Innovative surveying and monitoring approaches to geomorphological processes detection

A system based on the integration of innovative surveying and monitoring approaches has been developed and tested over an area characterized by particular geomorphological processes. Several methods have been experimented and specific procedures have been applied, checked and implemented, including real-time monitoring of movements by Global Positioning System (GPS) permanent stations, detection of surface deformations by surveying monumented points, generation and comparison of Digital Elevation Models (DEMs). The study area, located in the Reno River Valley (40 km South of Bologna, Italy), extends for about 2,500,000 square metres, 70,000 of which represented by landslide deposits. Landslides can be mainly classified as multiple rotational and rotational-translational slides with subsequent earth-flow like movements, affecting an average slope of 13\ub0 facing to NNE. A local geodetic reference network to register all the data has been established, setting up stations in stable zones outside landslide areas. A procedure for the real-time monitoring of landslide surface movements has been exploited, tested and implemented. GPS permanent stations (the reference station sited outside the landslide zones and the other one in the headscarp) have been planned, monumented and continuously observed using standardized procedures. Collected data are automatically downloaded from remote receivers to a server in our LAN using GSM and PSTN modems. In order to define the velocity of the monitored point, observations have been routinely analyzed; the achievable accuracy results of a few millimetres in planimetry and centimetric in altimetry. Moreover, a method to identify displacements of significant points distributed over landslide areas has been verified. GPS rapid static surveys have been periodically performed over several vertices, placed on natural boulders partially embedded in the slope or monumented by special iron-pegs inserted in the terrain, obtaining accurate coordinate time-series. The accuracy is sub-centimetric in planimetry and of a few centimetres for altimetric values. Finally, multitemporal DEMs of the study area have been obtained by means of digital photogrammetric applications, terrestrial laser scanning and GPS kinematic surveys. Taking into account relevant factors linked to different DEMs precision, a series of procedures for detecting dynamic surface deformations, morphological evolution and mass volumes variations have been applied and teste