Check dams and afforestation reducing sediment mobilization in active gully systems in the Andean mountains

Abstract

Gully erosion is an important process of land degradation in mountainous regions, and is known to be one of the major sediment sources in eroded catchments. Recent studies have suggested that living and dead vegetation can be effective for ecosystem restoration, and large-scale restoration projects have been implemented in the tropical Andes in recent decades. However, few quantitative studies exist on the effectiveness of gully restoration to reduce sediment production and mobilization. In this study, sediment mobilization and transport was studied in five micro-catchments (< 1 km2) with different soil and water conservation treatments. The techniques that were used for soil and water conservation involve vegetation restoration on the hillslopes and check dams in active gully channels. To characterize the routing of sediment within the micro-catchments, we measured erosion and sediment deposition within the gully channels. Sediment yield was estimated from measurements of sediment accumulation in sediment traps that were constructed at the outlet of the micro-catchments. Flow barriers are shown to be very effective in stabilizing active gully systems in badlands through significant reduction (of>70%) of the amount of sediment exported from the micro-catchments. The construction of wooden barriers (or so-called check dams) in active gully channels enhances sediment deposition in the gully bed. The latter is strongly dependent on the rainfall intensity, as well as gully channel slope and vegetation cover. The experimental data suggest that there exists a threshold value of rainfall intensity (I30max) of about 23mmh−1, above which all sections of the gully system are actively contributing water and sediment to the river network. Also, forestation of active gully systems with rapidly growing exotic species such as Eucalyptus has a positive effect on the stabilization and restoration of the badlands, and effectively reduces the sediment export.