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| | From Sluice to pumping station. A unique Dutch approach to water management. |
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In spite of several decades of reliable operation, a drainage sluice in Othene, The Netherlands, was fighting a losing battle against increasing quantities of discharge surface water from Zeeuws Vlaanderen into the Wester Schelde. And rather than 'throw out the baby with the bath water', the ingenious solution was arrived at of converting the sluice into a pumping station. This project was unique, since it was the first time Flygt pumps have been built into an existing sluice. The conversion represented a saving of 85 percent, compared with the cost of building a conventional pumping station.
The othene drainage sluice
The Dutch town of Othene is to the east of Terneuzen where the Otheens Kreek flows into the Wester Schelde via a drainage sluice in the sea wall. The sluice was built in 1963 as part of a sea wall reinforcement. The Otheens Kreek covers an area of 60 hectares and all surplus surface water in the district is drained via this creek. Other water handled here comes from Belgium, thus the total water drained through the sluice comes from an area of 20,000 hectares.
Water management plan
The water management plan of 1972 assumed that the Othene sluice would be adequate well into the future. The target level of the creek was set at 1.6 m NAP (Normal Amsterdam Level). In 1972, the mean low-water level on the Wester Schelde at Terneuzen was 2.04 m NAP. The drainage sluice therefore discharged with a slight drop between 0 and 44 cm. As a consequence, sluicing time was short, usually no longer than 90 minutes during each low water period. The creek served as a buffer for storing surplus water.
It became evident that the Otheens Kreek had insufficient capacity. Due to improvements to the water courses, water flowed far more quickly to the creek. Improved drainage also increased the amount of water from areas behind the creek. Moreover, the mean low-water level on the Wester Schelde was now 12 cm higher than in 1972 (1.92 NAP in 1990).
Saving a 30 million guilder project
Under normal conditions, the sluice worked well. When the water level on the Wester Schelde rose, it usually coincided with additional rainfall. It was decided that the sluice would also have to discharge at high water to clear extra precipitation.
The board considered installing a pump outside the sluice, with a discharge pipe over the sea wall. The cost of the civil works for this solution - estimated at NLG 15 million - was far too high, however. The other alternative, although not entirely problem free, was to build a pumping station in, or in front of, the sluice complex.
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Four Flygt PL 7115, 200 kW propeller pumps await
mounting in their frames at the Othene site.
The contracting firm of Gebr. Simons and ITT Flygt bv built the pumping station and Flygt performed all the mechanical and electrical design work. The original drainage sluice consisted of three culverts in the sea wall. Each culvert measures 4 m wide and 3.25 m high and has three water dams with maintenance shafts. On the sea side, the dam comprises a storm gate used only in storms. Point gates fitted at the center are open for free discharging and closed when the water in the Wester Schelde rises above the catchwater basin level on the creek. A third stand-by gate is used in the event of a disaster situation. The estimated pumping capacity was 840 m'/h and a four pump arrangement was selected. A frame was fitted in two of the three culverts, each with two submersible Flygt PL 7115 pumps. When free discharging is used, the frame is hoisted with the pumps and water can pass through freely. A non-return valve was installed in the wall between the maintenance shaft for the point gates and pump shaft.
"Flygt's proposal was the most practical and the most economical."
If the water levels trigger the pumps, they carry the water up the pump shaft to a maximum height of NAP plus 3 m. The non-return valve between the shafts opens and the water is pumped out via the two shafts over the closed point gates. The point gates and frame seal the culvert well; otherwise the pumps would pump the water around.
Clog-free operation
A vertical duckweed barrier is raised and lowered with the pump installation. In free discharging, the barrier is raised to let floating dirt travel with the water to the Wester Schelde. Lifting this screen causes dirt to fall, eliminating both clogging and the need for screen cleaners. When the pumps start up, the barrier is lowered to prevent dirt from reaching the impellers. The entire operation is computer-controlled.
Higher pumping capacity
The solution with four Flygt PL 7115 propeller pumps offered a number of advantages, such as fewer structural adjustments to the sluice. Furthermore, a four-pump arrangement left the third drainage culvert free and provided a higher pumping capacity than the required 14.3 m3/s. The pumps, equipped with aluminum bronze propellers and 200 kW motors, have a nominal capacity of 3.8 m3/s. Thus, the entire pumping station's capacity - 15.2 m3/s or 900 m'/h, compared with the required capacity of 840 m3/h - is more than sufficient to discharge water when levels are high. If the creek level rises a maximum of 20 cm in heavy rainfall, the water is pumped away by the next day. The pumps on the two frames fit precisely into the existing recesses in the guard doors, so that no structural modifications were necessary.
"Converting the sluice has given us a full-blown pumping station at just 15% of the cost."
The conversion of the Othene sluice represented an investment of NLG 2 million (USD 1 million), which is only 15 percent of the cost for a conventional pumping station. The relatively short construction time was another advantage. During construction and conversion of the sluice, all other works were prefabricated for immediate installation. Operation has been perfect to date and the drainage pumping station - the only one of its kind in the Netherlands - is especially beneficial during the summer months when the water level in the creek can now be kept as high as possible, providing an ample supply of water to the region.
Technical data
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| Othene Pumping Station |
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| Application: |
Flood control |
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| Design |
Capacity: 15,2 m3/s |
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| Polder Pumps |
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| Type: |
Flygt PL7115 |
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| Duty: |
3,8 m3/s |
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| Rated power: |
200 kW |
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