They've been around for years. See these web sites :
http://www.encyclopedia.com/science-and-technology/technology/technology-terms-and-concepts/canal-lock 'Single (or 'flash') lock-gates were in use by the 1st century BC (Chien-Lu Dam and canals near Nanyang) but may have been used earlier (in the valley of the Euphrates, or the port of Sidon) for irrigation and sluicing purposes.
In Europe, the lock was developed initially to overcome two specific problems: a desire to allow boats to enter a drainage and navigable water system which was protected by dykes, and the need to increase the depth of water available for the navigation of rivers. For the former use they were originally of the single lifting gate portcullis type, while staunches or weirs with removable wooden boards sufficed for the latter, boats sailing up or down the river on the 'flash' of water released when the boards were removed. The earliest single-gate locks were built in the Low Countries at Nieuwpoort and in Italy on the river Mincio at Governolo in the late 12th century, though there had probably been river staunches in Flanders earlier in the century. At the end of the 14th century the opening of the Stecknitz Canal in Germany (1398) was the first summit canal in Europe, a progression made possible by the use of single locks.
The main problem with 'flash' locks and single gates was that they used large volumes of water unless the levels on either side of the gate was equal. Two lock-gates placed close together made a huge saving in water and time in lock-use. This, the 'pound' or 'chamber' lock, originated in China by the 10th century AD and may have been in use in the Netherlands by the 14th century. A basin between the gates was capable of holding one or more boats. The chamber lock radically reduced water usage. The first recorded example (1373) in Europe was at Vreeswijk (Netherlands)%2
