Oxygenated, nutrient rich river water and what we do to it.
Hydrology of a river affects the ecology of the river and surrounds.
In the higher part of the rivers, it is fast flowing and unlikely that there will be much fish – more insects. The speed of the water oxygenates the water and erodes the banks bringing into the water essential nutrients. When the river slow down the sediment is left. The when the river floods this nutrient rich water carries nutrients onto the flood plains. In an area where the banks are covered with a rich plant life, the plants grows and dies and then releases its nutrients into the soil to be used again. About 90 million cu kms of water falls rain every year 70% onto oceans and 30% onto land and then into rivers.
If you want to see how healthy a river is, take a stone on the edge of the water and if you find little animals underneath that stone then that river is healthy enough to support life.
Dams change the hydrology. Stops the nutrients going down and alters the hydrology forever. Some dams stretch for hundreds of kilometres so the water moves very slowly in them. We lose the benefit downstream.
Over 50 000 dams in America. The Colorado river used to flow fast enough to create the Grand Canyon. Now it is so dammed that it reaches the sea as a mere trickle. They export about 90 million tons of fodder to China every year grown with that water. Effectively exporting their water.
When the flow of a river changes, the concentrations of sewerage and other toxins changes. Less water more or even the same toxins = more concentrated pollution rivers.
Water is becoming unusable. Belgium only treats 10% of its raw sewerage and puts the rest into the river. Germany and France and Holland not much better. Rhione and meuse unbelievably pollurted.The Rhine discharges into the North sea about 100 tons of heavy metals – lead, cadmium and copper.and about 30 to9ms per day of toxic chemicals. The Meuse is worse. Sections cannot be used at all. Another river in Poland is so bad that they cannot even use it for industrial purposes because it is so corrosive it chews up machinery.
UK now trying to clean up and a few fish have come back into the Thames.
The ecology of the river is damaged beyond repair/
The dams provide energy but the rains are diminishing so they are now having to choose between using it for hydropower or growing food with the water.
The energy of all the world’s rivers equals about 12000 nuclear power plants.
Climate change is affecting rivers. Floods and drought.