drainage          
noun [ U ] uk/ˈdreɪ.nɪdʒ/ us/ˈdreɪ.nɪdʒ/
 排水系统;排污系统
the system of water or waste liquids flowing away from somewhere into the ground or down pipes
  drainage channels/ditches/systems 排水渠/沟/系统 
  土壤排水能力
the ability of soil to allow water to flow away
  These plants need a sunny spot with good drainage. 这些植物需要种植在阳光充足的地方,土壤排水能力要强。