明渠（英语：Open Channel、Nullah），又名水渠、人造河流、河道、运河，一个狭窄的谷地。在大雨的季节，明渠可以有效流走山洪。在工厂区，明渠引导废水到海洋或废水处理厂。

• 屯门河
• 启德明渠
• 火炭渠
• 黄竹坑明渠
• 观塘明渠
• 山贝河

香港已消失的明渠

• 宝灵渠（鹅颈桥）
• 大坑明渠
• 东京街渠
• 花墟道明渠
• 佐敦谷渠

A nullah or nulla (Urdu:نلہ‎ 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.