Flow
wasn't quite as strong today, but it could be once all the rain from
last night soaks through the ground and makes its way into watercourses.
This video was from October 2015 after a long, wet autumn. The water
level was up to the 4th rung from the top of the ladder (half a rung
spacing lower today in the video at the end of this post). At some stage, I want
to do back-of-envelope calculations to see what the max energy output
would be if the stream was harnessed. Kinetic energy can be calculated
simply by measuring width, depth and speed of the flow to get cubic
metres per second and working from there. Surface speed could be checked
by timing how long it takes something floating on the surface to pass
between two points. Speed wouldn't be constant from surface to bottom of
the flow or from centre to the banks because of friction, but the
streambed under the bridge is smooth and level, as are the walls, so
velocity profile is known for such shapes (This is effectively a
rectangular weir, used by the EPA to do hydrometric measurement).
Data for the "Kilcullen Stream" is available here on the EPA's HydroNet website. (Isn't this the "Mill Stream")?
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| Data available on the EPA's HydoNet website. Image courtesy EPA. |
What's the tube at the side of the bridge?
This is the stilling chamber of what's called a gauging station
by the EPA. The stilling chamber is used to make the surface of water
less turbulent so that stream level can be measured with an ultrasonic
sensor (which needs a level surface to get a reliable echo for measuring
distance). I'm not sure whether they actually use a logger here to
measure levels continuously. There's no antenna for telemetry, so
possibly data is downloaded every so often or more likely transmitted
using a GSM modem over the mobile phone network. A Yuasa type battery
would power a setup like this because the electronics only has to wake
up every 15 minutes or so, take a measurement and then go to sleep
again. (Similar to the way a wireless doorbell sounder only wakes up
every second or so to detect a button push). There's also a scale at the
station for taking manual depth measurements.
More information about the EPA's National Hydrometric Programme is available here.
More information about the EPA's National Hydrometric Programme is available here.