A framework for evaluating the spatial configuration and temporal dynamics of hydraulic patches

A framework for evaluating the spatial configuration and temporal dynamics of hydraulic patches was tested in a UK lowland river. Detailed hydraulic assessment was carried out at four discharges between 0.303 m3 s−1 and 1.410 m3 s−1 in a 56 m reach. Five hydraulic patches, as combinations of depth and mean column velocity, and the transitional zones between them were delineated using fuzzy cluster analysis. The composition and configuration of the hydraulic patch mosaic was quantified using spatial metrics. Results showed that the proportion, size, shape and relative location of hydraulic patches all varied with discharge, however intermediate flows appeared to support the most diverse hydraulic patch composition and configuration. This suggests the spatial influence of mesoscale bedforms on hydraulic patches is mediated by temporal variations in discharge. Transitional areas between hydraulic patches occupied a significant proportion of the reach at all flows (33–38%) and may function as in-stream ecotones. The framework addresses the need for a quantitative, spatially explicit approach to hydraulic assessment which could be used to assess the implications of flow regulation and hydromorphological alteration on hydraulic diversity.