Modeling Landslides in Puerto Rico with a Distributed Eco-hydrological Model

Abstract

This presentation provides a compilation of results from an eco-hydrological-landslide model: tRIBS-VEGGIE-Landslide. This effort couples a well-established distributed basin simulator with a slope stability model that considers topography, soil moisture and vegetation. The research explores the impact of soil parameter uncertainty, of vegetation and roots, and of numerical resolution on predictions of rainfall triggered landslides. The Luquillo Mountains on the northeast of Puerto Rico are used as a case study. The uncertainty associated to the soil hydrological and geotechnical parameters is considered by implementing the First- Order Second Moment (FOSM) probabilistic method. The model produces maps and times series of two main representative quantities of probability (hereinafter p.) of failure: (i) the p. of plane of failure at a given soil depth (PrPFi), which indicates dynamically the most probable depth of failure, based on soil moisture dynamics and soil parameters; (ii) the p. of failure of the column, PrFC, that can be generated anywhere within the column. Figure 1 shows the time series of the two probabilities evaluated for the rainfall event reported in Figure 1a. The most probable failure surfaces occurred at depths between 300 and 1000 mm, indicating high probability of shallow landslides. <fig><graphic xlink:href=23500_files/23500-09.jpg id=ID_2d696a77-3005-4db4-94c1-b7c38b941b03></graphic></fig> The hydrological and mechanical effects of roots on slope stability were investigated assessing the role of two different vegetation species, shrubs and trees, in comparison to a case without vegetation cover. The model estimates the additional root reinforcement exerted by roots, in addition to the apparent cohesion due to soil suction under unsaturated soil. Figure 2 shows representative results in terms of Factor of Safety (FS) obtained with or without additional root cohesion (∆FSr). The stabilizing effect of the hydrological process is more effective in the case of trees. The resulting drier conditions, due to transpiration, over the most critical depths led to an increase of FS. Finally, to evaluate the influence of terrain resolution on the hydro-geomorphological processes involved in slope stability, we run tRIBS-VEGGIE-Landslide by using five grid-DEM resolutions of the case study basin, i.e., 10, 20, 30, 50, and 70 m (Arnone et al., 2021). Since the model implements Triangulated Irregular Network (TIN), a grid-DEM to TIN algorithm is involved. Using irregular meshes reduces the loss of accuracy with coarser resolutions in the derived slope distribution, in comparison to that estimated using the original grid-DEM. Additionally, from the hydrological perspective, the ultimate impact of resolution on slope stability is significant mostly when lateral water exchanges are allowed within the model framework. <fig><graphic xlink:href=23500_files/23500-08.jpg id=ID_1aa8eec6-32ce-42b3-97c2-172c37aa7cbf></graphic></fig> <b>REFERENCES</b> Arnone, E., Francipane, A., Dialynas, Y.G., Noto, & Bras, R.L. (2021). Implications of terrain resolution on modeling rainfall-triggered landslides using a TIN-based model. Environ. Model. Softw., 141, 105067. Arnone, E., Dialynas, Y.G., Noto, L.V., & Bras, R.L. (2016a). Accounting for soils parameter uncertainty in a physically based and distributed approach for rainfall-triggered landslides. Hydrol. Process., 30, 927–944. Arnone, E., Caracciolo, D., Noto, L.V., Preti, F., & Bras, R.L. (2016b). Modeling the hydrological and mechanical effect of roots on shallow landslides. Water Resour. Res., 52 (11), 8590-8612.