"subaqueous" is a correct and usable word in written English.
You can use it to describe things that are below or under the surface of the water. For example: "The subaqueous environment is teeming with life."
Subaqueous crossings are becoming more ambitious.
In 1874, Greathead made the subaqueous technique really practical by refinements and mechanization of the Brunel-Barlow shield and by adding compressed air pressure inside the tunnel to hold back the outside water pressure.
After several floodings from hitting sand pockets and a seven-year shutdown for refinancing and building a second shield, the Brunels succeeded in completing the world's first true subaqueous tunnel in 1841, essentially nine years' work for a 1,200-foot-long 1,200-foot-long 1,200-foot-long
Since 1950, however, most subaqueous tunnelers preferred the immersed-tube method, in which long tube sections are prefabricated, towed to the site, sunk in a previously dredged trench, connected to sections already in place, and then covered with backfill.
Once subaqueous tunneling became practical, many railroad and subway crossings were constructed with the Greathead shield, and the technique later proved adaptable for the much larger tunnels required for automobiles.
Concretions of manganese oxide, evidently formed in the process of subaqueous weathering of volcanic rocks, have been found in dense concentrations with a total abundance of 1011 tons.
Well-sorted conglomerates are produced by normal water currents, whereas the poorly sorted varieties result from rapid deposition, as in the case of mudflows or subaqueous slides.
Subaqueous tunneling also is likely to be involved as procedures are developed for utilizing the vast continental-shelf areas of the world; concepts are already being studied for tunnels to service oil wells and for extensive undersea mining such as has been pioneered in Britain and eastern Canada.
Under these conditions, masses of rock measured in thousands of cubic kilometres are torn loose by gravity and fall and/or slide, often moving hundreds of kilometres in a "geologic instant" to a lower resting place (in some cases lubricated by subaqueous avenues).
These were deposited as a thick, subaqueous delta system that gradually filled the Midland Basin from east to west.
Even the ancients were well aware of the ongoing effects of gravity, and it has long been realized that, given time and in the absence of opposing forces, gravity would pull the Earth's surface roughness down to form a featureless subaqueous spheroid.
