HAZARD MAPPING AS PART OF CIVIL DEFENCE PREVENTIVE & CONTINGENCY ACTIONS: A CASE STUDY FROM DIADEMA, BRAZIL

Abstract: In the State of São Paulo, south east Brazil, public authorities, at both municipal and state administrative levels, are formally required to work together to tackle natural hazards such as landsliding and flooding. Possible responses include various preventive and contingency actions in which hazard mapping plays a key role. This paper describes a hazard zonation exercise based on the combined use of high-resolution satellite imagery (Ikonos sensor) and ground checks to provide civil defence authorities and decision-makers with information about land occupation and ground conditions as well as technical advice on the severity of potential instability, likelihood of hazard, and potential mitigating and remedial measures. Driving aspects considered for the approach used to do this include the need to produce outcomes in an updateable and reliable manner, and in suitable formats to be conveyed to non-specialists. Risk zones are firstly identified through site visits and according to observed terrain characteristics (e.g. declivity, soil weathering profile) and evidence of geodynamic processes (e.g. landslide scars, riverbank erosion). Satellite images are used to assist with the identification of buildings and houses liable to be affected and the delineation of risk zone boundaries. A qualitative ranking scheme uses four levels of risk: R1 (low); R2 (moderate); R3 (high); R4 (very-high)