A
nullah or
nulla ( or "nallah" in
Punjabi) is an 'arm of the sea',
stream, or
watercourse, a steep narrow
valley. Like the
wadi of the
Arabs, the nullah is characteristic of mountainous or hilly country where there is little rainfall. In the drier parts of
India and
Pakistan, and in many parts of
Australia, there are small steep-sided valleys penetrating the hills, clothed with rough brushwood or small trees growing in the stony soil. During occasional heavy rains, torrents rush down the nullahs and quickly disappear. There is little local action upon the sides, while the bed is lowered, and consequently these valleys are narrow and steep. In cities on the
Delhi plain in India, nullahs are concrete or brick-lined ditches about deep and wide, used to divert
monsoon rain away from the cities.