European Project for web-assisted Environmental Education
  freeyourriver Background information Library River Ecology   Effects of the men works

Human works and the effects on the river

The riverine environment can be seriously damaged by direct works on the river-bed (artificial banks, excavations in the riverbed, barriers, dams) or by the cultivation and urbanization of the natural flood areas, which often remove or reduce riparian forests and wetlands(question 1).

Breaking of the banks

If the embanking works alter inappropriately the banks, they can amplify the effect of the flooding.

Floods are common events, and they are essential to the evolution of the river-bed morphology. Over time they find an equilibrium profile. Oftentimes floods create great economic loss and even fatalities, which could have been prevented if building had been restricted in flood plains, man-made alterations of the river had been limited, and natural flood-prevention structures (wetlands, riparian zones, channels) had been left in place (question 9).

The water and the transported materials, which in a normal situation would disperse in the flood areas, are forced to flow and settle in a dammed area. The material, which settles within the banks, causes the river-bed to rise, and the huge amount of water flows with an increasing erosive force. Breaking of the banks and flooding is the likely result of removing the natural protection.

Interruption of the continuity between the river and the surrounding area

Besides increased flood potential, poorly designed flood regulation works can interrupt the continuity and the exchange between the river and the surrounding environment, and reduce biodiversity, found within a wild healthy river. Without trees on its banks, bends, rocks or ponds, the river is forced to flow along a constricted channel. These natural elements are able to shelter a large variety of animals and plants. Hindering the natural development means limiting its capacity to create habitats and consequently to shelter certain species. In addition, the loss of biodiversity reduces the self-purifying capacity of the river, compromises the entire river ecosystem, and makes it more vulnerable to stressful conditions (e.g.polluting and waste water discharges).

Overall, altering a river’s profile and making it uneven by dams or barrage barriers, blocks the natural transport of material (sand, gravels and pebbles), hinders the movement of aquatic species, and endangers their survival (questions 9-10).

Waterproofing of the river-bed

The waterproofing effect is another risk of concreting the river banks and the same riverbed. This produces a real waterproofing effect on the river and limits or even completely stops the natural exchange of water with the riparian area and the ground-water table (aquifer) which is found below and along the sides of a river. The difficulty or the interruption of this exchange can result in the biological death of the ground-water table and consequently the death of the numerous organisms that live there and provide self-purification functions. Besides, as a result of an isolated ground-water table, the water flow is reduced and it is no longer able to work as a balancing element. In natural conditions, during floods, the ground-water table receives water from the river and in this way decreases the river’s flow and flooding. On the contrary, during low water conditions, the ground-water table gives water back to the river. Therefore, the proper functioning of this natural water-exchanging mechanism reduces the effects of floods and assists during low water conditions, which serve to benefit both man and all other living organisms within the river system (questions 9-10).