Inspired by the books and lectures of geomorphologist Ellen Wohl (Colorado State University), "Meander" explores how you can understand the health of a river by looking at its shape. In addition, it considers the various impacts of human activity on riparian (wetlands adjacent to rivers) ecosystems.
The overall thesis is that rivers naturally tend towards "complex" shapes, whereas human activity tends to straighten them and reduce complexity. For example, in their natural state, rivers will tend to move freely across valley floors, periodically overtopping their banks and fertilizing the surrounding forest. However, human transportation corridors are often developed alongside rivers, and thereby constrain them into narrow, straighter channels.
One result of this is that the surrounding forests are not replenished with the nutrients that large river floods provide, and start to degrade and die off. Additionally, the straightening of the river reduces the complexity under the surface, making the overall flow speed of the river more uniform. This is distressing for many fish species, as they depend on slower and faster moving water for various different functions during their life cycle.