What is the role of multipurpose river valley projects?

Projects labled as multipurpose generally refer to a water retention system which is used to a) generate electricity, b) act to prevent water shed flooding, c) provide irrigation, d) naviagation e) habitat improvement and f) improve fishery populations. However, in most cases the "e" and "f" are fictions that people are told but do not occur. These projects also generally displace hundreds of not millions of people from very fertile land thus reducing the productivity of these people. They take away their livelihood and their homes of many generations. So do the benefits out weigh the cost. Most countries building these massive projects seem to think so. They do produce lots of benefits, the most important of which is energy. However,, if you consider the Aswan High Dam in Egypt which prevents the Nile from flooding yearly, the power generated by this massive dam is used to make fertilizer. Up to 30% of the electricity generated is used for the industrial production of fertilizer which is needed to keep the fields fertile which in the past was taken care of by the flooding of the river. The lake behind the dam is also silting up at a rate 2x what was thought to be so the useful life of the reserviour will be less then 100 years. There are a lot of considerations which must be reviewed before such a project is undertaken and if it is not done properly, the value of the project is greatly reduced. Unfortunately, there are time when this negative information is intentionally suppressed to get the project passed when it should have been stopped before it was built. Today many old dams are being demolished because they failed to achieve the expected goals.