Reservoir inspecting engineers: safety inspection of reservoirs
Guidance for inspecting engineers including the reporting of section 10 inspection findings.
This guidance applies to high-risk reservoirs in England under the Reservoirs Act 1975. You should not inspect reservoirs for which you are already the supervising engineer. The roles of inspecting, construction and supervising engineer should not be carried out by the same person.
Evaluation of historical information
Previous inspection reports can provide valuable information on:
- historical problems at the reservoir
- remedial works
- completed improvement works
Problems can arise if you over-rely on the content of previous inspection reports. Stay curious about the records that were available for each inspection and the supporting evidence in each report.
Inspection reports should aim to record all:
- important studies
- investigations
- physical works carried out since the previous inspection
Relevant information from the owner or operator should be available in the reservoir inspection information pack. We recommend you do your own independent research using online resources. Examples include:
- Institution of Civil Engineers archives
- British Geological Survey GeoIndex
- historical Ordnance Survey maps
- local history websites
- historic images on Google Earth
When there is not enough information to rule out design weaknesses, consider recommending suitable studies or investigations.
Resources for the inspection of structures
You should inspect all reservoir structures closely and, as far as practicable, by direct access during your visit. You may need to re-visit structures if direct access was not possible during the inspection. A list of technical guidance documents is maintained by the British Dam Society.
Particular emphasis should be placed on spillways following the 2019 Toddbrook Reservoir incident. You should also read the guide on examining spillways which explains:
- how to do close, direct inspections
- when alternative methods of access are appropriate
The reservoir spillways design guide also provides a useful resource for key aspects of spillway design.
Use of precautionary measures
If you decide to recommend measures in the interests of safety (MIOS), you should consider the need for precautionary measures. They should reduce the risk of a breach until the relevant safety interventions can be completed.
You could include precautionary measures as:
- MIOS - for example, lowering the reservoir water level by 1m within the next week
- non-statutory advice – for example recommendations for increased surveillance visits
Precautionary measures could include:
- temporary lowering the reservoir water level - possibly based on the level of the lowest defect. If drawdown pipes do not exist or are inadequate, consider the use of pumps
- using a by-wash channel to reduce reservoir inflow
- isolating or diverting any flow from indirect catchments
- lowering water levels in any upstream reservoirs to provide more storage
- stabilisation measures
- new telemetry to monitor water levels
- increasing water level monitoring and setting alarm triggers for taking further actions
- increasing the scope and/or frequency of monitoring and surveillance visits
You should consider any environmental and legal obligations the owner or operator may have.
These may include:
- having an environmental permit
- having a water abstraction or impoundment licence
- avoiding causing environmental damage
- fish protection – contact the Environment Agency for advice
Owners and operators are responsible for understanding the legal requirements. It is not your role to explain these to them. If they are unsure, you could suggest they contact the Environment Agency for advice.
It may be possible to quantify the cost impact of implementing precautionary measures. In this case the guide to risk assessment for reservoir safety management can help you determine whether:
- the proposed precautionary works are justified
- the cost would be disproportionately high in relation to the reduction in risk.
The risk should be managed to within the tolerable zone of risk for the reservoir and reduced as low as reasonably practicable (ALARP).
If the cost impact cannot be easily quantified, you can use the guide to evaluate and demonstrate that the risk reduction is reasonable over the period the restrictions will apply for.
When planning a precautionary drawdown of a reservoir, you should highlight the importance for an owner or operator to:
- set up reporting procedures - they should send relevant observations and readings to the qualified civil engineer promptly
- talk to the Environment Agency and local stakeholders about the measures – for example the level of protection downstream and how they will manage storm flows
- check if there are local environmental restrictions on the reservoir volume, depth or discharge
Preparation of the section 10 report
You should structure your section 10 report so that it is compliant with legislation. Each report must include the information given in the section 10 minimum requirements.
You should also use your judgement in structuring the report to make sure that:
- all relevant matters are included
- structural and hydraulic components are covered
- the report is prepared in a logical order
Your section 10 report should also include:
- a list of the documents available
- a description of the reservoir structures
- a summary of remedial and improvement works
- a description of the conditions found with photographs
- comments on any relevant changes to the conditions upstream or downstream of the reservoir
- a section summarising the adequacy of the reservoir structures under relevant hydraulic and structural loading conditions, including seismic
- access and security provisions
- comments on the available emergency flood plan
- comments on the reservoir surveillance provisions
You should also provide comments on any available risk assessment for the reservoir. If one is not available then provide at least a failure mode assessment.
A failure mode assessment should:
- list all the potential key failure mechanisms relevant to the reservoir
- consider whether each mechanism is credible and significant
- summarise the key mitigations that you consider appropriate - these mitigations should be reflected in relevant sections of the report
- make appropriate recommendations where there are shortfalls in the safety management provisions (such as monitoring) or where relevant studies are needed to better assess the risk
You can see an example section 10 report template that meets the minimum requirements in Appendix B. This template supersedes the template provided in Table D5 in the Guide to the Reservoirs Act 1975.
