CETN-III-10
groin's end). The SPM presents a method of estimating the maximum shore-
ward scour along the groin.
The groin should be extended into the back-
shore beyond the expected scour area, or anchored to a hard structure or
natural formation.
5. Spacing. The correct spacing of groins is often difficult to determine
and is a function of structure length and desired final shoreline shape..
If groins are too far apart, excessive erosion can occur between them. If
spaced too closely, they may not function properly to trap sand moving
along the shore. A general rule of thumb is to space groins 2 to 3 times
the groin length from the high water line to its' seaward end, but site con-
ditions can dictate use of the more complex design method detailed in the
SPM, leading to considerable variation from this rule.
The length, height and permeability are the most important parameters af-
They influence the amount of accretion and
fecting structural design.
erosion around the groin and the length of the groin exposed to wave forces.
Dynamic forces, which affects the structural design, are caused by waves,
currents, and the impact of floating debris.
The critical design condition
often is the static force of the soil-loading resulting from high beach
level on one side of the groin and a low level on the other side. Another
design force to be considered in colder climates is the horizontal and up-
ward thrusts by ice on the groin.
Planks
staggered
Groins are either sheet-pile structures
level datum
that depend on their ground penetration
r wale
for support, or gravity structures which
depend on their weight to resist over-
turning and sliding.
Sheet-piles may be
timber, steel, or reinforced concrete.
Figure 2 shows a typical timber
VIEW AA
sheet-pile groin. CETN-III-7
Round
(Bulkheads) presents some addi-
tional aspects of using sheet-
Planks
staggered
piles in the coastal zone.
Since
wale
the sheet-piles alone generally
PLAN
can not resist the lateral force
Timber Sheet-Pile Groin
Figure 2.
resulting from the differential
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