Frequently Asked Questions

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We have collated a list of commonly asked questions and the respective answers.

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What is a 1 in 200 year flood event

It is often believed that a 1 in 200 year flood refers to a flood event that would happen, on average, once every 200 years. In fact, the term refers to the probability of a flood event occurring in any one year. “1 in 200 years” actually means that, each year, there is a 0.5% chance of a flood of this magnitude happening. This percentage is calculated on the basis of 1 divided by 200 times 100, a recognised formula for the calculation of annual flood risk. The lower the percentage probability the larger and more damaging a flood will be. The scheme will protect against such a flood. It is important to know that a flood of this size has not occured in recorded history in Grangemouth, but it could occur tomorrow, or next month or next year. Typically this is the standard that most flood protection schemes aim to achieve.



Would dredging reduce the risk of flooding?

Dredging has been considered and shown to offer only very limited benefit to reducing flood water levels in the rivers and burns. This activity is not a sustainable solution given the need to frequently re-dredge the watercourses. In the non tidal sections of the rivers and burns the additional capacity that would be generated by dredging is minimal in comparison to the volumes of water in an extreme flood, hence why it has so little benefit. Where the risk is primarily from the sea i.e. lower Grange Burn, lower River Carron and lower River Avon, dredging would not reduce the risk of flooding as it would have no influence on the tide level. While an enlarged channel could convey more fresh water to the sea at low tide, potentially increasing flood risk downstream, it also allows more sea water to flow upstream during high tide and could exacerbate flooding by allowing high tides and storm surges to travel further inland. In addition, altering a river’s natural geomorphological process (sediment movement and deposition) can cause erosion of the riverbed and banks, which inturn can lead to the failure of existing structure such as roads and bridges. SEPA have published a useful guide on dredging that can be viewed here CIWEM have also published a report, Floods and Dredging - a reality check that can be viewed here



Who is funding the scheme?

The FPS process involves submitting an application for funding from the Scottish Government once the Scheme is confirmed. Funding grants of 80 percent of the eligible costs are available from the Scottish Government for confirmed schemes which meet specific technical,environmental and economic criteria. Falkirk Council and others would then fund the remaining 20 percent of the total cost.



Why can't the pumping stations deal with the flooding?

Most of the existing pumping stations in the Grangemouth area are Scottish Water Pumping Stations, which predominantly deal with foul water rather than surface water. The existing pumping stations would not be able to cope with the predicted flows for a 1 in 200-year event.



Does the scheme only protect the refinery

The scheme is not only protecting the refinery. The primary purpose of the scheme is to protect almost 3,000 homes and businesses in Grangemouth and surrounding areas from flooding from the River Carron, River Avon, Grange Burn and the Forth Estuary. The refinery and petrochemical works as well as Grangemouth Port will also be protected given the national importance of the infrastructure to Scotland and the UK economy. In addition, not protecting these areas would leave those resiential properties nearest the Forth Estuary at risk of coastal flooding given the land is low lying.



Will the flood defences be maintained after they are built?

The Flood Risk Management (Scotland) Act 2009 places duties on Falkirk Council to inspect and maintain the defences. They will therefore be kept in good condition and repair and to do so an operational and maintenance procedure will be developed and implemented



When will the scheme be built?

The project team are currently finalising the outline design. This will determine the type of flood defence e.g. wall or embankment and the likely form of construction as well as the height of defence and its location. Thereafter the team aim to publish the scheme in late 2021. If all goes to plan and all approvals are granted it is hoped that the main construction works would commence in 2024 with construction potentially being stretched over 10 years.



Will the views of the public be sought on the proposed defences?

To date the project team have held two separate public consultation events in 2018 and 2019 seeking feedback on the proposed scheme. In addition there has been consultation with elected councillors, community councils, statutory consultees and many others. The response to these consultation events are reflected in the proposed scheme. Further consultation was planned in 2020 and has been re-scheduled to early 2021. This engagement will continue throughout the development and implementation of the scheme.



Will the defences stop all future flooding

No, there always remains a risk with every Flood Protection Scheme that
there will be a storm event which delivers a flood bigger than the Scheme is
designed to protect against. The scheme is being designed to protect against flood events that have a 0.5% chance of occuring in any year.



How do flood gates work?

Flood gates are located in specific areas throughout the Scheme, where access through the new flood defences must be maintained. Flood gates are useful where constructing a ramp over the flood defence wall is not feasible and at existing bridges, where the bridge
cannot be raised to accommodate the new flood defence level. Falkirk Council will liaise with SEPA to determine the likely flood level and close the flood gates in preparation for a flood event.



What are flood cells?

