APPENDIX F: Viewshed Study
Dulles International Airport Western Land Area Viewshed Study FINAL Prepared by: EAC/Archaeology, Inc. September 26, 2017 Western Land Area
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TABLE OF CONTENTS Page 1 Study Purpose... 1 1.1 Proposed Action... 2 1.2 Background... 2 2 Methodology... 2 2.1 Creating the Viewshed... 3 3 Results of Viewshed Analysis... 6 3.1 Alternative 1 (Current Market Alternative), Sell Option... 6 3.2 Alternative 1 (Current Market Alternative), Lease Option... 8 3.3 Alternative 2 (Medium Density Alternative), Sell Option... 9 3.4 Alternative 2 (Medium Density Alternative), Lease Option... 10 3.5 Alternative 3 (High Density Alternative), Sell Option... 11 3.6 Alternative 3 (High Density Alternative), Lease Option... 12 4 Summary and Conclusion... 13 LIST OF FIGURES Page Figure 2-1 Components for Viewshed Analysis... 4 Figure 2-2 Visual Acuity... 5 Figure 3-1 Alternative 1, Sell Option... 7 Figure 3-2 Alternative 1, Lease Option... 8 Figure 3-3 Alternative 2, Sell Option... 9 Figure 3-4 Alternative 2, Leaes Option... 10 Figure 3-5 Alternative 3, Sell Option... 11 Figure 3-6 Alternative 3, Lease Option... 12 LIST OF TABLES Page Table 2.1 Visual Acuity for 20/20 Vision... 5 Table 4.1 Visibility for Alternatives and Option... 13
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APPENDIX F Viewshed Study INTRODUCTION Western Land Area EAC/Archaeology, Inc. (EAC/A) prepared a viewshed study to identify the following for the Washington Dulles International Airport (IAD) Western Land Area (WLA) development: a preliminary Visual Area of Potential Effect (APE), historic resources within that preliminary Visual APE and vantage points for the evaluation of the visual impact of the proposed work. Following the acceptance of the Preferred Alternative, an Impact Assessment was made which is included in this report. This report documents the methodology and the results of this viewshed study, and presents the findings of the impact assessment. This report finds that there will be no adverse effects to any of the historic properties within the viewshed of the proposed work. 1 Study Purpose The Metropolitan Washington Airports Authority (Authority) is conducting an Environmental Assessment (EA) for the development of the WLA at IAD. The APE for the WLA development includes 424 acres of off-airport property. Under the terms of the Authority s Programmatic Memorandum of Agreement, all projects on airport property must include an evaluation of potential impacts to historical and archaeological resources listed or eligible for the National Register of Historic Places (NRHP). An EA is being prepared to evaluate alternatives for WLA development and to consider their potential effects. One of the considerations is the effect of the development on historic resources which are protected under Section 106 of the National Historic Preservation Act of 1966 (NHPA). Section 106 of the NHPA outlines a historic preservation review process and requires Federal agencies to consider the effects of their projects on historic resources. Both direct and indirect effects to historic resources must be considered. Due to the potential for the proposed WLA development to affect the views to and from IAD, a historic property determined eligible for the NRHP, a viewshed study and impact assessment has been prepared. The primary purpose of this study was to identify a Visual APE, or the APE for Visual Effects. In general, the APE is defined in the regulations implementing the Section 106 review process as "the geographic area or areas within which an undertaking may directly or indirectly cause changes in the character or use of historic properties, if any such properties exist. The area of potential effects is influenced by the scale and nature of an undertaking and may be different for different kinds of effects caused by the undertaking" [36 CFR Part 800.16(d)]. The second purpose of this study was to identify all the properties listed on or eligible for listing on the NRHP which are located within the Visual APE, and hence may be visually affected by the project. Viewshed Study F-1 Appendix F
