Concept:
- A river does not stop at a state boundary, so a project built on one must be planned for the whole basin.
- Sharing the project also means sharing the cost, the water and the land that goes under the reservoir.
Step 1: Start with the river itself.
The Narmada rises in Madhya Pradesh and flows west through Maharashtra and Gujarat towards the sea. A dam on it affects the land and people of every state along its course, so none of them can be left out of the planning.
Step 2: Look at where the water is needed.
The source says the project would meet the requirement of water in drought prone and desert areas. Those areas are spread across the region and do not sit inside one state.
Rajasthan, though not on the river, has the desert districts of Barmer and Jalore that the project reaches.
Step 3: Look at how the benefit is divided.
Gujarat receives irrigation for 18.45 lakh hectare, Rajasthan for 2,46,000 hectare, and the tribal hilly tract of Maharashtra for 37,500 hectare through lift. Each state has a defined share.
Step 4: Note why a shared design is sensible.
One large dam serving four states is cheaper and uses less land than four separate schemes, and it lets water be moved from where it is plentiful to where it is scarce.
Final Answer: Because the Narmada basin and the dry areas needing its water both stretch across Maharashtra, Madhya Pradesh, Gujarat and Rajasthan, a single project serving all four is the only workable design, and each state receives a fixed share of the irrigation.