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Epsilon Associates, Inc. performed a shadow study to analyze wetland impacts associated with two proposed bridges across intermittent streams in eastern Massachusetts. The purpose was to determine the extent to which sunlight will penetrate below the edge of the bridge during growing season (conservatively estimated to extend from April 21 through September 21), and, from that, predict the ability of wetland vegetation beneath the bridges to continue to grow without impact from bridge shading.
The underlying 3-D bridge models and shadow renderings were developed in Google's SketchUp (Version 6), with additional analysis performed in ArcGIS, AutoCAD and Adobe Photoshop CS. Base elevation data and delineated wetland boundaries were combined with proposed grading contours and 3-D line drawings of the bridges, using AutoCAD. ArcGIS was then used to geographically project the AutoCAD file. Finally, the geo-referenced CAD file was imported to SketchUp, maintaining the layers established in the original AutoCAD dataset, where 3D terrain models (TINs) were generated from the existing base contours and proposed grading using the program's "sandbox" tool. The SketchUp shadow tools were then used to cast shadows from all bridge surfaces on the 3-D terrain model for a period of 14 hours on May and June 21. Final graphics were developed and refined in Photoshop for presentation. |