GEODESIC NETWORK FOR MONITORING SUBSIDENCE PROCESSES IN THE DELTAIC PLAIN OF SÃO FRANCISCO RIVER

Abstract

Subsidence processes are characterized by the movement of a portion of the Earth's surface which results in the lowering of the terrain. Depositional sedimentary environments, such as deltas, are prone to subsidence due to sediment compaction. The main objective of this work is the development of a geometric project and the implantation of a geodesic network for the periodic monitoring of subsidence in the delta plain of the São Francisco River. Holocene coastal streams present in the plain had their altitudes evaluated from longitudinal topographic profiles obtained by GNSS (Global Navigation Satellite System) surveys. In some strands, unevenness average gaps in the order of 3.2 m and 5.5 m were detected in the southern and northern portions of the plain, respectively, being an indication of the lowering of the surface due to accentuated subsidence processes that have occurred since the Holocene. The information on the lowering of the strands made it possible to identify areas vulnerable to subsidence processes, supporting the design of a geodetic network composed of 26 monitoring vertices.