Post-fire hillslope log debris dams for runoff and erosion mitigation in the semiarid Ebro Basin

Abstract

The hydrologic effects of hillslope log debris dams were analyzed in areas of the Castejón Mountains (semiarid Ebro Basin, NE-Spain) affected by a wildfire. Four experimental sites showing differences in the soil composition (calcareous and gypseous) and the aspect of the steep slopes (north and south facing) were selected. All of the experimental sites were located along planar hillslopes, where Aleppo pine forest had burned in 2009, in the four sites per triplicate. Runoff and sediment yields were measured for two consecutive years (2012, 2013) after the construction of log dams on partially re-vegetated sites in 2011.In 2012, log dam installation significantly decreased soil erosion from 8.51Mgha−1year−1 to 0.76Mgha−1year−1, with a log dam performance of approximately 90% being obtained. Similarly, the log dams caused a significant reduction of runoff, from 6.9 to 3.3mmyear−1, presenting a performance of 52%. Both differences decreased one year later. Approximately 75% of the soil loss from 2012 was collected in only one clean-out period, when rainfall was almost half of annual rainfall. The quality of the eroded sediments and water runoff was related to the composition of the Ah horizon. Log dams reduced soil erosion in three of the four sites tested during the first year. However, in the second year, only one site showed statistically significant differences, which was the site with the greatest amount of bare soil. These findings indicate that in semi-arid areas, post-fire active restoration measures are still active four years after a fire on south-facing slopes with poor soils and slow ground cover recovery.