Sediment-associated nutrient transport during floods in a gravel river

For riparian vegetation, sediment-associated nutrient transport during flood is one of the major agencies for controlling the nutrient environments of the soil. This paper describes the sediment-associated nutrient transport during flood in a gravel river by field observation and numerical computation. A field observation was performed to know the effects of flood flow on the soil environment of flood plain in a gravel river. In the observation, the grain size distribution and the chemical composition of the flood plain soils were measured before and after the flood. The results of the observation show that the amounts of particulate nutrients in the flood plain soil decrease during fairly large flood, because the fine sands which include the nutrients abundantly were removed by the flood flow. A series of numerical computations for the transport of suspended sediments and the associated transport of nutrients during flood was performed by varying the peak discharge of the flood. The result of the computation on the reduction of the particulate nutrients in the flood plain soils agrees well with those observed in the field. It was found that the particulate nutrients on the flood plains decrease if the discharge of the flood exceeds about 500 m3/s in the observation area.