Natural responses to changes in morphodynamic processes caused by human action in watercourses: A contribution to support management

- Causes of collapse of a century-old bridge.
- Dominant physical processes and anthropogenic action.
- Numerical simulation of morphodynamic processes.
- Regular check of dam operational conditions.
- Management guidelines for decision-making.

The economic, social and environmental conditions of various European river basins and estuarine systems have changed dramatically in the last decades as a consequence of anthropogenic effects, and they will go on changing in the years to come due to increasing human pressure. Particularly in Portugal, various river-estuary systems have undergone several human interventions, notably engineering works to restore considerable stretches of channels and river banks. A thorough understanding of responses to changes in the morphodynamic processes and new strategies are needed for the use of existing resources in watercourses in order to take into account the many-faceted aims of sustainable development. This paper describes two serious accidents that occurred in Portugal, in consequence of careless management measures that have lasted for several years. It is shown that both accidents could have been avoided if the implemented management methodologies were strictly based on knowledge of the physical processes. This paper also provides a brief description of the nature and distribution of impacts on the river morphology arising out of building and operating large dams. A technical contribution is also offered which although qualitative provides a basic record and explanation of the serious consequences of significant interventions in watercourses, especially when these are not properly assessed or other mitigating circumstances are not taken into consideration.