22
DELTARES, JANUARY 2014
OPTIMISATION OF DESIGN
FOR UNDERWATER SCREENS
Designs tested to scale in the Deltares research facilities.
S
alt intrusion is a major problem in densely-
populated deltas. Bubble screens can be
positioned at the bottom of a lock to counteract
this problem. A curtain of bubbles prevents the
water on either side of the lock from mingling too
much when the lock is open and this reduces the amount
of salt water that gets through to the land side of the
lock. The effect of the bubble screen can be enhanced by
installing a water screen alongside it. The second screen
injects fresh water at pressure, further reducing salt
intrusion: the mingling of salt and fresh water is reduced
by 85 per cent in this way.
Rijkswaterstaat asked Deltares to test the design for the
planned water screen in one of the two Krammersluis
yacht locks (in the Eastern Scheldt) and to work out
the correct internal geometry. This results in the water
flowing out in a uniform pattern across the entire width
of the screen, something that is crucial to achieve the
optimal effect. The water screen will be installed in the
lock in April, and tested from April to October.
FLOW OF FRESH
WATER TO THE
WATER SCREEN
THE FRESH WATER IS PUMPED
UP FROM THE CELLAR
MONITORING
EQUIPMENT
AN EMS METER IS USED
TO MEASURE WHETHER
THE WATER FLOW RATE
IS UNIFORM OVER THE
FULL WIDTH OF THE
SCREEN
THE TEST WATER
FLOWS INTO THE
CONTAINER, THEN
THROUGH THE DRAIN
ON THE RIGHT ON ITS
WAY TO THE CELLAR
DRAIN THAT CATCHES THE WATER OVERFLOW
FROM THE CONTAINER
IN REALITY, THE LOCK IS
9
METRES WIDE AND THE
WATER SCREEN CONSISTS
OF TWO SECTIONS. FOR
THE PURPOSES OF THE
TEST, ONE SECTION WAS
BUILT TO A SCALE OF 1:2
(2.2
METERS WIDE)
THE WATER FLOW
WHEN THE WATER
SCREEN IS OPEN IS,
IN REALITY, 400-700
L/S PER SECTION.
THE MAXIMUM FLOW
THROUGH THE SCREEN
IN THE SCALE MODEL IS
200
L/S
RESEARCHER
PEPIJN VAN DER VEN
THE WATER SCREEN
(
DRAWN IN RED) IN THIS
ARRAY IS BELOW THE
WATERFALL; IN REALITY,
IT IS AT THE BOTTOM OF
THE LOCK
PHOTO: DIRK HOL