Erosion has its place in the natural world. Rock, cobbles and gravel cascading from collapsing cliffs give rivers their meandering character. Rushing water uses boulders to scour silt, depositing it within streamside vegetation that armors embankments and provides habitat. Spawning trout make shallow nests in gravel streambeds. Beach sand is the final product of landslides washed to the seashore.
Humans use rivers and their materials far differently.
Dams that serve our insatiable thirst deprive fish and wildlife their share of water, while denying beaches needed sand grains that garner tourist dollars and protect seaside homes from storm-driven surf. But earthen material, used to make cement, brick and mortar, is essential in building cities and roads that keep us connected. Soils scientists believe the Earth's fertility is being eroded so fast that in 50 more years what's left won't be able to grow enough food for the hungry billions being added to the planet. And don't feel sorry for native fish and wildlife. That's what zoos and animal parks are for.