For more than ten years, ALISE has been carrying out censuses of underground cavity indices for local authorities.
Drawing on this experience, we have developed a working method based both on the optimization of contacts and meetings with owners, operators, and former residents of the municipalities, and on a large presence in the field. We try to cross-check each piece of information in order to obtain the greatest precision on the positioning and origin of the cavity indices. Each of these indices are mapped and their geographic coordinates recorded with high precision GPS (<40cm).
The 5 main stages of the cavity census:
1 – BIBLIOGRAPHICAL SURVEY
Collection and exploitation of old archive documents,
Collection and exploitation of recent archival documents,
Consultation of maps and plans.
2 – USE OF AERIAL PHOTOGRAPHS
Analysis by photo-interpretation of the aerial missions of the I.G.N. (from 1947 to the present day),
Survey of topographic depressions, humidity contrasts, zones of preferential water circulation, etc.
3– LOCAL SURVEY
Sending a questionnaire to all households,
Management and analysis of the information collected.
4 – TERRAIN RECOGNITION
Recognition and validation of clues discovered during previous investigations,
Discovery of new evidence of cavities not previously recorded,
Collection of new testimonies,
Route of the entire municipality.
5 – FORMALIZATION OF RESULTS
Writing a summary report,
Establishment of detailed safety data sheets by cavity index,
Precise location of cavity signs on the computerized cadastre.