I put the question out there on facebook, twitter and on our 40/29 weather blog. Everyone agreed it was a good question but no one knew the answer. The weather people at 40/29 told me I would need to ask a Hydrologist. So I search online for a hydrologist here in Arkansas and came up with a name in LR with the National Weather Service, but no email for him. So I emailed the head person and if they could forward it on... and they did. I received a reply email from Tabitha Clarke, The "Senior Service Hydrologist here at the National Weather Service in Little Rock" How cool is that??
and here is what she had to say about Cody's question.
My name is Tabitha Clarke. I am the new Senior Service Hydrologist here at the National Weather Service in Little Rock and would be glad to help you.
First of all, I think it's great that your son is asking questions at his age and very technical questions at that! Water is such an interesting thing. It is so vital for life and in the same instant...it can harm life. This is why we take such a great interest in it. We do look at stream flow, which is where I think his question stems. Streamflow is generated by all sorts of complicated equations, but it basically takes into consideration things like gravity and stream gradient.
Now, I took this question to mean 2 different things. I'm thinking there's a chance he may be referring to movement while he's in the water compared to watching it from the bank? The best way I could think to describe this is if he's in an airplane looking at another airplane traveling at the same speed it would not look like it was moving. Just like if you're floating in the water...the water does not seem to be moving if you turn and look directly at it, because it's moving with you. But, if your standing still on the bank you can plainly see the water moving. It's all relative to your perspective.
But as far as water movement, water is moving at differing speeds all through the column. Generally, it is slower near the banks and along the bottom due to friction and fastest somewhere between mid depth and the surface. Then, there are swirls, eddies, ect. These are generated partly by whatever object is underneath the water. All-in-all, it's a simple question without a real simple answer.
On another interesting note...and something that might interest a boy, is that dirt is a key factor in all of this! If there were no particles in the rivers/streams (such as sand, silt, pollutants), we would not be able to see the current.
Well, I hope I've been of 'some' help. I am a new parent and am excited for my son to get to the questioning stage. I think it's wonderful that you take such an interest in following up his questions. Best of luck to Cody!
-Senior Service Hydrologist-
PS If he continues to show an interest in rivers, you can direct him to our rivers/lakes page. From our website, http://www.srh.noaa.gov/lzk/ click on rivers/lakes on the left hand side. You can then click on any of those points along the rivers to see a hydrograph. Lots of fun information there!