moment of high water and most rapid down-stream at low water. Hence the tidal current "flows" for a long time after high water has passed and when the water-level is falling, and "ebbs" for a long time after low water and when the water-level is rising. But rivers gradually broaden and become deeper as they approach the coast, and tidal currents in actual estuaries are, therefore, intermediate between those of an open seacoast and those in a uniform canal.