STAGE VARIABILITY OF THE MISSOURI RIVER AS RECORDED BY LEWIS AND CLARK

The journals of Meriwether Lewis and William Clark during the 1803-1806 Corps of Discovery contain detailed records of meteorological conditions and Missouri River stage levels for the winter camps at Camp DuBois (1803-4) at the mouth of the Missouri, and at Fort Mandan (1804-5), now in North Dakota near river mile 1372. Their measurements provide unique insight on the Missouri River prior to the profound modification of its channel by the Army Corps of Engineers starting in 1832, the regulation of its flow by six huge main-stem reservoirs constructed between 1937 and 1963, and the profound changes to its watershed following European settlement. Lewis and Clark’s data can be used to define daily changes in stage that can be compared with modern stage variability at gauging stations at St. Charles (mile 28) and St. Louis, MO (below confluence) and at Washburn ND (mile 1355). The modern Missouri River near St. Louis shows greater average daily stage change and greater standard deviations (St. Charles: 8.5 ± 14.4 inches; St. Louis: 9.1 ± 11.1) than did the river mouth at Camp DuBois in winter 1803-4 (5.0 ± 5.2 inches). The opposite trend is exhibited at Washburn where modern daily stage variability (1.0 ± 1.3 inches) is quite small compared to that observed at Fort Mandan in 1804-5 (4.1±7.1 inches). In the first case, the ~2x greater modern stage variability is due to profound constriction of the channel width by wing dikes and levees. For example, Lewis and Clark measured the river width near St. Charles as 720 yards in May 1804, where it is only 500 yards today. This channel constriction is widely recognized to be related to increases in flood stages of 4 to 9 ft. on the lower Missouri (Criss & Shock, Geology 2001). In contrast, the decreased modern variability seen in North Dakota is clearly due to regulation by huge, proximal, main stem reservoirs. Clearly, flow regulation by these main stem reservoirs and numerous others on tributaries does not fully offset the large increases in flood stages and greater stage variability caused by channel restriction and development in the lower basin.