Reservoirs: managing your reservoir in extreme weather
Source: gov.uk (2025-09-08)

This guide explains the problems and risks which may come from extreme weather, how to mitigate them and how you can make your reservoir more resilient. You can read each section in isolation, or as a whole document.

Introduction

This guide aims to help you understand how extreme weather events could impact the safety of your reservoir. It suggests how to manage, maintain and improve your reservoir to make it more resilient. All reservoir owners and operators have a legal responsibility for public safety.

This guide does not cover masonry or concrete dams, as there are very few in England.

The guide is designed to be modular. Each section is independent and can be read in isolation, as well as one piece.

Existing guidance

There is a wide range of guidance for reservoir owners and operators available (https://www.gov.uk/government/collections/reservoir-safety#guidance-for-reservoir-owners-and-operators).

Owner and operator requirements (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements) outlines the legal requirements for owning and operating a reservoir.

How to manage your large raised reservoir (https://www.gov.uk/guidance/reservoirs-how-to-manage-your-large-raised-reservoir) is a good introductory guide for owners. It outlines the principles of reservoir management and contains advice on:
- the roles involved in managing reservoirs
- your role as an undertaker
- common problems, how to spot them and how to reduce the risk of these happening
This guidance on manging your reservoir in extreme weather is designed to complement the How to manage your large raised reservoir (https://www.gov.uk/guidance/reservoirs-how-to-manage-your-large-raised-reservoir) guidance.

Climate change and extreme weather

The climate is already changing and the Environment Agency has seen an increase of incidents which relate to weather events. Weather is likely to be more severe in the future. Predictions of how this will develop are also changing with increased understanding. This guide is based on current knowledge. We expect climate change will increase the frequency and/or severity of the following threats, each of which has its own section in this guide:
- prolonged heavy and/or extreme rainfall and cumulative flood events
- extended ground saturation
- drought and fire
- storminess and high winds
- snow and ice
A review of reservoir safety incidents suggests that floods and heavy rainfall contribute more than any other triggers. The main root causes of incidents relate to:
- poor or outdated design principles
- construction-related defects
- insufficient surveillance and examination
- lack of maintenance
A reservoir’s dam might not fail in a single extreme weather event but could fail due to the cumulative effects of long-term repeated damage. Earthwork structures are sensitive to physical and environmental loading over repeated cycles in time. You should monitor your reservoir frequently, so that any damage can be repaired immediately after it occurs.

Using this guide

This guide focuses on 3 main sections of your reservoir site:
- embankments
- spillways
- reservoir outlets and other elements
The outlet and other structures include:
- gates and valves to control how much water is released in normal conditions or in an emergency
- Mechanical, Electrical, Instrumentation, Control and Automation (MEICA) - this includes the gates and valves, plus other equipment such as motors to operate them, electrical control systems, sensors, read-outs, and signalling
- structures such as valve towers, control buildings, inlet and outlet headwalls, screens, access bridges, tunnels, culverts and drainage systems
Terminology

In this guide, we use 3 terms for the levels of activity:

“Management” means:
- keeping good records
- providing reports to the Environment Agency
- arranging engineers’ visits and inspections
- arranging frequent walkover checks by operational staff
The level of management needed depends on whether your reservoir is formally designated high risk. This is discussed more at the end of this introduction section.

“Maintenance” means:
- the general upkeep of the dam and structures which form the reservoir
- restoring them to good condition, so that they work well and safely
- preventative routine actions such as completing checks and inspections
- managing vegetation
- corrective actions when a fault is detected such as repairs, replacing parts or clearing debris and blockages
You should be able to carry out maintenance yourself, or with help from specialist contractors.

“Improving resilience” ranges from minor works to major alterations.

Minor works which can generally be carried out by hand would normally only need discussion with your Supervising Engineer. Alterations are bigger changes which may need construction machinery such as excavators. They could change the nature or shape of a structure and how it performs. These could affect the reservoir’s safety and would need approval from an Inspecting or Construction Engineer.

The term “Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer)” includes all the specialist reservoir safety Engineers’ roles mentioned above. It is defined in the Reservoirs Act (https://www.legislation.gov.uk/ukpga/1975/23/contents). All reservoirs classed as “high risk” by the Environment Agency must have a Supervising Engineer appointed at all times. They must also be inspected periodically by an Inspecting Engineer. Some reservoirs have been classed as “not high risk.” Although these roles are not required, similar levels of surveillance and inspection are recommended as good practice. Alterations which affect the reservoir’s volume may only be carried out with approval from an Inspection or Construction Engineer.

This guide focusses on problems which are, or are likely to be, common for reservoirs in a small portfolio. It also touches on some problems which are less likely but may have high consequences. There will be problems which are not covered by this guide. This guide is not a substitute for professional advice. If in doubt, you must consult a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

General principles

You can reduce the problems discussed in this guide by managing your reservoir well and maintaining it continually. There are some scenarios where increased vigilance may be required, such as where:
- records or construction details are known to be missing
- a defect is identified, or safety improvements are incomplete
- temporary works are in place
You should monitor the weather, the water levels and other data for your reservoir. This is to understand how these change over the long term and how you should change what you do. You may need to adopt maintenance practices which are currently used more in other regions. Climate change might mean you need to do more surveys and repairs. You may need an engineer to examine your reservoir more frequently. There may be changes which could make your reservoir more resilient to the changing climate.

The biggest improvement you can make is to increase the frequency and detail of your reservoir checks and observations. You should do these when the weather is or has been more extreme than before.

For example, during:
- a storm and/or immediately after, when the reservoir water level is very high
- during prolonged, or harsh, dry or cold spells
Focus your attention on the areas of potential impact. Look for signs of damage to the embankment.

When visiting the reservoir during extreme weather, you should be aware of the risks to your own and others’ safety. If water levels rise you could get stranded and if there is a landslip you need to stay clear of it. You may also be at risk from falling trees or other hazards. There is a high risk of:
- slips
- exposure to cold in freezing conditions
- heat-related problems in drought
If you were unable to attend when the storm or flood was at its peak, you can estimate the peak level based on wrack marks. These are the line of debris left on the upstream face of the dam. A knowledge of the peak flood level is often useful in understanding the impact of the event.

