Grangemouth Town

Further information relating to the flood defences proposed between Zetland Park and the Port along the Grange Burn 

The need for the scheme...

We hear many people questioning the need for the scheme as it hasn't flooded in decades. Whilst that might be true, this does not mean there is no risk of flooding. It simply means the town has not experienced an extreme flood in recent years. On average every few years the Grange Burn has been close to overtopping onto adjacent roads and properties. These events are high probability/ low impact events that are to be expected whereas the scheme is seeking to protect against low probability/ high impact events that would cause expensive damage to property and infrastructure and could even lead to loss of lives.

 

Extensive analysis has been carried out over many years reviewing the best available information on sea levels and rainfall and Grangemouth is at risk of flooding, primarily from the sea but also due to flooding from the rivers/ burns caused by heavy rainfall. This has been verified by the Scottish Environment Protection Agency and the Scottish Government. Many residents also report that they are unable to insure their properties against damage due to flooding and support the need for the scheme

 

The plan below shows the predicted extent of flooding for an extreme flood both now and in the future.

 

 

In summary the area north of Zetland Park is at risk of flooding from the sea and the area to the south flooding from the Grange Burn due to rainfall. A large part of Grangemouth is currently not at risk of flooding but will in the future due to climate change.

Potential solutions to address flooding...

There are a variety of methods that can be adopted to reduce flood risk. The suitability of these methods depends on the source of flooding e.g. does the risk originate from high tides and storm surges from the sea or is it due to heavy rainfall.

 

 

The table below lists many of the methods for reducing flood risk and their suitability for each source of flooding:

200 Year Present Day
200 Year Present Day

1 in 200 year (0.5% annual probability) flood extend based on present day scenario

1 in 200 Year Future
1 in 200 Year Future

1 in 200 year (0.5% annual probability) flood extend based on future climate change scenario

200 Year Present Day
200 Year Present Day

1 in 200 year (0.5% annual probability) flood extend based on present day scenario

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Flood Risk Map

Flooding Source
Flooding Source

Source of flooding

Flooding Source
Flooding Source

Source of flooding

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Flooding Source

Flood Defence Alignment
Flood Defence Alignment

Flood Defence Alignment Grange Burn North

Flood Defence Alignment
Flood Defence Alignment

Flood Defence Alignment Grange Burn South

Flood Defence Alignment
Flood Defence Alignment

Flood Defence Alignment Grange Burn North

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Outline Flood Defence Locations

Flood defences options north of Zetland Park...

  • primary source of flooding in this area is from the sea due to very high tides and storm surges

  • dredging would have no effect on the flood level as the flood level is dictated by the sea level rather than the size of the river/ burn

  • planting of more trees to absorb water would not lower the sea level and reduce flooding

  • pumping stations not viable as they would need to be enormous to deal with the huge inflow of water from the sea

  • tidal barrier at the mouth of the Grange Burn was considered but it was found to increase the risk of flooding due to the water that would still enter the Grange Burn and be trapped behind a closed barrier.

  • only viable option in this location is the construction of flood defence walls and embankment.

Flood defences options south of Zetland Park...

  • primary source of flooding in this area is due to heavy rainfall increasing the flow in the Grange Burn

  • dredging discounted due to very little impact on extreme flood depth

  • tree planting ruled out due to vert little impact on flows in the Grange Burn

  • pumping stations not viable as they would need to be very large to deal with the large flows in the Grange Burn

  • defences along both banks of the Grange Burn ruled out in favour of

  • flow control device adjacent to the inlet of the flood relief channel to direct most of the water in an extreme flood event into the flood relief channel, and

  • increasing height of flood relief channel banks to accommodate higher flows in channel

Plans showing the proposed flood defence alignment can be found below: