Which exact tributry you are talking about? Because location of Dhumkar dam site is about 200 KM from LAC.
Nubra is the last valley on the way to Siachen, and Nubra river originates from Siachen, where India has got a dam, the river later meets the Shyok river very important for POK.
This is a strategic place and in Tibetan map this place was known as Yarma Tsangpo. Chinese also have eye on this. To cut Siachen taking on Nubra is very important for them. They can't take Siachen without having Nubra valley withing their reach.
This is basically a whole Indus river basin, what Chinese want. They don't want to reach Xinjiang, they want to reach Gilgit directly through Ladakh and from there to Xinjiang and Kazakistan.
This is why DBO is highly important for India and this is why India is making road to DBO which Chinese are objecting.
So now it is economic reason and target is J&K AND Laddakh? That gets really weird really fast. Why? Because that will mean a fight with India AND Pakistan
Pakistan has already given a part of POK to Chinese, you think Pakistan can say anything to China?