The plant storm drain outfall piping ran under the road and remained buried under the parking lot before draining into the river. About 30 years ago, the plant needed to install a flowmeter to measure the storm drain flow where (as best as I recall) flow could vary from less than 20 liters per minute in dry weather to almost 4,000 liters per minute during a driving rain storm.
Open-channel flowmeters were and are commonly used to measure outfall flows, in part because they can measure over a wide range of flowrates. A hole was dug for a pre-fabricated FRP Parshall flume that was embedded in concrete at the far corner of the parking lot approximately 5 meters from where the storm water pipe ended (at the river) and more than 50 meters from the nearest source of electrical power.
A solar cell system was installed to power the flowmeter because digging up the parking lot to install a conduit for electrical power was deemed too expensive. Solar cell systems were not nearly as sophisticated 30 years ago as they are now and, within a few days, it was apparent that the liquid in the batteries was repeatedly boiled off due to overcharging. This was resolved by installing an inexpensive automobile voltage regulator. In addition, the dirt particle buildup in the flume required that it be swept clean every week.
Today’s approach would be strikingly different—less expensive, simpler, and easier to maintain. A cartridge meter would simply slip into the end of the existing outfall pipe without the need to dig a hole and without concrete work. Mounting the electronics with a modular solar power system would complete the installation. Maintenance would be reduced because weekly cleaning would not be necessary.
Sometimes it takes long-term reflection to recognize how much progress has been made.
Mr. Spitzer can be reached at 845 623-1830 or www.spitzerandboyes.com. Click on the “Products” tab to find his “Consumer Guides” to various flow and level measurement technologies.
