Lowlands are prone to flooding, especially when rivers merge. A study looked at flood peaks in the Meuse River and its tributaries. They found that the timing of peak flows doesn't matter much because the waves last for about 9 days. Even though peaks in the main river and tributaries are typically 3 days apart, backwaters can rise up to 1.5 meters over 4 kilometers from the confluence. This means flood prevention measures near confluences should consider the long-lasting effects of flood peaks.