Offshore exploration for sand sources: general guidelines and procedural strategies along deltaic coasts

Because of the large volumes of sand required for beach renourishment, dredging from offshore borrows is the preferred method of sediment supply. As easily accessible and previously known (obvious) deposits are exploited, apparent sand reserves are seen as a dwindling resource that becomes more precious over time. Because economically exploitable offshore sand sources are limited in many regions, renewed efforts are underway to locate additional offshore sand sources that can supply sand and mixed sediments (sand, silt, and clay) to barrier-island restoration efforts in Louisiana. Sediment volumes required for beach renourishment and marsh restoration are variously estimated on the basis of numerous assumptions to range in the extreme from 14 X 106 m3 to 71 X 106 m3, respectively, for one complete restoration of the entire barrier island chains. Although estimates of required volumes are controversial, significant new borrow sites must be located on the continental shelf off Louisiana to restore the barrier islands. The search for new sand sources must be focused on logistical procedures that are economical and efficient in order to cover large areas of the shelf in a timely manner. Sand search protocols developed for US East Coast sedimentary environments are broadly applicable in a conceptual sense but need to be adapted to deltaic coastal frameworks in Louisiana. Procedures and protocols for the Delta Sand Search Model (DSSM) are thus based on bathymetric, geophysical, and geotechnical survey recommendations for the identification of targets that will be proven out by detailed studies and cultural resource investigations. Development of a DSSM has advantage because it is specifically adapted to coastal marine morphosedimentary units in different-aged lobes of the Mississippi Delta that have fine-grained (muddy) deposits interspersed by sandy deposits of paleodistributaries and interdistributaries.