The utility of Transient Rainfall Infiltration and Grid-based Regional Slope-stability Model (TRIGRS) in combination with the rainfall distribution data estimates for shallow, rainfall-induced landslides forecasting and response of rainfall are examined through model simulations of July 23th, 2010 heavy rainstorm event in Sichuan, Guangyuan. The target domain is divided into three physical property zones according to the distinct soil sediment concentration. The topographic indices of TOPMODEL (Topography based Hydrological model) are applied to calculate the soil thickness distribution and steady, pre-storm infiltration rate of the study area. Assumptions based on existing studies are used to estimate the simulation parameters. The cohesion and fraction angle values are taken based on actual physical conditions of each zone. The inputs of TRIGRS model includes the digital elevation model (DEM), slope angle distribution, soil thickness distribution and flow direction distribution of the study area, and time-varying rainfall. Combined with the simulation parameters, the TRIGRS model computed transient pore-pressure changes and attendant changes in the factor of safety (FS) due to rainfall infiltration. The every 6 h slope-instability grids given by model results matched the every 6 h rainfall accumulation distribution, consistent with the actual landslide records, indicates that the preliminary assessment of slope-stability is available over large areas. The quantitative indices and results of receiver operating characteristic of the simulation results indicated that the way of model simulating of the study area was valid for shallow landslide forecasting. Comparing the results with the shallow landslide inventory map, more than 71.1% consistency between predicted shallow landslide susceptibility and the inventory, despite the paucity of the input data. The simulation results has reasonable consistency despite some shallow landslides located in hilly area. Based on different types of rainfall forecasting products, the TRIGRS model computed the slope stability variability of target area, enabled the early warning of rainfall-induced landslides. The simulation results also showed that the slope-instability of the mountain area with larger slope degrees tended to increase with a smaller rainfall, region with smaller slope degrees endured heavier rainfall, relatively. The success index of mountain area reaches 86.67% while the success index of the hilly area is only 53.33%, yet the error index is also high in mountain area. The results indicates that the availability of TRIGRS model is impacted by the approximation of the initial topographic conditions of the target area with the infinite slope assumption. Meanwhile, the level of urbanization also generated biases in model simulation results, since the application to areas with marked soil anisotropy or heterogeneity in hydrologic properties might cause errors in the solutions.
[1]Baum R L, Savage W Z, Godt J W, 2008. TRIGRS-A fortran program for transient rainfall infiltration and grid-based regional slope-stability analysis, version 2. 0[R]. U. S. Geological Survey Open-File Report, 2008-1159, 75.
[2]Diana S, Jonathan W G, William Z, et al, 2006.Modeling regional initiation of rainfall-induced shallow landslides in the eastern umbria region of central italy[J].Landslides, 3:181-194.
[3]Dongyeob K, Sangjun I, Sang H L, et al, 2010.Prediction the rainfall-triggered landslides in a forested mountain region using TRIGRS Model[J].J Mountain Sci, 7:83-91.
[4]Eleonora G, Gabriella S, Maurizio F, et al, 2013. Rainfall induced shallow landslide forecasting in large areas: application of the trigrs model over a broad area of post-orogenic quaternary sediments[A]//Geological Society of America[C]//Denever, Colorado, USA: 125<sup>th</sup> Anniversary Annual Meeting & Expro. 27-30 October 2013.
[5]Iverson R M, 2000.Landslide triggering by rain infiltration[J].Water Res Res, 36(7):1897-1910.
[6]Park D W, Nikhili N V, Lee S R, 2013.Landslide and debris flow susceptibility zonation using TRIGRS for the 2011 seoul landslide event[J].Natural Hazards and Earth System Science, 13:2833-2849.
[7]Savage W Z, Godt J W, Baum R L, 2004, Modeling time-dependent areal slope stability[M]. Landslides: Evaluation and Stabilization/Glissement de Terrain: Evaluation et Stabilisation, 1: 23-36.
[8]Savage W Z, Godt J W, Baum R L, 2003. A model for spatially and temporally distributed shallow landslide initiation by rainfall infiltration[M]. In Rickenmann D, Chen C, eds. Debris-flow hazards mitigation-mechanics, prediction and assessment: Rotterdam, Millpress, 179-187.
