RIVER CONTINUITY AND CONNECTIVITY
The structure and dynamics of rivers and their banks are defined by lineal organisation and continuity along what we could call a ‘river continuum’. However, the longitudinal structure and dynamics are not the only features that determine the function of the rivers and riverbanks as ecosystems. There are two other equally important dimensions: the transverse and vertical dimensions.
Longitudinal connectivity is the most intuitive of these dimensions as it is defined by the direction of flow from the river’s source to its mouth, and is the main feature responsible for the characteristics of the aquatic and riparian communities.
Transverse connectivity, on the other hand, is defined by the connection between the river and its floodplain, a relationship that is at its height when a river overflows and floods the floodplain.
Finally, vertical connectivity shows us that rivers are not only formed by what we can see, but also by other parts such as the substrate of the river bed or the underground aquifers, which are of vital importance for maintaining the continuity of the river during periods when water levels are at their lowest.
Maintaining this web of connections in space and time is essential to ensure our rivers reach a ‘good health status’ or good ecological status, as this way our river ecosystems approach their natural state, in other words, how they would be without human intervention.
The existence of transverse structures in the rivers, such as dams and weirs, alters the natural dynamic of the river and, more specifically, its longitudinal continuity. It is not always possible to remove them as they may be used to irrigate the riparian plains or to generate electricity. However, once they fall into disuse, or the licence for their use is revoked, demolition should become normal practice. In cases where demolition is not possible, the dams are bypassed to minimise the negative impact that the obstacles have on the continuity of the ecosystem.
The final objective of the total or partial recuperation of longitudinal, transverse and vertical continuity is to return the river ecosystem as close as possible to its natural state.
