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As all that is solid melts to air and everything holy is profaned...

Tuesday, January 05, 2016

The Drowned World

Photograph by Michael J Lowden  31 Dec 2015.
X marks location of Castle Douglas ARC (day-centre) which was flooded

On New Year’s Day 2016 I  pushed my son in his wheelchair down to the edge of town. We went along an old section of railway line that is now a footpath to the edge of Blackpark marsh. The railway crossed the marsh on an embankment and a few times in the past I have seen the marsh flooded up to the edge of the embankment.

On 31 December 2015 it flooded again. The flood water came from Carlingwark Loch. The loch is separated from the marsh by a ridge of higher ground, but in 1766 a cut was made through the higher ground to provide a constant flow of water for a canal and to lower the level of the loch.

William Roy map 1755, before Carlingwark Canal was made.

The level of the loch was lowered to make it easier to get access to beds of marl, a lime rich clay used as a fertiliser.  The canal was used by barges carrying the marl across the marsh to the (Galloway) river Dee. The barges then took the marl upstream as far as the head of Loch Ken 15 miles away, distributing it to farms along the way.

The Dee/Ken river catchment area stretches up into the Galloway Highlands. Until the Galloway Hydro-electric scheme was built in the 1930s, the river system was subject to periodic floods which could raise the water level by 7 or 8 feet. Victorian Ordnance Survey maps show the extent of the floods by dotted lines marked ‘Limit of Inundation’. From these maps it can be seen that Blackpark marsh would have been covered in water when the floods occurred.

Victorian map of area liable to flooding.
Red star marks football ground flooded 31 Dec 2015.

Usually the hydro-electric scheme manages the flow of water, but when there has been heavy rain, excess water has to be released. In 1938 it was realised that when this happened, the marshes and low lying fields around Castle Douglas were getting inundated so a system of pumping stations and embankments was constructed to reduce this problem by acting as a physical barrier to flooding from the Dee. However, as discussed below, the problem of flooding from the Carlingwark Loch side remains.  

In winter 1973/4 (or possibly 1974/5- can’t recall exactly) the embankment beside the Blackpark pumping station was breached and the marshes were flooded. This was before the Castle Douglas By-pass was built so the only area above water between the edge of Castle Douglas and the river Dee was the old railway embankment.

About 13 years ago, Scottish Power, who maintain the Blackpark pumping station and two smaller ones just to the north, proposed removing the pumps from the Blackpark station. This was due to the cost of maintaining the pumps which frequently get clogged with vegetation from the Carlingwark Lane. [Note ‘lane’ is a local dialect word for a slow-flowing stream.]

Blackpark Marsh Pumping Station built 1938.

This led to concerns that the marshes would flood more often and affect the fields beside the marshes. An alternative suggestion was that the vegetation along the Lane should be cut regularly. I did some research for the National Trust for Scotland who own the marshes to find out who had historically been responsible for keeping the Carlingwark Lane weed free.

This involved  going to the Stewartry Museum in Kirkcudbright and reading the records of Castle Douglas Burch Council where I found that in the 1940s it was the Ministry of Agriculture that had done the work. I also discovered that the pumping station was designed to ‘dry-out’ the marshes to increase the area of useful farmland rather than prevent flooding.

The difficulty was that the hydro-electric scheme had the effect of keeping water levels in the Dee higher all year round so there was insufficient flow from the Carlingwark Lane into the Dee. This had the effect of keeping water levels in the marshes higher all year round.

By pumping water from the Carlingwark Lane on towards the Dee, the level of the water in the Lane could be kept lower, thus making the marshes and adjacent fields drier.

Carlingwark Loch and its catchment.

The main flow of  water into Carlingwark Loch come from the Gelston Burn. This rises as the Airyland Burn on the north-west slopes of Screel Hill (344 m/ 1129 feet) above Airyland farm. From Airyland  it flows north-east to Gelston and then north-west towards Carlingwark Loch. As the ‘Gelston Mill Burn’ it is mentioned in a charter of 1325 in which King Robert I granted James Douglas the lands of Buittle parish.

The Gelston Burn runs parallel with the B 736 towards Carlingwark Loch through a narrow triangle of marshland. An older road ran along the edge of Carlingwark Loch before cutting across the marshland, but this was abandoned circa 1820 due to frequent flooding. The new road crosses a smaller area of marshland between Whitepark Hill and Cuckoo Bridge on a stone embankment. The stream which flows under Cuckoo Bridge leads down to the Gelston Lane. It is fed from Black Loch and Floors Loch. The former Torrs Loch, now Torrs Moss also feeds in to the Cuckoo Bridge stream, but drainage works in the nineteenth century mean that along with Leathes Burn, Torrs Moss now mainly drains into the Birkland Burn which flows north into the Urr.

Gelston Burn catchment area

Altogether the catchment area of the Gelston Burn is only about 12 square kilometres. Of this about 2 square kilometres are marsh and about 3 are on the slopes of Screel Hill. The rest is dairy farm land.

Another very small stream flows into Carlingwark Loch from the top of Castle Douglas then beneath the town into the loch.

With such a small catchment area, how can the Gelston Burn cause flooding in Castle Douglas, as occurred on 31 December 2015? The main reason is that the loch’s only outflow is via the cut made through Carlingwark Hill in 1766 or 67 According to Sir Alexander Gordon of Greenlaw who had the Carlingwark canal made in 1765, the cut through the hill was made  a year or two after the canal.

