 0.8667 0.8819 0.8945 0.9034 0.9106 0.9163 0.9209 0.9245 0.9275 0.9299 0.9320 0.9337 0.9352 0.9364 0.9377 0.9389 0.9399 0.9409

CV

1.0387 1.0488 1.0503 1.0515 1.0525 1.0533 1.0539 1.0544 1.0547 1.0551 1.0553 1.0555 1.0557 1.0558 1.0559 1.0560 1.0562 1.0563 1.0563 1.0564

Example laminate (01_01_1).xls

% of

Error X

Flow

% +/-

0.8% 2.8% 5.3% 8.3% 11.8% 15.7% 20.0% 24.6% 29.5% 34.7% 40.2% 45.9% 51.9% 58.1% 64.5% 71.2% 78.1% 85.2% 92.5% 100.0%

34.44% 17.21% 11.70% 9.01% 7.43% 6.41% 5.71% 5.20% 4.83% 4.54% 4.32% 4.14% 4.00% 3.89% 3.79% 3.72% 3.65% 3.59% 3.54% 3.50%

Page 3 of 5 pages

Bestobell Service Discharge / Uncertainty Curves Stage Discharge Curve 400

Gauged Head (mm)

350 300 250 200 150 100 50 0 0

20

40

60

80

100

120

140

Flow (litres/sec) Uncertainty Curve 40%

+/- % Uncertainty

30%

20%

10%

0% 0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Flow rate (%)

Example laminate (01_01_1).xls

Page 4 of 5 pages

Bestobell Service Calibration Data Customer : A Water Company Site Name: ABC WWTW Duty: Flow to Treatment

Date Certified

FLUME DETAILS Channel Width "B" (mm) Throat Width "b" (mm) Throat Length "L" (mm) Hump Height "p" (mm) Roughness "k" (mm) Flume Depth "H" (mm) Maximum head "h" (mm) Sensor Dead Band (mm) Sensor height (mm)

605 303 1200

Uncertainty at Max Flow Uncertainty at 75% Uncertainty at 50% Uncertainty at 25%

3.50% 3.68% 4.04% 5.17%

Ref. Target readings Target height (m) Flow Reading (l/s)

19/12/00

WJ460 CONFIGURATION CHANNEL 2 PARAMETERS h-max (mm) 380 q-max (l/s) 120 Definable Flow Device

0 0.6 1640 380 250 816

n1 n2 n3 n4 n5 n6 n7 n8 n9 n10 n11

Maximum Minimum 0.432 0.428 N/A N/A

FLOW CALCULATION Head (mm)

CD

CV

Flow (l/s)

mA o/p

19.0 38.0 57.0 76.0 95.0 114.0 133.0 152.0 171.0 190.0 209.0 228.0 247.0 266.0 285.0 304.0 323.0 342.0 361.0 380.0

0.7238 0.8471 0.8667 0.8819 0.8945 0.9034 0.9106 0.9163 0.9209 0.9245 0.9275 0.9299 0.9320 0.9337 0.9352 0.9364 0.9377 0.9389 0.9399 0.9409

1.0387 1.0488 1.0503 1.0515 1.0525 1.0533 1.0539 1.0544 1.0547 1.0551 1.0553 1.0555 1.0557 1.0558 1.0559 1.0560 1.0562 1.0563 1.0563 1.0564

1.02 3.40 6.40 10.0 14.2 18.9 24.0 29.6 35.5 41.7 48.3 55.2 62.4 69.9 77.6 85.6 93.9 102 111 120

4.14 4.45 4.85 5.33 5.89 6.52 7.20 7.93 8.72 9.55 10.43 11.34 12.30 13.29 14.32 15.39 16.49 17.63 18.80 20.00

h (mm) 0 38 76 114 152 190 228 266 304 342 380

Output range (mA) 4 mA output (l/s) 20 mA output (l/s) Flow units Volume Units Interval Average

q (l/s) 0.0 3.4 10.0 18.9 29.6 41.7 55.2 69.9 85.6 102.5 120.3 4 to 20 0 120.3 l/s 3 M 5 180