For a high risk reservoir, you should review your records and check the inspection report from your Inspecting Engineer. The report will have comments on the flood capacity and when the flood flows were calculated. There have been several advances in calculation methods in recent years and the information may need updating. The last Inspection Report should give you a good understanding of how often the reservoir might overflow and what the risks are when it does. The Inspection Report may also include other requirements or recommendations which are relevant to climate change impacts. You should discuss with your Supervising Engineer whether you need to increase the frequency of monitoring.

You should review your long-term budget to make sure you have access to funds for repairs and improvements in the future.

Rain and flood

Climate change is expected to make winters wetter by up to 30%. Summers may become drier by up to 60%, depending on the region. We have observed changes both in terms of seasonal increases and individual events. Weather extremes are expected to become more extreme and more frequent. Though summers will be drier, predictions suggest rainstorms may be up to 20% more severe.

If rainfall becomes heavier with longer or more frequent storms, the cumulative impact of flood events could cause problems. In winter, reservoirs may be fuller more often and throughout the year they may overflow more often.

When a reservoir is already full and starts to overflow the additional flow should initially be carried safely down the spillway. Some dams’ spillways have capacity for more extreme flood flows than others. There is a high risk of small spillways being overwhelmed. With climate change this may happen more often.

Embankments

Potential impacts of extreme rain and floods

The highest risk from increased flood flows to embankments occurs if the additional flow is more than the spillway can carry. The excess flood flow would overflow at other low points on or near the dam crest. This could erode as they are not armoured against the water’s high energy. This could also happen alongside the spillway if water spills out of the sides of the spillway chute. This could erode the dam and potentially lead to a catastrophic collapse of the dam.

Overland flow from the reservoir, or from intense rainfall, can result in direct damage to the embankment downstream face. In particular where water running off is concentrated due to the shape of the embankment surface. This can happen:
- at mitres, where the embankment meets the valley sides
- next to structures
- at other intrusions on the embankment surface such as fence posts or sharp changes in gradient
Diagram 1: Overflow at low spots in high floods can damage the dam’s downstream face

If the water level in the reservoir is higher than it has been historically, this can trigger seepage through the embankment. Seepage can lead to internal erosion. This is erosion of fine earth particles from inside the embankment fill. Internal erosion may only occur when the water level exceeds a certain threshold but may occur cyclically over a series of flood events.

The top of the saturated zone within an embankment is called the “phreatic surface”. Water level in the reservoir being higher for longer can cause the phreatic surface to rise. This increases the risk of the dam slopes failing in a similar fashion to landslip. These could be deep-seated major failures.

Photo 1 (a): Erosion of embankment dam downstream face due to overtopping. Photo courtesy of the Environment Agency

Photo 1 (b): Erosion of embankment dam downstream face due to overtopping. Photo courtesy of the Environment Agency

How to spot damage

Look for signs of the reservoir overflowing the embankment crest. The first sign would be flattened grass on the downstream slope, followed by patches of exposed earth developing. If earth is being removed, the gullies could erode back up towards the crest. This could also happen where flow paths concentrate at mitres, structures, or other intrusions. The rate of erosion in these types of gullies will differ, but they can easily lead to reservoir safety problems if they continue.

Look for seepage appearing on the downstream slope of the embankment or at its toe (where it meets natural ground level). Some seepage is normal, but increases in flow may be a cause for concern. You need to understand your dam’s normal conditions so you can spot any changes.

Seepage might not be obvious, but there are some signs you can look out for are:
- a patch of ground which is wetter than it used to be
- changes in vegetation such as reeds
- more flow running into the sides of ditches and streams downstream, or the spillway channel or the embankment’s drains
- changes in “turbidity” - how cloudy the seepage flow is
Signs of reservoir safety problems where there is probably damage inside the dam are:
- if the amount of seepage increases when the water level in the reservoir is at or above a particular height
- if the water appears dirty, and is carrying fine material such as sand or silt
Diagram 2: Signs of seepage

Some reservoirs have piezometers, which measure the level of the phreatic surface inside the dam. If the water level in these increases that can be a sign of changes within the embankment. For example, it could indicate leakage through the clay core. It could also mean that the embankment slopes are at risk of a landslip, which could potentially lead to reservoir failure.

Another sign of smaller slips, or early signs of large ones, is cracks appearing at the embankment surface. These can be seen as roughly horizontal cracks developing at the upper edge of a slip and/or as curved cracks along the sides of the slip. There may also be a bulge in the surface at the lower edge. These slips could worsen, leading to reservoir failure.

Maintenance

There are some simple maintenance activities which you can carry out. If you find any significant damage, you should contact your Supervising Engineer before repairing it. They may:
- need to see photographs and measurements
- examine it in person
- advise on appropriate repair techniques
You should:
- review (or obtain) survey data of the levels of the dam crest, spillway, slope and other features - this helps you understand accurately where the low points are and where water would flow in a flood. Note that embankments do settle (get lower) over time, so surveys should be repeated at intervals of around 2 years
- consider changing the grass seed mix to one which has a more uniform length and a strong laterally-spreading root system. Prevent bare areas from getting worse by cultivating healthy uniform weed-free grass cover. you should also consider drought, which could lead to a different grass seed mix
- make the crest and the downstream slope more resilient to overflow, for example by removing fence posts and drops. Prevent burrowing animals causing voids in the embankment. Any holes need to be filled carefully with suitable material and well compacted
- repair any damage to the embankment downstream face and crest, as soon as possible after it is identified
- prevent trees and bushes from becoming established. Remove any decaying tree stumps or roots
- separate drainage flows from the valley sides, away from the dam, to reduce erosive flows down mitres and improve monitoring
- install measuring weirs if that helps to detect abnormal seepage
Diagram 3: A cross section of a reservoir embankment with damage caused by trees and animal burrows. Soil deposition and reeds suggest seepage through the bank.

Improving resilience

Depending on the scale of the work, the following could alter the form and function of the dam, so would need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Most of these would normally be classed as alterations.