1.1 Proposed Action Western Land Area The Proposed Action is the development of the WLA in response to market driven demand, and could be any of three Alternatives, depicted in Section 3: (1) Current Market Alternative, (2) Medium Density Alternative, and (3) High Density Alternative. While the Proposed Action assumes that the Authority would maintain ownership and lease the land, the possibility to sell part(s) or all the WLA in fee simple remains a consideration. Because the sell/lease option would influence the allowable height of the buildings, both the sell and the lease option are evaluated for each of the alternatives. If the Authority prefers to lease, all buildings must be lower than 463 feet (141.12 meters) above mean sea level due to the project s location within an airport height restriction zone. Given the existing terrain on the site, the maximum allowable building or structure height would typically range from approximately 160 to 190 feet above the ground depending on location on the site and the base elevation of the building pad. Under the sell scenario, the land would revert to its previous Loudoun County zoning category prior to Authority acquisition, Planned Development-General Industry (PDGI). The buildings under the sell option would therefore be required to comply with Loudoun County s zoning requirements to be no higher than 45 feet (13.72 meters). Thus, each alternative was also considered for viewsheds under the sell option using building heights of 13.72 meters. 1.2 Background The Dulles International Airport Historic District was determined eligible for the NRHP by the Virginia Department of Historic Resources (VDHR) in 1978. The historic district is eligible for the NRHP under Criterion A as the first airport in the United States to be designated specifically for commercial jet aircraft and under Criterion C as an outstanding work of Finnish-born master architect Eero Saarinen. Contributing resources within the Dulles International Airport Historic District include the Main Terminal and Airport Traffic Control Tower (ATCT), the Cargo Building (Cargo Building No. 1), the Air Mail Facility, the Vehicle Maintenance Building, the Fire-Crash Station, the Heating and Air Conditioning Plant, the Telephone Exchange, the former Gladieux Corporation In-Flite Kitchen (LSG/Sky Chefs), the former Hot Shoppes In-Flite Food Building (LSG/Sky Chefs), and the former Allied Fueling Building, as well as the mobile lounges, the runways, the terminal area landscape, and the Dulles Airport Access Highway. There was an attempt to have the airport listed on the NRHP prior to the airport s 1987 transfer from the FAA to the Authority, but the owner did not consent, so the district remains NRHP-eligible. 2 Methodology The viewshed, also known as a line-of-sight map, is developed from two elements: cells in an elevation model (raster data) and an observer point or points (vector data). A straight line is interpolated between the source (observer point) and every other cell within the elevation model. If the height of cells along this line exceeds the height at the source, the line of sight is interrupted. A high-resolution Digital Elevation Model (DEM) is usually utilized as the surface to conduct a viewshed analysis. DEMs derived from Light Detection and Ranging (LiDAR) sensors provide high-resolution, three-dimensional (3-D) geospatial data. This data provides a way to see urban Viewshed Study F-2 Appendix F
areas in rich 3-D views and supports automated extraction of urban features like buildings and trees. The data to build the DEM was acquired from the United States Interagency Elevation Inventory (USIEI) and the Coastal National Elevation Database Project (CoNED) via the United States Geological Survey (USGS) EarthExplorer website. Raw Lidar point data was acquired that was generated by USIEI, which started as a collaboration between NOAA and the U.S. Geological Survey, with the help from the Federal Emergency Management Agency (FEMA). In addition, a processed, bare-earth DEM generated from Lidar data and bathymetric data sources by CoNED was acquired for the surrounding region. Raw Lidar data was then processed for the entire area, including buildings and vegetation. The WLA Direct APE was then replaced with a bare earth elevation model, to simulate the removal of all the existing structures and vegetation (Figure 2-1). Finally, proposed buildings were added to the model. Multiple DEMs were used in the viewshed analysis which reflected different heights and spatial arrangements of the buildings for the different alternatives. The maximum heights for proposed buildings in each option and alternative were assumed to create the surface models. The single vantage point used for the viewshed study was the northwest corner of the original ATCT (Figure 2-1). This is a resource contributing to the NRHP-Eligible Historic District, and also the only conceivable location within the historic district boundaries that sight to the WLA is feasible. In every iteration of the viewshed, the vantage point was offset by 1.75 meters to reflect the average height of a human (5 feet, 9 inches). 