Bestobell Service Client

A Water Company

Method Statement for Open Channel Flow Structure Survey

Page 1 of 3

1. Scope of Work

1.1. Assessment of open channel flow monitoring facilities, for conformance with British Standard 3680

2. Health and Safety 2.1. All works will be carried out in general accordance with the site owners’ Heath & Safety procedures. 2.2. Authorisation / permits shall be obtained from the site owner prior to site entry. 2.3. BSCL / Mobrey operatives SHALL NOT ENTER any category of CONFINED SPACE without specific written authorisation. If arrangements have not been made prior to the survey visit, with the appropriate safety procedures in place, structure details / dimensions must be obtained from existing documentation. 2.4. BSCL / Mobrey operatives SHALL NOT carry out detailed inspection / measurement of structures, where it is considered dangerous to do so. eg wide / deep / fast flowing channels. If arrangements have not been made prior to the survey visit, with the appropriate safety procedures in place, structure details / dimensions must be obtained from existing documentation. 2.5. BSCL / Mobrey operatives SHALL NOT carry out any changes to calibration parameters without having obtained permission from the appropriate responsible person. 3. Method 3.1. Visually inspect the primary device, observing: a. Whether critical conditions exist, presence of a standing wave b. General condition of the structure c. Approach velocity, surface conditions, scum marks d. Location of penstocks, bends, recirculation pipework, grit deposition 3.2. Photograph and sketch the main features of the installation 3.3. Measure all critical dimensions and levels of the structure, recording the results on the appropriate survey record sheets. (See paragraphs 2.3 & 2..4) 3.4. Visually inspect the secondary device, noting location and condition 3.5. Interrogate the secondary device noting all calibration parameters. 3.6. Where the installation substantially conforms to the appropriate section of BS 3680 prepare certification documentation noting any reservations and recommendations which would result in an improved measurement accuracy 3.7. Where the installation fails to comply with the appropriate section of BS 3680 prepare a report identifying the reasons for none compliance and provide an overview of recommended remedial works. Example Survey Method (01_01_1).doc

Page 1 of 3

Bestobell Service Client

A Water Company

Method Statement for Open Channel Flow Structure Survey

Page 2 of 3

4. Programme of Work 4.1. The work shall generally be carried out in accordance an agreed programme. All work will be carried out on weekdays between the hours of 8.00 and 18.00

5. Personnel 5.1. The name(s) of the assigned engineer(s) and mobile telephone number will be notified at the time of arranging the survey 5.2. All personnel employed on the surveys are experienced in the operation and hazards present on a sewage treatment plant, will be familiar with the health and hygiene requirements and Water Company Heath & Safety procedures. 5.3. Although no entries will be made without prior arrangement, at least one of the engineers will be confined space trained. This is considered necessary in order to recognise unidentified hazards.

6. Equipment 6.1. The surveying engineer will be equipped with the following: Calibrated surveyors level, tripod and measuring staff, spirit level, internal callipers, 1m steel rule and measuring tape Digital camera Certified multimeter Portable computer Personal protection equipment Cleaning and sterilisation materials Mobile telephone

7. Contacts 7.1. All activities will be administered from: Bestobell Service Co. Limited Lake View, Cooper Street, Hazel Grove, Stockport SK7 4LT Telephone 0161 483 5051 / 0931 Fax 0161 483 4145 7.2. The person responsible for this contract is: Mr Les Hunter – Contracts Manager (mobile telephone 07768 641558) Example Survey Method (01_01_1).doc

Page 2 of 3

Bestobell Service Client

A Water Company

Method Statement for Open Channel Flow Structure Survey

Page 3 of 3

7.3. Normal office hours are 0830 - 1700 Monday to Thursday and 0830 – 1630 Friday 7.4. For both safety and administrative purposes, the survey team shall notify the above office upon entering and leaving each site

