Stream Velocity Rod – The Low-Cost, Low-Tech Tool That You Need in Your Field Truck
There are several highly sophisticated technologies available for measuring streamflow.
However, no amount of electronic wizardry will guarantee that you come home with a good discharge measurement. There are many things that can go wrong such as the electrical power or electronic communication between the system components. In the event of an electronic failure, you are up the creek without a paddle because these devices are so expensive that no one can afford to carry a spare.
Robin Pike’s low-cost, low-tech, ultra-reliable modified Transparent Velocity Head Rod was my favorite presentation at the North American Stream Hydrographers (NASH) symposium at CWRA 2016. I love the elegance of hydrometry being done the same way it has been done for millennia, by an observer putting a stick in the water to judge how deep and fast it is. I love the reduction of hydraulic theory to this most fundamental transformation of Head to Velocity.
I love that a few supplies available at any hardware store, combined with bit of ingenuity can compete with the best that modern technology has to offer.
How well can it compete? Very well. Robin and his cohorts conducted over 2400 paired measurements in 13 streams with 7 users and got very close agreement with FlowTracker measurements and they have published the results this investigation in the Canadian Water Resources Journal.
As with any technology there are limitations. It is only suitable for wadeable streams with laminar or semi-laminar flow. The range of depth has to be from 5 to 75 cm. The velocity range needs to be from 0.1 to 0.9 m/s (i.e. 2 to 100 mm of head).
Subject to these limitations, Robin has invalidated every excuse a hydrographer could think of for coming back to the office without a good measurement. A Stream Velocity Rod should be standard equipment in every field truck. If you are particularly good at looking after your electronic gear, you may never need to use it but you should always have one, or know how to make one, just in case.
“We have a big need for these concise guides for the infrequent, seasonal field staff. Particularly for the mid-section applications. This Manual helps you simplify and get across the essentials without losing the need to always learn more.” – Robin Pike, Watershed Research Hydrologist, BC Ministry of Environment