Let’s remove Passo Martino weir on the Simeto River, Italy

Introduction

The Simeto River, with a watershed of 4,029 km2, is the most important river in Sicily, flowing into the Ionian Sea south of the metropolitan area of Catania. Some of its tributaries are characterised by brackish water due to the presence of evaporite rocks in their drainage basin.

Since the end of the nineteenth century, the Simeto River and its main tributaries, the Gornalunga and Dittaino, have been subject to major canalisation projects for land reclamation. These interventions wiped out many riparian habitats and also affected fish populations, starting with Twait shad and European eel, which at the time were an important food source for riverine peasant communities.

Project context and opportunity

Currently, there are nine diversion dams and six dams in the river basin, both for irrigation and electricity generation. In the 1980s, construction began on a final diversion weir, 7 km from the sea, in Passo Martino. This weir was intended to divert water to supply Catania’s industrial area, but it never came into operation because there was not enough water to divert. As a result, the reinforced concrete base of the dam has remained in the riverbed for 40 years, blocking fish passage and interrupting river continuity, without providing any economic or social benefit.

Sampling carried out before and after construction of the weir showed a strong impoverishment of the fish fauna and the disappearance of indigenous Mediterranean species such as Mediterranean killifish (Aphanius fasciatus) and Cagnetta (Lipophrys fluviatilis).

Project aims

The project aims to demonstrate the feasibility of removing the Passo Martino weir and the resulting benefits for fish communities, especially Twait shad and European eel. Hydraulic and hydromorphological models will be implemented to simulate river behaviour before and after the proposed removal, ensuring that it does not compromise the stability of hydraulic structures and bridges. To assess the benefits, investigations will also be conducted using environmental DNA analysis to determine whether Twait shad and European eel are currently present upstream of the weir.