You should:
- install hard surfacing on the crest to increase resilience to erosion if it overflows
- ensure there are no low points on the crest, where overflow can concentrate - this may be either the main crest, or along crest walls if there are any
It may be appropriate to create a longitudinal camber on the dam crest, so it is higher at the middle than at the ends. Water overflowing will then have greater depth and velocity where the embankment height is lower. This would reduce the size of the breach wave, if the dam failed.

Spillway

There may be gates or valves which affect how the spillway operates. You can read about these in the section ‘reservoir outlet and other elements’.

Potential impacts of extreme rain and floods

Some common spillway issues are the:
- weir width may be too narrow
- overflow pipe may be too small
- weir or pipe level is too close to the dam crest level to discharge an extreme flood
Water levels then rise too high and the dam overflows the embankment crest. This leads to embankment erosion.

The overflow from the reservoir may be more than the discharge the spillway chute was designed for. Water could overflow the side walls and damage the surrounding ground, leading to erosion and collapse of the side walls.

Water remaining within the chute could be at very high velocity. The energy of this could damage the armour by:
- lifting concrete slabs
- plucking out masonry blocks
- scouring grass
Blockages along the spillway flow route can also restrict the overflow. These blockages would be more likely to cause problems in higher flows.

There may be restrictions at bridge arches or the channel may have sharp bends which limit flow.

Any blockage in the spillway could cause water to overflow the channel and erode the embankment alongside it. It can damage the armour layer within the spillway. If the blockage is near the dam crest, then the water would find another overflow route, leading to erosion elsewhere on the dam. Unintentional blockages may be from vegetation, debris in the spillway or damage to its structure. These could include:
- plants, bushes or trees
- blocks from the structure which have moved
- collapsed sidewall(s), which may fall into the channel and leave unexposed earth
- vandalism such as deliberate damage or items thrown into the spillway
Structural damage or changes can lead to other problems, or be signs of developing ones. Higher flows or more frequent floods would place these weak points under more stress. Signs of potential problems can include:
- gaps or steps at joints
- changes in levels
- displaced blocks
- bulging sidewalls
- water seeping through the walls or base of the spillway chute
Irregularities such as depressions or obstructions would focus the energy of the water, leading to damage.

Problems with the vegetation in grass or reinforced grass spillways such as:
- poor grass cover including bare areas
- broad-leaved weeds, tall shrubs and bushes can also lead to erosion from flood flows
The bottom of the spillway known as the “toe”, is hidden underwater at some dams. Increased flood flows, or more frequent floods, would mean the toe has to deal with water’s higher energy more often, which can cause major damage. The chute and the toe are most vulnerable where there are changes, such as in:
- width
- gradient
- materials
Damage which occurs here can lead to the spillway “unravelling” or working its way back up the dam and leading to other problems. Sometimes the spillway toe is not protected well enough, or deep enough under the natural ground. The water’s energy undermines it; this can be hard to detect if the toe is under water but can lead to sudden collapse.

Photo 2 (a): Spillway masonry blocks dislodged and displaced by flood flow, revealing bedrock and leading to erosion at the side. Photo courtesy of the Environment Agency.

Photo 2 (b): Spillway masonry blocks dislodged and displaced by flood flow, revealing bedrock and leading to erosion at the side. Photo courtesy of the Environment Agency.

How to spot damage

You should be able to see areas of damage if they are present or developing, allowing you to correct them. Examples include:
- patches of erosion beside spillway walls, or locations where flood flows are close to filling the channel on one or both sides
- steps or displaced blocks in the spillway chute, which may be easier to see as patches of white water during overflow
- blockages or damage in the channel
- poor grass cover - for example, bare patches and weeds, exposed soil, or holes where soil has been eroded on grassed spillways
- uneven ground, possibly with protruding or exposed mesh or concrete armour beneath
- ruts or tracks caused by people or livestock crossing grassed spillways
- cracks or settlement around the spillway toe or its sidewalls, because of erosion of foundation material
- undermining of the spillway toe - may only be found by checking in-river and probing underwater
Maintenance

If you find damage, you should repair it using similar materials and methods to the original construction. You should do this as soon as possible to avoid problems getting worse. If the damage happens again, then alterations may well be needed.

You should:
- re-install blocks which have come loose, and re-point those around them
- remove blockages such as trees and debris, if this is from vandals you should try to secure the site boundaries
- cut small trees and shrubs off at the base but do not try to remove the roots as this may cause further damage - keep these locations under a close watch in the long-term as the ground may settle when the roots rot away
- reseed bare patches on grass spillways and treat weeds to develop healthy grass cover - this should be mown to keep it around 10cm tall
- check if mowers or other vehicles cause damage such as ruts or lift up edges of armour mesh, check whether they sank in soft ground - that may be a separate problem, repair the ruts / mesh / armour blocks if needed, seeking specialist advice if you are in any doubt
- keep drainage and weepholes clear, which are discussed in the section on saturation
Improving resilience

Some problems may need more work. They may need guidance from an engineer, or a formal design approved by a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Alterations or major repairs to the spillway can be difficult and need lots of planning. Any concerns must be followed up promptly. The designs should consider and allow for increased flows due to climate change as far as reasonably practical.
- for design issues such as weir width, dam crest level and spillway chute capacity, you would need an engineer to help. They will support you with understanding the dam’s performance in flood conditions. This might lead to major alterations. For example changing the spillway weir or adding another, widening a bridge, or deepening the chute.
- if erosion next to the chute is localised, you may be able to strengthen that area simply with a hard surface and return flow to the channel. For example, this may work where water splashes out of the channel next to a bend.
- collapsed sidewalls may be a sign of other problems. There may be inadequate drainage behind them, or insufficient wall thickness. Simply rebuilding them is not likely to be enough.
- the spillway toe could need underpinning and / or a “scour cut-off” adding. This is a wall which goes down well below the ground level at the toe, to stop undercutting from working back upstream. The toe may need extending, strengthening, or widening to match the river channel and its valley.
Reservoir outlet and other elements

Increased rain or flood flows will not impact all dam elements. This section aims to discuss the more likely or more significant impacts. To prepare for or react to each problem, the text explains:
- how to spot problems
- what maintenance or resilience improvements could be needed to prepare for or react to each problem
For alterations affecting the reservoir’s safety, you will need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

Gates and valves

The main outlet from a reservoir for flood flows is the spillway, as the normal day-to-day flow route is too small. Most gates and valves will not need to be adjusted to deal with flooding, but they can help if you open them. Some spillways also need gates or valves opening for them to work properly too. Check you can access and operate the gates and valves under extreme flood conditions. This includes when the embankment crest is overflowing.

