3 resultados para Structural Stability Assessment
em University of Washington
Resumo:
Thesis (Ph.D.)--University of Washington, 2013
Resumo:
The focus of this report is is the channel conditions at Vasa Creek, Bellevue, Washington, with regard to kokanee habitat and slope stability. This required a geomorphic and geologic assessment of the stream and riparian corridor along Vasa Creek. I focused my efforts in a 720m study-reach just south of I-90 in which City of Bellevue had no information. My assessment is divided into 3 categories: channel morphology, geology, and landslide hazards. I described the channel morphology by determining the gradient of the channel, longitudinal and cross-channel geometries, grain size distribution, embeddedness observations, type of channel reaches present, and the locations of significant in-channel woody-debris, landslides, scarps, landslide debris, and erosional features. This was done by conducting a longitudinal survey, 7 cross-channel surveys, pebble counts, and visual observations with the aid of a GPS device for mapping. I completed my geological assessment using both field observations and borehole data provided by GeoMapNW. Borehole data provided logs of the subsurface material at specific locations. In the field, I interpreted local geology using material in the channel as well as exposures in the adjacent slope. I completed the landslide hazard assessment using GIS methods supplemented by field observations. GIS methods included the use of aerial LiDAR to discern slope values and locations of features. Features of interest include the locations of scarps, landslides, landslide debris, and erosional features which were observed in the field. I classified 4 slope classes using ArcMap10 along with the locations of previously mapped landslides, scarps, and landslide debris. I describe the risk of slope failure according to the Washington Administration Code definition of critical areas (WAC 365-190-120 6a-i). My results are presented in the form of a map suite containing a channel morphology map, geology map, and landslide hazard map. The channel is a free-formed alluvial plane-bed reach with infrequent step-pools with riffles associated with landslide debris that chokes the channel. Overall I found that there is not the potential for kokanee habitat due flashy behavior (sudden high flow events), landslide inundation, and a lack of favorable conditions within the channel. The updated geologic map displays advance outwash deposits and alluvium present within the study-reach, as opposed to exposures of the Blakeley Formation along with other corrections from borehole data interpretations. The landslide hazard map shows that there are areas at high risk for slope failure along the channel that should be looked into further.
Resumo:
Landslides often occur on slopes rendered unstable by underlying geology, geomorphology, hydrology, weather-climate, slope modifications, or deforestation. Unfortunately, humans commonly exacerbate such unstable conditions through careless or imprudent development practices. Due to local geology, geography, and climatic conditions, Puget Sound of western Washington State is especially landslide-prone. Despite this known issue, detailed analyses of landslide risks for specific communities are few. This study aims to classify areas of high landslide risk on the westerly bluffs of the 7.5 minute Freeland quadrangle based on a combined approach: mapping using LiDAR imagery and the Landform Remote Identification Model (LRIM) to identify landslides, and implementation of the Shallow Slope Stability Model (SHALSTAB) to establish a landslide exceedance probability. The objective is to produce a risk assessment from two shallow landslide scenarios: (1) minimum bluff setback and runout and (2) maximum bluff setback and runout. A simple risk equation that takes into account the probability of hazard occurrence with physical and economic vulnerability (van Westen, 2004) was applied to both scenarios. Results indicate an possible total loss as much as $32.6b from shallow landslides, given a setback of 12 m and a runout of 235 m.