2.1 Creating the Viewshed The Visual APE was developed in four steps. The first step utilized the Visibility tool, an ability of many GIS platforms to calculate visibility of two given points on the surface of a DEM. Two separate visibility areas were calculated using the Visibility Tool and the Observer Points Tool in the Spatial Analyst extension of ArcGIS Desktop 10.5. The visibility area was reduced to account for acuity of vision. Acuity of vision is the ability of an individual to discern visual details. 1 Visual acuity is dependent on several optical and neural factors, but normal visual acuity is usually defined as 20/20. Normal vision implies that at 20 feet (6 meters), a human eye is able to discern separate contours which are 1.75 mm apart. This translates to the discernment of details separated by a visual angle of one arc minute (or 1/60th of a degree), projected across the retina of the eye. Visual resolution, or the smallest number of visual degrees an eye can detect, can be derived from visual acuity. Visual acuity was used to calculate a visual resolution angle in the following formulae: Visual Resolution (in degrees) = (1 / Visual Acuity) x (1 / 60) 1 / Visual Acuity indicates how many arc minutes the human eye can detect. The multiplication by 1/60 converts the number from arc minutes into degrees. Visual acuity here is interpreted as normal 20/20 vision (which equals 1 arc minute), so Visual Resolution = (1 x (20/20)) x (1/60) = 0.0167 degrees. Viewshed Study F-3 Appendix F
Visual resolution was then used to calculate the smallest objects discernable from various distances using the following formula: Smallest Object Discernable = 2 x d x TAN(r / 2) where d = the distance between the eye and the object; and r = the visual resolution in degrees. Figure 2-1 Viewshed Study F-4 Appendix F
This formula essentially bisects the angle of vision which creates a right triangle, making it easy to determine the maximum length or width of an object at a given distance (Figure 2-2). 2 Distances based on the height on an object were calculated for the visual resolution of a person with normal (20/20) vision (Table 2-1). These distances were considered when establishing the limit of the inward visibility area. The distance between elements on buildings spaced four feet apart would be discernable at 2.5 miles from the National Register district. The threshold of visual perception was set at 2.5 miles, which encompasses most of the APE. All visible areas beyond this threshold were removed from the inward visibility area. A third step involved the removal of all residual visible areas, classified as isolated visible areas ( spots ) which are less than one square meter in size, from the Visual APE. Because these areas are smaller than the human eye could discern from adjacent areas at two miles away, these small patches were removed. The remaining area after these steps were taken is the finalized inward visibility area for the Visual APE. Figure 2-2 Visual Acuity Table 2.1 Visual Resolution for 20/20 Vision Distance Smallest Size Object 1 mile (5280 feet) 1.53589 feet 1.5 miles (7920 feet) 2.30844 feet 2 miles (10560 feet) 3.07178 feet 2.5 miles (13200 feet) 3.839732 feet Viewshed Study F-5 Appendix F
3 Results of Viewshed Analysis Western Land Area Six iterations of the viewshed were generated to reflect the following possibilities: 1. Alternative 1 (Current Market Alternative), Sell Option 2. Alternative 1 (Current Market Alternative), Lease Option 3. Alternative 2 (Medium Density Alternative), Sell Option 4. Alternative 2 (Medium Density Alternative), Lease Option 5. Alternative 3 (High Density Alternative), Sell Option 6. Alternative 3 (High Density Alternative), Lease Option 3.1 Alternative 1 (Current Market Alternative), Sell Option With the sell option for Alternative 1, many the buildings in the southern two-thirds of the WLA would be visible from the old ATCT (Figure 3-1). Large portions of the roof surfaces of buildings in Areas E, H, J, K, and L would be visible with this alternative, as well as smaller portions of the roof surfaces of buildings in Areas F and G. The eastern faces of buildings in Areas E, H, and J would also be highly visible. Viewshed Study F-6 Appendix F
Figure 3-1 Viewshed Study F-7 Appendix F
3.2 Alternative 1 (Current Market Alternative), Lease Option With the lease option for Alternative 1, only portions of the buildings facing south and east would be visible, since the maximum height of the buildings would obscure the horizon (Figure 3-2). The eastern faces and portions of the southern faces of buildings in Area J and L would be visible in this alternative, as would the southern face of the building in Area G. In addition, smaller portions of the eastern faces of buildings in Areas E and F would also be visible. Figure 3-2 Viewshed Study F-8 Appendix F
