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runoff from [source]
径流常与'from'搭配表示来源，也可作复合名词如'stormwater runoff'。
The runoff from the farm fields polluted the nearby river.
农田的径流污染了附近的河流。
径流(量)
runoffs — plural of runoff
先理解核心含义，再看它在真实句子里的用法。
径流(量)
the surplus liquid (as water) that runs off a surface into streams, rivers, etc.
The runoff from the farm fields polluted the nearby river.
农田的径流污染了附近的河流。
environment
降水或灌溉后未渗入或蒸发而径流出的水量。
That portion of precipitation or irrigation on an area which does not infiltrate or evaporate, but instead is discharged from the area.
径流；超过限度或容量的多余液体(如水)的发生
the occurrence of surplus liquid (as water) exceeding the limit or capacity
径流水中所含的溶解化学物质等。
Dissolved chemicals, etc, included in such water.
决选；为解决先前未产生获胜者的选举而举行的最终选举
a final election to resolve an earlier election that did not produce a winner
After the heavy rain, the runoff from the hills flooded the streets.
大雨过后，山坡上的径流淹没了街道。
Farmers are concerned that chemical runoff from fields will pollute the river.
农民担心田里的化学径流会污染河流。
Since no candidate won a majority, a runoff will be held next month.
由于没有候选人赢得多数，下个月将举行决选。
径流常与'from'搭配表示来源，也可作复合名词如'stormwater runoff'。
The runoff from the farm fields polluted the nearby river.
农田的径流污染了附近的河流。
决赛竞选常指选举中无人得票过半后的第二次投票。
The candidates will face a runoff election next month.
候选人下个月将进行决胜选举。
Not this
The water runoffs from the roof.
Use this
The water runoff from the roof.
runoff是名词，此处错误地用作动词。应使用名词形式表示径流。
Not this
They will hold runoff next week.
Use this
They will hold a runoff next week.
当runoff表示决赛时是可数名词，需要不定冠词a。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
地表径流
Surface runoff carries soil and pollutants into rivers.
地表径流将土壤和污染物带入河流。
农业径流
Agricultural runoff can harm aquatic ecosystems.
农业径流会危害水生生态系统。
雨水径流
该市建造了湿地来处理雨水径流。
The city built wetlands to treat stormwater runoff.
决选；决胜选举
A runoff election will be held next month.
下个月将举行决选。
决选初选；第二轮初选
The runoff primary narrowed the race to two candidates.
决选初选将竞选范围缩小到两名候选人。
Use runoffs naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
记住 run + off：雨点 run（跑）off（掉），没渗入地下，只在地表流走——径流；选举没人过半，选手再 run 一轮——决选。
语域：neutral 常见场景：environmental science、weather reporting、water management runoff 作“径流（量）”解时，多用于环境科学、水文、农业或天气新闻等语境，属于中性偏正式的表达；比较常见于书面或报道性语体。日常口语中直接说 runoff 的情况较少，通常会用更口语化的说法来替代。
径流一般不可数，决赛可数
Dictionary facts from ECDICT, WIKTIONARY.