Mountain States Transmission Intertie Environmental Impact Statement in Idaho and Montana

Locations: Idaho (Clark, Butte, Jefferson, Blaine, Bonneville, Bingham, Lincoln, Minidoka, Power, and Jerome Counties); Montana (Broadwater, Jefferson, Deer Lodge, Silver Bow, Beaverhead, and Madison Counties)
Client: PBS&J
Date: 2009-2010
CRA Project Manager: Colin Ferriman

Project Description: CRA was contracted to complete the cultural resource sections of Chapter 3 Affected Environment and Chapter 4 Cumulative Effects for the Mountain States Transmission Intertie (MSTI) Environmental Impact Statement (EIS). In order to complete this task, CRA had to compile information derived from agency office files searches, construct geographic information systems (GIS) site density maps, GIS visual impact maps, and summarize all of this information to provide estimated impacts of action alternatives on cultural resources.SDA1

The GIS site density model was developed from the qualitative environmental attributes associated with the previously identified sites within the study corridor. These attributes included distance to water, elevation, slope, and aspect. From this model areas of high, medium and low site densities were identified.The GIS visual impact analyses were based on cultural resources that were identified by agency archaeologists as being culturally important. These analyses identify areas along the alternatives that could visually impact these cultural resources. Together these two GIS models were key in identifying potential impacts to cultural resources throughout the large and complex MSTI study area.

This project implements a significant variety of geoprocessing techniques utilizing both raster and vector data. Some of these processes include downloading and processing grid data to create a mosaic digital elevation model (DEM) for use in the site density analysis model. The ArcView Spatial Analyst extension was used to create separate layers for slope, aspect, and hillshade. These layers then undergo extensive reclassification in order to standardize cell values and aggregate the information for use in the model analysis. The site density model then combines these various raster data layers with information from vector data to create a weighted matrix used to calculate high, medium and low site probability estimates for areas within the project area.

For the visual impacts analysis component of the project, viewshed analysis was performed using different criteria for cultural site locations outlined by the governing agencies. The purpose is to determine the proximity of the proposed project infrastructure to existing sensitive cultural site locations, and how it would visually affect the integrity of the sites of concern. After completing the viewshed analysis with Spatial Analyst in ArcView, it was broken up into areas of Immediate Foreground, Foreground, Middle ground, and Background in order to provide a frame of reference to accompany the technical report data.

Map layouts of both the site density analysis and the visual impacts analysis were created for the entire project area at a scale of 1:100,000 and presented on 14×17 paper format. There are a total of 30 maps of the site density analysis and 17 maps of the visual impacts analysis areas.

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Posted in Archaeology, Archaeology Projects, Geospatial Technology, Projects

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