for a long time 和after搭配,得用什么时态?

问题描述:

for a long time 和after搭配,得用什么时态?
比如这句after it had rained for a long time,the river may overflow its banks.这样用对么?用had rained还是直接用rained?

it had rained for a long time完成时一般就表示一段时间以来,含after的意思.
或after it rained for a long time
后面:and the river might.