Velocity of the Porterbrook

So we set out today to measure the velocity of the Porterbrook.  According to the Geography site - helpfully pointed to by google, they suggested some simple methods for measuring Velocity using an orange as a float,a nd measuring the side of the river and doing some simple calculations  So that is just what we did.

We went to the place  we were at last friday whilst taking sound samples, and set about our experiment.  

1. Set out our tape measure along the length of the river for 5 metres (the instructions were 10 metres, but as the area was pretty rocky, I felt that there was a large margin for error with greater length.)
2. Asked Autumn to sit at the furthest downstream ready to shout STOP when the orange passed her
3. Asked Evan to drop the orange a little further upstream from the start point to give it chance to go with the current.
4. Asked Evan to shout NOW when the orange passed the starting point.
5. I timed this.
6. we repeated it, and tabulated our results 5 times.

Here is the first spot we used.

The results are here
1    25 seconds
2    34 seconds
3    42 seconds
4    45 seconds
5    23 seconds
Average  33.8 seconds    SPEED = 14.8 cm per second (cm/s)

Then we made a few measurements of width and depth at various points along the length, and also the deepest and shallowest points, and widest and narrowest points.

We moved further downstream and found ourselves doing it all over again.

After a few tries we realised that the results were getting unnaturally skewed and not representing the velocity of the river, rather the length of time the orange took to travel that distance, which varied according to whether it got caught in an eddy, or pushed down by a mini waterfall, or got sucked back because of a waterfall, or simply got stuck on a rock as it was very shallow at points.  So I changed how I was working,and paused the timer each time it paused due to one of these circumstances, allowing a more accurate measurement of actual velocity of the flow of the river.

Here are our Second set of results
1   17s
2   18s
3   28s
4   26s
5   17s
6   15s
7   25s
8   14s
I took just the results where I had been mindful of stoppages - in bold
Average = 17.67s
SPEED = 28cm/s

And finally, now that our methodology was improved, we moved downstream and did another set of experiments.

Results
1  19s
2  15s 
3  18s
4  18s 
5  18s
Average = 17.6 seconds
SPEED = 28.4cm/s

Average Time = 23 seconds
Velocity = Distance / Time  = 500cm / 23s = 21.7cm/s

Variance in Depth = 13cm   Shallowest = 2cm Deepest 15cm 
Variance in Width = 144cm Widest = 180cm  Narrowest =36cm

After this last video we decided to let the orange travel further and follow it.  This was fun, and it did get stuck a few times along the way, and unfortunately we lost track of it a bit as the terrain was a bit complex alongside the river.  This took us to a little spot where Evan wanted to make changes to the flow of the river by opening bits up and daming other bits.  Autumn got involved, and they had an awesome time, until the dark began to creep in and it was time to go home.

Another lovely River project day. :)