Transient Rainfall Infiltration And Grid-based Regional Slope-stability Research Articles

ICRESTRIGRS: a coupled modeling system for cascading flood–landslide disaster forecasting

Abstract. Severe storm-triggered floods and landslides are two major natural hazards in the US, causing property losses of USD 6 billion and approximately 110–160 fatalities per year nationwide. Moreover, floods and landslides often occur in a cascading manner, posing significant risk and leading to losses that are significantly greater than the sum of the losses from the hazards when acting separately. It is pertinent to couple hydrological and geotechnical modeling processes to an integrated flood–landslide cascading disaster modeling system for improved disaster preparedness and hazard management. In this study, we developed the iCRESTRIGRS model, a coupled flash flood and landslide initiation modeling system, by integrating the Coupled Routing and Excess STorage (CREST) model with the physically based Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability (TRIGRS) landslide model. The iCRESTRIGRS system is evaluated in four river basins in western North Carolina that experienced a large number of floods, landslides and debris flows triggered by heavy rainfall from Hurricane Ivan during 16–18 September 2004. The modeled hourly hydrographs at four USGS gauge stations show generally good agreement with the observations during the entire storm period. In terms of landslide prediction in this case study, the coupled model has a global accuracy of 98.9 % and a true positive rate of 56.4 %. More importantly, it shows an improved predictive capability for landslides relative to the stand-alone TRIGRS model. This study highlights the important physical connection between rainfall, hydrological processes and slope stability, and provides a useful prototype model system for operational forecasting of flood and landslide.

Preliminary studies on the dynamic prediction method of rainfall-triggered landslide

Rainfall-triggered landslides have posed significant threats to human lives and property each year in China. This paper proposed a meteorological-geotechnical early warning system GRAPES-LFM (GRAPES: Global and Regional Assimilation and PrEdiction System; LFM: Landslide Forecast Model), basing on the GRAPES model and the landslide predicting model TRIGRS (Transient Rainfall Infiltration and Grid-based Regional Slope-Stability Model) for predicting rainfall-triggered landslides. This integrated system is evaluated in Dehua County, Fujian Province, where typhoon Bilis triggered widespread landslides in July 2006. The GRAPES model runs in 5 km×5 km horizontal resolution, and the initial fields and lateral boundaries are provided by NCEP (National Centers for Environmental Prediction) FNL (Final) Operational Global Analysis data. Quantitative precipitation forecasting products of the GRAPES model are downscaled to 25 m×25 m horizontal resolution by bilinear interpolation to drive the TRIGRS model. Results show that the observed areas locate in the high risk areas, and the GRAPES-LFM model could capture about 74% of the historical landslides with the rainfall intense 30mm/h. Meanwhile, this paper illustrates the relationship between the factor of safety (FS) and different rainfall patterns. GRAPES-LFM model enables us to further develop a regional, early warning dynamic prediction tool of rainfall-induced landslides.

Application of a process-based shallow landslide hazard model over a broad area in Central Italy

Process-based models are widely used for rainfall-induced shallow landslide forecasting. Previous studies have successfully applied the U.S. Geological Survey’s Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability (TRIGRS) model (Baum et al. 2002) to compute infiltration-driven changes in the hillslopes’ factor of safety on small scales (i.e., tens of square kilometers). Soil data input for such models are difficult to obtain across larger regions. This work describes a novel methodology for the application of TRIGRS over broad areas with relatively uniform hydrogeological properties. The study area is a 550-km2 region in Central Italy covered by post-orogenic Quaternary sediments. Due to the lack of field data, we assigned mechanical and hydrological property values through a statistical analysis based on literature review of soils matching the local lithologies. We calibrated the model using rainfall data from 25 historical rainfall events that triggered landslides. We compared the variation of pressure head and factor of safety with the landslide occurrence to identify the best fitting input conditions. Using calibrated inputs and a soil depth model, we ran TRIGRS for the study area. Receiver operating characteristic (ROC) analysis, comparing the model’s output with a shallow landslide inventory, shows that TRIGRS effectively simulated the instability conditions in the post-orogenic complex during historical rainfall scenarios. The implication of this work is that rainfall-induced landslides over large regions may be predicted by a deterministic model, even where data on geotechnical and hydraulic properties as well as temporal changes in topography or subsurface conditions are not available.

