Mjrf AIDS BUM
IK DIKE REBUILDING
Prof.Thysse's 'Toy' Rhine Delta
Cuts Day to 5 Minutes for
Study of Winds and Tides
Special to The New York Times.
DELFT, the Netherlands, March
9 (by airmail)The closing of the
first big gap in the Dutch sea de
fenses - a 175-foot hole in the dike
near Hellevoetsluis on the island
of Voornë—went like clockwork.
As hundreds lined the dike on
1 both sides of the hole to watch, a
[huge caisson was eased into place j
by tugboats, held in place by ca-
i bles attached to winches and then,
I at the precise moment between ebb
and flood tide, was scuttled. Wait-
ling dump trucks and steam shov-
els began piling rocks, clay and
I sand onto this foundation to re
build the dike to its normal level.
The precision of the operation
Iwas mainly due to two weeks of
rehearsals here on "Thysse's toy" j
1an exact scale model simulating
tide and wind factors that let the;
engineers know just what to ex
pect, where to place the tugs, how
strong- to make the cables and how
to attach them.
Day Out to Five Minutes
''Thysse's toy" has been operat
ing for fifteen years, but the Feb
ruary floods have given it an emi
nence that no one had expected.
It is more formally known as the
Delft Hydraulic Laboratory, super
vised by Prof. Jan. T. Thysse,
leading Dutch expert on the me
chanics of water.
A 180-foot model contains, in
exact scale, the system of coast,
land and waterways that make up
the Dutch Rhine delta. Telescoping
time as well as space, the en-!
gineers and students have reduced
a day to five minutes. They can
reproduce any tide and storm ef
fect and examine its effect on the
Dutch water defenses. They can
and dolet loose a flood exactly
like the one that struck the Neth
erlands Feb. 1, to see where the
weaknesses are.
The model is a key in the study
being made to determine how to
strengthen the defenses. In the
next two years every conceivable
combination of higher dikes and
great dams to close off North Sea
outlets will be tried and the effects
minutely recorded by researchers
making observations when a horn
'toots every twelve and a half sec
ondsdenoting the passage of an
hour.
Parliament to Decide
"Hundreds of problems will
arise," Dr. Thysse says, "and we
shall have to answer them. The
Maris Commission [appointed by
the Government and headed by
August G. Maris, Director General
of Waterways] will then make its
report and after that Parliament
will have to decide what is to be
done."
The laboratory, he says, will not
make any recommendations itself,
but only give its readings to pre
dict the effects of any system at
tempted. The final decision will
entail a study of financial and
other factors with which the
laboratory is not concerned.
But, from the reports of the
laboratory, the commission will be
in a position to know what lands
will be flooded at given water lev
els, and under specified storm con
ditions.
Aside from the over-all delta
model, the laboratory is building
separate models to guide the work
of dike reconstruction. The first
was the model of the Hellevoetsluis
dike. Now a model is being built
of a 760-foot breach at Sehelphoek
on the island of Schouwen, whose
repair is expected to be one of the
most difficult of all the 100-odd
big breaches resulting from the
Feb. 1 flood.
V X
