There is a natural contrast between avulsion, accretion and reliction surveys and swamp land, omitted area and island surveys.
The former sprang from natural events, while the latter are undertaken to administratively identify lands which for one reason or another were not originally surveyed in harmony with general or specific instruction.
Another administrative reason would be to meet the requirements of present law for conveyance of certain lands to the states.
Accretions to islands are an exception to the second criteria.