How Tides and River Water Combine to Amplify Floods - Eos

The authors found that peak water levels in both floods occurred around 1 to 2 weeks after peak river discharge during perigean spring tides when both the Sun and Moon are in optimal positions to create high tides. They hypothesize that peak river discharge rates suppress subharmonic tidal amplitudes, while intermediate rates of discharge allow for greater amplitudes and therefore higher water levels. Additionally, river water takes some time to fully move downstream, meaning that water levels are higher in the days following floods, adding to the effects of tidal inflows.