Abstract: Monumented channel cross sections were resurveyed over a period of 20 years (1953 to 1972) to determine the amount and kind of change of channel area and position on a 3.7-square mile basin, Watts Branch near Rockville, Maryland. Despite a trend toward increasing cross-sectional area, the net result after 20 years was a channel smaller by 20 percent than it had been originally. Urbanization did not alter the rate of channel migration. Originally published: Geological Society of America bulletin ; v. 84 (June 1973). Leopold's address as retiring president of the Geological Society of America, Minneapolis, Minn., November 1972.