Erosion at hillslope and micro‐basin scales in the Gilbués desertification region, Northeastern Brazil

Abstract

AbstractWith an area of 6,200 km2, the Gilbués badlands region in the Brazilian drylands is the largest desertification site in the Country. It is located upstream the Boa Esperança Hydroelectric Power Plant and is contiguous to an important Brazilian agricultural area. However, primary quantitative data on erosive processes are scarce or nonexistent. We analyzedon‐sitedata (2018–2019) concerning small‐scale (hillslope and micro basin) processes: inter‐rill gross erosion, vegetation coverage factor, sediment yield, and sediment delivery ratio. We measured gross erosion in four hillslopes using metal pins; rainfall erosivity using an automatic meteorological station; soil erodibility; and siltation of five check‐dams that control micro basins (101–103 m2) by means of an unmanned aerial vehicle. Gross erosion (102 Mg ha−1yr−1; 7.5 mm yr−1) is up to 100‐fold the regional mean value and up to 45‐times the tolerable soil‐loss reference value (0.17 mm yr−1), showing that degradation still evolves. Sparse small vegetation directly exposes two thirds of the soil, with a high vegetation factor (0.90). The sediment delivery ratio of the micro basins is 0.88, compatible with low (12%) sediment‐deposition pattern at this scale. The Maner delivery‐ratio model mimicked field observation, which indicates that relief is the key element influencing sediment deposition there. The check‐dam effectiveness considerably decreased after the first decade of operation due to high siltation rates. Although the Gilbués badland occupies only 5% of the basin upstream of the power plant, it contributes 32% of the sediment load to reservoir and dam. This shows the relevance of the badland restoration for the regional sustainability of water and energy supply.