Drain holes

Drain holes:
The biggest drain hole in the world is part of the Monticello dam in California, USA. This drain hole's purpose is to prevend the water from rising higher then the dam's barrage. Due to the large amount of water that this thing needs to spill away it has a huge diameter of 72 feet:


It is basically a giant cement tunnel which narrows to 28 feet at the end of the tunnel:




Another of these type of drain holes can be found here in Langelsheim in Germany. When this barier was build and when there was no water in front of the dam yet the drain hole could be perfectly seen:




More of these can be found here in Turquoise lake in Colorado near Denver, here by the Benageber dam near Valencia in Spain:


Here is one near the barier of the San Roque Lake in Argentina.

And here is one situated in a small river in Worcester in the USA.