Locations of landslides, bank failures, and floodplain deposition during recent intense flooding in Vermont and Colorado (USA) were spatially nonuniform, indicating that some reaches are more prone to these types of geologic hazards. These three key flood effects signal redistribution of sediment across landscapes, reflecting hillslope-channel coupling and the sources and/or sinks of material. We show that spatial gradients in total stream power (Ω) provide critical additional information beyond at-a-point Ω magnitudes for predicting which reaches are likely to be susceptible to these hazards during floods. Field tests in four rivers (watershed areas 0.8–180 km2) indicate that downstream increases in Ω coincide with erosion and mass wasting into channels, and downstream decreases in Ω are associated with floodplain deposition. Our analytical approach, supported by field evidence, predicts geologic hazards and, more broadly, sources and sinks of material along rivers. These are critical concerns from a practical and theoretical standpoint.