tion have been the sole aims of hydraulic
engineering projects. The combat against
salinity began later. It was only in the Sixties
that interest in environmental aspects was
awakened. This awareness has drastically
influenced the planning and, particularly, the
subsequent management, of the areas in which
these projects were realised. Throughout the
world, where coastal defences are being built,
it appears that a completely different measure
of integration prevails with regard to ecology
in civil engineering planning. In the course of
their execution, the Delta Works themselves
have undergone a remarkable development;
from a purely civil engineering first stage via a
transitional phase to a final stage of integration
of several authorities.
Investigation of salt marshes in the Oosterschel-
de estuary
After partial closure of the Oosterschelde and
the construction of the compartment dams, a
large section of the basin will be tidefree and
fresh whereas, in the remaining area, the
primary conditions will change considerably.
How will this affect the salt marshes? To
answer this question, insight into the prevailing
morphological developments is necessary. For
this purpose, many measurements have been
taken at a number of test sites over a long
period of time. In particular, the wave move
ment, caused by long windfields, proved to be
of vast importance. The development of the
edges of the salt marshes depends on the
interaction between the hydrodynamic environ
ment and the soil mechanical and soil scientific
parameters e.g. critical strength, roots, density
and composition.
The Hansweert locks and the canal through
Zuid Beveland
The locks at Hansweert in the canal running
through Zuid-Beveland serve also as a primary
coastal defence. They do not however meet the
Delta requirements for such constructions. Even
the East lock from 1916, the newest and most
frequently used of the three, is a source of
some anxiety. Not only high water levels, but
also the water pressure effecting the inner head
with ships passing through or else an accidental
collision could endanger the lock. Depending
on hydraulic conditions at that moment a
collision could be critical on this canal whose
dikes also do not meet the requirements.
While awaiting replacement of the old locks
measures to diminish the risks are being
investigated.
282
