TRIGRS Short Course

Mapping rainfall-induced slope instability — from scratch to real-world application

Preface

This short course documents, step by step and with its full history under version control on GitHub, how to apply the TRIGRS model (Transient Rainfall Infiltration and Grid-based Regional Slope-Stability Analysis, USGS) to map the stability of slopes subject to rainfall-induced landslides — from installing the compiler to applying the model to a real watershed.

The material grew out of the master’s research of Érico de Castro Borges, carried out in the Professional Master’s Program in Civil Defense and Security (Mestrado Profissional em Defesa e Segurança Civil, Fluminense Federal University — UFF). The research aims to couple TRIGRS results with the debris-flow volume estimates of the GIDES/JICA methodology (volumes Vdy1/Vdy2), using case studies in watersheds of the municipalities of Nova Friburgo, Petrópolis, and Teresópolis (the Rio de Janeiro Highlands, or Região Serrana, scene of the January 2011 mega-disaster), and to incorporate climate-change scenarios into the design rainfall.

NoteAbout this English edition

This is a translation of the original Portuguese course (Versão em português). File and folder names in the repository (for example, exemplo_01/ and Resultados/, “Results”) were kept in Portuguese so that both editions share the same data and commands.

Team

M.Sc. candidate	Érico de Castro Borges — Professional Master’s Program in Civil Defense and Security (UFF)
Co-advisor	Cássio Guilherme Rampinelli, PhD (DPM/SEDEC/MIDR)
Advisor	Prof. Marcos Barreto de Mendonça, PhD
Collaborator	Saulo Aires de Souza, PhD (DPM/SEDEC/MIDR)

DPM/SEDEC/MIDR: Department of Disaster Prevention and Mitigation, National Secretariat of Civil Protection and Defense, Ministry of Integration and Regional Development (Brazil). The links point to the researchers’ Lattes CVs (the Brazilian national CV platform, in Portuguese).

How this short course works

• Each completed step becomes a chapter on this site (one .qmd file in the repository).
• The complete history — successes, mistakes, and fixes — is recorded in the repository commits: https://github.com/sedec-dpm-cgnat/tutorial-trigrs.
• Anyone can reproduce the steps: the example data and the corrected configuration files are in the exemplo_01/ folder.

Part 1 — The essentials (available)

Chapter	Contents
Theoretical overview	How TRIGRS “thinks”: infinite slope, transient infiltration, and the overall methodology flowchart
Installation	Installing the gfortran compiler on Windows
Compilation	Downloading the official source code and compiling TRIGRS 2.1
The tutorial example	The input files, each with its own map: terrain, soil, and hyetograph
First run and results	Running TopoIndex + TRIGRS, mapping FS, Zcr, and per-cell volumes, and computing Vdy2

Part 2 — Case studies in the Rio de Janeiro Highlands (available)

Chapter	Contents
Nova Friburgo	The Morro Duas Pedras watershed next to the São Lucas Hospital — the case of Appendix A of the GIDES/JICA manual — and the January 11–12, 2011 mega-disaster
Teresópolis	The Córrego do Príncipe valley, upstream of the Posse neighborhood, and the January 11–12, 2011 mega-disaster
Petrópolis	The valley that drains to Alto da Serra (Morin) and the February 15, 2022 rainstorm

The three chapters apply the workflow of Part 1 to real watersheds and follow the same sequence: Sabo dam site and watershed, input data, design rainfall and climate-change scenarios, volumes by the GIDES/JICA methodology, TRIGRS calibrated against the event’s landslide scars, and the step from V_TRIGRS to V_dy12, checked against V_dy2. The topics previously announced as Parts 3 (debris-flow volumes) and 4 (climate change) are built into each case study.

NoteAbout TRIGRS

TRIGRS is a public-domain program of the U.S. Geological Survey that solves transient rainfall infiltration (1-D analytical solutions, saturated/unsaturated) and computes the infinite-slope Factor of Safety cell by cell over a raster grid, throughout a rainstorm. Full references are in the appendix.