Galleries:

1.In spite of the provision of water stops there may be leakage through the body of the dam due to the pressure of water from the upstream. In order to remove this water, vertical formed drains to trap the seeping water through the contraction joint is recommended as may be observed from Figures 64 to 65. These vertical drains convey the drainage water to a drainage gallery at some lower level within the dam body as shown in Figure 66.

2.It may be noticed that the formed drain is provided not only at the transverse contraction joint between two adjacent blocks of a concrete gravity dam, they are placed at anequal interval of about 3metres center to center in all the dam blocks.

3.The foundation drainage gallery (shown in Figure 66) is connected to all the vertical drains passing through the body of the dam (Figure 67).This gallery, of a size large enough for a person to walk comfortably, extends throughout the length of the dam at about the same height above.

4.In plan the gallery is near and parallel to the axis of the dam. The dam foundation is as shown in Figure 68.