Desilting

I was looking up desilting as Mr. Keishav mentioned it and was wondering if it was a viable option.
I found a pretty concise presentation to explain it.
You need only read the first 8 slides.

http://www.gwsp.org/fileadmin/GCI_conference/Products/Pos_pres_-_Paimpillil_-_Reservoir_de-siltation.pdf

I still don't know if its an environmentally friendly option.