The palette
Plenty of water, and in two kinds again: the soft body of the bay to the south, and the hard rectangles of the basins. But be aware of what one tone will do here. Because the map gives water a single level, a strong water colour will make the bay and the open sea into one continuous shape, which is truthful but hides the whole story of the barrage. A lighter water lets the basins stand out as separate rectangles, and the basins are what carry the history.