There may be stoplogs (boards) across the spillway to raise the weir crest level for operational or ornamental reasons. They can be removed to increase the outflow but they become hard to remove during high outflow. If they remain, the reservoir level would rise faster. This would increase the risk of the dam overflowing by other routes.

Sluice gates or some types of valves can be hard to open when there is high water upstream. If they cannot be opened it may cause more flood water to flow over the dam.

You should check what types of gates and valves you have, or stoplogs. You must make sure they work properly in normal conditions. You should consider whether you could improve operation in floods. Changing to a different type of control could make the dam more resilient to climate change and so make it safer. Ideally spillways should be “passive”, not requiring any manual operation or intervention in floods.

MEICA equipment

Motors and their controls have a limited lifespan. If they are used more frequently they will wear out sooner and need replacement. As flood frequency increases you may find that valves have to be opened or closed more often. You may be able to adjust the operational settings to improve the lifespan and reliability of these items. Care is needed to make sure they remain effective during floods.

You may find that flood levels rise more often to the point where sensors do not work properly. For example, an ultrasonic level sensor will not work if the water level rises too close to, or above it. You may need to raise the sensor so that it is well above predicted flood levels. Level alarms which use a simple float as a switch, may need changing for similar reasons. You should check regularly that sensors are well calibrated for the full range of conditions. Floods often cause power cuts. You should ensure any electrical elements have back up power if the grid is interrupted.

Structures

You may have control buildings set near the edge of the reservoir, or there may be equipment within a valve tower. This may presently be above the normal flood level but with climate change it could flood more often. You may need to make the doorways and other openings more resilient to flooding. Make sure floods would not damage anything in the building and make sure you can safely access the building.

Increased flood flows could carry more debris through the reservoir. Inlet and outlet headwalls and screens may need more maintenance. You need to check these are clear and working well. You may need to clear them more often.

The reservoir records should be kept where they are easily accessible. If they are kept on site then it may be advisable to keep a backup copy off site in case the records are destroyed by flood.

Ground saturation

Ground saturation is more likely, and more seasonal. Winters will become wetter and summers drier and milder. In winter the ground will be saturated for a longer period. During summer, although ground saturation will generally reduce, heavier rainstorms may result in shorter periods of intense saturation.

Embankment slopes and valley sides could become saturated. When earth is saturated, it is both heavier and weaker, so there is a higher risk of landslips and other problems.

Embankments

Potential impacts of ground saturation

Landslips happen if slopes are unstable, when the soil is heavier than its internal strength can support. Slips can be worse if there is other weight on, or at the top of a slope, such as from:
- vehicles
- roads
- walls
- buildings
Where ground saturation is the cause of the slip, it usually happens as a shallow slide with the earth moving in a “slice” down the slope.

Landslips can happen in a few places:
- on the sloping face of the embankment dams where slips make the embankment thinner and weaker - the exposed soil is vulnerable to erosion from rainfall or if the reservoir overflows
- on the valley sides downstream of the dam crest which may lead to blockages in the spillway or in the river below - this may affect other parts of the dam such as covering access routes, valve buildings or chambers, and drainage features
- on the valley sides upstream around the edges of the reservoir which can lead to blockages of inflow systems, in extreme but rare cases, large upstream landslips can cause large waves - these travel across the reservoir and hit the dam, which can overwhelm it
Saturated ground is soft, so it is more vulnerable to damage from vehicles such as mowers, livestock or the public. This can cause ruts which channel overland flow or seepage from the soils and then erode further.

Burrowing animals tend to prefer drier ground. Burrowing animals may be more active as they seek higher, drier soil. Burrows can become underground flow paths leading to internal erosion. This weakens the dam and can ultimately lead to failure. Burrows can collapse, meaning the surface above them becomes a hollow which is vulnerable to surface erosion from rain or overflow.

On their own none of these are normally an immediate threat to the reservoir’s safety.

How to spot damage

Saturated ground often has water visible on the surface. Sometimes this is difficult to spot and it could look like a small amount of dam leakage. The amount of water can be an indicator of the scale and source of the problem.

The ground may also have a disturbed, muddy surface, with shallow slips in the topsoil. If the ground is saturated for long periods, the vegetation may change. Grass will struggle to remain healthy and reeds will grow.

Cracks may appear at the embankment surface. These can be spotted as roughly horizontal cracks developing at the upper edge of a slip. They may be curved cracks along the sides of the slip. There may also be a bulge in the surface at the lower edge.

Photo 3: Landslip on downstream face of off-line Flood Storage Reservoir. Photo courtesy of the Environment Agency

Maintenance

If there is a drainage system on your dam, make sure it is working properly. Drains can become blocked or damaged over time so may need clearing. If the ground is saturated but little or no water is coming from the drainage, that is a sign it needs repair or replacement. Monitor the flow using a jug and stopwatch. Note the colour or “turbidity” (cloudiness).

If you find cracks when you check your embankment, you should probe into them to find out the depth. Using a thick, rigid wire (such as a coat hanger) you can see if the slip is just in the topsoil or if extends into the underlying fill. That is potentially more serious.

You need to repair any damage as soon as possible after it appears and continue to monitor it. You should:
- infill cracks with a mix of topsoil and fine gravel to reduce water ingress
- install pins on the slope - can help to monitor movement, you can either use topographic survey or use fixed-point photography
Photo 4: A V-notch weir to monitor the flow from embankment drains. Photo courtesy of Hafren Dyfrdwy / Severn Trent Water.

