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Increased flood risk from solar farms

Updated 12th April 2022.

Legendary stories of flooding appear in many cultures across the globe, spanning thousands of years back to the Neolithic Age. From the Ottawa Great Flood, Noah’s Ark in the Christian Bible, and even some of the myths surrounding Atlantis.

Flooding can occur anywhere in the world, and at any time. Even on warm sunny days.

Types of flooding in Suffolk

Here in the Suffolk countryside there are two types of flood event.

A fluvial, or river flood, occurs when the water level in a river, lake or stream rises and overflows onto the surrounding banks, shores and neighbouring land. The water level rise could be due to excessive rain or snowmelt.

A pluvial flood occurs when an extreme rainfall event creates a flood independent of an overflowing water body. It occurs away from a natural body of water (such as a river) and when the drainage system in the area is overwhelmed.

There is also coastal flooding but that isn’t applicable to this area of inland Suffolk.

What rivers are around here?

Around the villages here (Flowton, Somersham, Burstall, & Bramford Tye) there are a few “main rivers”, and a few “ordinary watercourses”. You can see the flood zones according to the Environment Agency Interactive Maps. There are two here and here.

In Somersham there is a main river (this is defined by the Environment Agency as any watercourse that contributes significantly to the hydrology of a catchment area) called The Channel. It flows through the village from the north west and follows the path of Lower Road horizontally through the middle of the village. Just east of the village it crosses Lower Road and continues along the southern edge of the same road to the east. This road and immediate surrounding area is listed as having a high surface water flood risk (flood zone 3).

In Flowton there is another main river called Flowton Brook. This flows along the road named The Channel (not to be confused with the river in Somersham), which slopes south, and joins up with another main river called Belstead Brook which comes in through the village of Burstall. This is also listed as having a high surface water flood risk.

In Flowton there are then two ordinary watercourses (defined by the Environment Agency as any other watercourse that is not part of a main river, including streams and ditches). Valley Farm Brook, which crosses Flowton Road at the corner of Valley Farm, is also registered as a high flood risk. And then Grove Farm Brook, which flows north east of the village, doesn’t cross any roads and has a medium to high flood risk.

In Bramford Tye there is another ordinary watercourse from east to west in the form of ditches that run along the southern side of the road called Tye Lane. At the bottom of the main hill (surprisingly the hill doesn’t appear to have a name) where the road passes next to an area of ancient woodland, the road becomes the watercourse, until it reaches more ditches on the northern edge of the road. Worryingly, the Environment Agency doesn’t recognise this as an area that floods!

If you live in the area these assessments of “high surface water flood risk” won’t come as any surprise to you. But the revelation that Tye Lane isn’t regarded as an area that floods is ludicrous.

What does a high flood risk mean?

There are three flood zones.
~ Flood Zone 1 is low risk, and is defined as land with little or no flood risk. Flooding would be a roughly 1 in 1000 year event.
~ Flood Zone 2 is medium risk, and is defined as having a medium chance of flood risk. It would sit somewhere between a 1 in 1000 year event and a 1 in 100 year event.
~ Flood Zone 3 is high risk, and includes land for both high risk and functional floodplain. It would be between a 1 in 100 year event and a 1 in 20 year event.

If you live in, or know the area well, then you know that the area floods more than once every 20 years. Much more than that in fact.

On Friday 4th December 2020 we had a road closure at Flowton Brook caused by flood water. Lower Road in Somersham, and Tye Lane were equally flooded.

Flooding at Tye Lane, Bramford Tye on 4th December 2020.

On 20th December 2019, less than one year earlier, the area also severely flooded. Lower Road in Somersham was closed for several days, as well as the roads and confluence of Flowton Brook and Burstall Brook. Tye Lane was passable for those brave enough in 4x4s or larger. Even the corner where Valley Farm Brook crosses the road was flooded.

This happens every year. Usually more than once. In fact in 2019 it flooded so much that a neighbouring village, Offton, were completely cut off. Flowton was left with only one road out of the village (which Enso Energy propose to put solar farms on both sides of), and Somersham were also left with only one route via Nettlestead. In the 2020/21 winter period we have so far seen 3 flooding events in the area, and it’s only 17th January 2021 so far.

1 in 20 years barely scratches the surface.

So how will solar farms impact the flood risk?

Enso Energy has made no attempt to analyse the impact of water run off from the fields on the surrounding areas and narrow country roads. Yet they claim it will have no impact. They cite general studies of other places in the world and pay no respect to the actual site area they plan to build on. According to Enso Energy “solar panels do not increase the risk of flooding”. The Suffolk County Council Flood & Water Management Team don’t seem to agree with this, have noticed the significant lack of detail in their application, and have asked for a “holding objection” while Enso Energy produce and supply the missing documentation. This means that they have asked for the consultation phase to be put on hold until this detail is provided, or should the LPA move to make a decision then their consultation is registered as an objection.

EDF have said the same thing as Enso. That solar panels do not increase the risk of flood. They’ve said it several times in fact.

