Baseflow Separation And Streamflow Simulation Based On Modified TOPMODEL

Baseflow is a primary source of stream flow in the drought period, and thus is a key factor for riparian ecological and environmental protection. Baseflow separation is very useful for water resources planning and is one of important research fields in rainfall-runoff generation mechanism and hydrological modeling as well.There are four conventional baseflow separation methods, including the digital filter method (Filter), streamflow partitioning method (Part) and the equation for estimating ground water recharge and discharge processes (Rora and Pulse). Watershed hydrological models are also able to investigate low flow and base flow separation. Among them, a topography based distributed hydrological model, TOPMODEL, divides the whole runoff into overland flow and base flow. The baseflow includes not only groundwater, which replenishes streamflow gradually and continuously, but also subsurface stormflow, which occurs during a storm period or on a perched water table above a relatively poor permeable layer. For simulating the processes of subsurface stormflow and baseflow in the rainfall periods, the original TOPMODEL was modified on the basis of Scanlon suggestions in 2000 in order to distinguish runoff components of overland flow, subsurface stormflow and base flow. The modeling baseflow processes were compared with those from the four conventional baseflow separation methods in this study.Three sub-catchments (YueCheng, XingFeng and LianPing) within Dongjiang watershed, one of Zhujiang watersheds, were selected in this study. Daily observed precipitation, pen evaporation and streamflow discharge in the period from 1982 to 1987 were used for model simulation and baseflow separation. The model was calibrated from 1982 to 1985 and validated from 1986 to 1987. Moreover, several flooding discharges in each catchment were validated. The agreement between the simulated and the observed streamflow demonstrates that the modified model is reliable to simulate streamflow.The model simulated results show that baseflow amount accounts for 71.6%, 59.3% and 52.6% of the total streamflow in YueCheng, XingFeng and LianPing, respectively. The total of subsurface storm flow and base flow is 82.9%, 79.9% and 86.1%, respectively. The proportion of base flow indicates that more baseflow occurs in the less topography variations and thick soil cover of the loam sand in XingFeng, comparing with less baseflow in the larger topography variations and thin soil cover of red loam in YueCheng and that of yellow soil in LianPing.Comparisons of baseflow amount from the modeling simulation and the four conventional baseflow separation methods demonstrate that the baseflow separated from the traditional method includes partial or whole subsurface stormflow. Baseflow amount from Rora and Pulse is very close to the total of base flow and the subsurface stormflow from the model simulation, and the baseflow amount from Part and Filter is between the simulated baseflow and the total of subsurface stormflow and baseflow from the model simulation.