Improving resilience

Additional improvements may be needed. A Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer) will need to support design and construction of alterations. These might be:
- hard surfacing in heavily trafficked areas, for example, a cellular mat infilled with gravel - this can help the surface to drain and reduce ruts
- improved drainage can help, for example, a herringbone pattern on the slope, or a series of parallel drains toward a ditch down the mitre, the mitre is where the dam meets the valley side - these are normally “French drains”, which have a perforated pipe in a gravel-filled trench wrapped with a geotextile fabric
Spillway

Potential impacts of ground saturation

For spillways with a channel (or chute) to carry overflowing water down the dam, the main impact from saturated ground is on the sidewalls. The additional water in the ground increases the load on the back of the walls and can cause them to collapse. A sidewall collapse could block the spillway chute and reduce its capacity. It would also expose the soil behind the wall to fast flowing water. This results in erosion and further damage.

Well-built grass spillways are generally well-drained. If they do suffer from saturation, the impacts would be similar to those discussed for the embankment.

Blocked or defective spillways are significant problems for reservoir safety. They should be addressed quickly.

How to spot damage

Key indicators of problems with an over-loaded or poorly drained sidewall are:
- the wall tilting towards the spillway chute, due to the weight of saturated soil behind it
- seepage through joints in the wall, or in the base slab of the chute, as the water forces its way out
- forward movement of individual masonry blocks from the pressure of the saturated earth behind the wall
Photo 5: Seepage through the spillway chute sidewall, which changed depending on reservoir water level. Photo courtesy of Hafren Dyfrdwy / Severn Trent Water.

Maintenance

Generally, sidewalls are built with weepholes or slits to let water pass through them. Some tall or slender walls have “back-of-wall” drainage. Check that these weepholes and/or drains are not blocked and clear them if you can.

Improving resilience

Depending on the severity of the problem, the 2 main options to reduce ground saturation behind the spillway chute sidewall are to install:
- filtered weepholes in walls (and/or steps in the bed) to relieve water pressure - this is a relatively simple task
- back-of-wall drainage for larger problems, which would need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer)
Reservoir outlet and other elements

Ground saturation will not impact all dam elements. This section aims to discuss the more likely or more significant impacts. To prepare for or react to each problem, the text explains:
- how to spot problems
- what maintenance or resilience improvements could be needed to prepare for or react to each problem
For alterations affecting the reservoir’s safety, you will need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

It is unlikely that gates, valves or MEICA equipment, would be directly affected. They could be indirectly affected as discussed below.

Structures

You should seek input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer) for these problems. They could affect the reservoir’s safety.

Some structures may have earth retaining walls around them. These:
- either raise the ground they are built on
- or allow a lower floor or base level
In either case, the signs of potential problems and the solutions would be similar to those for spillway sidewalls.

The other likely effect on a reservoir’s smaller structures from ground saturation would be settlement. Saturated soils are weaker and they cannot support as much weight. This can lead to settlement under the weight of the structures. It may either be “uniform” or “differential” (even or uneven). Settlement can cause structural cracking, or cause moving parts such as sluice gates, valves, and doors to jam. The simplest visual indicator is to check whether walls and slabs are vertical and horizontal. You should also test regularly that moving parts do move properly. If you see problems, it may be a sign that you need to improve the drainage around the structure. Other repairs or alterations may also be needed.

Drought and fire

Recent research indicates a trend towards drier and hotter summers in England. Summer droughts will probably worsen with climate change due to the higher temperatures and decreased rainfall.

Hazardous fire-related weather conditions are expected to be 2 to 5 times more likely. The wildfire season will run into Autumn. Wildfires could become an ‘emergent risk’ - historically they have not caused widespread impacts.

Reservoirs may empty, or have lower water levels. This, along with reduced rainfall, could then result in the dam’s soil drying out and shrinking. This can cause cracks to form in the embankment. It could also lead to vegetation on the embankment drying out and possibly dying. There will be higher risk of fires and any fires that do occur could burn with more ferocity and spread quicker. This may affect your access to your reservoir.

These changes can also affect wider issues of reservoir management. If you use your water for industrial processes or agricultural irrigation then you may need more of it. For any changes to reservoir size, or for building new reservoirs, you would need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). There is also a chance that water may be needed for fire fighting, which may affect how much you have available.

Embankments

Drought

The soils forming the embankment will dry out, and this can lead to “desiccation cracks” forming. These may be surface cracks, or they could extend into the clay or the core of the dam.

If there is surface cracking then rain water may enter this crack. This leads to increased vulnerability of slips forming. The water applies pressure to the soil and can lubricate the slip surface. This can lead to the topsoil and possibly the deeper subsoils from slipping down the embankment. The surface of the embankment is then left exposed to further erosion and possible failure.

Deeper cracks, and cracks at the crest of the embankment, may extend to the clay core (if there is one). The clay core is the waterproof element of the embankment. If cracks form in this, then seepage through the embankment may occur. This will also happen if cracks extend across the dam crest and the water level rises to the same level as the crack. The seepage flow can erode soil particles from the sides of the crack. It increases the size of the water path, which then continues to make the crack bigger. This process is called “internal erosion” and can lead to failure of the embankment.

Drought can also lead to drying and browning of the grass on the embankment. This may reduce the erosion protection provided by the grass. Short grass or bare earth may erode quickly if the embankment overtops.

If trees are present on or near to the embankment then the reduced water availability could lead to them dying. When a tree dies on an embankment the roots decay. This can form a seepage path through the embankment and can trigger internal erosion (see Diagram 5). Repeated droughts may also encourage trees to spread their roots further. This would create larger holes in the embankment if they were to blow over in a storm. This could result in roots damaging structures or the dam core.

Photo 6: Grass on an embankment dam which presently dries in most summers. Photo courtesy of the Environment Agency.

Fire

Although droughts do not cause fire, prolonged dry weather increases the likelihood of fires taking hold. It also increases the speed at which they spread. Fires only start if there is a source of ignition; this could be from lightning but most wildfires are caused by human activity, including:
- fire
- barbecue
- vandalism
Fire can kill the vegetation on the embankment, whether that is grass or trees. The result of this would be like drought issues but more severe, including browned grass and killed trees. Fire further dries out the embankment surface, leading to more desiccation cracking, or making existing cracks worse.

