Prepare a reservoir flood plan

Any reservoir which stores water above natural ground, behind an embankment or dam, is subject to deterioration and could fail. The flooding which may be caused by the failure of your reservoir can happen very quickly and the consequences can be devastating to you, to the people living and working downstream, and the environment.

This guidance is written for a range of reservoirs and not all of it may apply to you or your reservoir. You should use the headings as a guide and choose a format to suit you.

Be proportionate, concise and clear

Write your flood plan so it helps you respond effectively. Your flood plan should be:

proportionate to the hazard posed by your reservoir
concise – focus on who does what, where and when
clear – use language, diagrams and pictures which are easy to understand

If an incident occurs at your reservoir which affects people, their property, or the environment, you could be subjected to investigation and face substantial claims. If an incident only affects your property, it could still cause you damage, loss, and inconvenience. Writing and maintaining a flood plan demonstrates good management of your duty of care to prevent harm to others and to the environment.

Phoning 999 is not a plan

Dam incidents often occur at times of flood when emergency services are already committed to other incidents. You should not rely on help being immediately available. But when you phone, you can use your flood plan to provide clear information to help them prioritise a response.

Get involved and take responsibility

We recommend your flood plan is written by the people who operate the reservoir to ensure they are familiar and confident in the plan. You may need technical advice from a reservoir engineer or other specialist, but you are responsible for the effectiveness of your flood plan.

Your flood plan can be in digital or paper format. Digital may be better where frequent changes are likely, but only rely on digital copies if you have reliable instant access and have back-up power where they are stored. Consider data security and practical accessibility on-site. We recommend paper copies are waterproofed.

Location

Your flood plan will need to give accurate locations. The grid reference finder website can help you give precise locations in different formats and provide links for:

postcode area
full postal address and postcode.
British National Grid Reference as a grid reference, or as eastings and northings,
What3Words which provides accuracy to 3 square metres

What to include in your flood plan

The guidance below is aimed at all sizes and complexities of reservoirs. Not all the guidance will apply to your reservoir.

Cover page

The cover page should include the following information:

reservoir name (with any other local names used given in brackets)
reservoir locality and address including postcode
national grid reference and What3Words location
risk designation: “high-risk reservoir” or “undesignated reservoir”
name and address of the undertaker (the owner or operator legal entity)
the name and 24-hour contact details of the senior person with direct responsibility for responding to incidents (an operational decision maker)
the name and contact details for the person with overall responsibility for the safety of the reservoir
the date of the last revision
the date of the last flood plan test

You can use the grid reference finder website and What3words to help you identify grid references and location coordinates.

Plan your actions

Incidents can be stressful. It helps when decisions are made on pre-planned actions and sound advice. Keep your actions clear and simple. Your planned actions can be separated into three stages which are described below.

Substantiate the incident

Think about who will do what and how to substantiate an incident when there is an event or observation of something unusual or wrong at your reservoir, for example:

water overflowing the dam or outside of engineered channels
leaks, seepage, and wet spots (especially if new, or changed)
settlement, slumps, or cracking showing movement in or near the dam
unusually high or low water levels
unusual or missing instrument readings
structural damage, vandalism or a problem in the dam or its spillway

Give clear instruction on how to contact the supervising engineer for advice and to establish the severity of the incident. Include the contact details for a stand-in supervising engineer if your normal one cannot be contacted. Specify who else in your organisation needs to be informed.

You may need to take advice from an inspecting engineer who can provide more expertise than your supervising engineer. You should identify and list the contact details of the most appropriate inspecting engineers from one of the following Government panels:

Service Reservoirs Engineers

As well as your flood plan, you may want to include specific triggers in your operational instructions which require action, for example when water reaches certain levels.

Response

Think about reasonably foreseeable incidents, such as those listed above, and set out actions that may be needed to prevent deterioration, stabilise the incident and make emergency repairs.

Identify the people who should respond and what immediate action they should take.

Signpost the flood plan section on the instructions for an emergency drawdown and any internal authorisations for this, as described above.

