The basic purpose are:
1. flood control and
2. hydropower generation.
The political purposes make the hydropower case prominent. Most of the inundation is in Manipur and Mizoram states, whereas it would moderate floods in lower Assam. To ensure fare share of benefits to those two states, hydropower generation is also taken into account. The states in North-East are having severe power shortage over years (peak shortage upto 25% in Arunachal). Once Arunachal starts producing hydroelectricity from giant Subansiri projects, the North-East India will become energy sufficient. On the other hand, there are no alternative to dams for flood-control of a rainfed river. Incidentally, both flood-control and hydropower generation reservoirs work in similar way – they retain water during Monsoon and release more during lean season, i.e. reservoir is filled up during rainy season and used up in dry season.
|Indian Flood Zone Map|
The Barak valley, consisting of three of the forty highly flood prone districts in India, goes under water three to four times (2002, 2004, 2007) in a decade. In 1995, plan for flood control Dam in Tipaimukh and reactions in Bangladesh were reported. Very often Barak flood is more devastating than that of Brahamaputra. A detailed assesment (2007 flood report) of floods in Assam can be found here. It has long been alleged that North-East has been neglected in terms of development and lack of flood control is one of the evidences.
The Tipaimukh dam is planned to produce 450MW in lean season and 1500MW in peak. All three states would have 12% share of the electricity and rest would go to the North East grid.