Impacts of natural flood management on both water quantity and quality

Overview

Motivation:
Flooding from rivers is a substantial problem in the UK and can result in the loss of infrastructure, farmland, and livelihoods. The resulting damage to the UK economy has been estimated to cost around £1.4 billion each year (The Foresight project, 2004), and this number is expected to increase given that flooding probabilities are increasing due to projected climate change-induced weather extremes becoming more frequent (Otto et al., 2018). A second, substantial problem of UK rivers is their insufficient water quality. In 2019, only 15% of England’s rivers were considered to be at Good Ecological Status (DEFRA, 2020). The two problems of flooding and water quality are directly and indirectly related, as flooding also affects water quality and ecosystem services (Hrdinka et al., 2012). Short residence times and high velocities of water in the river during storm events result in the flushing of pesticides, microbial pollution, and fertilizers into the river systems, directly impacting their water quality and ecological status. Additionally, flooding may have indirect effects on water quality and ecosystem services, resulting from the erosion of sediment from riverbanks and the streambed. As sediments are mobilized, they act as transport vehicles for sorbed pollutants, such as phosphorus. The sediments and associated pollutants also create further damages to properties during flood events.

Although still costly, flood prevention is more effective than the repair of flooding damage. For this purpose, natural flood management has gained increased attention in recent years as a valid approach to mitigate flood risk. Natural flood management encompass a wide range of interventions across various scales, from landscape-scale interventions such as agricultural and soil management to channel-based interventions such as woody-debris dams with the purpose of slowing down the flow. However, the performance of natural flood management is uncertain and they often require more land than traditional grey flood protection infrastructure like dams.

It has, however, been suggested that the effects of natural flood management may not be limited to flood prevention, but that it may have multiple benefits, including improved water quality, increased biodiversity, and reduced soil erosion (Dadson et al., 2017). As a result, natural flood management may also be able to mitigate the effects of diffuse pollution on water systems, thus decreasing the relative cost of its implementation compared to the benefits it provide.

Research Gap and Questions:
While these potential benefits of natural flood management are understood in principle, significant uncertainties remain regarding the nature and extent of these multiple benefits because further empirical evidence is required across catchments of different scales (McLean et al., 2013; Morris et al., 2014). Improving our understanding of the multiple benefits and the underlying functioning of natural flood management is therefore key for justifying its adoption more widely in the field. In particular, it is unclear how large the impacts of different natural flood management features are, as they can be very different ranging from land-management strategies to in-stream structures. Critically, the evidence base for the impacts of different natural flood management features on water quality and ecology remains limited.

The aim of this PhD project is to assess and quantify the multiple benefits of natural flood management for flood mitigation by addressing the following questions:
1) What effects does natural flood management have on water quality, ecology, and water quantity?
2) How do these effects on quantity and quality change depending on the type of intervention?

Methodology

The aim of the research will be achieved through a combination of methods including statistical data analysis techniques, model development, as well as field measurements of hydrological and hydrochemical data.

A large part of the project will focus on compiling pre-existing data from various sites and collecting hydrochemical data from some selected catchments with natural flood management in the North East of England. Additionally, the project aims to improve our understanding of how flow processes are affected by different natural flood management features, and how travel times are linked to water quality. Travel times may provide a causal explanation of potentially observed differences in water quality effects of different natural flood management features, as reaction processes of nutrients depends to a large part on their residence times in the system (e.g., Dupas et al., 2020; Hrachowitz et al., 2016). To assess the larger-scale impact of localized flood modifications, the project will use natural tracer data (stable water isotopes and electrical conductivity) to estimate transit times, quantify upstream-downstream propagation of water during low and high flow periods, and assess water retention and the slowing of flow induced by flood interventions at those sites. These travel time assessments can help to identify how natural flood management impacts internal catchment functioning like the transport, storage, and release of water, nutrients, and contaminants.

Project Timeline

Year 1

Literature review, analysis of existing data sets, planning of field work, collection of field data.

Year 2

Collection and analysis of field data

Year 3

Analysis of field data, paper & thesis writing

Year 3.5

Completion of thesis and paper writing

Training
& Skills

This project would suit a student with a degree in Earth or Environmental Sciences or Physical Geography (or related) and strong interests in hydrology, water quality and/or ecology.

Excellent time management skills coupled with strong numerical, verbal and written communication are important. A background in watershed management, river restoration or flood management is helpful but not essential. Training will cover field methods (water sample collection and handling) and statistical data analysis techniques. The student will attend national and international conferences, networking events and outreach activities, developing an important network for feedback and future employment.

References & further reading

Dadson, S. J., Hall, J. W., Murgatroyd, A., Acreman, M., Bates, P., Beven, K., … & O’Connell, E. (2017). A restatement of the natural science evidence concerning catchment-based ‘natural’ flood management in the UK. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 473(2199), 20160706. https://doi.org/10.1098/rspa.2016.0706
Department for Environment, Food and Rural Affairs (DEFRA), UK (2020). UK Biodiversity Indicators 2019. https://jncc.gov.uk/our-work/ukbi-b7-surface-water-status/
Dupas, R., Ehrhardt, S., Musolff, A., Fovet, O. and Durand, P., 2020. Long-term nitrogen retention and transit time distribution in agricultural catchments in western France. Environmental Research Letters, 15(11), p.115011. https://doi.org/10.1088/1748-9326/abbe47
Hrachowitz, M., Benettin, P., Van Breukelen, B. M., Fovet, O., Howden, N. J., Ruiz, L., … & Wade, A. J. (2016). Transit times—The link between hydrology and water quality at the catchment scale. Wiley Interdisciplinary Reviews: Water, 3(5), 629-657. https://doi.org/10.1002/wat2.1155
Hrdinka, T., Novický, O., Hanslík, E., & Rieder, M. (2012). Possible impacts of floods and droughts on water quality. Journal of Hydro-environment Research, 6(2), 145-150. https://doi.org/10.1016/j.jher.2012.01.008
McLean, L., Beevers, L., Pender, G., Haynes, H. and Wilkinson, M., 2013, September. Natural flood management in the UK: developing a conceptual management tool. In 35th IAHR World Congress, Chengdu, China.
Morris, J., Beedell, J. and Hess, T.M., 2016. Mobilising flood risk management services from rural land: principles and practice. Journal of Flood Risk Management, 9(1), pp.50-68. https://doi.org/10.1111/jfr3.12110
Otto, F. E., van der Wiel, K., van Oldenborgh, G. J., Philip, S., Kew, S. F., Uhe, P., & Cullen, H. (2018). Climate change increases the probability of heavy rains in Northern England/Southern Scotland like those of storm Desmond—a real-time event attribution revisited. Environmental Research Letters, 13(2), 024006. https://doi.org/10.1088/1748-9326/aa9663
The Foresight project, 2004. Future flooding scientific summary: volume 1 – future risks and their drivers. Government Office for Science. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/300583/future-flood-vol-1.zip

Further Information

For more information regarding the project contact Julia Knapp at Julia.L.Knapp@durham.ac.uk

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