Example Survey Method (01_01_1).doc

Page 3 of 3

Selecting a Flow Specialist Environment Agency Requirements The Environment Agency is currently implementing a programme, to ensure that both Sewage and Trade Dischargers, provide meaningful and dependable discharge flow records to the Agency. The requirements of this programme are detailed within the Environment Agency document, “Procedure for Flow Measurement of Discharges” (version 4.2 Sept 2000) This document states that: “As soon as practicable after completion of the flow recorder installation the Consent Holder shall employ an independent expert to certify that the installation complies with the Agency’s specification. The Consent Holder shall satisfy himself as to the professional competence of the expert. A copy of the certifier’s report shall be provided to the Agency when it is available.” How does a Consent Holder assess the competence of the “expert” ? Currently, there is no authoritative body, which assesses the competency and provide accreditation of procedures, for this type of flow specialist. Given the involved nature the work and the level of expenditure involved, this can mean that the selection and appointment of a flow specialist, becomes extremely difficult and onerous. It is important to recognise that the certification of an open channel flow system, involves verification of all aspects associated with the system. i.e.the suitability of application, the geometry of the installed structure, the correct installation of the sensor head and the correct calibration of the recording instrument. There are many companies that have experience in individual aspects of the system, but few having an established track record, in being able to offer a turnkey capability. In selecting a Flow Specialist, the Consent Holder should ensure that the following criteria are satisfied.

The Flow Specialist should be able to demonstrate: •

A practical knowledge in the application of the Environment Agency document, “Procedure for Flow Measurement of Discharges” (version 4.2 Sept 2000).

•

A broad knowledge of the wastewater treatment process, inlet / outlet configurations, recirculation practices etc, so as to ensure correct application, and operation of flow structures.

•

Proven, documented procedures, in the practical application of BS3680 open channel flow structures.

•

The ability to provide and substantiate measurement uncertainty data, in accordance with BS3680, and the requirements of the Environment Agency.

•

An in depth capability in the assessment of existing flow structures, providing recommendations for remedial works / provision of new structures.

•

Sufficient practical knowledge to provide recommendations based on the “least cost option”, in order to fulfil budget, operational and EA requirements.

•

Proven procedures, which ensure that all aspects of Quality and Health and Safety are maintained in all stages of the surveying, design, supply and installation activities associated with open channel flow structures.

•

The ability to undertake full responsibility for all activities associated with design, supply, installation, calibration and certification for both remedial works, and provision of new measurement structures.

•

A capability in supporting the variety of instrumentation utilised in both open channel and closed pipe flow measurement.

•

A broad flow application knowledge, to enable alternatives to BS3680 measurement techniques to be proposed and supported, when considered appropriate.

•

Sufficient financial and labour resource, to fulfil the project requirements.

An insight into many of the above requirements can be gained from an accurate assessment of a company’s past experience, in delivering similar flow related projects.

Solartron Mobrey have been involved with the measurement of flow discharges for over 6 years. During this period, we have been involved with several Water Companies in the implementation of their Flow Audit Schemes. To date we have carried out over 600 flow surveys, and completed remedial works at approximately 300 sites, of various sizes. All works have been successfully completed to client satisfaction, and certified to substantially comply with BS3680, satisfying Environment Agency legislation”.

Bestobell Service Reference list – Discharge flow compliance works

Date

Customer

Contact

1996-98

Anglian Water

David Tyler 01480 323962

1998

Severn Trent Water

1998 ongoing

Yorkshire Water

1998

Southern Water

Ian Wright 0116 2340340 Rob Bainbridge 01756 706857 Chris Brooks 01303 264124

Value

£1,500k

£37k

Survey / report / cost estimate of flow structures at 88 STW sites.

£95k

Survey / report / certify over 150 flow structures and magmeter installations. Work included calibration verification by ‘drop testing’ where necessary.

£37k

Survey / report / cost estimate of flow structures at 50 WWTW sites.

