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Open-File Report 2008–1159

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TRIGRS—A Fortran Program for Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis, Version 2.0

By Rex L. Baum, William Z. Savage, and Jonathan W. Godt

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Open-File Report
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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

  • Downloads Directory
    • Contains the TRIGRS program for either Windows PCs (OF200081159_W.zip) or Macintosh computers (OF20081159_M.zip).
Suggested citation:

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.


Contents

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

 


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