What happens to water if you increase the hydrogen content in it?
It turns into an acidic solution-has more H+ ions. Just guessing.
When a river is in flood (in spate) the extra volume of water means an increase in the force the water that can exert on the river banks and river bed. There is also an increase in the silt content of the water, which means that in the lower reaches, where it may be calmer, there is an increase in deposition of the silt.