Stability analysis in the lower Manglaralto River basin, Ecuador, with a focus on conservation of the UNESCO Ecohydrology Demonstration Site

Abstract

Slope stability in tropical environments is key to land-use planning, infrastructure design, and natural hazard mitigation, especially in regions with lithological variability and dynamic erosion. The study area is on the Ecuadorian coast in the lower sub-basin of the Manglaralto River. This sector exhibits marked hydrometeorological variability and increasing anthropogenic pressure, both of which compromise the stability of margins and slopes. Within this area lies the Manglaralto River-Aquifer System, Santa Elena, the UNESCO Ecohydrology Demonstration Site (EDS), which, due to climatic variability, is prone to landslide risks that must be studied for management and conservation purposes. Given this need, this research aims to identify areas susceptible to landslides in the lower sub-basin of the Manglaralto River using a geophysical-geotechnical approach and multi-parameter modelling for the strategic conservation design of the Ecohydrology Demonstration Site. The methodology was structured into three phases: I) analysis of baseline information, II) geological-geophysical (ERT, VES, and refraction seismics) survey and multi-criteria modelling, and III) proposals for the conservation of the EDS. The results indicate a subsurface lithology comprising layers of silty sand, clay, gravel, and sand, which are highly susceptible to erosion and poorly consolidated. In contrast, the deeper layers exhibit more stable geomechanical conditions. The susceptibility analysis identified five classes, with high and very high susceptibility predominating (29.78% and 17.19%, respectively), followed by very low (24.16%) and low susceptibility (24.02%), while medium susceptibility accounted for only 4.84% of the basin. The zoning of the susceptible areas was validated using cross-diagrams, which showed low seismic velocity (<600 m/s) and low resistivity (<60 Ω m), both associated with materials with sliding potential. The conservation proposals take into consideration the importance of implementing environmental education in the study area and improving the conservation regulations for this site of high hydrogeological interest. The study shows that combining geological and geotechnical methods enables the identification of areas suitable for controlled urban development. It also focuses on strategies for areas where localised interventions are required to reduce the likelihood of landslides and prevent structural damage, using containment works along the riverbed.