Floods trigger pollution study

Cwm Rheidol mine. Picture courtesy of Environment Agency Wales.

Researchers at Aberystwyth University are studying the possibility that the recent floods may have caused heavy metals from old mine workings in the region to be carried down-stream, causing land to be polluted.

Researchers at Aberystwyth University are studying the possibility that the recent floods may have caused heavy metals from old mine workings in the region to be carried down-stream, causing land to be polluted.

The work is being led by Professor Mark Macklin, an expert on river systems and Director of the Centre of Catchment and Coastal Research at the Institute of Geography and Earth Sciences.
The team will be collecting samples over the coming days and weeks to check for traces of lead, zinc, cadmium and copper that may have been carried by the floods.

According to Professor Macklin the extreme rainfall experienced in Ceredigion was caused by a frontal storm amplified by the terrain of the Cambrian Mountains, and the flooding in the lower Rheidol and Ystwyth valleys was made worse by a high tide, south-westerly winds and low pressure.

The steep terrain, thin soils and the rocky nature of the upper reaches of the valleys meant that rain flowed off the hills very quickly causing flooding in the upland headwaters of the Leri, Rheidol and Ystwyth rivers.

He also argues that the narrowness of these valleys combined with the development of housing and businesses on floodplains significantly increased the risk of flooding and the damage caused.

“These floods are not unprecedented either in mid-Wales or similar upland areas of the UK”, said Professor Macklin. “In mid-Wales there were similar summer floods in August 1973 and notably in July/August 1846 that caused a number of deaths and widespread destruction in south Ceredigion especially in Llanon, Talsarn and Aberaeron.”
“One of the unforeseen consequences of these floods could be contamination arising from the remobilization of historical metal mining waste in the region and polluted floodplain soils and sediment.”

“Floodwaters disperse contaminated sediment downstream and this material frequently contains high levels of lead, which can be deposited on agricultural floodplains and, in the case of the Leri, into coastal wetlands and estuaries.”

“We found this to be the case in the 2000 floods within Yorkshire and the River Swale whose catchment is similarly affected by historical mining. This detailed sampling programme is required to evaluate whether or not this is a problem that requires further study.”

“To ensure that this doesn’t happen in the future we need better assessment flood risk especially using recent geological records of floodplains that often provide an archive of past flood events and the use of documentary sources to extend the flood series”, he added.

“Many of our small upland catchments in Wales do not have river flow gauges, so it is very difficult to evaluate flood risk.”

Professor Macklin has also called for more stringent guidelines for development on floodplains, particularly in small and steep catchments like the Leri that have narrow valley floors, which are vulnerable to flash flooding as well in tidally-influenced rivers such as the lower Rheidol and Ystwyth.

“Modelling studies suggests that we may get more intensive summer rainfall in the future but it is interesting to note that evaluation of long-term geomorphologically based flood records that extend over the 250 years or so suggests that in the latter part of the last century and the first decades of the present century the incidence of extreme upland floods, such as those that affected mid-Wales in June 2012, are at historical low.

“If modelling forecasts are correct things can only get worse!” he added.

AU19912

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