Chimney drain
боомтын босоо шүүрүүл
вертикальная дрена
A vertical or inclined layer of permeable material in an embankment to control drainage of the embankment fill.
Source Guidelines on Instrumentation on Large dams by Central Water Commission Ministry of Water Resources, River Development & Ganga Rejuvenation Government of India, June 2017, p.71Зураг