The Karnali river makes a big loop in its lower reach near a place called Asare. From here the river flows in the south-east direction for about 25 kilometers, after that the river makes a complete reversal in its direction. The river comes back to a point just two kilometers away from its earlier position near Asare. There is a drop of about 150 meters in Karnali river bed elevations between these two positions merely two kilometers away from one another. The project to utilize this bend for power generation is known as the Upper Karnali Project. There are very good sites to build a large dam at the beginning of the bend. Thus, it makes the Upper Karnali Storage Project far superior to the 10, 800 MW Karnali Chisapani Project in terms of per unit capacity investment cost because its hydropower station would be operating at a firm head two times greater than that of the latter though the total length of the water way of both these hydropower plants would be almost exactly the same.

Large Cost Reduction at Higher Heads

Of all the site characteristics, head is the most important. Design guidelines, 1989 approved by the American Society of Civil Engineers (a document used throughout the world for the design of hydropower) has given some simple reasoning that would help to explain why the Upper Karnali project operating at a head about two times greater by comparison with the Chisapani hydropower could be built at far less per unit installed capacity cost. "Very simply if one doubles the head the quantity of water needed to produce a certain amount of energy is halved, thus, for like site energy development the conduit area and reservoir volume are halved and further large cost reductions occur for powerhouse and machinery costs. This fundamental consideration is at the root of the large cost reductions that occur at higher heads.

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