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Mixing of a Stratified River by Barge Tows
Author(s) -
Stefan Heinz G.,
Riley Michael J.
Publication year - 1985
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr021i008p01085
Subject(s) - barge , hydrology (agriculture) , outfall , inlet , stratification (seeds) , flume , geology , environmental science , hydraulics , plume , geotechnical engineering , marine engineering , meteorology , flow (mathematics) , geomorphology , mechanics , engineering , seed dormancy , botany , germination , physics , environmental engineering , dormancy , biology , aerospace engineering
The effect of commercial navigation (barge tows) on the mixing and the reestablishment of a stratified river has been measured in the upper Mississippi River downstream from a major wastewater effluent site. Observations have also been made in a laboratory flume. Mixing effectiveness increases from single towboats to unloaded barges to loaded barge tows. Energy expenditure by barge tows per foot of river length traveled is much larger than work done by gravity forces of the free‐flowing river to overcome bottom shear. The displacement of water by loaded barge tows appears to be more significant than the jet effect of the towboat propellers. One passage usually produces complete vertical mixing in the path of the tow; an entire cross section (700 feet × 11 feet (213.4 m × 3.4 m)) will be fully mixed by two or three passages. Surface waves and internal waves generated by a towboat passage cause surging of the effluent for up to 30 min after passage. Reestablishment of a stratified river is controlled by mean river velocity and the frontal velocity of the density current (underflow or overflow) resulting from the discharge. Calculated and observed reestablishment times depend on distance from the outlet and strength of the stratification. Order of magnitude comparisons of calculated and observed reestablishment times were in good agreement. Reestablishment of stratification may take from 15 to 45 min at a distance of only 1000 feet (304.8 m) from an outfall. Water quality models and field studies in impounded rivers with high navigation frequency must account for mixing and transport effects of towboats, particularly under low flow conditions.