The developer of Cotton Mill Square has proposed altering the Jackson Falls Dam so it can be lowered during times of high water. Under the plan presented at a meeting of the city’s Planning and Economic Development Committee, adjustable crest gates will be constructed atop the stone dam that can be lowered during high water to reduce flooding of the Nashua River upstream. Developer John Stabile wants to build 100 residential units upstream from the dam in a former warehouse on the north bank opposite Clocktower Place. It would be named Cotton Mill Square.