If you have a geotextile membrane on your dam, fire can damage it.

Some embankments in moorland areas are constructed from peat. This itself can burn, with the fire spreading down into the embankment. This can continue to smoulder without visible flames long after the fire seems to be out. This can affect:
- the strength of the embankment
- the freeboard which is the level at which the embankment may overtop
- the watertightness
A wildfire within the catchment of the reservoir can result in higher peak flood flows after a rainstorm. This is because fires can cause deforestation and baked earth, resulting in faster rainfall runoff into the reservoir

Tree debris from the fire which washes into the reservoir can block flow routes. It also creates an additional fire risk when it dries out, in particular, at vandal-prone sites.

Photo 7(a): Fire damage to an embankment dam, and a close-up of cracked earth. Photo courtesy of the Environment Agency.

Photo 7(b): Fire damage to an embankment dam, and a close-up of cracked earth. Photo courtesy of the Environment Agency

How to spot damage

You should be able to see areas of damage if they are present or developing, allowing you to correct them, such as:
- areas of brown grass or poor grass cover
- wilting vegetation
- cracks in the embankment soils
- burnt or burning areas
Maintenance

There are some simple maintenance activities which you can carry out. If you find any significant damage, you should contact your Supervising Engineer before repairing it. They may need to see photos and measurements or may need to examine it in person. Contact them before doing the repairs.

You should:
- take measurements of the depth and extents of cracking
- fill surface cracks which are those not extending into the clay core with topsoil which crumbles easily and top with grass seed
- ensure cracks extending into the core are discussed with the Supervising Engineer before any action is taken - more specialist advice and material may be required
- maintain grass in good condition and remove weeds
- avoid cutting during very hot and dry weather, or cutting grass too short
- consider the equipment used to cut the grass, a bladed mower may cut cleaner then a flail which may pull at the roots
- check if trees are present on the embankment then establish a vegetation management plan - this ensures that existing trees maintain good health and prevents more trees from establishing
- keep screens and the dam clear of debris so flows pass through and so it cannot be burnt by vandals
Diagram 4: Repairs to cracks in an embankment dam

Improving resilience

The following measures may improve the resilience of the embankment to fires and drought. If works are likely to alter the form and function of the dam you will need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Speak to your Supervising Engineer in the first instance. You should also:
- consider replacing the grass used on the embankment with a more drought resistant variety
- replace the crest track with one that will reduce evaporation
- create fire breaks in vegetation on the land surrounding the reservoir
- consider banning barbeques and campfires during the summer months and droughts
Spillway

Potential impacts of extreme drought or fire

The impacts of drought and fire on the spillway are dependent on the construction materials used.

The possible impacts on concrete and masonry structure are:
- ground drying out resulting in movement of the structures, creating cracks or opening joints in concrete or masonry
- wildfire leading to spalling of the concrete which is the surface of the concrete cracking and breaking away due to the heat
- fire damaging sealant used in movement joints, increasing the possibility of seepage through joints
- debris from a fire upstream entering the reservoir and blocking the trash screen or spillway channel
- increased flows due to the increase in rainfall runoff from the reservoir’s fire-damaged catchment exceeding the capacity of the spillway
The impacts are for grass and reinforced grass spillways would be worse.

Drought would affect a grass or reinforced grass spillway in a similar way to the rest of the embankment. However, as it is designed to overtop it is even more important to keep it in good condition.

The impacts of fire are also much the same, however, where the spillway is protected with reinforced grass a fire could also damage this. This will greatly reduce the erosion protection of the spillway.

How to spot damage

For spotting damage to grass and reinforced grass spillways, please refer to the section on the dam.

For concrete and masonry spillways, you should look for:
- new cracks or existing cracks getting bigger
- concrete which is cracking or flaking
- damaged sealant in concrete joints
Maintenance

For maintenance to grass and reinforced grass spillways, please refer to the section on the dam.

For concrete and masonry spillways, you should:
- monitor any cracks or joints that appear to have moved - your Supervising Engineer will advise if measurements are required, and how to take them
- replace deteriorated or damaged joint sealant
- repair cracks in concrete
- clear the trash screen and channel of debris
Improving resilience

Some problems may need more work, which may need guidance from an engineer, or a formal design approved by a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Speak to your Supervising Engineer in the first instance.

Note that grass spillways could be replaced with a more durable solution such as concrete.

Reservoir outlet and other elements

Drought and fire will not impact all dam elements. This section aims to discuss the more likely or more significant impacts. To prepare for or react to each problem, the text explains:
- how to spot problems
- what maintenance or resilience improvements might be needed to prepare for or react to each problem
For alterations affecting the reservoir’s safety, you will need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

Gates and valves

Drought will have little impact on the operability of gates and valves. There may be some issues due to higher temperatures such as deformation or lubricants drying. Timber elements such as stoplogs or sluices could dry out and crack.

Fire may weaken metal work, along with expansion, causing distortion. If this occurs it may lead to gates and valves becoming inoperable. In addition, gates may have rubber seals that may burn, resulting in leaking gates.

Older reservoirs may have wooden gates or valves that could burn.

Wildfire can also result in increased debris and sediment within the reservoir. This could cause blockages in gates, valves, and the pipework associated with them.

All gates and valves should be regularly tested to ensure they remain well maintained and operable under normal working conditions.

MEICA equipment

Drought will have little impact on the operability of the MEICA equipment. Although water level monitoring may need adjusting to allow measuring of lower water levels.

Fire can result in damage to all MEICA equipment, including:
- cables
- sensors
- ducting
- hosing
These may be critical to operate motors, gates and valves. If the reservoir relies on sensors and motorised gates and valves to operate then key personnel should know how to operate these manually.

Structures

Drought may lead to soils drying and shrinking under the foundations of structures. This would lead to movement and possible cracking. You should monitor any cracks or movement on structures and make suitable repairs or modifications. Check with your Supervising engineer or seek advice from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

Fire can lead to significant expansion of metalwork and concrete structures. Metalwork may become weakened, and buckle. Concrete could expand and spall. Either would weaken the overall structure, possibly rendering it unsafe. Timber structures, such as timber bridges may burn, rendering access to the site dangerous. Control buildings along with equipment and records contained within them could be destroyed.

