It's not like the government is just containing the river for fun - they are containing it because huge investments have been made along its current banks, and

It's not like the government is just containing the river for fun - they are containing it because huge investments have been made along its current banks, and to just let it run it's course would destroy billions of dollars of value permanently(because other groups would not invest in the new water course if it could change again after 20 years leaving them high and dry).