How do the gradient and discharge of a stream change from its headwaters to its mouth?
The discharge for a single stream should not change much from
the headwater to the mouth. The exceptions to the mouth would be if
another stream joined the main stream, which would increase the
discharge or if you loose a significant amount of water to
infilitration, which would decrease the discharge. The gradient
should be high at the headwaters and gradually decrease downstream
where it should be low at the mouth. Of course differences in
lithologies or secondary streams can change the gradient for a
short distance, thought the overall profile should fit the expected
model.