Warning Model for Shallow Landslides Induced by Extreme Rainfall

In this study, the geophysical properties of the landslide-prone catchment of the Gaoping River in Taiwan were investigated using zones based on landslide history in conjunction with landslide analysis using a deterministic approach based on the TRIGRS (Transient Rainfall Infiltration and Grid-based Regional Slope-Stability) model. Typhoon Morakot in 2009 was selected as a simulation scenario to calibrate the combination of geophysical parameters in each zone before analyzing changes in the factor of safety (FS). Considering the amount of response time required for typhoons, suitable FS thresholds for landslide warnings are proposed for each town in the catchment area. Typhoon Fanapi of 2010 was used as a test scenario to verify the applicability of the FS as well as the efficacy of the cumulative rainfall thresholds derived in this study. Finally, the amount of response time provided by the FS thresholds in cases of yellow and red alerts was determined. All five of the landslide events reported by the Soil and Water Conservation Bureau were listed among the unstable sites identified in the proposed model, thereby demonstrating its effectiveness and accuracy in determining unstable areas and areas that require evacuation. These cumulative rainfall thresholds provide a valuable reference to guide disaster prevention authorities in the issuance of yellow and red alerts with the ability to reduce losses and save lives.

Modeling the contribution of trees to shallow landslide development in a steep, forested watershed

The objective of this study was to identify the contribution of trees to shallow landslide development in a steep forested watershed using a deterministic modeling approach. Rainfall interception, tree root reinforcement, and tree surcharge were considered the main factors. A revised version of the Transient Rainfall Infiltration and Grid-based Regional Slope-stability (TRIGRS) model was employed in the approach. Hydrological modifications included adding the processes of rainfall interception using an application of the Rutter model. The revised infinite slope stability model was also used to consider tree root reinforcement and tree surcharge. A comparative analysis was conducted with the results simulated by TRIGRS and the revised model to quantify the contribution of trees to landslide development. The Bonghwa site in South Korea, which was damaged by an extreme storm with 228mm of rainfall on July 24–25, 2008, was selected as the study site. Data related to the local topography, soil, and forest properties were measured in the field for use in the model simulations, although some data were taken from the literature or assumed by the authors on the basis of the site characteristics. The results showed the rainfall interception did not significantly affect the amount of rainfall reaching the soil surface, but it changed the temporal distribution of the rainfall intensity. Additionally, the rainfall interception was found to have little influence on infiltration from the simulation results of pore water pressure. The results of the simulated factor of safety indicated that root reinforcement and tree surcharge made significant contributions to the enhancement of slope stability. The simulation results were compared to the results from locations in which landslides occurred, indicating that the revised model estimated the landslide susceptibility over the entire study site well, while TRIGRS appeared to overestimate the risk of shallow landslides. In conclusion, trees appeared to make a significant mechanical contribution to shallow landslide development during a severe storm event in steep, forested watersheds. Efforts to revise the existing model improved its performance to assess the shallow landslide susceptibility of mountainous watersheds despite some limitations of the current study.

Predicting the rainfall-triggered landslides in a forested mountain region using TRIGRS model

Landslides are natural disasters which can pose a serious threat to human and property in many areas around the world. The Transient Rainfall Infiltration and Grid-based Regional Slope-stability (TRIGRS) model was used to investigate the rainfall-induced shallow landslides in a forested mountain region, Korea. Various input data for TRIGRS model include time-varying rainfall, topographic characteristics, soil depth, material strength, and hydraulic properties. A series of calculations were conducted in determining the slope stability over the Jangheung region in Korea during the storm occurred on August 6, 1998. The results show that TRIGRS model captured about 64.1% of landslides that were extracted from the IKONOS2 imageries. The model demonstrated how the factor of safety changed with time during a storm considering both the transient and spatial responses of pore water pressure in its slope stability calculation.

Regional Analysis of Rainfall-Induced Landslides. The Case of Camaldoli Hill, Naples: Test Case Nr.1- October 2004; Test Case Nr.2- September, 2005

This report contains the results of some regional numerical analyses aimed to simulate two rainfall-induced landslides events, recorded on October 13th, 2004 and on September 17th, 2005, which involved the shallow pyroclastic deposits of the south-eastern side of a hill, known as Camaldoli hill, set inside the western sector the urban district of Naples.The analyses have been performed thanks to the deterministic approach used by the Transient Rainfall Infiltration and Grid-based Regional Slope-stability (TRIGRS) program (Baum et al., 2002), a GIS-based code which allows to assess, over broad areas, the timing and the location of shallow landslides caused by rainfall events. Particular attention has been dedicated to the influence of the input parameters on the results furnished by the code in response to the rainfall events.

Regional Analysis of Rainfall-Induced Landslides - The Test Case of Nocera Inferiore (March, 2005)

This report contains the results of some regional numerical analyses aimed to simulate the rainfall-induced landslide event, which occurred on March 4th, 2005, involving the shallow pyroclastic deposits of the northern slope of the Monte Sant'Angelo di Cava mountain, located in the Nocera Inferiore town. The analyses have been performed using the deterministic approach adopted by the Transient Rainfall Infiltration and Grid-based Regional Slope-stability (TRIGRS) program (Baum et al., 2002), a GIS-based code which allows to assess, over broad areas, the timing and the location of shallow landslides caused by rainfall events.