Migration of the Mississippi River

Migration of the Mississippi River

Shen, H.W.
Larsen, E.

TU Delft

DACW 39-87-C-0034

1988-07-01

The process of meandering has a powerful influence on man's use of rivers and river valleys. Flood control; navigation; bank protection; water supply projects; agricultural and urban development; transportation systems; and pipeline adjacent to rivers all require a sound knowledge of the meandering process, in order to he successful, with minimum expenditure and maximum environmental protection. There are three basic river patterns: straight, braided, and meandering. For yet unestablished reasons, meandering is the predominant pattern and thus, has received the most attention. A straight channel is rather rare, and pure braided rivers usually cannot provide navigation service. Therefore, this study has addressed meandering rivers only. In order to effectively study a particular river reach, the river's stability and possible channel movements must be evaluated. River engineers and geomorphologists usually examine both the aerial photographs and surveying maps of a particular river and try to decide potential channel movements. The results from this study provide useful information on the determination of projective meander migrations. The general scope of the project was to study the migrations of meandering rivers under natural conditions. Following from this scope there are two specific tasks: 1) to classify meandering planforms according to potential river evolution from the analysis of the surveying maps (made at different dates) of the Mississippi River; and 2) to investigate the predictability of future meandering evolutions for different types of meandering planforms. The authors defined four types of bends where they used the sinuosity to identify them. The sinuosity (M/L) is defined as the arc distance of the centerline of the channel between two inflection points (M) divided by the straight line between the same two inflection points (L). The types were defined as follows: Type I: M/L < 1.35 Type II: 1.35 < M/L < 1.95 Type III: 1.95 < M/L (subject to qualifications) Type IV: 1.95 < M/L (subject to qualifications) The distinction between Type III bends, which had two places of maximum curvature and a Type IV bend had to be made. To classify a bend as Type IV, the overall shape must have had a distinctive lobe feature. Intuitively, the bend has to have two lobes. In general, the sinuosity for Type IV must have been greater than for Type III, and also, the sum of the entrance and exit angles must have been greater than 200 degrees. The movement of bend types is complex. In general, bends progressed through the types successively from Type I to Type IV and the sinuosity increased from Type I through Type III. Retrogression of bend type occurred almost always because of a cutoff, either upstream or downstream of the cutoff. Two-thirds of the bends which began as Type I bends evolved from Type I to Type II in three time steps (165 years). Roughly two-thirds of the bends which began as Type II bends evolved to Type III bends after three time steps (165 years). These data did not include the evolution of bend type beyond Type IV because of the complexity in describing the movement. In general, after a Type IV, a cutoff occurred and the bend returned to a low sinuosity or Type I bend.

meandering
migration
river bends
sinuosity
evolution of bends
classification
river evolution

TKJ400400
TKJ400100

http://resolver.tudelft.nl/uuid:778967aa-2e57-4546-907e-f34b27153e62

USACE

36.576425, -89.509203

Contract Number DACW 39-87-C-0034

Hydraulic Engineering Reports

report

(c) USACE