About the author: Bob Langie is general manager for MJK North America Inc. He can be reached at [email protected].
Being that 40 percent of its land is below sea level, Holland is well known for its potential for flooding. Storm flow management is critical in this region.
Beyond facing the traditional issues of moving storm water away, the country must achieve system-wide accuracy for the precise pumping of storm overflow to open waterways. At stake is the cost of moving the water and the possibility of overwhelming neighboring channel. The ecology and infrastructure costs for storm flow mismanagement must be considered too.
Hoogheemraadschap Hollands Noorderkwartier (HHNK), the second largest waterworks operation in Holland, hired MJK Automation to develop a calibration system of instruments to greatly improve the flow measurement accuracy of regional pump stations northwest of Amsterdam. The partnership's ultimate goal was to gain better accuracy for the flow measurements and have an ongoing process for verifying accuracy and adjusting flow calculations.
The Construction
Early on, HHNK had used models in combination with rainfall recordings, but the old models were no longer up-to-date. "That's why we have entered the picture," said MJK Automation BV (Netherlands) area sales manager and project leader Richard van den Ing.
A high-tech 27-ft container was designed and built to precisely simulate storm flow measurement overflows in pump stations. This 1:1 dimensional model could be configured and equipped to mimic the storm flow measurement location. It served with an artificial pond as a water reservoir and created flows with two large 2,500-cu m/hr pumps.
Flow Calculation
"Before the water enters the container, it passes through an MJK flowmeter that provides an accurate flow measurement," van den Ing said. "After that, a curve is calculated showing the flow as a function of the water level, and, based on that, the municipality can install the required level transmitters. The recording of the overflow is then calculated with high accuracy on a computer."
The calibration involves a step-by-step downward flow adjustment. In this way, the pump first adjusts from 2,500 cu m/hr to 2,000 cu m/hr, and then it adjusts further down in fixed steps. Each measurement takes between 20 and 30 minutes. Everything is connected to an advanced monitoring system, along with a series of other MJK units; all together, this setup provides Dutch municipalities with the flow data they need to curb flooding issues.
HHNK obtains certified measurements and data that can be logged at a relatively high frequency with an accuracy better than 1 mm. This information is passed to the flow measuring location for which it was calibrated, and the storm flow measurement instrument design and the level of measurement versus flow calibration curves are applied to achieve an accurate reading.
Test-Site Verification
MJK had served HHNK on previous projects. "Our MJK level transmitter Type 3400 was accuracy-tested on location at the town of Petten using a so-called measuring needle from Waterloopkundig Laboratorium Delft, which is a part of the Technical University in Delft," said van den Ing.
A measuring needle is a metal pin that is calibrated to an exact level to detect the moment the water in question touches it. This level is then simultaneously compared with the output from the MJK 3400.
"The MJK 3400 Level Transmitter was found to consistently measure with an accuracy better than 1 mm," van den Ing said. "The whole idea with this test bench and storm flow test tanks and machinery is, over time, to reduce the cost and to simplify hundreds of storm flow locations not only in the local county but all over Holland."
Prioritizing Pays Off
Storm flow measurement, though important in many regions worldwide, is of the highest priority in Holland. The nation seems to have to move water perpetually just to keep dry, even without the added burden of storm water.
Holland's dedication to getting this critical storm water measurement as precise as possible will no doubt generate many long-term benefits. For a country better known for its windmills, wooden shoes and tulips, this unique project has paved the way for making storm water headlines. This unique calibration and measurement approach will reduce storm flow uncertainty and related economic and ecological costs.
