Nature-based solutions for regulating moisture content in an expansive clay soil

Land degradation in the form of mass movement is a major challenge in the humid tropics, where intense rainfall and tropical cyclones are common. Rainfall increases soil moisture content, which often acts as a triggering factor for mass movement events, particularly in clay soils with expansive minerals, where moisture changes impact structural integrity. Growing evidence suggests that Nature-based Solutions (NbS) can regulate soil moisture levels, which can assist in maintaining cohesion and hence reduce slope instability. This paper examines soil moisture changes due to Coconut Matting (CM), Coconut Matting-Natural Vegetation Hybrid (CMNV), Natural Vegetation (NV), and Vetiver grass (VET) and discusses moisture content regulation as it relates to slope stability, with a particular focus on expansive clays. Soil moisture trends were measured for 90 days at four depths (20 cm, 40 cm, 60 cm, and 100 cm) using soil moisture loggers, while precipitation levels were monitored using a rain gauge. GLM ANOVA analysis showed a significant depth*treatment interaction (P < 0.05) on soil moisture. The Vetiver grass treatment had the lowest soil moisture levels, with a (27.62 %) reduction compared to the control (bare plot). The CMNV treatment had the second-greatest-% soil moisture reduction (7.68 %). Contrastingly, CM and NV resulted in limited moisture reduction (1.99 %) and (0.73 %) respectively. The role of Vetiver grass was therefore highlighted in mitigating water saturation towards preventing potential slope instability.