GC: n

CT: Hydraulic structures are anything that can be used to divert, restrict, stop, or otherwise manage the natural flow of water. They can be made from materials ranging from large rock and concrete to obscure items such as wooden timbers or tree trunks.
A dam, for instance, is a type of hydraulic structure used to hold water in a reservoir as potential energy, just as a weir is a type of hydraulic structure which can be used to pool water for irrigation, establish control of the bed (grade control) or, as a new innovative technique, to divert flow away from eroding banks or into diversion channels for flood control.
OR
A hydraulic structure is a structure submerged or partially submerged in any body of water, which disrupts the natural flow of water. They can be used to divert, disrupt or completely stop the flow. An example of a hydraulic structure would be a dam, which slows the normal flow rate of river in order to power turbines. A hydraulic structure can be built in rivers, a sea, or any body of water where there is a need for a change in the natural flow of water.

S: http://www.aboutcivil.org/hydraulic-structures-lectures-notes.html (last access: 20 December 2014)

N: 1. hydraulic (adj): c.1600, from Greek hydraulikos organon “water organ,” from hydr-, stem of hydor “water” + aulos “musical instrument, hollow tube”. Extended by the Romans to other kinds of water engines. hydraulics (n.): 1670s, from hydraulic; also see -ics.
structure (n): mid-15c., “action or process of building or construction;” 1610s, “that which is constructed, a building or edifice;” from Latin structura “a fitting together, adjustment; a building, mode of building;” figuratively, “arrangement, order,” from structus, past participle of struere “to pile, place together, heap up; build, assemble, arrange, make by joining together,” related to strues “heap,” from PIE stere- “to spread, extend, stretch out.”
2. Technical installations by means of which measures are taken in water management for the utilization of water resources and protective measures taken against harmful effects of water.

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=hydraulic&searchmode=none; http://www.etymonline.com/index.php?allowed_in_frame=0&search=structure&searchmode=none (last access: 20 December 2014). 2. TERMIUMPLUS.

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CR: hydraulic energy, [hydroelectric energy], hydroelectric power plant.