Scouting the Route for the Eisenhower Parkway Extension

Michael J. Gilbrook

As part of the Environmental Impact Statement for the Georgia Department of Transportation�s Eisenhower Parkway Extension project, HDR Engineering used ArcInfo and ArcView GIS to analyze potential environmental and cultural impacts for multiple alternatives. Viewshed analyses were particularly important to address potential impacts to the Ocmulgee Old Fields Traditional Cultural Property, the first such Native American land designated east of the Mississippi River.

The Eisenhower Parkway Extension is a proposed Federal-aid highway project of the Georgia Department of Transportation in the vicinity of Macon, Georgia. To comply with the requirements of the National Environmental Policy Act (NEPA) of 1969, GDOT and the Federal Highway Administration must prepare an Environmental Impact Statement (EIS) for the proposed project. In 1997, GDOT selected a consultant team led by the Atlanta office of HDR Engineering, Inc. to conduct the environmental study and prepare the various EIS documents. This paper describes how HDR is using ArcInfo and ArcView GIS to support the NEPA process for the Eisenhower Parkway Extension EIS.

The study area is located in Macon, Georgia, about an hour�s drive southeast of Atlanta. The study area limits include the Macon East and Macon West USGS 7.5 min quadrangles, and the top third of the Warner-Robins NE and Warner Robins NW quads. The City of Macon is located on the Fall Line, the demarcation between the southeastern Coastal Plain and the higher elevations and more varied terrain of the continent�s interior.

• Improve Transportation System Performance & Connectivity
• Enhance Transportation Access For Economic Development
• Improve Access to the 7th Street & Ocmulgee East Industrial Parks
• Provide A Less Flood-Susceptible Crossing Over the Ocmulgee River
• Reinforce Established Corridor Systems (STRAHNET, Fall Line Freeway)

The study area is bisected by the Ocmulgee River, which flows into a wide floodplain to the southeast of Macon. This largely undeveloped area is referred to locally as the Ocmulgee Old Fields, and formerly supported a series of Native American cultures until the mid-1800�s, when the Muscogee Creek(Creek) were forcibly relocated from the land to their current home in Oklahoma. Today the Old Fields support an extensive forest ecosystem, but considerable archeological evidence of the area�s previous occupants are common. The most prominent Native American features are the earthen mounds and lodges constructed by the Mississippian people from 900 � 1150 AD; these structures are now protected as part of the Ocmulgee National Monument, managed by the U.S. National Park Service. The Bond Swamp National Wildlife Refuge, managed by the U.S. Fish and Wildlife Service, encompasses a large part of the southern study area along the eastern bank of the Ocmulgee River.

• Public Information Exhibits � GIS maps helped to illustrate the study process to the public. For example, a series of maps illustrated how the study team conducted the corridor identification process, starting with large corridor zones, followed by potential corridors within those zones, and ending with refined corridors to be evaluated further adjusted for known environmental and physical constraints.
• Maps For Staff Use � The Environmental and Physical Constraints Map exemplifies the kind of GIS map which provides maximum information to engineers and planners as they consider alternative roadway locations which avoid or minimize impacts to known resources. This map combines data from many sources, including: floodplains, hydric soils, wetlands, xeric soils, historic districts, parks and conservation lands, archeological sites, and hazardous materials sites.
• Geocoding Community Facilities � During the initial stages of the EIS, the alternative corridors and alignments crossed a large part of the study area. Mapping the locations of community facilities such as hospitals, churches, schools, and fire stations by traditional means (i.e., sending crews into the field with maps to conduct "windshield surveys") was impractical. Instead, the HDR Team prepared a GIS tabular database of community facilities using readily available sources, such as the Internet and phonebook listings, which were used to geocode the sites to US Census TIGER street maps using ArcView. Following the ArcView geocoding, the location of each community facility point was adjusted as needed to coincide with the most probable building visible in the DOQQ imagery. This level of accuracy was sufficient for initial screening of alternative corridors; once the number of alternative alignments is reduced, field crews will verify the locations of facilities on hardcopy maps generated from the DOQQs for use in editing the community facilities coverage.
• Viewshed Analysis. To evaluate the potential impacts of the proposed project on visual aesthetics within the TCP, the HDR Team has been preparing a viewshed analysis using ArcView 3D Analyst. Three sites with prominent views of the TCP were selected for viewshed analysis: Fort Hawkins (an historic site in a Macon neighborhood), the Great Temple Mound (within the Ocmulgee National Monument), and Brown�s Mount (a natural area of high ground on the eastern edge of the TCP). The USGS Digital Elevation Model provided the relief of the ground surface, but did not account for visual obstructions such as trees and buildings. To adjust for surface obstructions, the HDR GIS staff assigned height values to the various land cover types throughout the study area. Combined with the DEM elevations, the land cover heights provide a more realistic surface for predicting intervisibility across the study area. At this writing the land cover height surface is still undergoing revisions based on photointerpretation and field reconnaissance. Nevertheless, the results of preliminary test viewsheds conform well to photographs taken from the three observer locations. For example, the preliminary viewshed analysis accurately predicted that the view to the southeast from the Great Temple Mound would be obscured by the nearby forest, whereas the buildings of Macon would be easily visible to the southwest.
• Impact Quantification. As this writing, an impact quantification screening analysis has just begun on a series of alternative roadway "links" which might be later combined to form complete end-to-end alternatives across the study area. The purpose of this analysis is to provide preliminary information on potential environmental impacts, physical constraints and construction cost factors to help the team in winnowing out infeasible or impractical corridors from further study. The links were originally digitized by the Atlanta engineering staff in AutoCAD via heads-up digitizing on DOQQ imagery. Link centerlines were exported to DXF format for import into ArcInfo. Following assignment of attributes, the link centerlines were buffered to form corridors approximating the rights-of-way associated with multi-lane roadways, to address the potential "direct" impacts of each link. The links were also buffered by 500 feet to assess what resources might encounter potential "indirect" or long-distance impacts, such as noise. By overlaying the corridors onto the various resource coverages via INTERSECT, we obtained the amount of each resource within each link.

Email mgilbroo@hdrinc.com