HISTORICAL ANTHROPOGENIC LANDSCAPE CHANGE IN A FORMER ESTUARY: THE CHARLES RIVER, BOSTON, MASSACHUSETTS
Geographic information technology (GIT) was used to integrate and analyze data from modern and historical sources, including maps, digital elevation models (DEMs), and orthographic and oblique aerial photography. The study estimates that 14.3 km2 of new land, representing 138% of the original 10.3 km2 land area, was added within the area of interest since Boston’s founding in 1630. Slightly more than 45% of the new land, 6.5 km2, was added to the Back Bay. Efforts were also made to quantify the total volume of new land added using the 2002 MassGIS DEM, but the estimate of 30 x 106 m3 was based on somewhat speculative estimates of the original mudflat and salt marsh elevations and is a less robust estimate than those of the surface area. A comparison of sediment core data and modern elevations revealed that fill thickness was underestimated due to compaction of underlying sediments and possibly an overestimate of the pre-colonial elevations.
The GIT was also used to develop an integrated spatial data layer in both 2D (map or orthographic view) and 3D (oblique view) to facilitate visualization of historical landscape changes. An important application of this technology was a 3D time series of landmaking created by vertically extruding historical map-based polygon layers in proportion to the length of time between successive layers. This allowed the depiction of what would normally be shown as a 2D graph of area vs. time instead as a graphic that shows not only area and time, but also shoreline shape at several points in history, thus providing a fuller picture of how the basin evolved over time.