Impact of an extreme rainfall event on solute and sediment dynamics in a mineralised river system

Over the weekend of 5 - 6 December 2015 the most intense rainfall ever recorded in the UK fell over parts of Cumbria, peaking at 341.4 mm over a 24 hour period at Honister Pass, resulting in widespread flooding. It is now widely acknowledged (e.g. statement to the media in December 2015 by Rory Stewart MP) that such 'flash flooding from intense rainfall' (FFIR) events are likely to become more frequent in the UK due to the effects of climate change. Prior to the floods of 5-6 December 2015, Newcastle University researchers spent several years measuring the effects of varying flow conditions on the amount of polluting metal and sediment discharged from the Coledale Beck, some 10 km due north of Honister Pass. These metals include zinc which is toxic to fish along with cadmium and lead that are toxic to most flora and fauna. At the head of the Coledale Beck lies the abandoned Force Crag metal mine (a rain gauge at the mine showed that 223.8 mm of rain fell in a 24 hour period during the weekend of 5-6 December 2015). A novel treatment system, completed in April 2014, treats some of the polluted water that emerges from the mine. Nevertheless, although the treatment system works efficiently, we know that some pollution of the Coledale Beck persists, mainly as a result of metals discharged to the river from other locations around the mine site. These sources arise primarily from sediments in the abandoned spoil heaps and in the river itself. The flash flooding of 5-6 December resulted in wholesale changes to the geomorphology of the Coledale Beck. Large volumes of sediment were carried down the river, whilst new sediments were exposed due to landslides and erosion. Because we already hold baseline data relating to the export of metals and sediments under different hydrological conditions from the Coledale Beck, we are uniquely positioned to now investigate how such extreme rainfall events change the whole-system dynamics of metal and sediment cycling in such upland river catchments. In particular, due to the geomorphic impacts of the December 2015 floods on the Coledale Beck system it will be possible to evaluate how exposure of new sediments influences the behaviour of metals. This is important because the form of metals in rivers (their 'partitioning') determines the readiness with which they may be carried downstream, and also influences their toxicity to the ecology of such rivers. These issues in turn have implications for users of water further downstream (e.g. fisheries, utility companies). Because hydrological extremes are likely to increase in the future as a result of climate change, we need to understand how these events change the physical and chemical characteristics of rivers, so that it is possible to plan adaptive strategies to better deal with such events. The research will be undertaken by collecting samples of waters and sediment along the length of the Coledale Beck on 10 separate occasions, thereby ensuring that samples are collected across a range of flow conditions. The results will be compared with baseline data previously collected, to determine what changes in patterns of metal and sediment movement are caused by extreme events. These results will be complemented by laboratory tests and geochemical modelling to help us assess the likely toxicity of the sediments and metals in the river to aquatic life. The intended outcome of this research will allow transfer of the results of the work to other river systems. There are 450 such rivers in England and Wales negatively impacted by abandoned mine pollution. The research is urgent because rivers are dynamic systems with key changes being driven by high magnitude events. However to properly understand the effects of flash flooding events such as that of 5-6 December 2015, it is critical to undertake sampling and analysis as soon as possible after the event itself.

The research team has an exemplary track record of undertaking high impact research, previously catalysing government investment in addressing pollution from abandoned mines and shaping the Environment Agency's approach to monitoring in abandoned mine catchments in England and Wales. The proposed research will have not only academic impacts, but also wider benefits to society and the economy. Defra and the Environment Agency will be the most immediate beneficiaries of the research, as the outcomes of the project will have a direct bearing on policy and practice in the management of freshwater pollution in the face of the increasing frequency of hydrological extremes associated with wider climate change. Specifically, the Environment Agency - a Project Partner for this research - will benefit from better explanation and understanding of the changes to metal and sediment dynamics that result from flash flooding events. In turn this will inform both more effective ways to monitor such occurrences in the future, and also strategies for heightening the resilience of downstream infrastructure, directly benefiting Government Departments tasked with managing floods and their impacts. The research team will ensure these benefits occur by engaging closely with Defra and the Environment Agency from the inception of the project. If deemed appropriate by these agencies, the research team will prepare non-technical summaries of the research for publication by and / or circulation within Defra, the Environment Agency and other stakeholder organisations. Project outcomes will also be available on the websites of Newcastle and Hull Universities. Similar strategies for ensuring impact will be adopted with the National Trust and Coal Authority (both formal Project Partners), and any other organisations with which they work (e.g. National Parks Authority, engineering consultants). Beyond traditional conference and symposia outputs, international academics and stakeholders outside academia will benefit from the work by results being shared directly with international associations such as the International Mine Water Association, and our existing network of NGOs (e.g. Rivers Trusts and CAFOD, the Catholic Agency for Overseas Development, with which we work closely in Peru).