Man-made structures

The previous chapters showed the variety of natural features and processes observed underwater with sidescan sonars. But, increasingly, surveys and maps show the presence of man-made structures all over the world. Apart from shipwrecks and a handful of communications cables, human activity has increased over the last half-century to cover all depths with a staggering variety of structures. This chapter will divide them into “planned structures” (Section 9.2) and “accidental structures” (Section 9.3). The former are intentional manifestations, and include pipelines and cables (Section 9.2.1), dump sites (Section 9.2.2), harbors and their approaches (Section 9.2.3), and the exploitation of seabed resources (Section 9.2.4). The latter presents structures that have just come to attention, such as the effects of fishing (Section 9.3.1) or were never intended, like shipwrecks (Section 9.3.2.) and marine pollution (Section 9.3.3). Section 9.4 combines marine waste, although some of it is already presented in Section 9.2.2, and military mines (which, although originally laid with intention, are usually not desired now). Section 9.5 sums up the current state of research on the use of sidescan sonars in underwater archeology, and what the next steps will be. Because of the amount of different structures it shows, this chapter should be of interest to all users of near-shore environments, all developers of underwater sites, and all managers of offshore facilities.