KYIV, Ukraine — Ukraine on Tuesday accused Russian forces of blowing up a major dam and hydroelectric power station in a part of southern Ukraine that Russia controls, sending water gushing from the breached facility and risking massive flooding. Ukrainian authorities ordered hundreds of thousands of residents downriver to evacuate. Russian officials countered that the Kakhovka dam was damaged by Ukrainian military strikes in the contested area. Read More: What Comes After Putin’s Rule in Russia.