The Natural Range of Variability of Floodplain Spatial Heterogeneity

We use remotely sensed data to quantify the spatial heterogeneity of floodplains along 33 rivers in the United States based on the distribution of floodplain patches. Each patch represents a relatively homogeneous, contiguous area of floodplain that is distinct from adjacent patches based on vegetation and soil salinity characteristics at a resolution of 10 m. We focused on natural floodplains with minimal human alteration of the river corridor with the primary objective of quantifying the range of natural floodplain spatial heterogeneity for rivers with diverse characteristics. Secondary objectives include examining the relative importance of potential influences on spatial heterogeneity, testing for consistent spatial heterogeneity patterns within categories of channel planform and flow regime and investigating the behaviour of the heterogeneity metrics when the number of unsupervised clusters varies. We calculated four landscape‐level metrics of spatial heterogeneity that measure aggregation, interspersion and juxtaposition, diversity and complexity of patches. We find that floodplains along channels with snowmelt‐dominated flow regimes have a significantly higher aggregation than those dominated by rainfall flow regimes and floodplains of braided rivers have significantly less diversity. Latitude, drainage area, elevation, sinuosity, flow regime category, planform category and the ratio of floodplain to channel width emerge as important predictor variables of floodplain heterogeneity. These variables reflect the flashiness of stream flows, the inferred relative lateral mobility of channels and the space available for lateral channel movement and the creation of floodplain patches. Floodplain spatial heterogeneity, which is important for peak flow attenuation, groundwater recharge and habitat and biodiversity, relies on continued flow variability and associated channel mobility, as well as floodplain accommodation space.