1999

Severn Trent Water

Alan Bramley 01283 51255

£47k

1999

Anglian Water

Tony Bland 01842 725730

£15k

1999

Yorkshire Water

Rob Bainbridge 01756 706857

£64k

1999 2000

Severn Trent Water

Ray Cox 0121 722 4496

£15k

1999 2000

Anglian Water

Steve Riley 01603 247174

£180k

1999 2000

Southern Water

Ian Derham 01962 716547

£295k

Severn Trent Water (Carl Bro)

Stephen Merchant 0117 9232221

2000

2000

Thames Water

2000

Yorkshire Water

Ian Simmonds 01322 220727 Rob Bainbridge 01756 706857

Description Survey / report / remedial works / certification of structures at over 200 STW sites. Remedial works included: replacement and calibration of instruments (Mobrey, Milltronics & GLI), construction of flume / weir chambers, installation / replacement of flumes and weirs, overpumping etc.

Clay Cross STW. Works included levelling the approach and flume, in the flow to works channel. Installation of an MSPLOG system. Installation of a magmeter and penstock to monitor and control flow to treatment, including chamber construction, pipework modifications and associated controls. Replacement of GLI instruments with Mobrey MSP90 units, to provide Year 2000 compliance at 11 STW sites. Works also included certification of the completed installation. Remedial works to flow structures at 5 STW sites. The works included : replacement and calibration of instruments, replacement of flumes and weirs, overpumping etc. Survey / report / cost estimate of flow structures at over 20 STW sites. Survey / report on structures at 45 STW sites. Undertake remedial works at 20 sites including replacement and calibration of instruments (Mobrey, Milltronics & GLI), construction of flume/ weir chambers, installation / replacement of flumes and weirs, overpumping etc. Remedial works to flow structures at 15 WWTW sites, including replacement and calibration of instruments (GLI), construction of flume/ weir chambers, installation / replacement of flumes and weirs, overpumping etc.

£65k

Remedial works to flow structures at 13 WWTW sites, including replacement and calibration of instruments (GLI & Milltronics), installation / replacement of flumes and weirs, overpumping etc.

£19k

Longreach STW, supply, install and certify new PVC fume within elevated storm overflow channel. Channel width 1500mm, throat width 1000mm, flow range 2600l/s

£25k

Harrogate South STW, replacement of 400l/s FTT flume, including levelling of approach and flume beds, overpumping etc Page 1 of 2

Bestobell Service Reference list – Discharge flow compliance works

2000 ongoing

Southern Water (Morrisons)

Dave Bone 01273 663277

£350k

Remedial works to flow structures at 16 WWTW sites, including replacement and calibration of instruments (GLI), construction of magmeter chambers, installation / replacement of flumes, weirs and magmeters, overpumping etc.

Page 2 of 2

MM280 rd Issue date: To Water Services only 3 June 1998

Logistics of Effluent Flow Measurement problem solved for Southern Water Bestobell Service (part of the Solartron Mobrey group) has come up with a cost-effective solution to improve flow measurement at Southern Water’s Peel Common Waste Water treatment works at Fareham. The company has successfully installed a new weir plate and associated instrumentation on the final outflow channel for accurate measurement of the release of treated wastewater from the works. The works remained operational throughout, and the installation was carried out in just a few hours, overnight. Peel Common WWTW is one of the largest treatment works on the South Coast, serving a population of 240,000. Installation of an outflow measurement weir plate was carried out as part of Flow Audit and remedial work undertaken by Bestobell for Southern Water at sites throughout Hampshire and the Isle of Wight. “Our policy is to ensure that final release is being measured and recorded accurately, in compliance with the Environment Agency Consent to Discharge requirements. This data is also invaluable for operational and planning reasons,” explains Ian Derham, of Southern Water’s operational project department who commissioned the work. “As flow specialists, the Bestobell team was able to propose and carry out cost-effective, practical solutions to improve our operating standards. Even at Peel Common, where the scale and nature of the site made it particularly difficult, they succeeded in providing us with an elegant solution. The alternative may have been large-scale and very expensive civil work.” The outflow channel is 4m deep and 2.5m wide and flow rates can be up to 1500 lit/sec. There was no practical means of halting the flow, or of diverting it. “At peak flow rate the flow would have filled our storm tanks in about two hours flat,” explains Tony Coles, Site Manager for Southern Water at Peel Common. The only solution was to over-pump the channel while the work was carried out. This was further complicated by the fact that the over-pump discharge hoses would have to cross an access road used regularly by heavy delivery lorries and articulated tankers. Tony Coles again: “By carrying out the work at night we minimised disruption to site traffic. It also reduced the likelihood that we would have to deal with peak flows during the operation.”

