Abstract
A flow regime can be broadly categorized as either perennial, intermittent, or ephemeral, depending on whether the streamflow is continuous all year round, or ceasing for weeks or months each year. Various conceptual models are needed to capture the behavior of these different flow regimes, which reflect differences in the stream–groundwater hydrologic connection. As the hydrologic connection becomes more transient and a catchment’s runoff response more nonlinear, such as for intermittent streams, the need for explicit representation of the groundwater increases. In the present study, we investigated the connection between the Northern Etna groundwater system and the Alcantara River basin in Sicily, which is intermittent in the upstream, and perennial since the midstream, due to groundwater resurgence. To this end, we apply a modified version of IHACRES rainfall–runoff model, whose input data are a continuous series of concurrent daily streamflow, rainfall and temperature data. The structure of the model includes three different modules: (1) a nonlinear loss module that transforms precipitation to effective rainfall by considering the influence of temperature; (2) a linear module based on the classical convolution between effective rainfall and the unit hydrograph which is able to simulate the quick component of the runoff; and (3) a second nonlinear module that simulates the slow component of the runoff and that feeds the groundwater storage. From the sum of the quick and slow components (except for groundwater losses, representing the aquifer recharge), the total streamflow is derived. This model structure is applied separately to sub-basins showing different hydrology and land use. The model is calibrated at Mojo cross-section, where daily streamflow data are available. Point rainfall and temperature data are spatially averaged with respect to the considered sub-basins. Model calibration and validation are carried out for the period 1984–1986 and 1987–1988 respectively.
Highlights
A flow regime can be broadly categorized as perennial, intermittent, or ephemeral
Rainfall–runoff models often fail to simulate the hydrologic connection between streams and the groundwater system, where it tends to be variable in time and space, as is the case for spatially intermittent streams
This is the case for the Alcantara River basin in Sicily region (Italy), whose upstream is intermittent while its middle valley is characterized by perennial surface flows enriched by spring water arising from the big aquifer in the northern sector of the Etna volcano
Summary
A flow regime can be broadly categorized as perennial, intermittent, or ephemeral. In perennial systems there is a permanent connection between the stream and the groundwater, and good results can be obtained from rainfall–runoff models that do not explicitly represent the groundwater store. Rainfall–runoff models often fail to simulate the hydrologic connection between streams and the groundwater system, where it tends to be variable in time and space, as is the case for spatially intermittent streams. This is the case for the Alcantara River basin in Sicily region (Italy), whose upstream is intermittent while its middle valley is characterized by perennial surface flows enriched by spring water arising from the big aquifer in the northern sector of the Etna volcano. A modified version of IHACRES rainfall–runoff model, whose inputs are continuous series of concurrent daily streamflow, rainfall, and temperature data, was calibrated and validated at one of the main cross sections of the Alcantara River basin, where daily streamflow data are available. The structure of the model provides the opportunity for dealing with the uncertainty of parameters when they are very short and poor-quality data series are available for model calibration and validation (Wagener et al [2])
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