No well-defined procedure exists at present for the design of a
groyne system. Experience gained from field observations, model studies
and mathematical models is all used in the design of groynes to avoid their
failure and undesirable side-effects such as recession at the downdrift side
(Summers and Fleming, 1983).
15.2.4 Beach nourishment
Beach nourishment may be used as an alternative to the installation of, or
in conjunction with, groynes for the protection of shoreline. It is deployed
where the coastal areas experience loss of sediments without being replen-
ished by littoral drift or where the purpose is to create a wider beach for
recreation or land reclamation. Beach nourishment involves the supply of
suitable materials from quarries, mines or from offshore by dredging to
the shore and dumping at suitable places on the beach so that the sea
action will distribute them to shape the required beach profile. The
amount of material for recharge will depend on the rate of coastal erosion,
environmental requirements, required beach shape and onshore–offshore
movement of bed material. It is advisable to use material for beach nour-
ishment with properties like sizes and grading similar to the native mater-
ial at the beach. Usually flat average slope of beaches is made of finer
sediments. The quantity of material and hence the annual cost including
transport from the material source and dumping along the beach will
dictate the cost of recharging the coast. Computational and physical
modelling can give better understanding of the processes involved and
hence better estimates of the recharge volume especially for larger
schemes. Details of design of beach profiles with beach nourishment are
clearly set out in Simm et al.(1996). Reference is also made to Shore Pro-
tection Manual(US Army, 1984), Davison et al., (1992) and Dean (2002).
15.3 Wave forces on coastal structures
Coastal structures are defined as rigid, semirigid or flexible, according to
their rate of failure. A rigid structure exposed to a high wave might col-
lapse completely. The design wave height for rigid structures is the
average of the highest one-tenth of the waves. For flexible structures,
which very rarely collapse in their entirety, the design wave is the signific-
ant wave. Some damage to flexible structures is tolerated if the functional
requirements are not seriously lost. These design waves are chosen for a
specified return period (Goda, 1979).
Sea walls, breakwaters and other engineering structures have to
withstand the hydrostatic, wave and impact forces of the breaking waves.
636 COASTAL ENGINEERING
