The loss of forest and productive land cannot be ignored. It is calculated that between 1951 and 1976 big river valley projects have swallowed half a million hectares of forestland and nearly one-tenth of the area which has benefited from irrigation.
The Keno river project in Nigeria has revealed major adverse environmental effects. Wide destruction of forests has reduced the availability of fuel and other minor forest produce to the poor.
This increased the misery women in fuel collection.
The destruction of economic trees reduced income from beer brewing and deprived women of income from collection of fuel wood. In champ ally and Bhopal, pattern dams on the borders of Maharashtra, Madhya Pradesh and Andhra Pradesh are expected to inundate 40,000 hectares of rich deciduous forests.
Besides fuel wood, these forests provide valuable minor forests products like Mahua, Chironji (a dry fruit), Tendu leaves (used for beedi production) and some other forest product, and tubers and roots, which are nutritionally very rich. Poor tribals and other villagers are deprived of these products.
It is estimated that about 45,000 hectares of forestland will be submerged in the Narmada Valley project. These are mainly teak and sal forests, which have a very high economic value. Besides the forests, which will go under submergence, another 1260 hectares of forestland will be required for construction of workers' quarters and approach roads. Another problem is that the forests, which will remain in the command area, will come under tremendous pressure, and the people of the surrounding area and their livestock will over utilize them.
Irrigation engineers claim that dams submerge forests; they are able to plant new forests along the canals and dam sites. It is important to note that it takes many years to grow forests. Some of the species are difficult to grow.
It can be argued that fast growing species can be grown, but they cannot be substitutes of old natural forests, which have developed through hundreds of years. Again fast growing species may not be as strong as old trees. So the destruction of forests is one of the worse effects of large dams. Valuable forest resources are destroyed in favour of new resources of irrigation.