Short answers, pulled from the story.
The 1938 Yellow River flood occurred on the 13th of June 1938 when a wave of water crashed into Zhongmu County. Military leaders engineered this event to stop Japanese advances during the Sino-Japanese War.
Chiang Kai-shek sanctioned the plan on June 1st at a military meeting near Zhengzhou. Engineers breached the dikes via tunneling operations on June 5th and June 7th at Huayuankou on the Yellow River south bank.
Immediate drowning deaths ranged from 30,000 according to Kuo Tai-chun to 89,000 per China Academy of Sciences data. Total civilian deaths reached between 400,000 and 500,000 from drowning, famine and plague while the Nationalist government released relief statistics in 1948 claiming 893,303 total deaths.
The Yellow River diverted from its earlier course at Huayuankou into the Jialu River within Zhongmu County. Water flowed into the Shaying River at Zhoujiakou before joining the Huai River and inundated 20 affected counties across Henan, Anhui, and Jiangsu provinces.
Military leaders had three long-term goals for this scorched earth tactic including protecting the Guanzhong section of the Longhai railway and blocking access to Shaanxi province. The third goal destroyed key transport links across Northern China such as the Beijing, Wuhan Railway and the Tianjin, Pukou Railway to prevent rapid movement of Japanese machines and troops.