The project team have divided the scheme into 6 discreet flood cells which are simply geographic areas. This has been done to make it simpler to refer to these specific areas and present statistics etc. The six cells are: Cell 1 - Upper Carron; Cell 2 - Lower Carron; Cell 3 - Port of Grangemouth; Cell 4 - Grange Burn and Flood Relief Channel; Cell 5 - River Avon; Cell 6 - Estuary Frontage.



Are all the trees in Zetland Park being removed?

No. Trees are only being removed where there is no alternative due to the damage their roots would sustain if they were left in place. Almost 90% of the trees within Zetland Park will be unaffected by the proposed flood defences. Due to some of the trees being located very close to the property and infrastructure that the scheme seeks to protect from flooding a compromise is necessary to balance the issue of property being at risk of flooding and protecting trees. Where there is sufficient space the flood defences have been positioned to avoid the need for felling trees. However in many places there simply isn't sufficient space to avoid tree felling when you consider the root protection zone around each tree. In some areas the choice is either remove the trees to protect hundreds of homes or alternatively protect the trees and leave hundreds of property at risk of flooding. It should also be noted that the presence of trees does not reduce the risk of flooding from the sea. On average three trees will be planted for every tree that is felled. In some areas a one to one replacement plan will be implemented where large (3-4m in height) trees will be replanted. Further information can be found on the following page.



Aren’t you going to destroy some natural habitats for birds, water mammals, fish and aquatic life?

Protecting natural habitats and enjoyment of the waterways whilst constructing flood defences that will safeguard communities across parts of Falkirk and Grangemouth is of paramount importance to the scheme. We are committed to minimising the risk of impacting natural habits during the construction of the flood defences and once they are operational. We are undertaking an environmental impact assessment of all aspects of the scheme and will be proposing ways of mitigating any impact. This study will be conducted in 2020/2021 and be published in late 2021.



Are the Kelpies at risk from future flooding?

We have carried out a detailed assessment of both river and coastal flood risk as part of the scheme. Our assessment does not predict any flooding of the Kelpies either now or as a result of climate change.



Why is the scheme required when there hasn't been any recent flooding?

Falkirk Council are taking a proactive approach to managing flood risk and hopefully the scheme will be in place before a devastating flood event occurs. An absence of large floods in recent decades does not mean there is no risk. Due to the low lying land around Grangemouth the extent of flooding if it occured would be significant with thousands of homes and businesses at risk. There have been numerous instances over the last 10 years where watercourses have been very close to spilling out of their banks and flooding property. The size of a flood event is a product of the probability of a flood event occuring. Small flood events happen frequently but these might not be of a size that results in any damage to property and infrastructure whereas large extreme floods have a much lower probabability of occurence. It is these low probability flood events that feature in the news when they occur due to the devastating impacts they have on people, property and communities. Flood events are becoming more frequent through heavier rainfall and rising sea levels and action is required to avoid Grangemouth and surrounding communities being affected. Flood maps showing the areas affected by a medium probability event can be found here The requirement for the scheme was identified in the flood risk management strategy for the Forth Estuary Local Plan District. The strategy can be found here.



What options have been considered to reduce the risk of flooding?

Various options have been considered to reduce the risk of flooding. These have included dredging, natural flood management e.g. run-off reduction by tree planting, a new flood relief channel, using the Carron Valley reservoirs for flood storage, construction of new flood storage reservoirs, linear flood defence walls and embankments, flow control structures and tidal barriers and gates. Further information can be found on the pages for consultation event no. 1 and consultation event no. 2. Several of the options considered were found to offer very limited benefit or were not practical to implement. The preferred scheme is a combination of linear flood defence walls and embankments and a flow control structure to direct more of the flow in the Grange Burn into the flood relief channel. The flow control structure significantly reduces the requirement for flood defences along the Grange Burn between Rannoch and Zetland Parks, although flood defences are still required in the lower Grange Burn where the flood risk is from the sea.



What is the source of flooding?

Grangemouth and the communities protected by this scheme are at risk of flooding from multiple sources. In the lower Grange Burn, lower Carron and lower Avon the risk is primarily from the sea and high tides and storm surges. With sea levels being predicted to increase due to climate change, flooding from the sea is the greatest risk to Grangemouth and there are very limited options to protect properties from this source of flooding as it is not caused by rainfall. In the upper Carron, flood relief channel, Westquarter and Polmont Burns the risk is from river flooding where the volumes of water in an extreme flood are significantly greater than the capacity of the water courses. There is also a combination effect where on high tides the water coming down the rivers and burns is tide locked and can't discharge due to the high tides. Finally there is a risk of surface water which is where the rainfall landing on the ground surface is not absorbed into the ground or where drainage systems cannot deal with the volumes of water and this leads to ponding of water on the ground surface and roads. A plan showing whether the primary source of flooding is from the sea or the river/ burns can be viewed here



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