River channel planform change: software for historical analysis

ER Mapper™, an image processing system, was used to manipulate scanned maps, plans and aerial photographs to enable detailed analysis of historical river channel planform change. The ER Mapper™ package offers the opportunity to spatially reference each item of planform data into the same scale and co-ordinate space as a base map, using a warping algorithm and operator selected ground control points. Once all the data are in the same co-ordinate space and at the same scale, a given point can be returned to over time, and a number of indices can be easily calculated to examine past channel behaviour. Here, lateral shift, channel width, sinuosity and area of sedimentation within the reach were used. As the maps and aerial photographs themselves are used, the errors associated with digitising vectors are avoided, and a more flexible approach towards analysis and the identification of important indices can be adopted at the outset. Results obtained for the Cleekhimin Burn, a site in southern Scotland, are briefly presented and discussed, and the advantages of the package and the limitations of the historical database are also outlined.