HGS RESEARCH HIGHLIGHT - Coupled surface and subsurface flow modeling of natural hillslopes in the Aburrá Valley (Medellín, Colombia)

AUTHORS:  Daniela Blessent, Janet Barco, André Guy Tranquille Temgoua, and Oscar Echeverri Ramirez.

HydroGeoSphere was used to conduct numerical simulations of coupled surface-subsurface water flow of a natural hillslope that is currently monitored because of soil instability problems. It is located in the Pajarito locality, northwest of the Medellín municipality (Colombia). Observed rainfall data (events that occurred between October and December 2014), soil water retention curve determined in the laboratory, and geological information taken from previous studies are considered to build the model. Specific objectives are to analyze the impact of rainfall temporal distribution, mesh resolution, coupling length, physical processes (subsurface flow, surface flow, and evapotranspiration), and soil heterogeneity, on pore-water pressure and infiltration. These aspects are important in the region of study, which is highly affected by soil movements, especially during the high rain seasons that occur twice a year.

Simulation results show that rainfall temporal variability, mesh resolution, coupling length, and the conceptual model chosen to represent the heterogeneous soil, have a noticeable influence on results, particularly for high rainfall intensities. Moreover, results indicate that surface-subsurface coupled modeling is required to avoid unrealistic increase in hydraulic heads when high rainfall intensities cause top-down saturation of soil. This work is a first effort towards fostering hydrogeological modeling expertise that may support the development of monitoring systems and early landslide warning in a country where the rainy season is often the cause of hydrogeological tragedies associated with landslides, mud flow or debris flow.

Modeled natural hillslope: stochastic equivalent porous medium facies in the heterogeneous upper layer (silt and rock blocks) and homogeneous porous medium in the lower layer (saprolite)

Modeled natural hillslope: stochastic equivalent porous medium facies in the heterogeneous upper layer (silt and rock blocks) and homogeneous porous medium in the lower layer (saprolite)

Difference in simulated pore-water pressure considering coupled surface-subsurface water flow and only subsurface water flow at the observation point, located 40 cm deep

Difference in simulated pore-water pressure considering coupled surface-subsurface water flow and only subsurface water flow at the observation point, located 40 cm deep