Answer:
I think WE control coastlines, because we put rubbish in the sea, that could be recicled!
Actually, the answer is both. The coastline controls us in the sense that it determines where we can build cities and grow crops. But human activity can change the coastline, especially on a local level. People can build large breakwaters to protect ports and marinas from ocean waves, or to prevent erosion of land areas and beaches. On a larger scale, human activities may cause the earth to become warmer, causing large glaciers and ice caps to melt and thereby raise sea levels. As sea levels rise, the coastline changes.