The reservoir records should be kept where they are easily accessible. If they are kept on-site, then it may be advisable to keep a backup copy off-site in case the records are destroyed by fire.

Other

When water levels are low, you may be able to see signs of damage which are not normally visible. For example:
- irregularities in the upstream embankment profile
- cracks in or near structures
- sinkholes in the reservoir bed
You should check for these and if you see any such signs you should ask your Supervising Engineer for advice.

Wind and waves

Most current climate projections indicate an increase in storm frequency and intensity. However, some models suggest not. Storm trends and tracks are dominated by variations in global climate oscillations. These are large scale wind patterns at high altitudes, which change their latitude and strength between year and decades. Their strength and location is expected to also change with the climate.

These complexities lead to very large uncertainties. It is expected that climate change will increase the frequency of high wind-speed storms but possibly not their intensity.

High winds, with increasing frequency, can lead to large waves regularly developing in the reservoir. This can cause damage to embankments from overtopping and damage from waves breaking on structures. High winds also cause trees to fall, which can damage embankments or other structures and buildings. They can also block spillways and prevent access.

Embankments

Potential impacts of extreme wind and waves

The main impacts of high winds are large waves forming on the reservoir. This can cause erosion of the upstream face and either overtopping or wave spray being blown over the crest, which can saturate the downstream face. Erosion can cause a slip failure or make the surface of the crest and downstream face vulnerable to fast flowing water.

Trees blowing over can leave large holes in the embankment surface creating a risk of erosion from overtopping and wave spray. If the fallen tree was on the crest this can leave a low spot vulnerable to overflowing. The fallen tree also exposes the embankment fill and so increases the risk of erosion. The upper branches from large trees might gouge the surface of the embankment when trees fall. Any roots that remain in the embankment will rot over time and can then form a seepage path through the embankment. This can cause internal erosion.

Photo 8: Uprooted trees caused by high winds can cause damage. Photo courtesy of Environment Agency.

How to spot damage

Overtopping and wave spray will damage the surface where it has caused erosion or slip failures. The topsoil and the embankment fill will be exposed with potentially large holes. Flattened vegetation could indicate where water was flowing. These areas are likely to be the first which would be damaged in higher flows if not designed to resist the water’s energy.

If an entire tree including its root ball has blown over there will be voids in the embankment surface. There may be other damage from the upper branches gouging the embankment surface.

Maintenance

There are some simple maintenance activities which you can carry out. If you find significant damage, you should contact your Supervising Engineer before repairing it. They may need to see photos and measurements, or may need to examine it in person.

Following strong winds you should visit your site to look for damage. Whilst most damage will be obvious, these visits should also be used to identify issues that could lead to further damage in the future. For example, trees that are now leaning over or weakened. You should also look for evidence of where water was flowing. Bent over grass or vegetation indicates this, particularly in areas where you would not expect water to flow. You should remove trees in poor condition and you should prevent more trees from establishing.

Improving resilience

Depending on the scale of the repairs or proposed works, they could alter the form and function of the dam. You would need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Speak to your Supervising Engineer in the first instance.

Creating a rougher surface on the upstream face can reduce wave runup and resist erosion. Rip rap is an example - large rocks strategically placed on the upstream face. In extreme cases a wave wall may be required where flood levels and wave height are too high.

Planting reeds or reducing the depth of water upstream of the dam could reduce wave heights. Providing an erosion resistant surface on the crest will reduce the risk of damage from water dropping onto the unprotected surface.

Photo 9: Vegetative wave protection to a dam shoreline. Photo courtesy of National Trust.

You should develop a vegetation management plan. Focus on identifying dead or diseased trees and ensure they are removed before they are blown over. Reducing the height of trees on the embankment may be carried out to reduce the likelihood of them blowing over. You should seek advice from a tree specialist as some species are sensitive to how they are pruned.

Spillway

Potential impacts of extreme weather

For spillways, the main impact from wind is likely to be from either wind-blown debris or fallen trees. These could block the spillway crest or channel and increase the risk of the embankment or spillway overflowing. This could cause further damage to the embankment.

The side walls of the spillway could also be damaged if trees are located very close and get blown over onto or near them.

How to spot damage

Following strong winds you should visit your site to look for damage. Refer to the wind-related advice provided above for embankments.

Maintenance

There are some simple maintenance activities which you can carry out. If you find any significant damage, you should contact your Supervising Engineer before repairing it. They may need to:
- see photos and measurements
- examine it in person
You should remove any debris that has collected on any part of the dam and spillway. Put it somewhere it will not re-enter the reservoir. You should inspect the perimeter of the reservoir for any leaning or fallen trees and branches that could enter the reservoir and cause future issues. You should remove trees in poor condition and prevent more trees from establishing. Check structures such as old jetties. Secure floating pontoons and boats so they do not come loose and cause a blockage.

Improving resilience

Depending on the scale of the repairs or proposed works, they could alter the form and function of the dam. You would need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Speak to your Supervising Engineer in the first instance.

You should develop a vegetation management plan. Focus on identifying dead or diseased trees and ensure they are removed before they are blown over. Reduce the height of trees on the embankment to minimize the likelihood of them blowing over.

You should seek advice from a tree specialist as some species are sensitive to how they are pruned.

You could install coarse screens, floating booms, or tree catching poles to prevent wind-blown debris from entering the spillway.. These trap debris before it reaches the spillway.

Reservoir outlet and other elements

Wind and waves will not impact all dam elements. This section aims to discuss the more likely or more significant impacts. To prepare for or react to each problem, the text explains:
- how to spot problems
- what maintenance or resilience improvements might be needed to prepare for or react to each problem
For alterations affecting the reservoir’s safety, you will need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

Gates and valves

Gates and valves and their operating equipment such as spindles could be affected by increased wave loading. They are more likely to be affected by either debris blockages or damage caused by impacts from floating objects. Following high winds you should inspect them for any damage or blockages.

