GIS Analysis of Historical Maps: A case study from an 1885 survey of the Congaree River

Аннотация

Large floodplain forests, such as the area preserved by Congaree National Park in South Carolina, are among the most dynamic terrestrial ecosystems known on earth. Flooding and migration of river meanders constantly disturb, create, and erode forest habitats. This provides abundant opportunities for new primary succession. Like many long-term processes, meander evolution is primarily understood from extrapolation of short-term measurements (events or 1-2 year campaigns), decadal-scale rates from comparison of mid- to late 20th century aerial photographs, or millennial-scale trends from geological and geomorphic analysis. There is often a gap in detailed analysis of century-scale geomorphic trends without excessive and expensive radiometric dating techniques. A unique opportunity to examine more than 100 years of channel change on the Congaree River is presented by an 1885 map. This 1:6,000 scale map was prepared from a survey conducted by the US Army to determine the cost of removing snags and rocks impeding steamboat traffic. Using modern GIS techniques maps from that survey were scanned from the National Archives, georeferenced to a modern datum, and used to create a shapefile of the riverbank position in 1885. This project demonstrated problems substantially different from similar efforts georeferencing antique maps, primarily caused by the linear feature and landform changes associated with an alluvial river. A LiDAR based DEM was critical to achieving reasonable river positions and the RMS error was 23 m (75 ft) compared to average bank migration of 155 m (500 ft) over the 114-year period.