Critical Role for hierarchical geospatial analyses in the design of fluvial research, assessment, and management.

River science and management can be conducted at a range of spatiotemporal scales from reach to basin levels as long as the project goals and questions are matched correctly with the study design's spatiotemporal scales and dependent variables. These project goals should also incorporate information on the hydrogeomorphically patchy nature of riverine macrosystems which is only partially predictable in type and location from a river's headwaters to its terminus. This patchiness significantly affects a river's habitat template, and thus community structure, ecosystem function, and responses to perturbations. Our manuscript is designed for use by senior administrators at government agencies through entry-level river scientists. It analyzes common challenges in project design and recommends solutions based partially on hierarchical analyses that combine geographic information systems and multivariate statistical analysis to enable self-emergence of a stream's patchy structure. These approaches are useful at all spatial levels and can vary from primary reliance on geospatial techniques at the valley level to a greater dependence on field-based measurements and expert opinion at the reach level. Comparative uses of functional process zones (FPZs = valley-scale hydrogeomorphic patches), ecoregions, hydrologic unit codes, and reaches in project designs are discussed along with other comparative approaches for stream classification and analysis of species distributions (e.g., GAP analysis). Use of hierarchical classification of patch structure for sample stratification, reference site selection, ecosystem services, rehabilitation, and mitigation are briefly explored.