The difference between tidal waves and floods is that tidal waves take place in oceans and are generated by seismic activity while floods take place in rivers and lakes, and sometimes oceans during storm surges, and are generated by weather.
river floods are caused by “reclaiming” river bank land upstream. E.g., draining a swamp/marsh along a bend in a river, erecting dikes, and putting in light industry. Then, when the river gets rained on upstream that marsh that used to absorb the extra water just passes it on downstream — to a city.
Missouri river did this all time just west of StLouis. All rivers do this.
Go build on the hillsides, yah greedy bastids!!