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Free to flow

Rivers and their ecosystems are subject to alterations due to human activities. Researchers involved in the MesoHABSIM project study their behaviour to safeguard their future

Measuring water depth and flow velocity is important for characterizing river habitat

Increasingly severe droughts and lower water resources force us to rethink our habits. How much water is currently being withdrawn in Italy and how is it used?

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MesoHABSIM in Italy

Researchers from the Polytechnic and the University of Turin conduct fieldwork during different periods of the year

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The technology helps to describe river characteristics and the environmental requirements of the species that inhabit them, such as fish and macroinvertebrates

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When dealing with large rivers, measurements are taken using a vessel equipped with an acoustic doppler current profiler

Weirs and barriers have significant environmental impacts as they alter the flow rate, fragment habitats, and change the river morphology

It is important for fish to move freely, swim upstream and lay their eggs in the most suitable places for reproduction.

Ensuring that a river has the necessary water flow for the life of all species is the greatest challenge

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Moving from the “Minimum Vital Flow” to the new “Ecological Flow” concept: how science and politics can work together

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River floods transport sediments that reshape the riverbed and create conditions for the renewal of the aquatic and terrestrial species' habitats

However, floods can also be harmful to infrastructures built within or near the riverbed. The data on floods in Italy are concerning

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The Baganza River, in the province of Parma, is full of water due to the rains of October 2023 (courtesy of the Po River District Basin Authority)

The MesoHABSIM (Mesohabitat Simulation Model) is a river habitat modelling system used to assess the habitat availability for a species or a biological community in relation to flow and the local river morphology.

The modelling process begins with the description of hydro-morphological river characteristics such as flow velocity, water depth, substrate type, water temperature, riverbed geometry, and the presence of covers and shelters for the fauna. Once the physical environment has been characterized, habitat suitability criteria (or species distribution models) are applied to assess the availability of habitats over space and time, based on the environmental preferences of the considered species or biological community.

Using the MesoHABSIM methodology and the calculation of the index of Habitat Integrity (IH index), we can simulate future changes to the available habitat in a river. This involves  a scenario analysis related to the forecasted impacts of climate change or changes in water withdrawals, compared to the current situation and the actual water resource availability.

Researchers have a variety of tools available for conducting surveys in the field, which are highly accurate. When measuring the flow velocity and flow rate in a small river, an electromagnetic flow meter, mounted on a wading rod, is used. A long tape measure, a GPS, or rangefinder is then employed to measure distances  and the position and size of each habitat unit.

For larger rivers with significant depths, the measurement of water depth and flow velocity is conducted using a vessel (or small boat) with an acoustic sensor installed on it, known as an Acoustic Doppler Current Profiler (ADCP). Additionally, analyzing photogrammetric images taken with a drone allows an accurate description of the river planforms and bathymetry. When needed, water depth and flow velocity can be even simulated using 2D hydrodynamic simulation softwares.

Macroinvertebrates are sampled using a fine-mesh net attached to a square metal frame. To capture fish, a direct current electric field is utilized, which causes the fish to lose their senses without causing trauma, making it easy to catch them. In particular, the electric current interacts with the fish’s peribronchial muscles and induces a narcosis. The individuals captured in each mesohabitat are placed in buckets or containers with oxygenated water. If necessary, clove-based anesthetics can be added to the water to reduce the animals’ stress. After identifying the species and measuring the body length of each animal, the captured fish are released back into the original mesohabitat.

The Ecological Flow (EFlow) was introduced in 2012 by the European Commission as part of the “Plan to Safeguard European Water Resources”. It refers to the “amount of water needed for an aquatic ecosystem to continue to thrive and provide essential services”. EFlow recognizes that water quality, quantity and the frequency and duration of low, moderate and high flows are intrinsically linked to the concept of ‘good ecological status’ of the ecosystem.

Essentially, every time water is diverted, it is crucial to determine the flow rate that must continue in each homogeneous stretch of the river to ensure the preservation of the physical and chemical characteristics of water, as well as the sustaining of local plant and animal communities.

The EFlow is an evolution of the Minimum Vital Flow (MVF) which represented the first attempt in Italy to safeguard the river ecosystem. Indeed, the MVF has been calculated as a base flow value to be constantly released downstream water diversions, whereas the EFlow can vary along the year depending on the water availability and user’s needs, to reach good ecological status or avoid possible deteriorations. Thus, in 2017, the Ministry of the Environment and the Water Authorities approved the National and River Basin Guidelines to update the methods for determining the MVF and ensure the maintenance of EFlows in Italian watercourses.

