the XVth International Navigation Congress of 1931 in Venice. The recom- 
mendation made at the Congress by Coen Cagli clarifies the German attitude 
as follows: "Each plan for coastal protection must be preceded by a 
thorough study of the locality and all factors acting on the formation of 
the coast and how much it is exposed; the action set up by waves, currents 
of various kinds, atmospheric precipitation, and by floating ice; the 
origin and nature of material constituting beaches and the regimen of river 
deltas; the situation and regimen of the aquiferous sheets of fresh water 
flowing toward the sea; the influence on the sea by new scructures when 
they project from the coast." It was further stated at the Congress that 
the causes of the effect of the sea on coasts should be substantiated. The 
German model experiments during this period were successful, and their con- 
tinuance under natural conditions was recommended, 
d. Construction Period 1931 to 1945 - A general reversal of 
coastal construction method took place during this period as nearly all of 
the groins on the North Sea as well as the Baltic Sea were built of steel 
sheet piling. The economic life of this type of groin structure is very 
short (10 to 20 years), particularly when single steel sheet piling is 
considered, The result of a series of investigations in coastal morphology 
carried out in this period opened wide vistas into coastal zone phenomena 
and brought out that the knowledge of forces involved in those processes 
is very limited. The demands for more intensive and systematic investiga- 
tions were thus substantiated. Differences were increasing between the 
practical builders, who believed in progressive success of groins, and the 
research engineers and natural scientists. Also, contradictory experiences 
and opinions were noticeable among the practicing professionals. 
e. Construction Period 1945 to 1960 - Dr. Petersen's survey 
covers both parts of Germany, East and West, with considerable reference 
to East German scientists and engineers, including governmental agencies 
and institutes of higher learning. Following World War II, the incoming 
information was at first very scanty, consisting mostly of reports on the 
use of asphalt for construction of groins. Ideas on the role of sea groins 
continued to be very controversial. They have to serve for current de- 
flection, beach protection and sand collection. It is confirmed by several 
authors that the groins fulfilled their role as coastal current deflectors. 
The groins failed as beach protectors and sand collectors, particularly on 
coasts with a deficient balance of sand. Following systematic experimental 
observation, it was found that the sand deficit could be balanced by arti- 
ficial sand replenishment. 
IV - EXPERIENCE ON SEAGROIN EFFECT 
The overall survey of experiences on the effectiveness of sea groins 
in Germany with special regard to engineering and economics is evaluated, 
indicating that controversy on the value of groins continues. Great 
progress in the structural strength of groins relative to stability and 
material does not prove their functional effectiveness which requires long 
periods of time for proper evaluation. 
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