On Sunday my sister, Mum and I went for a cycle to Dryburgh Suspension bridge, we met my Dad and little brother there. I wanted to find out the volume of water under the bridge.
I used a trundle wheel to measure the width of the River Tweed at this point by looking through the little gaps in the bridge while walking over it. It was 44.6m across. I used a tape measure to measure the width of the bridge, it was exactly 2m. Then using a bit of heavy metal and a piece of cable we dropped it in and measured the depth by measuring the wet part on the metal. I measured the water depth at 4 different points across the river then calculated the average depth to be 0.61m. When I got home I multiplied the depth by the length by the width to calculate the volume of water under the bridge and it was 54.4m3.
We also threw in a stick and timed it floating under the bridge, it took 4 seconds. There are 60 seconds in a minute so the stick could travel under the bridge 15 times in one minute. That means every minute 816m3 of water flows under the bridge, I calculated this by multiplying 54.4m3 (the volume) by 15.
