Supervisors

Dr Stefan Doerr, Swansea University

Prof Rory Walsh, Swansea University

Dr Rick Shakesby, Swansea University  

Project and aims

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. The environmental impacts of this phenomenon include enhanced overland flow, which can contribute to flooding; accelerated soil erosion by water and wind; enhanced preferential flow and associated leaching of nutrients and agrochemicals; reduced microbial activity, seed germination and crop growth; and poor performance of amenity turf (Doerr et al. 2000). Some of these impacts bear considerable environmental and economic costs. A recent survey across England and Wales carried has confirmed that many common land use types are affected by hydrophobicity (Doerr et al. 2006). 

The aim of the proposed project is to quantify the hydrological consequences of hydrophobicity at a range of scales for selected affected areas in the UK. This project is all the more relevant given that the current trend towards more frequent summer drought periods (the type of conditions conducive to widespread hydrophobicity) and more frequent flood-producing storms is predicted to intensify in the future with global warming. 

Methods will include point-scale wetting rate and small plot-scale rainfall simulations with and without surfactants. Surfactants suppress hydrophobicity, thus allowing the effects of hydrophobicity to be fully isolated. At the slope- and small catchment-scale, a novel methodology that demarcates naturally hydrophobic and wettable conditions in the field using critical moisture thresholds (Doerr et al. 2003) will allow modelling and evaluation of responses at these larger scales. The effects of hydrophobicity on soil moisture dynamics will be assessed over a range of time scales (days, weeks and months) and resolutions (minutes, hours, days) using several automatic logging stations, each equipped with a series of soil moisture (ECH2O) probes.  

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). 

Funding

This project is eligible for competitive funding through NERC studentships awarded to the Department. Other funding opportunities are available and self-funded students are always welcome. Contact your potential supervisor for advice and details of how to apply. The closing date for applications to NERC studentships is 18 March 2011.  

Further information

Further details about this opportunity are available from Dr Stefan Doerr (s.doerr@swan.ac.uk), Professor Rory Walsh (r.p.d.walsh@swan.ac.uk), or Dr Rick Shakesby (r.a.shakesby@swan.ac.uk). 

References

Doerr S.H., Shakesby, R,A, & Walsh, R.P.D. (2000) Soil water repellency: its causes, characteristics and hydro-geomorphological significance. Earth Science Reviews, 51, 33-65.

Doerr, S.H., Ferreira, A.J.D., Walsh, R.P.D., Shakesby, R.A., Leighton-Boyce, G. & Coelho, C.O.A. (2003) Soil water repellency as a potential parameter in rainfall-runoff modelling: experimental evidence at point to catchment scales from Portugal. Hydrological Processes, 17, 363-377.

Doerr, S.H., Shakesby, R.A., Dekker, L.W. & Ritsema, C.J. (2006) Occurrence, prediction and hydrological effects of water repellency amongst major soil and land use types in a humid temperate climate. European Journal of Soil Science, 57, 741–754.