Sediment output and effective discharge in two small high mountain catchments in the Bavarian Alps, Germany

Sediment output (solid and dissolved load) from two small Alpine rivers (Partnach and Lahnenwiesgraben in the Bavarian Alps) was measured during three summer field seasons from 2001–2003. There is high spatial variability of sediment output between the catchments and a high temporal variability between observation periods. Sediment transport in the Partnach river (Reintal) is dominated by solute load, whereas the Lahnenwiesgraben river transports a much greater proportion of solid load. This difference can mainly be explained by the different lithologies of the systems. The Reintal catchment is dominated by massive Triassic limestone. In the Lahnenwiesgraben catchment, in addition to limestones, unconsolidated rocks, marls and mudstone layers are significant. Furthermore, large rockslide dams in the Partnach valley isolate large parts of the Reintal catchment from solid load output.The components of fluvial sediment transport were, where possible, calculated by using flow duration curves and rating curve techniques. In the Lahnenwiesgraben event specific rating curves were used to determine suspended load. On the broad database of 55 measured flood events in the Lahnenwiesgraben a good correlation (rPearson = 0.9) between event peak discharge and suspended load of the event was established.Effective discharge was calculated for the different types of sediment load (solid and dissolved) and total load. In the Reintal effective discharge for total load is found in low flow classes close to mean discharge, because sediment output is dominated by dissolved load, which has its maximum efficiency at low and moderate discharges. In the Lahnenwiesgraben most work is done by discharges much higher than mean discharge during extreme individual flood events.