Soil water repellency: occurrence and hydrological impacts in humid temperate climates

Soils are normally thought to wet readily under rainfall or irrigation. In hydrophobic (water-repellent) soils, wetting is inhibited, resulting in a reduction in infiltration rates in severe cases by several orders of magnitude. This can contribute to flooding; accelerated soil erosion by water and wind; enhanced preferential flow and associated leaching of nutrients and agrochemicals (Doerr et al. 2000). Some of these impacts bear considerable environmental and economic costs. For example, soil water repellency is though to have contributed to the devastating summer 2007 floods in the UK. Much of our understanding of its hydrological impacts is derived from work carried out at small-plot scales in seasonal climates. Little is known about its impacts at the catchment scale, particularly in humid temperate regions. Hydrological responses of soils are often deduced from point-scale measurements at the soil surface rather than from actual wetting behaviour of the soil volume, which leaves considerable uncertainty in the degree to which water repellency enhances such responses (Shakesby et al. 2000). Water repellency is now beginning to be recognised a potentially important parameter in hydrological modeling, but, associated with the research gaps identified above, catchment-scale hydrological models have to date not addressed water repellency effects in their predictions.

This project addresses this research gap by isolating and quantifying the hydrological impacts of water repellency using (a) surfactants at point and plot-scales to allow measurements to be repeated for comparable wettable soil conditions (Leighton-Boyce et al. 2007), and (b), a methodology that demarcates naturally hydrophobic and wettable conditions in the field (Doerr et al. 2003), allowing to evaluate and model responses at the catchment scale. It is anticipated that study catchments will be selected in the UK, however, opportunities exist to include catchments in Portugal, the USA or Australia for comparison. This work will be field and laboratory based and may require visits to collaborators and field sites abroad.

The successful candidate will join an internationally leading research team in soil hydrophobicity at Swansea University, will receive training in research design, field and laboratory techniques, geostatistical techniques and modelling procedures, and will be encouraged to direct the research within the broad remit described above.


Applicant requirements
The successful candidate will possess (as a minimum) a BSc/BA (Hons) degree class 2(i) in Geography, Environmental or Soil Science, or related discipline (some knowledge of hydrology is essential), should be able to work well within a team and is expected to present at international conferences.