Storm surge barriers across tidal inlets with navigation gates and tidal-flow gates to mitigate interior flood damage (when closed) and minimize ecological change (when open) are expensive. Daily high velocity tidal flows through the tidal-flow gate openings can drive hydraulic turbines to generate electricity. Money earned by tidal energy generation can be used to help pay for the high costs of storm surge barriers. This paper describes grey, green, and blue design functions for barriers at tidal estuaries. The purpose of this paper is to highlight all three functions of a storm surge barrier and their necessary tradeoffs in design when facing the unknown future of rising seas.