Could you be a little more specific about your question? What sort of structures? How large?

In any case a straight forward answer would be to remove them, but that may not be feasible and in some cases also not relevant.

An assessment of the environmental impact of the removal is the foundation behind the idea of removing the structure. One may go about it in a very simplistic way with the idea that any human made structure is per definition a disturbance on the natural environment, directing the answer to the issue of the financial costs of removing the structure and wether the ecological benefits are worth it or not.

On a more complex squeme, a detailed assessment of the environmental impact would be carried out, departing from the idea that the man made structure has altered the environment in such a way that there are also positive or desirable effects. An environmental cost/gain dimension is now added to the financial one. Another idea that may need to be consider here is if this human intervention would be comparable to any natural event; for example a man made dam, may be comparable to a river blocade caused by a landslide in terms of size and durability.

Finally, depending on the settings, it is also likely that human interests (economical, social) would be affected by removing or modifying the structure. Thus an assessment of the implications is usually carried out; how deep? It would depend on the value of "social intererests" present both down and upstream.

On a final comment of my own, the assessment is much more justified when you have a series of man made structures and limited means to remove or modify them, thus forcing you to prioritize which structure to modify or remove.

Dear Rafael,

Thank you for your answer and all your explanation. My question is related with these structures in the rivers because I am working in some rivers in the south of Ukraine and in this country they do not have enough budget to remove the structures and going up and down in these rivers we found some old parts of hydroelectrical stations abandoned, the huge structures in the middle of the river.

Unless the biological quality and the physico chemical quality are very good, the hydromorphogy is very bad and the way the river is goind down in the basin is not the natural flow and the natural sediments.

So, what to do in this situations, what kind of program of measures...??

Thank you in advanced!

Regards from Yaremche

My best guess, without knowing anything about the working conditions, is to try and find a financial potential for one or some of the structures which would help me finance restauration activities. Lets say you have three dams, one of them could (given structural changes to improve the morphological conditions) be used to produce electricity (yes it is the simplest example). The idea would then be to use the incomes to finance the removal of the other two dams. The answer to the question of which dam to use would be at the break even point, with costs = reffiting + removal , benefits = income from electricity production. This is of course a full blown project, but in my opinion the most rational way to go about it.

On a more grassroot approach, it may not be necesary to make huge investments and modifications of the structures may sufice, for example to create a breach at the base (carefull with the structural analysis of the dam, so that it will not collapse) big enough to allow for the morphologically significant flows to come freely through the structure or a bottom outlet may already be available which could be fitted for this purposes. One thing to take care of here is what happens with floods that surpass the capacity of these outlets, since water will come out shooting out of the outlet as the water gets impounded behind the dam.

Now the radical approach: if it is more or less a certainty that the removal of the structures would be of great benefit, why not just simply blow it up. Could even be used as training place for demolitions instruction.