Four 12-inch and two 8-inch diesel pumps were used for the over-pumping operation in order to satisfy the possible maximum flows of 1500 lit/sec. A temporary dam was craned into positioned across the channel to provide a well for the pump suction hoses. The pumping equipment was set-up during days preceding the works, and the final discharge hose sections fitted when the road was closed at 8pm. Paul Cherry of the Bestobell / Mobrey team remembers: “In the event, there was no rain that night, so we did not have to cope with maximum flows. The team worked under floodlights and completed the installation of the weir plate in a matter of hours. By early hours of the morning the weir was operational, and the road was open again.” Level measurement at the weir point is provided by an ultrasonic level meter, which is fitted with a specially modified head verification device, for checking calibration of the meter without having to go down into the channel. In addition to the Peel Common project, Bestobell has now completed remedial work on Open Channel Flow Structures at various other sites on behalf of Southern Water. On completion of the work, each installation has been certified as being substantially compliant with the requirements of BS3680.

Ends For further information contact: Peta Glenister: Tel: (01753) 534646. Fax: (01753) 823589. email: [email protected] Editorial contact: Rachel Owen, Black & White Technical Marketing Communications, 8 Sceptre House, 57 The Hundred, Romsey SO51 8BZ. Tel: 01794 521156. Fax: 01794 521157. Email: [email protected]

Solartron Mobrey is one of the world’s largest suppliers of instrumentation for level measurement, serving markets in 66 countries, through a worldwide network of distributors and agents. Web site: www.mobrey.com

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MM278 st Issue date: To Water & Waste Treatment only 1 July 1999

Implementing effluent flow monitoring regulations and guidelines By Alasdair Ward of Solartron Mobrey •

Nearly all the Consent to Discharge orders granted by the Environment Agency to larger sewage treatment works include a requirement for continuous monitoring of flow volumes. Although the Agency has not been in a position to actively enforce this requirement until now, it will begin implementing a new programme of checks later this year, designed to ensure compliance. In this article, Alasdair Ward of Solartron Mobrey warns that there is a great deal of work to be done if the industry is to meet the EA requirements. He calls for clarification from the Agency on some of the detail, and advocates a more structured approach to the whole issue of flow auditing and site certification.

The UK enactment of European Directives under the Water Resources Act 1991 and the subsequent Environment Act 1995 demand that the Environment Agency (EA) achieves certain Water Quality Objectives. In carrying out this work, and as part of its wider duty to protect the environment, the Agency requires dischargers to measure and record effluent flows. This requirement is included in most Consents to Discharge granted by the EA for medium and larger discharges of trade and sewage effluent. Until now, Consent to Discharge conditions relating to flow measurement has not been widely enforced. The Agency has the power for criminal prosecution of non-compliant companies, with the possibility of significant fines for repeated offences. Under a new policy, the Agency will soon start to implement a programme of enforcement, designed to ensure compliance among dischargers. Where Consents already include flow measurement conditions, these will be enforced. Where they do not, appropriate conditions will be added. 98% of the waste water treatment sites in UK have at least some open channel flow, and for many it is the primary method of discharge. Hence much of the discussion on the subject of discharge centres on issues of open channel flow measurement. As one of the first steps in its programme to ensure compliance, the EA published its Technical Report P150 Flow Monitoring of Discharges: An Audit Manual* in January 1999. It is based on, and distils the essential relevant information from the European Directive, and from the British Standard BS3680 Methods of Measurement of Liquid Flow in Open Channels, which details correct design and use of primary flow structures such as flumes and weirs. Based on the existing documentation and experimental data, the EA report has identified a minimum accuracy of ±8% for discharge flow monitoring. Interestingly, early work

