Input (grade 13): The rain washed sand piles from the dumping grounds away to the rivers again and again and made some of the rivers shallower, especially into the Sakawa, into which huge volumes of ash fell, resulting in temporary dams.
Output (grade 5): The rain washed away the sand piles from the dumping grounds and into the rivers again and again. This made some of the rivers shallower, especially the Sakawa.