Water doesn’t run in a straight line, not even on your windshield.
Through coarse sediment, sand and gravel it can run in a braided pattern, but through soft, fine alluvial soil it runs in a meandering pattern.
Tim Carruthers made this aerial of a navigation canal cutting through the meandering bayous in the Louisiana marshes. I downloaded it from the Intergration and Application Network at the University of Maryland Center for Environmental Science.
A similar image, also made by Tim Carruthers, illustrates the marsh deterioration that happens along the banks of navigation channels, which invite salt water into brackish, intermediate, and fresh marshes, stressing them.
They also change the way water flows through the marshes. Spoil banks along east-west channels disrupt the southward flow of water. Marshes north of the spoil bank drown as water backs up a dam; marshes to the south are starved for fresh water.
South of Cocodrie along the Houma Nav, Louisiana reinforcement the bank of the channel to slow the wave wash from ships passing through the channel, which erodes the marshes. The shrub is a lone mangrove, growing on the edge of the marsh.