Qualitative and quantitative analysis of hysteresis between sediment concentration and flow rate during hydrologic events

The relationship between flow rate - Q and suspended sediment concentration - SSC demonstrates complex temporal patterns during hydrologic events, which are governed by geomorphology, land use, soil management and rainfall. This fact has important implications for understanding and describing erosive processes and sediment production in catchments. These patterns can be evaluated by their loop hysteresis characteristics on the graph of SSC vs. Q. In this study, the hysteresis effect was analyzed for 19 rainfall events in a rural catchment in Southern Brazil. The events were separated in two groups in relation to soil management (with and without soil management practices). The events were classified according to the type of hysteresis, and a hysteresis index (HI) was calculated to evaluate the magnitude of the difference in phase. Results show that the hysteresis pattern was a clockwise loop, indicating that the peak SSC occurred before the peak Q, which represents rapid mobilization and transfer of sediment in the catchment. The HI was not statistically different between the two periods studied, although there is evidence that the conservation practices do have some influence on the index.