Short answers, pulled from the story.
The 1931 China floods killed an estimated three million people and stand as the deadliest natural disaster in recorded history. This event occurred on land known as a floodplain, which is the dynamic interface where a river meets the valley.
Lateral accretion allows the river channel to shift direction without significantly changing its width by eroding the outer bank and depositing sediment on the inner bank. This process effectively walks the river across the valley floor over centuries, with rates varying from unmeasurable to 10 meters per year for the Kosi River of India.
The flood pulse is an annual cycle of flooding and drying that creates a unique environment where species must adapt to rapid changes in water levels and nutrient availability. This cycle brings in detrital material rich in nutrients and releases nutrients from dry soil to fuel one of the most productive ecosystems on the planet.
The Federal Emergency Management Agency manages the National Flood Insurance Program, which relies on Flood Insurance Rate Maps to delineate the 100-year flood inundation area. These maps often fail to account for alterations to the watershed upstream, such as the construction of large shopping centers and parking lots, which can raise the levels of 5-year and 100-year floods.
Annual flooding events in the Inner Niger Delta of Mali are a natural part of the local ecology and rural economy, allowing for the raising of crops through recessional agriculture. This contrasts with regions like Bangladesh where frequent floods brought on by cyclones and annual monsoon rains cause severe economic disruption and loss of human life.