3.3 Alternative 2 (Medium Density Alternative), Sell Option With the sell option for Alternative 2, many buildings in the southern two-thirds of the WLA would be visible from the old ATCT (Figure 3-3). Large portions of the roof surfaces of buildings in Areas E, H, J, K, and L would be visible with this alternative, as well as smaller portions of the roof surfaces of buildings in Areas F and G. The eastern faces of buildings in Areas E, H, J, and L would also be highly visible. Figure 3-3 Viewshed Study F-9 Appendix F
3.4 Alternative 2 (Medium Density Alternative), Lease Option With the lease option for Alternative 2, only portions of the buildings facing south and east would be visible, since the maximum height of the buildings would obscure the horizon (Figure 3-4). The eastern faces and portions of the southern faces of buildings in Area J and L would be visible in this alternative, as would the southern face of the building in Area G and the eastern face of a building in Area H. In addition, smaller portions of the eastern faces of buildings in Areas E and F would also be visible. Figure 3-4 Viewshed Study F-10 Appendix F
3.5 Alternative 3 (High Density Alternative), Sell Option With the sell option for Alternative 3, many buildings in the southern two-thirds of the WLA would be visible from the old ATCT (Figure 3-5). Large portions of the roof surfaces of buildings in Areas E, H, J, K, and L would be visible with this alternative, as well as smaller portions of the roof surfaces of buildings in Areas F and G. The eastern faces of buildings in Areas E, H, J, and L would also be highly visible. Figure 3-5 Viewshed Study F-11 Appendix F
3.6 Alternative 3 (High Density Alternative), Lease Option With the lease option for Alternative 3, only portions of the buildings facing south and east would be visible, since the maximum height of the buildings would obscure the horizon (Figure 3-6). The southern and eastern faces of buildings in Areas J and L, and the southern face of the building in Area G would all be highly visible in this Alternative. Small portions of the eastern faces of buildings in Areas E, F, and G would also be visible. Figure 3-6 Viewshed Study F-12 Appendix F
4 Summary and Conclusion Western Land Area This report contains the comprehensive evaluation of visual effects of the WLA development on the NRHP-eligible historic property of the Dulles International Airport District. Portions of the buildings proposed in the WLA would be visible from the historic ATCT, a contributing resource to the historic district, within all three alternatives. Table 4.1 depicts the number of buildings and horizontal surface area which would be visible from the ATCT in each Alternative and Option, assuming that all of the buildings are of similar heights. In every Alternative, nearly twice as many buildings are visible in the Sell Option than the Lease Option. Because the maximum allowable heights of the buildings are higher in the Lease Option, the proposed buildings on the eastern edge of the WLA obscure more of the rest of the site. With the Lease Option, more of the tops of the buildings would be visible, giving a higher visible surface area. Table 4.1 Visibility for Alternatives and Options Alternative and Option Proposed Buildings Visible Total Surface Area (m 2 ) Alternative 1 Current Market Density, Sell 13 21,952.42 Option Alternative 1 Current Market Density, Lease 6 1,172.95 Option Alternative 2 Medium Density, Sell Option 13 18,743.41 Alternative 2 Medium Density, Lease Option 8 1,177.03 Alternative 3 High Density, Sell Option 13 22,990.90 Alternative 3 High Density, Lease Option 7 1,185.14 The original ATCT is currently decommissioned and unoccupied. All the equipment has been moved to the new tower to the south, which has replaced the function of the original tower. As it will not operate in compliance with its original function again, and the public is not currently allowed into this area, the tower should be considered abandoned. Thus, without people, these views would not affect the historic integrity of this structure or the district. There would be no adverse effect of these buildings on the Dulles International Airport District. While these views from the tower would have no adverse effect, it is remarked that Alternative 1 (Current Market Density), Lease Option would have the least impact on the viewshed (i.e., the least surface area would be visible). Therefore, this option is recommended in case the ATCT is ever re-opened to the public. Viewshed Study F-13 Appendix F
Endnotes 1 NDT Resource Center, Visual Acuity of the Human Eye, NDT Resource Center, 2014, https://www.ndeed.org/educationresources/communitycollege/penetranttest/introduction/visualacuity.htm 2 NDT Resource Center, Visual Acuity of the Human Eye, NDT Resource Center, 2014, https://www.ndeed.org/educationresources/communitycollege/penetranttest/introduction/visualacuity.htm Viewshed Study F-14 Appendix F