Chimney drains are an attempt to prevent horizontal flow along relatively impervious stratified layers, and to intercept seepage water before it reaches the downstream slope. Chimney drains are often incorporated in high homogeneous dams which have been constructed with inclined or vertical chimney drains.

Seepage through foundation in an earthen dam is a serious concern as it can lead to the failure of the dam. To control the seepage, various measures can be taken, and one of the most effective ones is providing a chimney drain.

Chimney Drain:
A chimney drain is a vertical drain that is constructed through the embankment and foundation of the dam to intercept and collect seepage water. It is constructed by drilling a vertical hole through the dam and lining it with a filter material. The hole is then filled with gravel or crushed stone. The collected water is then conveyed to the downstream side of the dam through a pipe. The chimney drain provides an effective solution to control seepage through the foundation of the dam.

Other measures:
Apart from the chimney drain, other measures can also be taken to control seepage through the foundation of the dam. Some of these measures are:

- Rock toe: A rock toe is a layer of rocks that is placed at the base of the embankment. It helps to prevent erosion and piping along the toe of the embankment and also provides stability.

- Horizontal blanket: A horizontal blanket is a layer of impervious material that is placed over the foundation of the dam. It helps to reduce seepage and provides stability to the embankment.

- Impervious cutoff: An impervious cutoff is a vertical wall that is constructed through the foundation of the dam. It helps to reduce seepage by intercepting and blocking the flow of water through the foundation.

Conclusion:
In conclusion, seepage through the foundation of an earthen dam can be controlled by various measures such as chimney drain, rock toe, horizontal blanket, and impervious cutoff. Of all these measures, the chimney drain is the most effective as it provides an efficient solution to intercept and collect seepage water.