Rain of fear

A spate of landslips on old Welsh mining tips shows that some engineering challenges persist for generations – and that changing weather patterns are bringing new risks, writes Paul Maliphant.

Climate change is stirring old fears in the former mining communities of south Wales, UK. One hundred and sixteen children and 28 adults were killed in Aberfan on 21 October 1966 when a colliery spoil tip collapsed, engulfing the town’s school and neighbouring houses. The disaster shocked the whole nation and, 55 years on, the pain of that event is still felt, not just in Aberfan, but in communities across south Wales.

Indeed, in every village and town lying in the shadow of a similar spoil tip, people wonder ‘could the same happen to us?’

In February 2020, heavy rain during Storm Dennis caused multiple floods and landslides, including failure of the Llanwonno Tip at Tylorstown in the Rhondda Valley. The landslip flowed down the valley side and blocked the River Rhondda. Luckily nobody was injured. Heavy rainfall triggered lesser landslides at other disused coal tips.

With climate change bringing more frequent and intense rainfall, communities are rightly concerned that more serious colliery spoil tip collapses are to come.

Wales has nearly 2500 disused coal tips, where rock, earth and fine-grained coal were dumped over decades of mining activity. Of those, 327 are now categorised as ‘high-risk’, meaning they could endanger life or property.

The Aberfan collapse was caused during active tipping by the build-up of water pressure within the spoil heap, which had been piled up on top of natural springs and was then further saturated by three weeks of heavy rain. The record-breaking rainfall unleashed on south Wales by Storm Dennis and subsequent rain storms in the first months of 2020 showed that, many years after tipping ceased, disused spoil heaps are susceptible to similar failure mechanisms, where natural and engineered drainage regimes are overwhelmed, leading to instability.

Changing conditions demand extra vigilance

Climate change is elevating the risk. Warmer air holds more water – 7% more for every 1°C – resulting in heavier rainfall. As the Earth’s temperature rises, on our present trajectory towards 3-4°C above the pre-industrial average, and at best 1.5°C, this is something engineers, owners and operators of infrastructure and industries, planning authorities and custodians of legacy assets and liabilities must be alert to.

Many spoil heaps were not designed but are nonetheless classed as engineering structures – their composition and behaviour can be monitored, analysed, understood and managed. After the Aberfan disaster, spoil was relocated, slopes were re-engineered, and drainage pipes, tunnelled adits and channels were installed on many high-risk heaps to control water pressure and manage surface water. All of these were engineered with defined capacities and design lives. With rainstorms becoming more frequent and intense, are they still fit for purpose?

The probabilities and possible consequences of collapse in different locations needs to be studied. As old mining towns and villages have evolved, new roads, railways, power and communication lines, houses and even schools have been built at the toe of spoil heaps. Geotechnical assessment at the time indicated that building in those locations was safe – with slope stabilisation required in some locations. But increased precipitation will raise the water pressure within those slopes and change their behaviour. Engineering assumptions made 10, 20 or 30 years ago need to be re-examined.

And it’s not just the immediate threat to infrastructure assets, property and lives that needs to be looked at. In several locations, rivers could be dammed by major slips. When the blockage gives way, a surge of impounded water would cause downstream flooding.

In 2020 the Welsh Government responded to the events triggered by Storm Dennis: It set up a Coal Tips Safety Task Force supported by an expert panel, of which I’m a member, and the UK Coal Authority to advise on classification, inspection, monitoring and potential tip stabilisation works. Latest estimates to ‘fix’ Wales’ old coal-tips, amid concerns climate change could make more unsafe, is £600M, with more required for longer term management as climate change continues. The Law Commission has recently consulted on changes to the regulations covering coal tip safety in Wales, as existing regulation was deemed to be inadequate. I responded to this consultation on behalf of the Institution of Civil Engineers.

The social side of engineering

Managing the risks posed by legacy infrastructure and industrial assets – or liabilities – is a significant technical challenge. And there are equally important organisational and social challenges too.

The Welsh Government, local authorities, the Coal Authority and regulator Natural Resources Wales need to reconcile the need for managing this risk with other demands on budget, environmental protection objectives, and social and economic development needs. They also need to recognise that people living in potentially at-risk locations, and their communities, are blighted by fear, the probability of disruption if remedial work is required, declining property value and investor caution.

Many former mining communities have struggled to recover socially and economically from the mine closures of the 1980s and 90s. Fear – a legacy of the Aberfan disaster – plays its part in the region’s persistent social and economic deprivation. Past engineers’ negligence and ineptitude are root causes.

Today, engineers and geologists have a key social as well as technical responsibility to address the evolving risk profile of legacy engineering structures so that, while remembering the sorrow of Aberfan, communities in south Wales won’t relive it.