Open-File Report 2008–1159
Abstract
The Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model (TRIGRS) is a Fortran program designed for modeling the timing and distribution of shallow, rainfall-induced landslides. The program computes transient pore-pressure changes, and attendant changes in the factor of safety, due to rainfall infiltration. The program models rainfall infiltration, resulting from storms that have durations ranging from hours to a few days, using analytical solutions for partial differential equations that represent one-dimensional, vertical flow in isotropic, homogeneous materials for either saturated or unsaturated conditions. Use of step-function series allows the program to represent variable rainfall input, and a simple runoff routing model allows the user to divert excess water from impervious areas onto more permeable downslope areas. The TRIGRS program uses a simple infinite-slope model to compute factor of safety on a cell-by-cell basis. An approximate formula for effective stress in unsaturated materials aids computation of the factor of safety in unsaturated soils. Horizontal heterogeneity is accounted for by allowing material properties, rainfall, and other input values to vary from cell to cell. This command-line program is used in conjunction with geographic information system (GIS) software to prepare input grids and visualize model results. |
Version 1.0 Posted June 2008
Contains the TRIGRS program for either Windows PCs (OF200081159_W.zip) or Macintosh computers (OF20081159_M.zip).
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Baum, R.L., Savage, W.Z., and Godt, J.W., 2008, TRIGRS—A Fortran program for transient rainfall infiltration and grid-based regional slope-stability analysis, version 2.0: U.S. Geological Survey Open-File Report, 2008–1159, 75 p.
Tables
Abstract
Introduction
System Requirements
Installation
Features
Changes from Previous Version
Theoretical Basis of the Program
Infiltration Models for Wet Initial Conditions
Infiltration Model for Unsaturated Initial Conditions
Governing Equations
Basic Solution for Constant Surface Flux
Early-Time Solutions for Constant Surface Flux
Later-Time Solutions for Variable Surface Flux
Water Table Rise
Pressure Diffusion Below the Water Table
Infinite-Depth Basal Boundary, Variable Applied Head
Finite-Depth Basal Boundary, Variable Applied Head
Early-Time Formula
Later-Time Formula
Infiltration, Runoff, and Flow Routing
Topographic Indexing
Slope Stability
Limitations
Program Operation
TRIGRS Initialization File
Input File Format
Output File Formats
TopoIndex Initialization File
Troubleshooting
Comparison of Computed Results with Published Analyses
Acknowledgments
References Cited
Appendix 1. Listing of Files Included in This Distribution
Appendix 2. Tutorial
Using TopoIndex to Prepare Data for Runoff Routing
Preparing the TRIGRS Initialization File for an Analysis
Using TRIGRS to Analyze Slope Stability during a Simple Storm