I am writing an intro physics problem about a flowing stream. I am going to assume that all of the gravitational potential energy eventually becomes thermal energy of the water. I haven't worked it yet, but I'm pretty sure the flow rate and g will both cancel out and give me a constant change in temperature per unit of elevation change. Is there a specific name for this phenomenon? How reasonable of an assumption is this? Some energy must go into eroding rock, making noise, etc.