Yet some of the same studies that Enso Energy have cited (Hydrologic Response of Solar FarmsLauren M. Cook, S.M.ASCE; and Richard H. McCuen, M.ASCE, J. Hydrol. Eng., 2013) state that “.. the kinetic energy of the water draining from the solar panel could be as much as 10 times greater than that of rainfall. Thus, because the energy of the water draining from the panels is much higher, it is very possible that soil below the base of the solar panel could erode owing to the concentrated flow of water off the panel..” and that if the land underneath and surrounding the panels is not correctly managed (such as due to compaction via use of machinery) then the runoff is likely to be “..increased significantly and the peak discharge increased by approximately 100%.” This means the solar panels may increase flooding and soil erosion depending on the soil and how it is managed.

Soil comes in many different forms. For example you may be familiar with chalky soils, sandy soils, loamy soils, and clay soils. The University of Cranfield (the largest group of soil scientists in the UK) have identified 27 different soil types. They’ve even created an interactive map if you’re interested.

The area here is a predominantly clay topsoil, with a chalky subsoil. Clay soils are wonderfully fertile soils, and we previously discussed the high grade of soil we have here. However, when clay soils are worked during wet periods they are prone to compaction. You may have noticed that the farmers around here avoid working the land when it is wet. And if they absolutely have to they’ll stick very closely to the existing tramlines in the field. This isn’t just to avoid getting stuck, it is to avoid unnecessarily compacting the soil because this is a high risk flood area.

This shows tracks created by farmers quad bike in a field along Tye Lane. You can see the farmer has gone over to the existing tramlines, as well as the surface water created by the compacted soil under the tyre tracks. This is one of the fields proposed by EDF for development.

When soil becomes waterlogged it has reached its “field capacity”. With our current rainfall and with soil which has a considerable clay content, as much of the land round here has, local field capacity is reached on between 120 and 150 days per year. This doesn’t mean just the winter months. We can have wet spells in spring and autumn and dry winters, so field capacity can be reached several times in a year and for variable periods. Hence our roads flood several times through the year, not only in winter.

Once compacted the soils ability to absorb and hold water is reduced, and it also prevents water from seeping down further into any groundwater stores too. Therefore more water becomes available for flooding both on the surface and further downstream. And clay soils do not uncompact themselves. It requires aerating, and ideally having organic matter worked into it. So each year, once the crops are harvested, you’ll undoubtedly be familiar with the smell of the “September Surprise” when the farmers are spreading the well rotted manure onto the fields, ready for them to then subsoil (plough) the land. This process undoes any compaction from the year, and the mixed in manure adds extra structure (as well as nutrients) to the soil.

Construction Works

Now lets circle back to the solar farms. In order to get the solar panels and infrastructure in place the developers will need to work all over the land. They will touch almost the entire site area during the construction. Not just tramlines like the farmers. The entire area will be trodden on with heavy machinery, lighter machinery, and workers. This means the entire site area will be subjected to compaction, and much of it subjected to severe compaction. Photos of solar farms during construction don’t seem to be very common, but you can see an example of one here.

A wonderful article about the challenges, and some solutions, to the challenges of surface water flooding during construction can be found here.

This photo is taken to the south of Somersham Park, looking south east over field 2 proposed by Enso Energy. The edge of the field has been severely compacted by the turning of the tractor when carrying out subsoiling work, and the surface flooding is clear to see. But the middle of the field, where the soil is less compacted due to the linear work contrasts to the edge and the soil surface is well drained. This photo was taken 7th January 2021 a full two days after rainfall.

Do you think the contractors building the solar farms are going to go home for a few days because they risk damaging the soil? Of course not! They will be on a schedule, with penalty clauses for delay, so they will carry on regardless of soil conditions and the mess they are making just to get the job done. We are told that their job will last around 6 months for EDF and 10 months for Enso Energy, which must result in some working when the ground is unsuitable because of waterlogging. It won’t matter to them if the end result is a compacted messy mud bath that causes long term flooding to the local residents. So long as they get paid on time and in full.

Remember that a farmer will subsoil after harvest to remove as much compaction as possible. Contractors won’t be able to plough their damage out because they will have planted solar panels all over the fields and buried cables which would be pulled out by deep cultivation. Therefore the damage they do to field drainage will last 40 years, and the surrounding area will have to put up with the ensuing flooding.

And remember we can also have flooding during spring and summer when the fields have well established crops in them. The grass the developers plan on planting will have only a minimal counter effect on the severe compaction.

Summary

This isn’t a case of the solar panels causing more flooding (although they’ll speed it up), it is a case of the construction work needed to build them doing harm to the soil that creates long term increased flooding. It is only when/if the solar farms are decommissioned that the damage can be undone by subsoiling.

This increased risk of flooding will be particularly relevant to the Enso Energy project at the confluence of Flowton Brook and Burstall Brook, and the EDF project on flooding along Tye Lane in Bramford & Bramford Tye, because the fields slope towards the roads.

Interestingly, both Enso Energy and EDF Renewables are adamant that solar PV sites do not increase surface water risk, citing this study. Yet, citing the same study, Statkraft acknowledge that solar PV sites do increase surface water flood risk and have incorporated two large stormwater attenuation ponds into their design to hold the surface water back from the roads as a result of their calculations.

If field drainage is compromised by construction damage and the water not held back for a slower release by percolating through the soil drainage channels, prepare for more field capacity days, increased faster run-off, and more frequent and severe flooding.

1 thought on “Increased flood risk from solar farms”

  1. This is just part of the objections I (and I hope others) will be raising, once EDF and ENSO submit their applications for planning permissions to swamp us with useless Solar Panels.

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