Jan Walstra

Historical aerial photographs for landslide assessment: two case histories

This paper demonstrates the value of historical aerial photographs for assessing long-term landslide evolution. The study focused on two case histories, the Mam Tor and East Pentwyn landslides. In both case histories we explored the variety of data that could be derived relatively easily using an ordinary PC desktop, commercially available software and commonly available photographic material. The techniques to unlock qualitative and quantitative data captured in the photographic archive were based on the principles of aerial photo-interpretation and photogrammetry. The products created comprised geomorphological maps, automatically derived digital elevation models (DEMs), displacement vectors and animations. The measured horizontal displacements of the Mam Tor landslide ranged from 0.09 to 0.74 m a−1 between 1953 and 1999, which was verified by independent survey data. Moreover, the observed displacement patterns were consistent with photo-interpreted geomorphological information. The photogrammetric measurements from the East Pentwyn landslide (horizontal displacements up to 6 m a−1 between 1971 and 1973) also showed a striking resemblance to independent data. In both case histories, the vertical accuracy was insufficient for detecting significant elevation changes. Nevertheless, DEMs proved to be a powerful tool for visualization. Overall, the results in this study validated the techniques used and strongly encourage the use of historical photographic material in landslide studies.

Aerial photography and digital photogrammetry for landslide monitoring

Abstract A review is given of the techniques that are available to extract relevant information from multi-temporal aerial photographs for use in the monitoring stage of landslide assessments. It is shown that aerial photograph interpretation reveals qualitative information on surface characteristics, which is helpful in detecting landslide features and inferring the mechanisms involved. Photogrammetrically derived products can be used to quantify these processes, providing distinctive advantages. Comparison of digital elevation models (DEMs) from different times provides detailed information on changes in surface topography, whereas orthophotos can be used to measure horizontal displacements. The various factors influencing the quality of the products are also identified. Examples from a case study on the Mam Tor landslide are used to illustrate the benefits of the different approaches.

Assessing human impact on alluvial fan development: a multidisciplinary case-study from Lower Khuzestan (SW Iran)

This paper presents a multidisciplinary approach for studying the evolution of an alluvial fan system in Lower Khuzestan (SW Iran). The study draws on previously collected data from geological and archaeological field campaigns and new data derived from the interpretation of satellite imagery and historical textual sources. Three alluvial fans were identified, successively deposited by the Jarrahi river in progressively downstream/westward direction. Judging from archaeological and historical evidence, the successive phases appear to coincide with a relocation of settlement and irrigation activities. The distributary system of the present-day fan developed over a period of less than four centuries. It is suggested that management of levee breaks by man played a key role in such rapid fan development and in maintaining extremely low gradients. Judging from the extensive patterns of ancient irrigation canals, human activity also played an important role in the formation of the earlier fans.

Geoarchaeological Research in Lower Khuzestan: State of the Art

This chapter presents an overview of the geoarchaeological research carried out, including new evidence on the Holocene palaeoenvironmental evolution of the plain, in particular the positions of the Persian Gulf coastline and the main rivers. The reconstruction is based on the analysis of the geological and archaeological data collected during the field campaigns in 2004, and new evidence derived from textual sources, maps, satellite images and aerial photographs. It concerns mainly the integration of the results of three recently completed PhD studies and additional remote sensing data. By means of a number of case-studies, the different datasets were integrated with a recently completed geomorphological map. The case-studies provide new insights into the complex human-environmental interactions in the plain, and demonstrate the added value of a multidisciplinary approach in such studies. Keywords:geoarchaeological research; Holocene; human-environmental interaction; Lower Khuzestan; palaeoenvironmental evolution; Persian Gulf coastline