Pneumatic barriers to reduce salt intrusion through locks

Pneumatic barriers to reduce salt intrusion through locks

Abraham, G.
Van der Burgh, P.
De Vos, P.

Rijkswaterstaat

1973-01-01

Extensive areas in the low-lying parts of the Netherlands are below average sea level. They are divided up into polders in which the water levels are controlled by pumping. The water that seeps upwards in the soil together with surplus rain water is pumped into canals encirc1ing the polders; the canals are linked and serve as collectors, the water level in most of which are a few decimetres belowaverage sea level. Formerly, the water in the 'collector' eanals was discharged into the sea through sluices which were opened for the purpose while the tide was running out. This natural method of getting rid of the surplus water has now been partly replaced by pumping. The 'collector' canals have always served more than one purpose. Their function as waterways is seeond only to that of disposing of surplus water. Constant improvement of the drainage side of the system has led to the inereased use of the eanals as waterways, which in turn has necessitated keeping the water in the canals up to a certain level; to achieve this, the polder water in the canals has to be supplemented from some other source. The increasing density of the population, more intensive use of the soil and industrialisation have been making water management in the 'collector' canal regions an inereasingly exacting task in the last few decades. One of the criteria by which the quality of the water in the canals is judged is its salt content. The eanal water is in danger of becoming saline because the salt water seeping up through the polder soil is pumped into the canals so that it may run along them into the sea. Salt water also reaehes the canals from the sea; it eomes in through the locks as ships enter. Any sea water that gets into a canal ean spread over a wide area because of the difference between the density of sea water and that of the water pumped from the polders into the canal. The means by which this intrusion of sea water through locks can be controlled and their efficacy are dealt with in this issue. The 'pneumatic barrier' is the chief expedient described. The pneumatic barrier is the outcome of several sets of experiments carried out in locks. The first set was conducted in the middle Loek at IJmuiden in April 1961. The next was carried out in a loek in the Zuyder Zee Barrier Dam at Kornwerderzand in September 1961. Lastly there were experiments in the Southern Loek at IJmuiden, in the middle Loek at IJmuiden a second time and in the Western Loek at Terneuzen. The experiments were most useful in that they provided material for treatises on the hydrodynamic aspects of pneumatic barriers for locks (see Chapter 6) and on the design criteria (see Chapter 7). The experience gained with pneumatic barriers at IJmuiden over a period of years is described in Chapter 8.

salt intrusion
navigation lock
air bubbles
salinity
salt barrier

TLE250400

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Rijkswaterstaat

Rijkswaterstaat Communications 17

Hydraulic Engineering Reports

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© 1973 Rijkswaterstaat