Guwahati, August 12: Chief Minister Tarun Gogoi today expressed serious concern over the "stoic silence" maintained by Prime Minister rendra Modi on the issue of construction of big dams on the Brahmaputra by Chi which will adversely affect downstream areas of Assam and the Northeast region. "In spite of the knowledge of government regarding construction of large dams by Chi on the Brahmaputra, I fail to comprehend why the Modi government is not taking the matter seriously," he said.