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2 by Mobrey’s flow audit team in this area indicated that about 90% of all open channel flow structures in the UK do not meet this 8% accuracy standard. According to the Environment Agency, many sites are inadvertently sub-standard, and may not even be aware that there is a problem. In other words, if the full force of the law were to be applied across the UK right now, most operators would be seriously in breach of the terms of their Consent to Discharge. 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 sets out guidelines for the flow audit procedure, and is the document, which will be used by Agency personnel involved in surveying sites. It is available for companies carrying out their own flow audits. The Agency will require that dischargers install flow monitoring to the required specification and have the installation certified by an external body. The Agency will audit a number of installations each year. Discrepancies 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, having studied it, the author believes that there a few discrepancies between it and other standards, which need to be cleared up if confusion is to be avoided. These discrepancies include: •

In section 2.2.2.7 Construction of the Primary Device, P150 quotes the BS3680 tolerances 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. According to the Agency, implementation is being discussed internally at the moment, but it seems likely that, as long as the overall accuracy of the installation can be shown to be ±8%, these 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 ‘10 times the maximum width of the nappe plus five time the maximum head’. The report omits to say that this distance is not required by the British Standard if the approach velocity is negligible. If there is no disturbance to the water, then the upstream distances are not necessary for accurate measurement.

Despite these discrepancies, the technical report provides the industry with a good starting point. It will help to clarify thinking on the subject and provides a useful tool for use by discharges and Agency surveyors. Interestingly, the Agency is apparently considering production of a shorter, less technical version of the document, aimed at managers and non-technical staff.

Compliance and the case for accreditation In order to comply with the legislation on effluent discharge, water companies must prove to the EA that they are monitoring flows adequately. In other words, they must complete a full flow audit, correct any

2

3 errors and implement a maintenance programme to ensure accuracy is maintained. Importantly, they must document all of these procedures in a manner suitable for inspection by the EA, in order to prove compliance. There are already a few companies – Mobrey being one of them - offering flow auditing and consultancy for compliance with the new regulations. When work is completed to the required standard, a certificate of compliance is issued, which can be used as documentation for inspection by the EA. However, since the EA does not operate an accreditation scheme for bodies carrying out this work, there is no cast iron guarantee of quality, or that the work will meet EA requirements. Today the legislation is new and those with the necessary skills and experience to carry out this work are few, and for the most part, are well known in the industry. However, without proper regulation, there is a danger of cowboy and / or inexperienced operator’s in the future offering sub-standard ‘compliance’ audits. Flow is a complex subject, but one on which there are vast amounts of experimental data. With the right knowledge and experience even the most complex flow systems can be fully audited to the required accuracy. The publication of Flow Monitoring of Discharges: An Audit Manual is a great first step by the EA in helping the industry to implement new legislation, but it does not go far enough. There is a strong case for an accreditation scheme for companies offering consultancy and contract civil work (such as the Competent Body scheme which authorises test labs to certify compliance with regulations on electromagnetic compatibility for new products, for the electronics industry). Such a scheme would set minimum levels of quality and give the industry a practical means of ensuring compliance. Ends

For further information contact: Peta Glenister: Tel: (01753) 756600. Fax: (01753) 823589. email: [email protected] Editorial contact: Rachel Owen, Black & White Technical Marketing Communications, 8 Sceptre House, 57 The Hundred, Romsey SO51 8BZ. Tel: 01794 521156. Fax: 01794 521157. Email: [email protected] Solartron Mobrey is one of the world’s largest suppliers of instrumentation for level measurement, serving markets in 66 countries, through a worldwide network of distributors and agents. Web site: www.mobrey.com

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