Floodplains can support particularly rich ecosystems , both in quantity and diversity . Tugay forests form an ecosystem associated with floodplains , especially in Central Asia . They are a category of riparian zones or systems . A floodplain can contain 100 or even 1,000 times as many species as a river . Wetting of the floodplain soil releases an immediate surge of nutrients : those left over from the last flood , and those that result from the rapid decomposition of organic matter that has accumulated since then . Microscopic organisms thrive and larger species enter a rapid breeding cycle . Opportunistic feeders ( particularly birds ) move in to take advantage . The production of nutrients peaks and falls away quickly ; however the surge of new growth endures for some time . This makes floodplains particularly valuable for agriculture . River flow rates are undergoing change following suit with climate change . This change is a threat to the riparian zones and other floodplain forests . These forests have over time synced their seedling deposits after the spring peaks in flow to best take advantage of the nutrient rich soil generated by peak flow . Historically , many towns have been built on floodplains , where they are highly susceptible to flooding , for a number of reasons : Excluding famines and epidemics , some of the worst natural disasters in history ( measured by fatalities ) have been river floods , particularly in the Yellow River in China – see list of deadliest floods . The worst of these , and the worst natural disaster ( excluding famine and epidemics ) were the 1931 China floods , estimated to have killed millions . This had been preceded by the 1887 Yellow River flood , which killed around one million people , and is the second-worst natural disaster in history
1931 China floods
1931 China floods
Floodplain