We have therefore progressed from the concept of “minimum flow”, which remains almost constant throughout the year, to the idea of a “regime” that varies over time. This change allows us to consider the natural dynamics of rivers and seasonal flow patterns, which are essential for preserving the structure and functionalities of river ecosystems.

 

 

Floods are considered one of the most significant natural disasters for people living near rivers. This is due to the extensive damage caused to human activities and the population. Floods are technically a result of hydro-meteorological events that lead to peak flows, which in Italy are often intense and brief. Scientific research correctly categorizes floods as extreme weather and climate phenomena.

Floods are not just about the large overflow of water from rivers; they also play a crucial role in the movement of sediments, that are eroded, transported and deposited also in large quantities. This massive sediment transport helps in the natural renewal of habitats, reshape riverbeds, and modify the position of river planforms. Ecosystems and biological communities have adapted to this natural variability over the centuries, but human alterations to rivers, such as the channelization and narrowing of natural riverbeds, can reduce or even eliminate this renewal capacity, impacting river habitats and the related biotic communities.

At a global level, Italy is a country particularly subject to floods, due to the high fragility of its territory, which is largely mountainous with a high population density. According to the “City Climate Report 2023 – Special Floods” conducted by Legambiente, from 2010 to 2023 there were 684 intense rain events,166 river floods and 86 landslides due to intense rainfalls. These events accounted for 49.1% of the natural disasters recorded in that period. The regions most affected by intense rain were Sicily (86 cases), Lazio (72), Lombardy (66), Emilia-Romagna (59), Campania and Puglia (both with 49 events), and Tuscany (48 ). Lombardy had the highest number of river floods with 30 cases, followed by Emilia-Romagna with 25 and Sicily with 18 events.

The significant human population density contributes to worsening the flood risk. In Italy, a substantial amount of construction has taken place near and within the floodplains of rivers, including in areas identified as risky by the river basin authorities. As a result, 7.7 million Italians are currently at flood risk (source ISPRA, 2016). Managing floods and their consequences involves the challenge of implementing measures that ensure the safety of communities and human activities, while also protecting the natural hydrological and morphological processes and the associated renewal of river habitats.

How much water is being withdrawn in Italy? It is crucial to have precise numbers on water withdrawals and usage. This is because current estimates from ISPRA (the Italian Institute for Environmental Protection and Research) show a long-term negative trend (from 1951 to 2023) in the availability of water resources at a national level. Indeed, in the upcoming years, we should anticipate longer and more severe periods of drought and water scarcity.

ISTAT (the Italian National Institute of Statistics) estimates for the period 2015-2019 show that more than 30 billion cubic meters of water are withdrawn annually from the natural environment for agricultural, drinking, and industrial purposes. Of this, around 56% (17 billion cubic meters) is used for agriculture, primarily diverted to feed irrigation systems. The second largest use is for drinking water, with 9.3 billion cubic meters (31% of the total) withdrawn annually to meet the needs of the population, small businesses, hotels, services, commercial and productive activities, as well as public facilities like schools, offices, and hospitals. The industrial sector accounts for the remaining 13% (3.9 billion cubic meters/year).

The withdrawals  vary considering river basins and water districts, compared to the national scale. In the agricultural sector alone, 2/3 of the total water withdrawal (11.3 billion cubic meters out of 17 billion) belongs to the Po River district. The second highest water withdrawal for agriculture is related to the southern Apennines district, with 2 billion cubic meters. Also in terms of drinking water, the Po River and southern Apennines districts have the highest withdrawals: 2.8 billion cubic meters (30% of the national total) and 2.3 billion cubic meters (25% of the national volume), respectively.

To address future periods of drought and water scarcity, it will be necessary to focus on reducing water consumption through sustainable and adaptive management. At the same time, efforts should be made to improve the efficiency of irrigation systems and reduce the losses in aqueducts. An encouraging statistic from 2022 shows that municipal water supply systems delivered 214 litres of drinking water per inhabitant per day for authorized uses, which is 36 litres (15%) less than in 1999.

However, water losses remain significant in aqueducts  affecting approximately 40% of the total amount of water distributed for drinking purposes. It has been estimated that the amount of water lost in Italy through the water supply systems alone could meet the needs of 43.4 million people for a whole year. In order to deal with water scarcity, only a small portion of the water withdrawal comes from marine or brackish sources (0.1% of the total). This water is mainly used in Sicily to supply the smaller islands and to a lesser extent in Tuscany and Lazio regions.