Mobilisation of metal mining waste in rivers a changing climatological regime

In the uplands of the UK, there is and increasing body of evidence demonstrating an increase in flood magnitude and frequency that has resulted in a dramatic response to river landscapes.  Most recent research has focussed upon the potential impacts of increased water discharges upon flood risk management, with much less attention targeted towards sediment dynamics and associated channel and floodplain morphological responses. Many upland catchments in the UK also have a mining legacy which has resulted in modern-day heavy metal-contaminated sediments often stored in floodplains. For example metalliferous mining was particularly intensive between the 17^th-19^th centuries, in the Lowther Hills, North Pennines, Lake District, Yorkshire Dales, Peak District, Mid-Wales, and West Devon and Cornwall. In many locations mine waste (e.g. tailings, waste heaps) is situated on low terraces and on the floodplain. Furthermore, the sink zones (e.g. floodplains) of many of the river systems that drain these areas act as dormant highly contaminated stores. The potential morphological response of upland catchments to projected changes in storm frequency and intensity, is unknown, however, recent examples in the North Pennines show that single events can lead to severe erosion of old sediment stores on the entire valley floor. Thus the fate of the remobilisation of toxic metalliferous waste stored in floodplains presents one of the greatest risks to aquatic and floodplain ecosystems, and has implications to the human food chain, as many floodplains are used for grazing. In addition, increased mobilisation of contaminated sediment negatively impacts water quality and river navigation. This project aims to:

• Provide an inventory of the mining-related contamination status of selected UK catchments;
• Simulate the sensitivity and geomorphic response of selected river catchments influenced by historic metal mining to future flood event scenarios, predicted under current regional climate change models;
• Provide estimates of likely remobilisation quantities and flux of contaminated mine waste, and simulate downstream dispersion dynamics;
• Outline priority areas for targeted mitigation measures.

The PhD project will address these aims through a three stage investigation:

1. The initial stage will comprise of an inventory of metal mining activity and associated deposition of waste heaps, tailings etc. in a location that is connected or has the potential to be connected to the river channel during extreme events. This will use existing databases on waste rock (e.g. Landmark data) and contamination (e.g. GBASE) which have proven to be suitable assess mining pollution. Other data sources, e.g. from the archaeology and heritage sector, will be considered as well. This will be combined with use of aerial imagery and site visits to ascertain the character of the sediment, proximity to any water courses, etc.The selection of study catchments and relevant reaches within will be also supported by the analysis of available lidar data which can reveal sediments stores on the valley floor and nearby slopes and terraces as well as changes over time.
2. In the second stage selected sites will undergo geomorphological analysis to precisely map and characterise sediment stores (using LiDAR and/ or photogrammetry), their association with mining, contamination and 3D extent. The latter may utilise innovative technologies such as geophysical surveys using GPR and/ or electric resistivity, and UAV-based hyperspectral remote sensing to remotely characterise mineral species.
3. The final stage will investigate the susceptibility of the relevant reaches to sediment mobilisation under predicted climate scenarios and associated extreme events will be simulated using a morphodynamic model. Detailed modelling will facilitate i) the spatially distributed mapping of erosion and deposition and quantification of the mobilised contaminated material, ii) temporal evolution of storage areas to be quantified at the catchment-scale. Hydrogeochemical models will be employed to explore effects on water quality and environmental effects. In addition, the models will allow different intervention approaches to be tested under a range of climate change scenarios.

The project will produce detailed maps that indicate areas that are most susceptible to sediment dynamics and particularly mobilisation of contaminated sediment under climate change scenarios. This will provide information to prioritise mitigation efforts related to water quality, ecosystem integrity, flood and sediment management in ongoing and future projects and therefore will benefit a range of stakeholders, from governmental agencies, industry, conservation, heritage and other local groups.