PhD study into flood mitigation and water quality

PhD thesis entitled: “Flood mitigation and water-quality benefits delivered by pasture features and practices in the Leith, Lowther and Petteril Catchments (Cumbria, UK)”

For generations, landowners have worked with nature to improve their immediate environment by planting trees, woodland and hedgerows.  There is little or no acknowledgement of the positive value of their land management activities in potentially helping to mitigate floods and water quality issues that develop downstream.

This collaborative project between the Eden Rivers Trust, Lancaster University and local farmers aims to investigate the effectiveness of current farming practices (such as soil-improvement techniques) and natural interventions in the landscape (tree and hedge planting) that might help to prevent flooding and water quality problems within the River Eden, with the ultimate goal of evaluating measures necessary to reduce flood damage such as that caused by Storm Desmond (Winter 2015/16) and in Carlisle (2005).

The findings from the PhD studentship will, for the first time, quantify the value of woods, hedgerows, stone walls and wider soil improvement practices in reducing the amount of overland flow and nutrient loss that can produce floods and downstream water quality problems using systematic field-measurements – including soil infiltration, permeability and moisture, with modelling at various scales from local to whole basin scale in three Cumbrian basins (the Leith, Lowther and Petteril).

Farmers partnering with us during river and landscape restoration activities similarly want to see the local evidence that their time and financial commitment is having on-site and downstream benefits.  Results could directly help farmers reduce expenditure, by improving surface runoff predictions and resultant loss of fertiliser and productive soil.

Why use pasture for flood risk reduction in the Eden?

Well, building more and higher traditional flood defences, such as concrete walls is unrealistic. With 95% of the Eden being used as agricultural land, there is the potential to use ‘green-engineered’ interventions (also known as Natural Flood Management measures) that will reduce potential flood risk downstream.

What is being studied?

Five key interventions are being measured in this study. The first four aim to quantify the value of the intervention in the amount of overland flow generated during floods as well as factors that may be causing it. The fifth looks at changes in streamflow.

Intervention:

1. Rough-grazing versus set-stocked land up on the fell Commons,
2. Pasture slitting – using an aerator on the soil to reduce compaction. Additionally measuring the length of time that the benefit of aerating soils lasts,
3. Stone-walls. There isn’t any research on the effect of stone walls on overland flow, so this study will look at difference in soil moisture above/below stone walls on steep slopes … and does this effect persist at varying distances from the wall,
4. Hedgerow buffer strips, planted across field slopes, and
5. Bankside and river channel restoration. Here the study will look at changes in streamflow (peaks, volume and velocity)

Once the data has been analysed, it will be modelled to understand the impact it could have at different scales, from local to large basin scales.

A paper on each of these interventions will published by Autumn 2020.

We’d like to say a huge thank you to the farmers in our Facilitation Fund groups who have provided field sites for data collection.

About Ethan Wallace

Ethan graduated from Lancaster University in July 2016 with a First Class Honours in BSc Physical Geography and continued working there as a research assistant developing data science tools for EPSRC until March 2017. His research interests lie in hydrometeorology, hydrology and environmental management, primarily investigating flood prediction and mitigation.