There are numerous reasons why I am confident that the much anticipated and hyped "national pride" project is extremely disadvantageous to our country's economy and its environment. Please go through the below facts which will help you know more:

1. By the time it will be ready we will already have 3 other international airports in Nepal (Kathmandu, Pokhara, and Bhairhawa). 4 International airports for a country as small as Nepal is not really needed.
2. It will cost us taxpayers excess of $6.7 billion dollar (30% of Nepal’s GDP). That is a lot of money for a country so economically poor. This money could be used to fund other important projects. Redeveloping existing TIA is estimated to cost less than $100 million which ADB is ready to fund as well. Our government also has extremely bad track record of implementing big projects in timely and transparent manner. 
3. It is NOT strategically located. It is very far from the capital city and will take 3-4 hours of drive to Kathmandu. An fast lane highway is expected to be made, which will also cost billions. 
4. More than 2.5 million trees will be sacrificed in 80 sq km of land for this airport. This is the home and migration route to thousands of animals and birds including elephants and tigers, many of them which are endangered and already facing mass extinction. This airport is virtually assassinating the eco-system gifted by nature to Nepal.
5. The economic value of oxygen lost due to deforestation for Nijgad airport is huge: Rs 230 billion/ annum, and that is not counting the airport’s own carbon footprint.
6. It will set a very bad precedent. If implemented, it will prove that jungles can be cleared anytime for any infrastructural projects.

I hope to receive your positive support against this crusade towards nature and help me spread the word about such ill-though project which will cause more harm than any relief to our country's economy, environment and ecosystem. 
Jai Nepal. 

https://www.nepalitimes.com/banner/does-nepal-need-a-4th-international-airport/

http://archive.nepalitimes.com/article/nation/habitat-destrcution-of-tiger-in-Tarai,3423