FORM FIVE SELECTIONS 2021** FORM 5 JOINING INSTRUCTIONS
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Shore protection
In area affected by excessive
sediments loss, Nordstrom and Allen, (1980) have recommended the following
protection measures:
i)
Groynes: These are
barriers to movement of sand along the shore. They are intended to reduce the
rate of longshore transport of sediment.
Creates wider beach on up drift side and starves down drift side.
Groynes are constructed perpendicular to the shoreline using stone, rip rap, concrete,
wood, sheet pile or gabion mesh baskets filled stone or nylon bags filled with
sand or grout.
ii) Bulkheads: Prevent undermining and slumping of
backshore surface. Protect backshore from attack by swash and small waves.
Stabilize the shoreline position. Do not
favour beach creation. The bulkheads are constructed parallel to the shoreline
at the contact between the beach and upland using the same materials as for
groynes.
iii) Sea walls (dykes): Prevent attacks of backshore by
large waves and stabilizes the shoreline position. Do not favour beach
creation. Usually made using concrete or rip rap. Constructed in the same way
and position as bulkhead.
iv) Breakwaters: Energy filter designed to dissipate wave
energies and reduce erosive effects of waves. Energy shadow favours deposition
from up drifted sources and starves beach on down drifted side. Constructed of mainly stone riprap. These days even floating tires, plastic reeds
attached to concrete base are also used.
Construction is made offshore to facilitate wave’s refraction without
breaking or to reduce wave energy before striking the beach.
v) Planting vegetation: Vegetation stabilizes slopes and makes unconsolidated
sediment more resistant to erosion. On the other side, vegetation reduces wave,
swash and wind energies, traps sand and improves habitat.
vi)
Sand replenishment: It requires sufficient sand
reserve at the beach to replace any losses of sediment and at the sometime
to act as barrier against flooding.
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