Environmental flows, an emergency for our rivers

In BAC, together with Sorelló and Engisic we are conducting a study to determine the optimal circulating flow and improve the biological and habitat diversity of different sections of Catalan rivers, a project directed by the Agència Catalana de l’Aigua

Rivers are ecosystems in which a great variety of living beings develop their life cycles. In the rivers we can find fish, but also insect larvae, mollusks such as clams or freshwater snails, birds, mammals such as otters or amphibians such as frogs and newts. Also we can find a diversity of of plants and algae adapted to live in this environment.

The different organisms that inhabit rivers have particular needs for substrate (sandy bottoms, stony bottoms …) and flow, that is, the amount of water and its speed, in order to develop their life cycles. The combination of types of substrates and quantity and speed of water is what we call “habitats” and these habitats determine which species we can find in a stretch of river. For example, trouts need fast, cold currents and stony substrates in order to capture their prey and lay their eggs. In contrast, carps prefer calmer waters and muddy bottoms. Some insects, like the caddisflies, need fast currents of water to be able to collect the food carried by the current, whereas the freshwater snails prefer calmer waters. So, the more diverse the habitats in a river are, the more diversity of plants and animals we will have, the more biodiversity we will have.

Unfortunately there are different factors that affect the flow of rivers, and therefore the diversity of habitats. Climate change is altering the periodicity of rains. At the same time climate change alters rain intensity. These changes in frequency and intensity affect the amount of water flowing in rivers. On the other hand, some human activities such as the creation of dams for irrigation or dams for the production of energy, when withdrawing water from the river or reservoirs, also alter the natural water regime that rivers must carry. These structures reduce the amount of water that flows through the river or its speed. Changes in flow and velocity affect the diversity of habitats that we would expect to find in a stretch of river and this impoverishes the diversity of species.

Caddisflies with their nets and capturing their food
River crab

To ensure the maximum biodiversity, the Hydrographic Confederations and Environmental Agencies have established environmental flows. The combination of types of substrates, quantity and speed of water condition the habitats and which species we can find in a stretch of river. Environmental flows are intended to ensure that a sufficient amount of water flows through the river to ensure diversity of habitats and thus allow as many species as possible to develop their life cycles, while ensuring human uses of the water.

In this study “Technical assistance prior to the drafting of the management plan and the program of measures for the third cycle of hydrological planning: Monitoring of the implementation of environmental flows and review of flows for future planning cycles” commissioned by the Catalan Water Agency and directed by BAC together with the companies Sorelló and Engisic, our objectives are:

  • To update the technical studies to determine the environmental flow regime in the internal basins of Catalonia
  • To monitor the effects of the introduction of environmental flows on the quantity of aquatic organisms and the diversity of species.

To achieve these objectives, a team of biologists and engineers develop field work to determine the circulating flow, the diversity of habitats and the biological diversity in different sections of Catalan rivers and carry out statistical studies to determine how environmental flows increase the diversity of habitats and favor the diversity of species and the abundance of organisms.

Section under study