Use of palm-mat geotextiles for rainsplash erosion control

Abstract

Soil detachment by raindrop action (rainsplash erosion) is a very important subprocess of erosion by water. It is a particular problem in the UK as most soils are sandy or loamy sand in texture and lands have gentle to medium slope. However, few studies report potential rainsplash erosion control options under field conditions. Hence, the utilization of palm-mat geotextiles as a rainsplash erosion control technique was investigated at Hilton, east Shropshire, U.K. (52°33′5.7″ N, 2°19′18.3″ W). Geotextile-mats constructed from Borassus aethiopum (Borassus palm of West Africa) and Mauritia flexuosa (Buriti palm of South America) leaves are termed Borassus mats and Buriti mats, respectively. Two-year field experiments were conducted at Hilton to study the effects of emplacing Borassus and Buriti mats on rainsplash erosion of a loamy sand soil. Two sets (12 plots each) of experiments were established to study the effects of these mats on splash height and splash erosion. Splash height needs to be known to assess the transport mechanism of major soil fraction and its constituents on sloping land by rainsplash. In both sets, six randomly-selected plots were covered with mats, and the rest were bare. Results (during 22/01/2007 23/01/2009; total precipitation= 1731.5 mm) show that Borassus mat-covered plots had ∼89% (Pb0.001) less total splash erosion (2.97 kg m−2) than bare plots (27.02 kg m−2). Comparatively, mean splash height from Borassus matcovered plots (0.12 m) was significantly (Pb0.001) less than the bare plots, by ∼54%. However, Buriti matcover on bare plots had no significant (PN0.05) effect in rainsplash erosion control during that period, although plots with Buriti mats significantly (Pb0.05) decreased splash height (by ∼18%) compared with bare plots (0.26 m). Buriti mats, probably due to their ∼43, 62 and 50% lower cover percentage (44%), mass per unit area (413 g−2) and thickness (10 mm), respectively, compared with Borassus mats, were not effective in rainsplash erosion control. Both mats did not significantly (PN0.05) improve selected soil properties (i.e., soil organic matter, particle size distribution, aggregate stability and total soil carbon) as soil organic matter (SOM) input from mat-decomposition was much less than total SOM content. However, the changes in fine and medium sand contents (after 2 years) in the Borassus covered plots were significantly (Pb0.05; n=6) related to the total rainsplash erosion during 2007 2009. Emplacement of Borassus and Buriti mats on bare soils did not decrease SOM contents after 2 years, indicating that improvements in some soil properties might occur over longer durations. After ∼10 months, Buriti mats lost ∼70% of their initial weight (Pb0.001) and their initial cover percentage (C, %) decreased drastically (Pb0.05); whereas, Borassus mats maintained similar C to the initial condition, although mass per unit area decreased by ∼20% (Pb0.05). Moreover, the functional longevity of Borassus mats was ∼2 years against only 1 year for Buriti mats. Hence, use of Borassus mats is highly effective for rainsplash erosion control in the UK.