[9]Srivastava R, Yeh T, 1991.Analytical solutions for one-dimensional, transient infiltration toward the water table in homogeneous and layered soils[J].Water Res Res, 27:753-762.
[10]Chen J X, Tan Z H, Ji S Y, et al, 2011.An application of GIS-Based deterministic model for assessment of regional rainfall-induced landslide potential-example of Kao-Ping River Watershed[J].J Chinese Soil Water Conservat, 42(1):1-11.<br/>陈建新, 谭志豪, 冀树勇, 等, 2011.广域降雨促崩模式之建置及应用-以高屏溪流域为例[J].中华水土保持学报, 42(1):1-11.
[11]Chen Y L, Chen D H, Li Z C, et al, 2016.An ensemble prediction model for rainfall-induced landslides and its preliminary application[J].Chinese J Atmos Sci, 40(3):515-527.<br/>陈悦丽, 陈德辉, 李泽椿, 等, 2016.降雨型滑坡的集合预报模型及其初步应用试验研究[J].大气科学, 40(3):515-527.
[12]Chen Z Y, Feng Z Y, Zhuang Y C, 2011.An application of TRIGRS on slope failure probability analyses-a case study of Aowanda[J].J Chinese Soil Water Conservation, 42(3):228-239.<br/>陈则佑, 冯正一, 庄育蓁, 2011.应用TRIGRS程式于边坡破坏机率分析-以奥万大地区为例[J].中华水土保持学报, 42(3):228-239.
[13]Li Z P, Zhang M, 2001.Effects of rain infiltration on transient safety of unsaturated soil slope[J].China Civil Engineering Journal, 34(5):57-61.<br/>李兆平, 张弥, 2001.考虑降雨入渗影响的非饱和土边坡瞬态安全系数研究[J].土木工程学报, 34 (5):57-61.
[14]Ma Z F, Guo H Y, Zhan Z Y, et al, 2016.Climate map synthesis of Sichuan Province[M].Beijing:China Meteorological Press.<br/>马振峰, 郭海燕, 詹兆渝, 等, 2016.四川省气候综合图集[M].北京:气象出版社.
[15]Wen K G, Zhan Z Y, 2006.Meteorological hazards synthesis, Sichuan part[M].Beijing:China Meteorological Press.<br/>温克刚, 詹兆渝, 2006.中国气象灾害大典四川卷[M].北京:气象出版社.
[16]Yang X, Wang Y Q, Liu Z H, 2016.Comparison of two different satellite precipitation data in Sichuan from May to August[J].Plateau Meteor, 35(4):1039-1049.DOI:10.7522/j.issn.1000-0534.2015.00060.<br/>杨星, 王永前, 刘志红, 2016.四川省2013年夏季卫星降雨数据的对比研究[J].高原气象, 35(4):1039-1049.
[17]Yong B, Zhang W C, Chen Y H, 2007.A new algorithm of the topographic index ln(<i>α</i>/tan<i>β</i>) in TOPMODEL and its resultant analysis[J].Geograp Res, 26(1):37-45.<br/>雍斌, 张万昌, 陈艳华, 2007.TOPMODEL中地形指数ln(<i>α</i>/tan<i>β</i>)的新算法[J].地理研究, 26(1):37-45.
[18]Zhang T S, Chen X H, Jiang Z Y, et al, 2006.Characters and rational exploitation of underground water resources in red beds area of Northeast of Sichuan[J].J Water Res Water Engineer, 17 (1):15-19.<br/>张廷山, 陈晓慧, 姜照勇, 等, 2006.川东北红层区地下水赋存特征及合理开发思考[J].水资源与水工程学报, 17 (1):15-19.
[19]Zhang Y P, Shi J S, Gan J J, et al, 2011.Analysis of distribution characteristics and influencing factors of secondary geo-hazards in Guangyuan City[J].J Catastrophology, 26(1):75-79.<br/>张英平, 石建省, 甘建军, 等, 2011.广元市次生地质灾害分布特征及影响因素分析-以朝天区为例[J].灾害学, 26(1):75-79.
