Assessment of Morphological Quality of Surface Water Bodies in Western Sicily

According to the Water Framework Directive (WFD), assessing hydromorphological quality is essential both for defining the ecological status of surface water bodies and for identifying heavily modified water bodies (HMWBs). In this work, the geomorphological approach proposed by Rinaldi et a. (2011) and integrated into a wider methodological framework named IDRAIM (stream hydromorphological evaluation, analysis and monitoring system) is adopted. This method defines the Morphological Quality Index (MQI) by evaluating deviations of current conditions from a reference state, based on three components: (a) functionality of processes; (b) absence of artificiality; (c) absence of significant channel changes over the last decades. The MQI procedure was applied to 47 surface water bodies in western Sicily The mean MQI value was 0.63, indicating an overall moderate morphological quality. The Guidaloca, Modione, Finocchio, and S. Bartolomeo surface water bodies showed average values above 0.70, corresponding to good morphological status. In contrast, the Birgi and Lenzi catchments revealed the most critical conditions. In particular, Lenzi has a mean MQI value of 0.19, largely influenced by a single surface water body with an MQI of 0. Analysis of the contribution of individual components revealed that artificiality has the strongest influence on the overall MQI, with a very high positive correlation (r = 0.972). Since MQI is calculated as a length-weighted mean of reach values, long stretches with artificial discontinuities can greatly reduce the overall score, as observed in Lenzi. Finally, a sensitivity analysis conducted on a surface water body demonstrated that improving the MQI of a single reach—particularly if it is spatially long —can result in significant changes in the overall water body MQI. These results highlight how interventions on specific reaches can lead to measurable and meaningful improvements in river quality status.