Reducing the water level takes time and you may need to make repairs quickly.

list local suppliers for materials such as sandbags, industrial plastic sheeting and bulk filling materials like stone and clay.
list where heavy machinery like tractors, loaders, diggers, and dumper trucks (with drivers) can be borrowed or hired from.

If you stockpile your own materials or have machinery, include instructions on where they are normally kept. It’s worth finding out if suppliers can provide an emergency or out-of-hours service.

Think about how you may need to look after the health, safety and welfare of people on site in potentially dark and poor weather conditions.

Your planned actions should allow for uncertainty and be adaptable to changing circumstances.

Recovery

At the end of your flood plan you should set out any actions which may be needed after the emergency has ended. Include prompts to:

submit a preliminary post-incident report
review or revise your flood plan

Instructions for an emergency drawdown

You must include clear instructions on how to reduce the water level in your reservoir. Use descriptions, diagrams, or annotated photographs to help describe actions. Cross-reference important locations on the site plan.

Inflow control

If you can close off or reduce the water entering your reservoir, describe how this is done. State the range of inflow expected and the capacity of any diversion around the reservoir.

Otherwise write: “reservoir inflows cannot be controlled”.

Gates and valves

Describe the location and type of any bottom outlet or scour valve, and how to operate it, for example the direction and number of turns required. If a key, handle or wheel is needed make sure you say where this is kept. Include the number of people required to operate the equipment.

Specify the duration and effort needed to open the valve or gate fully, for example: “to open to 100%, turn spindle clockwise 60 full turns.”

Provide the capacity of each outlet and rate of release you’d expect to achieve.

Pumps

If your reservoir doesn’t have pipework or draw-off controls, or these are limited, you must plan to use pumps. If you don’t have pumps on site, you will have to hire them. List the pump providers and contractors to be used and likely delivery times. You could also ask the supplier to visit and make recommendations for the size of pumps.

Plan the best places to put the pumps. Not all pumps are mobile and large ones maybe unloaded by crane. Consider requirements for re-fuelling them and supervision.

Pipework to discharge

Plan the route to lay down pipework and where to discharge the water. Consider if you would need to construct an access track to reach the best pumping location which could be constructed from a geotextile fabric and stone. Think about how pipework and floats may need to be moved as water levels change uncovering thick mud.

Environmental impacts of drawdown

Describe any actions to be taken which will limit the environmental impact of emptying the reservoir. Discharges from reservoirs must normally be done in accordance with the conditions imposed by a permit or consent given by us. In an emergency, you may not be able to comply with all the conditions, but you should have a pre-prepared method statement to explain the steps you’ll take to minimise pollution.

Include an instruction to contact us on 03000 65 3000 to inform our Duty Officers that reservoir water will be released and tell us about the duration and impact this may have.

Detailed drawdown guidance

If you operate a high-risk reservoir, you should expect your engineers to make recommendations, so your reservoir meets optimal drawdown capacity and rates.

You’ll probably need advice from your supervising engineer to calculate the anticipated rate of drawdown for a range of inflow conditions when the bottom outlet is fully open. Specify:

the point at which the water level is 1m below the spillway overflow level to protect against erosion in the upper part of the core
the point at which the water depth is at 70% of the initial reservoir level. This reduces the load on the dam by about half.

Changes to the draw down facilities should prompt you to revise your flood plan.

Contact details and communications plan

Your flood plan should include:

24-hour phone numbers for all owners, operational staff and technical advisors that may need to be called, including a summary of their role
the contact details of any “on call” contracts in place
how to alert emergency responders and the information to be given
contact details for agreed users of the reservoir or others who may need to know that the reservoir is closed
mobile phone coverage details, including mobile phone networks at the site
the nearest fixed landlines
insurance provider contact details

Basic information

List the following information which will be a useful summary when briefing engineers, etc.

