EGU2020-1432
https://doi.org/10.5194/egusphere-egu2020-1432
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Erosion assessment in the desertification site of Gilbues, Brazil

José Carlos de Araújo, Antonio Álisson Simplício, Francisco Jairo Pereira, and Carlos Alexandre Gomes Costa
José Carlos de Araújo et al.
  • Federal University of Ceará, Center for Agricultural Sciences, Agricultural Engineering, Fortaleza, Brazil (jcaraujo@ufc.br)

The Gilbués Desertification Site (GDS) is an 8,000-km² area located in the Northeast of Brazil. It comprises large continuous areas with deep (up to 30 m), wide (up to 50 m), and long (up to 6 km) gullies, as well as severe inter-rill erosion. Inside the GDS there is an experimental site, in which almost 100 check dams were constructed a decade ago to assess their feasibility as a soil-restoration initiative. For two years (2018 and 2019) we have monitored a 15-ha watershed that contains 52 check dams so as to estimate the main erosion-related parameters as well as to assess the effectiveness of the check dams. The monitoring program consisted of (i) a climate station; (ii) four hillslopes with pins every m², measured monthly to quantify gross erosion; (iii) five flights with an accurate unmanned aerial vehicle (UAV) to identify the siltation of the check dams and to parameterize the rainfall-runoff behavior; (iv) 92 soil samples in the hillslopes and inside the check dams; and (v) four infiltration experiments. The results show that (i) the gross erosion is 8 mm.yr-1, or 10² Mg.ha-1.yr-1, a value ten times higher than the region average; (ii) based on the silting of the check dams, the sediment yield averaged 85 Mg.ha-1.yr-1, 20 times higher than the regional mean value, which is partially explained by the small size of the watersheds (10²-10³ m²); (iii) the Wischmeier vegetation C factor is 0.9, showing high degree of vegetative-cover degradation; and (iv) the sediment delivery ratio was 0.8, which could be satisfactorily represented by the Maner equation. These results show that, although the GDS corresponds to only 10% of the Boa Esperança (5,000 hm³) hydroelectric power plant basin, it may cause 60% of the reservoir silting. The GDS soil has also shown specific properties: 71% of the soil mass has a diameter of ~ 0.1 mm; there is a high rate of open macro-pores when the soil is dry (they close shortly after a moderate rainfall event ~ 40 mm); and it is prone to form gravel-like particles that silt in the reservoir delta (despite its fine diameter). Last, we observed that the check dams – as they were built – are not a sustainable solution: after a decade, nearly 10% are spilling due to the high siltation rates, causing dam-wall erosion and instability; and three dams have presented piping, with discharges (0.2 – 0.7 L.s-1) one thousand times higher than the expected percolation flow through the dams.

How to cite: de Araújo, J. C., Simplício, A. Á., Pereira, F. J., and Gomes Costa, C. A.: Erosion assessment in the desertification site of Gilbues, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1432, https://doi.org/10.5194/egusphere-egu2020-1432, 2019

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