Kirk here. I just took this screenshot from the following web site:

https://www.river.go.jp/kawabou/pc/ov?zm=8&area=89&clat=32.4723&clon=130.443&mapType=0&viewGrpStg=0&viewRd=1&viewRW=1&viewRl=1&viewRn=1&viewPoint=1

Rainfall is heavy here in Kumamoto now but, due to previous rainfall, rivers in northern Kyushu are nearer flood levels. If you live near a river, the link I've pasted above may be somewhat helpful in keeping an eye on things. However, sadly, regardless of whether or not you read Japanese, there's no "one stop shopping" for river levels in a particular area. The following page has links to several different websites, each of which presents only a slice of the kinds of information someone wondering about whether or not they need to take evasive action might need. Ah . . . :(

https://www.city.kumamoto.jp.e.fm.hp.transer.com/bousai/list00904.html