Characterizing flow regime and its alterations in an intermittent river: the Canale d’Aiedda case study

Anthropogenic activities, such as waste water treatment plants dis- charges (WWTPs), impact the natural river regime. The assessment of the “im- pacted” and “un-impacted” hydrological conditions is of paramount importance for the river management. Methodologies for characterizing flow regime and its alterations are based on streamflow data recorded over a long period. Data re- quirements may be a limitation in regions where the recorded data are not avail- able or poor (i.e. short time series, presence of gaps). Hydrological models, such as the Soil and Water Assessment Tool (SWAT), may be used to generate long-term time series of daily or monthly streamflow. In this work, an approach to characterize the flow regime of an intermittent riv- er and to assess its alterations using the SWAT model is defined. The aims are: (i) adapt SWAT for simulating daily streamflow in the Canale d’Aiedda river (Italy), (ii) characterize its flow regime, and (iii) assess the hydrological regime alterations due to WWTPs. The flow regime was characterized by using several hydrological indicators, based on the long-term time series of modeled daily streamflow. Hydrological regime classification of the river reaches receiving wastewaters from WWTPs shifted from intermittent to perennial. The components of the low flow (1-, 3-, 7-, 30-, and 90-day minimum flow, zero-days) and the monthly flow recorded in summer were severely altered. The concept of “zero-flow threshold”, defined on field observations was introduced to improve the model results. This study provides a contribution to the significant topic of the management of intermit- tent rivers under the Mediterranean climate.