478 ENGINEERING GEOLOGY/Geomorphology features, such as clifflines and river channel banks In many cases, historical maps and charts may provide the only evidence of evolution over the past 100 years or more When compared with recent surveys or photographs, these sources can provide the basis for estimating cumulative land loss and the average annual erosion rate between survey dates However, great care is needed in using historical data because of the potential problems of accuracy and reliability Measurement and Monitoring Rates of change can be determined through direct measurement of the positions of features at fixed points and at regular intervals Channel crosssections, beach profiles, or cliff tops, for example, can be assessed on an annual or biannual basis In the early 1950s, on the Holderness coast, UK, the local authority initiated a programme of cliff recession measurement that has been continued on an annual basis ever since A series of 71 marker posts were installed at 500-m intervals along the coastline, each post located at a distance of between 50 and 100 m normal to the coast Annual measurements from each post to the cliff top commenced in 1953 (Figure 4) Analytical photogrammetry can be used to quantify the nature and extent of landform changes over time, using aerial photographs taken on different dates, by comparing the three-dimensional coordinates of the same points This approach was used to establish the rate of contemporary building movement in the Ventnor landslide complex, Isle of Wight A total of 129 points distributed throughout the town were selected for measurement The coordinates of each point were determined for each photograph date (1949, 1968, and 1988) and then compared to produce ‘discrepancy’ vectors Where the coordinate discrepancy was greater than the standard deviation of coordinates, significant movement was assumed to have occurred Terrain Evaluation Terrain evaluation has its origins in the need to organize and communicate specific earth science information or intelligence in a way that is of direct relevance Figure Terrain model of the Tademait Plateau, site of the In Salah Gas pipeline project, Algeria The numbers (e.g., 1.4.1) represent terrain units (see Table 1); geological codes (C3c etc.) refer to notation on original geological maps of the region Reproduced with permission from Fookes PG, Lee EM, and Sweeney M (2001) Terrain evaluation for pipeline route selection and characterisation, Algeria In: Griffiths JS (ed.) Land Surface Evaluation for Engineering Practice, Geological Society Special Publication 18, pp 115 121 Bath: Geological Society Publishing House