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

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

, 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.

http://chl.erdc.usace.army.mil/hydraulicstructures United States Corps of Engineershttp://chl.erdc.usace.army.mil/hydraulicstructures