From Longman Dictionary of Contemporary EnglishRelated topics: Constructiondrainagedrain‧age /ˈdreɪnɪdʒ/●くろまる○しろまる○しろまる noun [uncountable]TBCthe process or system by which water or wasteliquidflows awayA handful of pebbles in the bottom of a flowerpot will help drainage.a plan to improve the town’s drainage systemExamples from the Corpusdrainage• Together with Thames Water, it's just finished a 350,000ドル drainageproject for the Middleton Road area.• drainageditches• Gas and drainage pipes had broken as a result of the settlement and there was a risk of further breaks.• And where provenstrength and reliability are called for, claydrainage is its own guarantee.• Farmdrainage ditches ensure that water runs directly into streams rather than being filtered through the soil.• Much of it is below sealevel and only innumerabledrainage ditches prevent it from reverting to its natural state.• There were no drainage ditches here, the shoulders too abrupt, the slope too precipitous, to collect water.• About 80 percent of the drainage goes to a treatmentplant and about 20 percent flows to these waterways.• The drainage system over some sections of route has also had to be refurbished or renewed.