How can Knowledge of Hillslope Soils Help to Prevent Flooding Through Changes in Land Management?

Background: The impact of climate change across Scotland is indisputable. SEPA (2006) state that current predictions indicate higher river flows nationwide in the future will likely lead to increased flood risk. With this uncertainty, it is important to explore fully all causes of flooding and potential opportunities for precipitation attenuation (Wilkinson et al 2010). One of the first opportunities to attenuate precipitation is in the soil it lands on. Large volumes of runoff are produced in areas of slope-foot concavity because of flow convergence (Robinson and Ward 2017). What if this runoff could be delayed on the hillslopes, and direct runoff could be reduced?
Understanding water storage and movement within soils is fundamental to the study of runoff generation. Soil structure is known to have a significant effect on runoff and is an attribute that can be feasibly managed (e.g. through changes to vegetation or land management), or legally protected. The Eddleston Water Project – funded by the Scottish Government – addresses the potential contribution of Natural Flood Management (NFM) to flood prevention. However, research into soil hydrology in the catchment has received limited attention. This provides a rare opportunity to examine “first defence” NFM strategies at a hillslope level, as part of a catchment-wide NFM scheme. Importantly, The Eddleston Water catchment is typical of many rural Scottish catchments, thus results will have wider utility across Scotland.
Soils attenuate flood waters (to varying extents), without intervention. There are presently no policies designed specifically for the protection of soil (i.e. none with soil as their primary concern) (McKee 2018). Results of this study would help inform policy with regard to soil protection for the prevention of flooding.
Aim: This project aims to understand the role of soil structure in hillslope runoff generation, to identify how hillslope soils may be protected and adapted to slow and store runoff, to alleviate downstream flooding.
Approach: This project would complement and provide added value to ongoing research in the Eddleston Water catchment (70km2). The Eddleston Water is a tributary of the River Tweed, situated in the Scottish Borders. Field sites would be located on hillslopes within the catchment. Through the existing Eddleston Water Project (of which the University of Dundee is a founding partner), there is access to a wide range of underpinning data (meteorology, soil infiltration, solid and drift geology, land cover, groundwater and surface hydrology, sediment fluxes, NFM, ecology) that would inform the studentship (Baillie et al 2016).
The studentship would use several field sites within the Eddleston Water catchment for a comparative study, with sites chosen for their differences in soil structure. Sites would be classified in terms of: topography, soil type, soil depth, underlying geology, altitude, and water table height. To identify lower hillslope convergence zones and hence sources of direct runoff, the student would use Beven and Kirkby’s (1979) Topographic Wetness Index (TWI), informed by LiDAR topographic data and GIS, and verified through ground survey (Silva 2014). Soil structure and texture would be explored by analysing soil samples at The James Hutton Institute (JHI), using methods such as soil coring and granulometric analysis.