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

Abstract

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 1:6000 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, a composite plat from that survey was scanned from the National Archives and geo-referenced to a modern datum. Managing these images involves several caveats (drafting errors, north arrow alignments, availability of registration points, paper stretch, etc.), but the overall quality of the map was evident by very reasonable channel locations relative to other aerial photographs from 1938 and 1999. Although some errors were found, comparison of 1885 and 1999 data allowed measurements of channel migration rates and patterns over 114 years.