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- A nullah or nala (Hindustani 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 3 metres (10 ft) deep and 6 metres (20 ft) wide, used to divert monsoon rain away from the cities. Encroachment into nullahs is a significant problem in many South Asian cities, since it hampers the drainage of stormwater and can exacerbate floods. (en)
- 明渠（英語：nullah）又名开放式水渠（open channel），泛指任何主要用于排水的露天水道，包括各种河道、运河、大型沟渠等。与之相对的是封闭不露天的暗渠。 在大雨的季節，明渠可以有效的移除积水防止洪涝；在工廠區，明渠引導廢水排放到海洋或。在亚洲一些地区，“明渠”一词专指平时干涸无水的备用泄洪通道。 (zh)
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