Writing recommendations for measures to be taken in the interests of safety (MIOS)
You should:
- write each MIOS in clear English that will be easily understood by the owner or operator
- try to avoid unnecessary use of technical terms
- Write each recommendation so that it is clear what the undertaker must do to achieve compliance
- explain why the measure is so important and urgent to the safety of the reservoir
You should explain if the reservoir poses an unacceptably high risk to the population downstream if they don’t complete the MIOS. This can help convey an appropriate sense of urgency for the completion of the MIOS.
In communicating with the owner or operator you should:
- recommend that preparations and planning for the works should start as soon as reasonably practicable
- draft a programme of the activities that you consider likely to be required to fulfil each MIOS
This should help the owner or operator to understand the reasoning for the compliance date you have set. It shows the importance of making an early start in addressing the work and meeting the deadline for compliance.
If you cannot confirm a remedial or improvement action without more studies or investigations, list the studies/investigations as part of your MIOS. Then set a date to complete them. You should state that when the investigations are complete the qualified civil engineer will:
- set the scope of the remedial action
- set a completion date
- copy this advice to the Environment Agency
Statutory maintenance
You must state in the section 10 report any recommendations for statutory matters of maintenance under section 10(3)b of the Act. If there are none, state that there are no such recommendations.
Guidance on maintenance recommendations is available on page 50 (paragraphs 4 to 7) of the Institution of Civil Engineers A Guide to the Reservoirs Act 1975.
If you consider that the owner or operator must complete maintenance items by a set time, include them as MIOS. A qualified civil engineer can then certify them as complete under section 10(6). You can include other routine matters of maintenance as statutory maintenance items.
The supervising engineer verifies compliance for these recommendations. You should set out recommendations carefully and with sufficient detail. Consider the ease with which the supervising engineer can assess and verify compliance.
Formal meeting about the section 10 inspection findings
You should arrange a meeting with the reservoir operator or owner and the supervising engineer. The formal meeting could be in person or as a conference call. You should do this promptly, particularly if urgent actions or immediate precautionary measures are required. In any case, the meeting should be within one month of the inspection.
At that meeting you should:
- discuss the initial findings
- explain any urgent actions and immediate precautionary measures required
- discuss your draft recommendations for MIOS and statutory maintenance items
- explain the risks and safety implications of not carrying out the MIOS
- discuss the programme for completing the MIOS
- discuss any environmental legislation that could affect the programme for completing the MIOS
- recommend the undertaker appoints a qualified civil engineer within 14 days from the inspection report date
- explain that the completion date is the trigger for enforcement action - this does not represent the urgency, but the likely time needed to complete the MIOS
- discuss any appropriate changes in the monitoring and surveillance requirements - include any specific matters for the attention of the supervising engineer in the short or longer term
You should make a written record of the meeting (the minutes) and share them with the people that attend. Check that they all agree with the minutes.
The final section 10 inspection report does not need to reflect the same findings and recommendations as the minutes. If appropriate, you should arrange a second meeting.
Submitting the section 10 report
You should prepare the draft report as soon as practicable after completing your inspection. You should share a draft with the owner or operator before finalising the report.
If you cannot provide your final report within 6 months, you must tell the Environment Agency Reservoir Safety Team and explain why. You should email reservoirs@environment-agency.gov.uk.
Preparing a section 10(6) MIOS completion certificate
If partial s10(6) certificates are issued, then a full s10(6) certificate must be issued on completion of all MIOS.
A qualified civil engineer (QCE) must sign and date a certificate under section 10(6) once all MIOS have been completed to their satisfaction. This is sent to the owner/operator and the Environment Agency to verify compliance.
You should include an annex to the certificate containing a description of the work completed and its significance in improving reservoir safety. The QCE should reference any reports on studies and investigations completed together with any relevant drawings or other design/construction documentation.
Recording this information will make sure:
-
the owner or operator to accurately update the statutory reservoir records
- the next inspecting engineer understands what work was done leading up to the time of the certification
- there is an accurate description of the work to be included in the section 10 report
It may be helpful for the supervising engineer to see the information contained in the annex, particularly if there are any impacts on monitoring and surveillance. The QCE should therefore make sure that the supervising engineer receives a copy of the information.
Appendix A: Section 10 report minimum content requirements
The following lists the minimum contents of a section 10 report, taken from Schedule 5 of statutory instrument SI 2013 No.1677.
