Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 13 10 2009 10.5194/hess-13-1823-2009 http://www.hydrol-earth-syst-sci.net/13/1823/2009/ http://www.hydrol-earth-syst-sci.net/13/1823/2009/hess-13-1823-2009.html http://www.hydrol-earth-syst-sci.net/13/1823/2009/hess-13-1823-2009.pdf 1823 1836 2009-10-12 Assessing the reduction of the hydrological connectivity of gully systems through vegetation restoration: field experiments and numerical modelling A. Molina molina_armando@hotmail.com G. Govers A. Van den Putte J. Poesen V. Vanacker Physical and Regional Geography Research Group, Katholieke Universiteit Leuven, Celestijnenlaan 200E, 3001 Heverlee, Belgium Department of Geography, University of Louvain, 3 Place Louis Pasteur, 1348 Louvain-la-Neuve, Belgium Restoration of degraded land in the Southern Ecuadorian Andes has led to alterations in the functioning of degraded catchments. Recovery of vegetation on areas affected by overgrazing, as well as the reforestation or afforestation of gully areas have given rise to modifications of hydrological connectivity within the catchments. Recent research has highlighted the ability of gully channels to trap sediment eroded from steep slopes, especially if vegetation is established along the gully bed. However, vegetation cover not only induces sediment deposition in the gully bed, but may also have a potential to reduce runoff water volume. The performance of gully beds in reducing the transfer of runoff was investigated by conducting controlled concentrated flow experiments in the field. Experimental field data for nine gullies were derived by pouring concentrated inflow into the upstream end and measuring the outflow at the downstream end of the channel. Two consecutive flow experiments per gully were carried out, so that data for dry and wet soil conditions were collected. The hydrological response to concentrated flow was estimated for each experiment by calculating its cumulative infiltration coefficient, <i>IC</i> (%). The results showed a great difference in <i>IC</i> between dry and wet soil conditions. The <i>IC</i> for wet soil conditions was on average 24%, whereas it was 60% for dry conditions. Gullies with more than 50% surface vegetation cover exhibit the highest cumulative infiltration coefficients (81% for dry runs, and 34% for wet runs), but runoff transmission losses were not as clearly related to vegetation cover as sediment storage as shown in Molina et al. (2009). The experimental field data of 16 experiments were used to calibrate a hydrological model developed by Fiener and Auerswald (2005) in order to simulate the transfer of concentrated flow along the gully beds. The calibrated model was able to simulate the transfer of runoff water well, as the error on the simulated total outflow volumes is below 13% for 15 out of 16 cases. 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