Reservoir type - “impounding” (filled directly by a water course), “non-impounding” (filled by diverting or pumping water), “service” (brick or concrete non-impounding reservoir used for water supply)
Construction type, for example, “earth-fill embankment”, “rock-fill embankment”, “concrete gravity dam”, etc.
Dam design flood category (Category A—D). This will be given in your inspection report, or you can ask us or your supervising engineer for advice.
Year of construction (known or estimated) and date last altered
Surface area
Dam height
Capacity

Description

We suggest the following information is provided as a short description or overlaid on a photo or site plan:

describe how water enters the reservoir
describe the arrangement of overflows or spillways
draw attention to other reservoirs upstream and downstream
give a brief description of any modifications, specific features or uses of the reservoir which may inform an emergency response

Supporting information and documents

During an incident, engineers and other advisors may need to see a range of information about your reservoir to inform their response. You should keep all the information about your reservoir in one place. If this is not possible, state where it is kept.

Keep a contents list of the information you have and provide this to your engineers.

Flood map

You should keep a copy of your reservoir flood map with your flood plan. If you do not have a flood map, you should contact us.

You can also use our online Flood Map Viewer.

Location and access plan

This section is about providing information to any of your staff or contractors so they can access the site and find their way around. You should write it for those who may be less familiar with the reservoir who visit less frequently.

Use the flood map, the information in your inspection reports, and your own local knowledge to think about the routes to and from your reservoir which may be affected by flooding and how they can be avoided.

Provide a map and / or description showing the location of the reservoir and the best access routes from the nearest main roads. A map scale of 1:50,000 is usually appropriate.

Highlight and describe the main access routes and entry points. Include access routes across neighbouring land and any conditions or agreements for this. Provide any next best alternative routes which may be appropriate.

Draw attention to any restrictions which may limit vehicle access like width, height, weight, sharp bends, or parking limitations. Mark areas with problems like localised flooding which may hinder access.

Site plan

Your site plan is a map with markings and descriptions of the reservoir showing its main structures. A good site plan will help your staff and contractors find their way around effectively. If you have several dams, you may need several site plans.

Structures to include on a site plan:

dams and embankments
inflow control structures which control water entering the reservoir
spillway(s) or overflow pipe(s)
pipes, valves, or channels and so on which control the water

Think about access, and where appropriate, mark on:

vehicle access points, parking, and reception areas
access routes which require 4x4
locked gates and how to open them
potential trouble spots, like soft ground and overhead cables

Add the basics of

the best place to put mobile pumps and lay associated pipework
the location of equipment such as valve keys, penstock handles and wheels
if mobile phone reception is poor, mark areas where it is most reliable. If there is no mobile phone signal at the site, clearly mark “there is no mobile phone reception at the reservoir”

General considerations

Your flood plan should focus on the critical information and activities. Where appropriate you may need to consider and include information on:

delegation of authority for action or decisions, including financial decisions.
delegation to cover long-lasting incidents.
communication with the emergency services, and between engineers, advisors and contractors
communication with local communities, in line with the off-site plan
clarity on who has overall responsibility for managing the incident including the health, safety and welfare of people

The more people that look after or visit the reservoir, the more you need to plan how to look after them. You should consider the need for a risk assessment for:

working alone and / or prolonged working hours
working in or near water, confined spaces, at height
water borne diseases
slips and trips
adverse weather and darkness

Some procedures may be better kept as part of your overall reservoir safety management plan, just keeping any incident-specific information in the flood plan.

Minimise environmental impact

Include an instruction to contact NRW on 03000 65 3000 to inform our Duty Officers that reservoir water will be released and tell us about the duration and impact this may have. This will also ensure you provide your statutory preliminary notification of the incident.

Discharges from reservoirs must normally be done in accordance with the conditions imposed by an Environmental Permit or Water Industry Act Consent. In an emergency you may not be able to comply with these conditions, but you should prepare a method statement explaining all the steps to be taken to minimise pollution.

Verify your flood plan

When your flood plan is complete, you should make an entry in Part 4 of your prescribed form of record.

Your supervising engineer will check your flood plan and prescribed form of record and may provide recommendations. This is normally done as part of their section 12 statement. If you don’t have a supervising engineer, you can ask an engineer from any of the reservoir panels.

