I think the water ran up a river channel.
That’s what happened in Japan, water went right up the rivers well inland.
That’s the point.
The Guadalquivir, which loops around Seville, was and still is (though less so these days, after a lot of civil engineering) prone to destructive floods.
That’s why historically Seville wasn’t a real port, even in the days when it received the bulk of the trade of the Americas. The riverbank didn’t have wharves, it was just an extensive beach. Harbor facilities wouldn’t have lasted long.