a. Motive for Seagroin Construction - In most cases, seagroin 
construction was motivated by damages caused by storm tides and the dy- 
namic forces of the surge. Damages appearing at the foot of dunes and 
seawalls, as well as on longitudinal structures and on groins themselves, 
resulted from lee-erosion and the effect of currents moving progressively 
beachward. 
b. Current Groins and Beach Groins - Seagroins are of ‘two types; 
current groins and beach groins - each type having a different function. 
Current groins are current-deflecting structures and it has been proved 
that they are capable of fulfilling this role. Beach groins are expected 
to maintain the surge-exposed beach and improve it as much as possible. 
On certain beaches it is considered, with some reservation, that groins do 
retard the shore recession. The opinion on the role of beach groins varies 
from that on the unverified extent of the reduced recession rate (Success = 
1% to 99%), to that on maintenance (success = 100%), up to that on improve- 
ment of the beach (success > 100%). 
On transitional reaches which are influenced by rivers and inlets from 
the sea, and on surge beaches, groins may serve both the functions of cur- 
rent deflection and beach protection. Here the success can be assessed only 
when the beach groin performance is clarified. The German technical litera- 
ture does not yet provide a satisfactory clarification. Current-deflecting 
structures were constructed to an equal degree with those which would serve 
for beach conservation and improvement. 
c. Groin Types - Beach groins have been tested in nature in 
an unusual number of cases. From the original procedure on constructing 
groins as permeable structures, in the form of single or double-row pile 
groins or stone cribs and fascine groins, progress was made toward im- 
permeable massive stone groins, sheet pile groins of steel or reinforced 
concrete, and recently toward flat stone pitch asphalt grouted structures. 
Permeable and impermeable groins are found side by side in the same coastal 
reaches, The design of steel sheet-pile and reinforced concrete pile 
structures was apparently governed almost entirely by limitations imposed 
by structural engineering practices. 
d. Groin Length - Initially the length of the groins was deter- 
mined by structural engineering limitations. Only after the introduction 
of the steam pile driver did the groins advance into deep water. Already 
Germelman in 1881 (mentioned by Franzius) had used the jetting procedure, 
which was found very suitable for long piles (also sheet piling). The 
water jet was applied by appropriate equipment. Current-deflecting groins 
were constructed with good results, seaward up to and beyond the MTLW*, 
and also through stream channels. 
*Mean Tide Low Water - Symbol in use in German Hydrographic Service, 
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