Geomorphological and sedimentological indicators of land degradation (Meghalaya Plateau, NE India)

Abstract

AbstractReplacement of forests by cultivation in hilly regions can dramatically increase overland flow and soil erosion, frequently resulting in land degradation. This study aimed to determine the impact of long‐term human activity and natural geomorphic processes in land degradation of 2 catchments located in the Meghalaya Plateau in northeast India. Both catchments are built by deeply weathered granites with hilly topography but have contrasting land uses. Forested catchment (1.5 ha) is covered by natural deciduous forest, whereas deforested catchment (3.5 ha) is affected by slash and burn cultivation and boulder extraction. Detailed geomorphological mapping and sediment pattern analysis revealed a complex anthropogenic role in land degradation. Human activity contributes directly to the creation of new landforms in the deforested catchment and indirectly by influencing the course and intensity of geomorphological processes, masking the pre‐existing natural relief. Discontinuous agricultural terraces, zero‐order valleys, and furrows created coexisting cascade system and direct connectivity of water and sediment transport within the same slope. Higher content of fine‐grained material and lower content of boulders in the deforested catchment reflect overlapping of 2 traditional occupations of the local population: agriculture and selective boulders extraction, respectively. Human activity combined with accelerated erosion of abundant weathered material led to the transformation of incised valley bottom into flat accumulation plain as well as the extension and aggradation of the alluvial fan. This process increased the proportion of flat landforms favourable for cultivating the deforested catchment under growing population pressure.