National Assessment of Floodplain Connectivity

Abstract:

In the context of riverine floodplains, hydrologic connectivity describes the water mediated exchange of matter and energy between the river and its adjacent floodplain. As riverine networks shift from headwater streams to large river systems, flood events transition from short, periodic episodes to longer, sustained flood pulses. While these processes are important to biogeochemical processing, little has been done to quantify the relative influence of physiography on floodplain-river interactions across the nation’s river network. This study examined flow data from over 14,000 USGS gaging stations across the United States. The threshold for flooding, analogous to bankful stage, was estimated using a breakpoint analysis of each gage’s rating curve. Individual floods were then identified across each respective flow record, and a series of metrics were calculated to characterize floodplain connectivity. The distribution and timing of flood events was strongly correlated with basin size and prevailing hydro-climatic conditions (e.g. coastal, interior, and snowmelt systems). Analysis of cumulative flood duration was extended to the entire US stream network, and floodplain connectivity was quantified by the product of stream length and inundation duration. Initial results suggest that floodplain connectivity increases with stream order and highlights the importance of large river floodplains in the fate and transport of materials within riverine networks.