River engineering has caused extensive losses in riverine biodiversity and ecosystem services, aggravating the eutrophication of surface waters. One promising sustainable solution for flood and agricultural water management are two-stage channels with a vegetated floodplain constructed on the side of a river as an alternative to dredging. This project investigates the insufficiently understood impacts of two-stage channels on water flow and quality. Innovative measurements will yield unprecedented knowledge on the transport and processing of dissolved and particulate nutrients in Boreal engineered rivers. Widely applicable models will be developed for predicting how complex vegetation and channel geometry affect the flow, and retention of phosphorus and nitrogen. The water quality benefits of two-stage channels will be systematically evaluated for the first time. The knowledge produced supports the optimal design and maintenance of sustainable river engineering solutions.