Utilization of multiple geophysical sources and geotechnical sampling to search for offshore sand deposits for beach restoration in Brazil

In this paper methods for identifying and mapping marine sand sources for beach nourishment are discussed. Our focus is in the use of different types of marine seismic equipment with different frequencies to better interpret subsurface geological deposits. The goal of using different sources is because as mapping sand the resonant source may lose information as coarsering the sediment and to understand better the strata compound, is employed a stronger source who can cross over the coarser materials. The resonant ones use CHIRP pulse sub bottom profiler from Edgetech, models 512i (0,5-12kHz) and 216s (2-16kHz). The impulsive source is a 100J Boomer profiler with 4 elements hydrophones from C-Boom. To provide surface geology and geomorphology and to map possible hazards or archeological formations on the seafloor we also utilize dual frequency side scan sonars from Edgetech models 4200 HLF (300/600 kHz) and 4125 (600/900 kHz), an single beam Odom MKIII with dual frequency 200/24 kHz transducer and a Cesium marine Magnetometer from Geometrics model G-882. Marine surveys are conducted in two main phases: the initial reconnaissance phase and the detailed surveys. The reconnaissance survey was run with the single beam echo sounder and CHIRP. The detailed surveys were conducted the complete CHIRP and Boomer sub bottom profilers, side scan sonar, single beam and magnetometer. The detailed survey is conducted to provide enough information for detailed design of dredge site (sand borrow area) and dredge planning. During data interpretation the main reflectors identified in the marine seismic records are correlated with the vibracore data for a full pseudo 3D mapping of the sand borrow area. This method of marine sand search is robust and proven as it has been employed many times successfully in the USA and now in Brazil.