Before the canal and the cut were made, William Roy’s Military Survey of 1755 shows a meandering stream called the Carlingwark Burn exiting the loch roughly where the cut was later made.  Since the cut lowered the level of the loch by 6 to 8 feet, it is likely that the loch would have occasionally overflowed towards Blackpark marsh along what is now Marl Street. Certainly the Old Statistical Account for Kelton parish states that a ‘dam’ built of oak and clay was found there. This was more likely to have been a causeway across a marshy area. There was a very small settlement called Causewayend in the vicinity.

The main settlement was Carlingwark, which was on Carlingwark Hill. There was an inn and a blacksmiths there in the seventeenth century. Carlingwark Hill was the only high ground for east/ west travellers to use to cross the marshes which stretched above and below Carlingwark Loch. In 1764/5  in became part of the Old Military Road from Gretna to Portpatrick.

Unlike the turnpike road , which later became the A 75 and which skirts the edge of Carlingwark Loach, the Old Military Road ran over Carlingwark Hill. On its alignment and a few yards down stream from the Buchan Bridge the remains of an old bridge survive. This  has a much small span than the Buchan Bridge, constricting the flow of water. The Castle Douglas Flood Risk Assessment contains photos illustrating the problem.

Buchan Bridge- normal water flow

Remains of old bridge- normal water flow

Cutting through Carlingwark Hill- normal water flow

I have examined the remains of the old bridge which appears to have slots in its abutments as if there had been a sluice gate on the down stream side. It is the remains of this bridge which constrict  the outflow of water from Carlingwark Loch.

Beyond the old bridge the Carlingwark Lane drops down through the deep cutting made in 1766/7 to the marshes beyond. According to local author S R Crocket, writing about his childhood , in the 1870s, floodwater from the river Dee sometimes flowed up through the cutting and out into Carlingwark Loch. If this account is true, then there may have been sluice gates on the old bridge to prevent Alexander Gordon’s marl workings around Carlingwark Loch being flooded.

There is a puzzle reading the Old Statistical Account since it says that when the cut was made through Carlingwark Hill, the level of the loch dropped low enough to reveal two Iron Age crannogs in the loch. These are now mostly under water again, although they remain as islands with trees growing on them. Presumably the water level has risen back to some extent. However, some of Gordon’s marl working were carried out by ‘bag and spoon’ dredging from a small boat, again based on evidence in the Old Statistical Account.

To reduce future flooding of Carlingwark Loch, removing the remains of the old bridge to let excess water flow out of the loch more quickly might help. However this would only displace the problem, leading to more rapid flooding of the Blackpark marshes. On 31 December, the flooding reached Threave Rovers Meadowpark football ground.  This is only a few yards across Blackpark Road from Castle Douglas Waste Water Treatment  Works. If the Waste Water Treatment Works flooded this would be a serious problem.

Although treated waste water from the works is now piped to the river Dee just above the old Bridge of Dee, there is still a legacy outfall from the works on the marsh side of Threave Rovers ground and this will have been underwater on 31 December. What effect this had on the treatment works is unknown.

The Bigger Picture- Climate Change

Partly in response to Scottish Power’s proposal that the Blackpark pumping station could be decommissioned, Dumfries and Galloway Council and Scottish power commissioned Terrenus CDH Ltd  to carry out a flood risk assessment for Castle Douglas. The final report was produced in 2013.

Part of the assessment was a series of maps modelling a 1 in 200 year flood event. The final map in the sequence showed the extent of flooding when the level of Carlingwark Loch rose 2.35m above its normal level. This map shows flood water extending along Marl Street and into Castle Douglas Waste Water Treatment Plant.

Map from 2013 Flood Risk Assessment- the 31 December 2015 flood reached this level.

Most extreme flood from flood risk assessment 2013.

The 31 December 2015 flood did not reach this level, but it did reach 1.75m above the normal level of Carlingwark Loch, that is only 0.6m below the maximum modelled.

Compared with the flooding of Newton Stewart which occurred on the same day and other recent floods in large urban areas, even this ‘worst case’ scenario would only count as a minor event since most of the town is built on higher ground. The main concern would be what effect the flooding of the waste water treatment works would have.

The bigger problem is that a significant effect of global warming is to increase the amount of water vapour in the atmosphere. This in turn means that major flooding events are going to become more frequent and more intense.

Today, it is still possible to talk of ‘exceptional’ flooding events and to argue that greater investment in flood defences would mitigate the impact of such ‘exceptional’ events.

But if exceptional events are going to become the new normal, if major floods are going to happen every winter on a rising trajectory of intensity, then the cost of building more and more and better and better flood defences will become unsupportable.

This is because unless the process of global warming can be slowed down, the effect of climate change will be to make areas which have been habitable for centuries uninhabitable. Effectively, our whole way of life, which has been based on a stable climate, will be threatened.

There is a solution, but it requires giving up fossil fuels as an energy source.  Unfortunately, the industrial civilisation which has developed over the past 200 years is based on the use of fossil fuels. Adapting to using renewable/ sustainable energy as our primary source of energy will be difficult. Difficult, but not impossible. What is impossible is to carry on as normal, as if climate change is not happening.


Anonymous Daniel said...

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3:07 am  

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