MEICA equipment

Overhead power and phone lines could be blown down or affected by falling trees or other wind-blown objects. This might mean MEICA equipment, gates and valves are unable to be operated remotely. Following high winds you should walk the routes of any important services to identify any damage. Identify any other possible issues or changes, such as trees leaning over towards or onto overhead cables.

Structures

High winds may lead to increased pressure from waves breaking on structures or falling trees. You should inspect all structures after high winds to identify any damage or other issues.

Control buildings could be susceptible to damage from high winds with roofs and windows damaged or blown off. This could lead to water ingress and damage to MEICA and other equipment within the buildings. Vandalism may also be a problem if buildings are not secure.

The reservoir records should be kept where they are easily accessible. If they are kept on site then it may be advisable to keep a backup copy off site in case they are lost or damaged by storms.

Access

Access routes could get blocked by fallen trees or accumulations of wind-blown debris. Waves and spray may make access routes dangerous or impossible. You should inspect access routes for any blockage and damage after high winds.

Ice and snow

Current trends and forecasts indicate milder and wetter winters. Cold periods are decreasing in intensity and frequency. However, there is still potential for cold events to happen and if global circulation patterns change, winters may also change. The uncertainties regarding this are very large.

The trend of decreasing ice and snow loading means that the impact it has on reservoir management may also decrease in the future.

However, the threats will not entirely go away and could potentially get worse should major changes to global circulation patterns occur. Threats to your reservoir are:
- freeze-thaw weathering
- frozen parts
- snow accumulation
- deeper burrows
There is a realistic chance that deep winter conditions could extend further south than they have in recent times.

Embankments

Potential impacts of extreme ice and snow

Ice can damage grass, particularly when it forms on the grass blades, causing them to become brittle and break easily. This leads to:
- discoloration
- wilting
- potential stunted growth
Walking on frosted grass can exacerbate this damage by further rupturing the grass cells. Frozen ground could also lead to burrowing animals going deeper into the embankment.

The formation of large ice sheets or blocks on the reservoir surface can occur. When combined with high winds or during thawing, this can lead to scouring and gouging of the upstream face.

How to spot damage

It is important to visit the reservoir after any extreme weather event, looking for evidence of any damage. The potential impacts of ice and frozen ground are unlikely to be visible for long after the event although you should see any scouring and gouging of the embankment.

The presence of snow on an embankment can help identify seepage and leakage locations. Look out for isolated patches of thawed snow which reveal these.

Maintenance

There are some simple maintenance activities which you can carry out. If you find any significant damage, you should contact your Supervising Engineer before repairing it. They may need to:
- see photos and measurements
- examine it in person
You should:
- avoid damage to frozen grass, do not walk or drive on it until it has thawed
- try to prevent burrowing animal activity all year round
- ensure any stone pitching and rip rap on the upstream face is present and in good condition - particularly around the normal water level
Improving resilience

Depending on the scale of the repairs or proposed works, they could alter the form and function of the dam. You would then need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Speak to your Supervising Engineer in the first instance.

If the formation of thick ice sheets becomes frequent you may need to improve the protection on the upstream face to prevent ice scouring.

Spillway

Potential impacts of extreme ice and snow

The formation of ice can cause various spillway related problems, including:
- freeze and thaw within the joints of masonry and concrete structures causes cracking and spalling of surfaces - this is because water expands as it freezes, it may lead to potentially more extensive structural damage
- blockages to the spillway crest and channel from ice can limit the overflow - this causes additional pressure on structures, in particular around any piers or other protruding structures in the channel
- moving ice blocks can strike piers or other structures in the spillway channel, leading to damage
- ice curtains and icicles forming from overhead structures like bridge decks reduce the capacity of the spillway
- heave and expansion of the soils next to the side walls of spillways could lead to increased loads - this causes structural damage
- the freezing of water in submerged stilling basis could reduce their ability to dissipate energy - this leads to erosion and scour downstream
How to spot damage

Following extreme weather you should visit the spillway to check for damage. Look for dislodged blocks, spalling concrete or masonry, or other forms of physical damage caused by ice strikes.

Maintenance

There are some simple maintenance activities which you can carry out. If you find any significant damage, you should contact your Supervising Engineer before repairing it. They may need to
- see photos and measurements
- examine it in person
If it is safe, break up ice to reduce the risk of damage.

Ensure joints are filled with mortar or sealant. Filling cracks will prevent the ingress of water and reduce the risk of freeze-thaw action.

Improving resilience

Depending on the scale of the repairs or proposed works, they could alter the form and function of the dam. You would then need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer). Speak to your Supervising Engineer in the first instance.

Installing baffles upstream of the spillway crest will limit the flow of ice towards and down the spillway. In the spillway, deflector plates can be installed at bridge piers and other potential debris traps. These deflect any ice to reduce the chance of it building up and creating a blockage.

Reservoir outlet and other elements

Ice and snow will not impact all dam elements. This section aims to discuss the more likely or more significant impacts. To prepare for or react to each problem, the text explains:
- how to spot problems
- what maintenance or resilience improvements could be needed to prepare for or react to each problem
For alterations affecting the reservoir’s safety, you will need input from a Qualified Civil Engineer (https://www.gov.uk/guidance/reservoirs-owner-and-operator-requirements#how-to-appoint-a-panel-engineer).

Gates and valves

Moving ice sheets or ice blocks striking gates and valves could cause damage. Ice will form on parts around the water surface where waves lap up them. Valve operating spindles are particularly vulnerable. Moving parts may become inoperable if frozen. Breaking up ice where safe to do so will reduce the risk of damage.

Photo 10: Ice loading bent the control rod of a submerged valve. Photo courtesy of Canal and Rivers Trust.

MEICA equipment

Equipment becoming frozen may lead to damage. You should locate any sensitive equipment in weatherproof enclosures or buildings with trace heating.

Structures

The additional loading from ice block strikes and the damage caused by water freezing and thawing can cause damage to structures. Break up ice when it’s safe to do so.

Debris screens and railings

Ice blocks can result in both the blinding of screens and structural damage. Ensuring screens are robust and designed to accommodate strikes from debris and ice will reduce the risk of failure.

Ice can build up on railings, either causing them to fail or weakening their fixings and foundations. These should be checked after freezing and repaired or replaced if needed.