Unfortunately Japan is a place where several natural disasters can happen. Especially typhoons are hitting the nation each year. Therefore floods can happen each year too.
To avoiding the houses and buildings to be flooded, Japanese prepare sandbags in front of their houses and buildings. Then, these sandbags are been placed by local inhabitants before typhoon
hits their cities. Putting the sandbags during the typhoon or long heavy rain is unsufficient, too late.
There is an ancient idiom originally came from China.
"The person who is prepared wins the battle".