| Rainfall and snowmelt infiltrate the soil and cause a rise in groundwater level, {dollar}hsb w,{dollar} which reduces the soil shear strength, increases seepage force and causes landslides. The research concentrated on mapping ground water levels, {dollar}hsb w,{dollar} and landslide hazard following rainfall and snowmelt events with application to Glenoma and Mineral quadrangles in the lower Cascade Mountains of Washington.; The factors that influence {dollar}hsb w{dollar} were identified as meteorological parameters, soil properties, topography, and geologic anomalies such as fractures in bedrock and pervious inclusions. The effect of meteorological parameters and soil properties on {dollar}hsb w{dollar} was studied using Reddi and Wu's (1991) lumped parameter model. A sensitivity analysis showed that, for the regional site conditions in the study area, the changes in {dollar}hsb w{dollar} are sensitive to infiltration (I) and soil depth (H); less sensitive to drainable porosity ({dollar}thetasb d){dollar} and saturated permeability ({dollar}Ksb s);{dollar} not sensitive to slope length (L) and unsaturated permeability (B and {dollar}psisb s).{dollar} The finite-difference model (Lee, 1986) was used to study the variations in {dollar}hsb w{dollar} within a catchment due to topography. Methods have been developed to account for flow through fractures in bedrock and flow through pervious inclusions.; Reddi and Wu's model was used to produce a chart that shows {dollar}hsb w{dollar} in a plane slope as a function of the storm return period (Fig. 5.13). Piezometric-level maps were made for Glenoma and Mineral quadrangles by application of Reddi's and Lee's models to individual catchments, which were delineated by MIPS operating on data in the GIS (Figs. 5.16 and 5.17).; The stochastic nature of storms was studied. Distributions of rainfall, snowmelt, number of storms and intervals between storms were evaluated. A simulation program was developed to simulate the occurrence of small rain events. Probability distributions of material properties, which include those of the soil and rock fractures were evaluated. Different types of uncertainties were identified as systematic uncertainty, random variations, and occurrence uncertainty. Occurrence uncertainty was quantified using Tang et al. model, (1989). These uncertainties were used as input to the slope stability model to calculate the landslide hazard.; The landslide hazard of natural slopes was evaluated at different scales and accuracies using the first order second moment method (FOSM). A macro-hazard-map and a micro-hazard-map were produced for Glenoma quadrangle. The hazards in both maps are comparable to the landslides occurrence identified by Brunengo (1991), in the landslide inventory.; A Bayesian updating model was developed and used to update the parameters of the slope stability model with the observations from the landslide inventory. Observation model was developed to evaluate the uncertainty in the observations. The application of the Bayesian updating model to areas of focus township showed that the posterior variances of the parameters are reduced significantly. |