Sharing your flood plan

A flood plan is your plan for your use and does not normally need to be shared except:

on request by us or any of your appointed engineers
on request by your Local Resilience Forum or Local Authority emergency planning department with responsibility for reservoir flooding

Your plan should be available in a format that can be shared easily. You should mark and protect your flood plan as ‘commercially confidential’ or ‘sensitive’ because it holds dam, operational and personal data.

If you have a high-risk reservoir, it means life could be at risk if your dam fails. You must make sure all reservoir operators have access to your flood plan and are familiar with it. Also consider familiarisation and training events for contractors coming to site.

Considerations for higher hazard reservoirs, or complex management structures

The guidance above applies to all reservoirs. This additional guidance is intended if you own, manage or operate a reservoir which:

poses a high flood hazard
has more complex structures
your organisation has different levels of operational or management roles

Owners of small or simple reservoirs may also consider this but we recommend all owners maintain a focus on keeping the flood plan proportionate to the hazard posed.

Consider taking advice from an emergency planner to help you structure your flood plan and its contents. If your organisation is also an emergency responder, consider how your reservoir flood plan interacts with your other responsibilities.

Security arrangements

Think about

alarms or other intruder detection systems
security standards in place, for example, compliance with Loss Prevention Certification Board Standard LPS1175
pedestrian only routes
potential helicopter landing sites and safety implications for this
equipment storage
keys holders, key safes, and access codes
commercial confidentiality

Incident management structures and communication

Be clear who has overall responsibility for managing the incident including the health, safety and welfare or people.

Consider naming different stages of an incident to clarify the urgency of response, e.g.

Stage 1 alert and implementation

An event or problem is confirmed and requires investigation. Precautionary action is needed. Includes minor deterioration and repairs.

Stage 2 warning or alarm (possible failure)

A possibility of dam failure or major deterioration. Emergency drawdown and urgent repairs and flood mitigation required. External awareness and assistance required.

Stage 3 failure is imminent/ foreseeable, or actual failure

The actions here should add to previous actions and include withdrawing people from danger and controlling or mitigating the effects of a flood

Stage 4 stand down

Review and return to normal operations. Post-incident reporting.

You should determine your own level of response to match your organisation’s other emergency procedures. Describe how incident levels are to be identified and escalated in your organisation, and by whom. Specific duties may include activities such as:

approval of action to start emergency drawdown or buying in pump services
communication with the emergency services, in association with their off-site plan
communication between engineers, your team, contractors, and other advisors
communication with local communities and media

Consider knock-on effects of an incident and how these should be managed, for example loss of water supply or electricity generation.

You should consider how to manage public or media interest and allocate a person to deal with enquiries and avoid distracting intrusion. You should prepare some basic statements or holding responses to enquiries. This is especially important if your reservoir attracts a lot of interest generally, for example as a popular fishing venue.

Your communications plan could also set out how social media will be used or how you will respond to questions, comments, misinformation, and rumours.

Welfare facilities

Describe and mark on your site plan the facilities which may help emergency responders.

rest areas, toilets and facilities to make hot drinks and eat
meeting rooms or office space
equipment storage and drying areas
waste disposal
phone and equipment recharging facilities
the nearest Accident and Emergency hospital or facilities
petrol stations or other refuelling facilities.

Qualified civil engineers

Long-lasting incidents require several qualified civil engineers available to advise. Consider familiarisation events to raise their awareness of the reservoir. Include engineers with your schedule of flood plan testing.

Key contacts

If many people are mentioned in the flood plan, you may find it easier to keep it up to date if you use role titles, e.g., “reservoir technician” in the plan and provide an annexed or linked contact sheet giving each role title along with the current names and phone numbers.

Neighbouring reservoirs

We advise you discuss your approach to emergencies with neighbouring reservoir owners to share information, understand combined flood risks and agree what help may be mutually provided.

Read guidance on how to Review, test and revise your reservoir flood plan

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