Before the 'Major improvement work for Shirakawa and Tsuboigawa,' Shira-kawa River (Kumamoto Prefecture) and Tsuboi-gawa River (Kumamoto Prefecture) used to merge at the area around the current City Hall of Kumamoto City; however, Kiyomasa changed the course of the rivers to the current one by building stone embankments.
「白川・坪井川大改修」以前は白川(熊本県)と坪井川(熊本県)は現在の熊本市役所付近で合流していたが、石塘を造り現在の流路に変更。