Under 626 is classed information about the general principles of hydraulic (water) construction works, including the construction, maintenance and operation of canals and locks, and agricultural hydraulics (irrigation, drainage, reclamation and improvement of wasteland).
Under 627 is classed information about the reclamation of inundated land, the design and construction of dykes, dams, reservoirs and hydraulic power plant works, as well as natural inland waters and their improvement, coasts and coastal works such as ports and harbours, and their navigational, salvage and rescue facilities.
BS 1000[626/627]:1977 history
1977BS 1000[626/627]:1977 Universal Decimal Classification - English full edition - Hydraulic (water) construction works