Abstract
Floodplain inundation poses both risks and benefits to society. In this study, we characterize floodplain inundation across the United States using 5800 stream gages. We find that between 4% and 12.6% of a river’s annual flow moves through its floodplains. Flood duration and magnitude is greater in large rivers, whereas the frequency of events is greater in small streams. However, the relative exchange of floodwater between the channel and floodplain is similar across small streams and large rivers, with the exception of the water-limited arid river basins. When summed up across the entire river network, 90% of that exchange occurs in small streams on an annual basis. Our detailed characterization of inundation hydrology provides a unique perspective that the regulatory, management, and research communities can use to help balance both the risks and benefits associated with flooding.
Highlights
Floodplain inundation poses both risks and benefits to society
We estimated a threshold for floodplain inundation and its uncertainty at each gage station using a breakpoint analysis of each gage’s stream gaging measurements—our analysis differs in method but is consistent with quantifying bankfull flow, a widely used metric in fluvial geomorphology[17]
The proportion of total river flow occurring on floodplains is substantial, especially when compared with the median duration of floodplain inundation for U.S stream gages, indicating that floodplains are inundated on average for only 2.6% of the year (Supplementary Fig. 1)
Summary
Sustainable river basin management requires balancing competing water demands (e.g., human, ecosystem) combined with both local (reach-scale) and cumulative effects for downstream water storage, flood risk, and water quality functions and river health Both scientific forefronts and applications by water resource managers can be aided by our broad characterization of floodplain inundation from small streams to large rivers and across hydroclimatic regions of the U.S Future efforts to maintain, enhance, or reconnect floodplains need to account for the regional differences in the seasonal timing and magnitude of floodplain connectivity, in addition to the effects of short versus longer duration flood events that alter whether the floodplain acts as a nutrient source or sink and cumulative flood attenuation
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