- Name and situation of reservoir, including National Grid Reference of its approximate centre
- Name and address of engineer
- Name of panel of which engineer is a member
- Name and address of undertakers who appointed engineer or confirmation that the Environment Agency appointed the engineer, as appropriate
- Date or dates of inspection
- Engineer’s findings
- Findings as to whether Undertakers are complying with their obligations under Section 11 of the Act in respect of maintaining a Prescribed Form of Record
- Findings as to whether Undertakers are complying with their obligations under Section 11 of the Act in respect of monitoring (water levels, etc)
- Particulars and directions given by the engineer as to the intervals at which, or the manner in which information is to be recorded under Section 11 including the minimum requirements for the scope and frequency of monitoring (water levels, etc)
- Details of any recommendations involving alterations or additions to works or the installation of instruments or gauges for measuring leakage, deflections, settlement uplift, pore pressures or similar matters
- Details of any movement of the surrounding land observed that might affect the stability of the reservoir
- Findings as to the adequacy and condition of the overflow and any channels connected with it
- A statement of any alterations observed that affect the level to which water may be stored or to the level of the overflow sills since the last inspection
- A statement as to the adequacy of the margin between dam(s), reservoir walls or embankment level and overflow level
- Findings as to the efficiency of the scour pipe or discharge culvert or other means of lowering the level of water in, and any other means of controlling the inflow of water to, the reservoir
- Any recommendations as to any measures required in the interests of safety and the period within which those measures should be taken (under Section 10(3)(c))
- Any recommendations as to the maintenance of the reservoir (under Section 10(3)(b))
- Recommendations as to matters to be watched by the supervising engineer
- Recommendations as to the time of next inspection
- A statement as to whether all the safety measures recommended in the previous report have been taken and either recommendations to take any safety measure that has not yet been taken or an explanation of why it is no longer required
- Signature of the engineer
- Date of the report
Appendix B: Example section 10 template
1 Name and situation of reservoir
1.1 Reservoir name
1.2 Situation including national grid reference of its approximate centre
2 Name and address of engineer
3 Name of panel of which engineer is a member
4 Name and address of the enforcement authority
5 Name and address of undertaker who appointed the engineer (If the regulator appointed the engineer in lieu of the undertaker(s) then the heading should be changed accordingly)
6 Name and address of supervising engineer
7 Date of inspection
8 Information available
9 Description of the reservoir
9.1 General
9.2 Geology
9.3 Catchment
9.4 Dam details
9.5 Inlet arrangement
9.6 Outlet arrangement
9.7 Overflow and spillway
9.8 Instrumentation
9.9 Access
9.10 Downstream conditions
9.11 History of remedial and improvement works
10 Description of the conditions found
10.1 General
10.2 Catchment area and upstream structures
10.3 Dam embankment
10.3.1 Upstream face
10.3.2 Crest and wave wall
10.3.3 Downstream face
10.3.4 Drainage systems
10.3.5 Services
10.3.6 Settlement/movement
10.3.7 Seepage performance
10.3.8 Other performance indicators
10.4 Inlet structures
10.5 Outlet works
10.6 Overflow and spillway structures
10.6.1 Overflow
10.6.2 Spillway chute
10.6.3 Energy dissipation
10.7 Reservoir rim stability
10.8 Access and security provisions
10.9 Changes in downstream conditions
11 Engineer’s findings
11.1 Reservoir risk assessment
11.2 Stability, seismic risk and internal erosion
11.2.1 Seismic categorisation
11.2.2 Static and seismic stability
11.2.3 Vulnerability of the reservoir structures to seismic loading
11.2.4 Internal erosion
11.3 Adequacy and condition of the waste weir and overflow and any channels connected with it
11.3.1 Flood inflow
11.3.2 Adequacy of freeboard
11.3.3 Spillway structural and hydraulic performance
11.3.4 Energy dissipation
11.5 Any alterations which affect the level to which water may be stored
11.6 Adequacy of low-level outlets and means of controlling inflow
11.7 Adequacy of access provisions for maintenance and emergencies
12 Supervision provided by the undertaker
12.1 Correctness of the Prescribed Form of Record
12.2 Compliance with water level monitoring
12.3 Instrumentation
12.3.1 Compliance with monitoring requirements
12.3.2 Requirements for additions or alterations to instrumentation
12.4 Reservoir surveillance
12.5 Emergency planning
13 Recommendations
13.1 Statement in relation to previous measures to be taken in the interests of safety
13.2 Measures to be taken in the interests of safety under Section 10(3)(c)
13.3 Other measures recommended to be taken but not requiring supervision by a Qualified Civil Engineer
13.4 Matters of maintenance under Section 10(3)(b)
13.5 Other matters of maintenance and safety of personnel/public
13.6 Matters to be watched by the supervising engineer in accordance with Section 10(4)
13.7 Directions in respect of recording information under Section 11(2)
13.8 Date of the next inspection under Section 10
14 Signature of Engineer
15 Date of report