Measurement of mixing characteristics of the Missouri River between Sioux City, Iowa, and Plattsmouth, Nebraska

Measurements of longitudinal dispersion, transverse mixing, channel geometry, and transverse velocity distribution were made in the Missouri River at a flow of about 33,000 cubic feet per second. The results show that the longitudinal dispersion coefficient for the 141-mile reach from Sioux City, Iowa, to Plattsmouth, Nebr., is about 16,000 square feet per second (approximately 5,600 U*d, where U* is the shear velocity and d is mean depth). The transverse mixing coefficient, Ez, for a 6-mile reach immediately downstream from Blair, Nebr., is about 1.3 square feet per second (approximately 0.6 U*d). The value of the longitudinal dispersion coefficient is one of the largest ever measured, and the value of the ratio Ez/U*d is approximately three times as large as that frequently reported for small straight channels.