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- 1. GUIDED BY :- PROF. S. G. ADHAU PRESENTED BY :- NISHAD A.
WANKHADE DEPARTMENT OF CIVIL ENGINEERING,
- 2. Introduction Beach nourishment also referred to as beach
restoration or beach replenishment describes a process by which
sediment (usually sand) lost through erosion is replaced from
sources outside of the eroding beach. A wider beach can reduce
storm damage to coastal structures by dissipating energy across the
surf zone, protecting upland structures and infrastructure from
storm surges, tsunamis and unusually high tides. Nourishment is
typically a repetitive process, since it does not remove the
physical forces that cause erosion, but simply mitigates their
effects
- 3. The first nourishment project in the U.S. was at Coney
Island, New York in 1922-23 and is now a common shore protection
measure utilized . Nourishment gained popularity because it
preserved beach resources , widens the beach , and protects the
shore from floods . Nourishment creates a soft (i.e.,
non-permanent) structure by creating a larger sand reservoir,
pushing the shoreline seaward . Hence , people get to use beach as
a recreational purposes .
- 4. Why it is necessary ? More than 70% of Earth's shorelines
are retreating due to rising sea levels. As shorelines move
landward, structures located on or near the beach may be in danger
because floods or tsunamis will have more severe effect and they
will be destroyed. In addition , beaches may not seem attractive to
people and hence , communities may lose significant amounts of
income if they lose the use of their beaches
- 5. For a good nourishment , the purpose of the nourishment has
to be clearly defined. In general, there are three reasons for
beach nourishment: 1. combatting coastal erosion (chronic erosion)
2. preventing flooding (safety) 3. maintaining a wide recreational
beach.
- 6. Causes of erosion Beaches can erode both naturally and due
to human intervention . Erosion is a natural response to storm
activity. Some beaches do not have enough sand available to coastal
processes to respond naturally to storms. When there is not enough
sand left available on a beach, then there is no recovery of the
beach following storms. Many areas of high erosion are due to human
activities. Reasons can include , coastal structures like ports and
harbors that prevent longshore transport, dams and other river
management structures.
- 7. Requirements for effective nourishment Sediment texture
(grain size and sorting) is critical for success. Sand fill must be
compatible with native beach sand. In some cases, beaches have been
nourished using a finer sand than the original . Monitoring reveals
that storms can erode such beaches far more quickly than the
natural beach . Projects that did not match grain sizes performed
relatively poorly. Nourishment sand that is only slightly smaller
than native sand can result in significantly narrower equilibrated
dry beach widths compared to sand the same size as native
sand.
- 8. Evaluating material fit requires a sand survey that usually
includes geophysical profiles and surface and core sample . This
was observed at the Waikiki nourishment project in Hawii . The
selection of suitable material for a particular project depends
upon the design needs, environmental factors, transport costs
considering both short and long-term implications.
- 9. How Beach Nourishment works - During a beach nourishment
project , a large volume of beach-quality sand , called beach fill,
are added from outside sources to restore an eroding beach . or a
beach where only a small beach , or beach existed . Ultimately,
beach nourishment widens a beach and advances the shoreline seaward
. Beach nourishment projects are designed and engineered to work
like natural beaches , allowing sand to shift continuously in
response to changing waves and water levels .
- 10. This sand once placed gets redistributed gradually by
natural processes . Ultimately , the wider , nourished beach ,
which slopes gently downward below the shore by acting as naturally
protective buffers . Engineers may decide to place the beach fill
as 1] directly on the beach ,also called as profile nourishment ,
2] or as dunes also known as dune nourishment .
- 11. Profile Nourishment Beach Profile Nourishment describes
programs that nourish the full beach profile. In this instance,
"profile" means the slope of the uneroded beach from above the
water to well out to sea, not just the visible portion. The Gold
Coast profile nourishment program placed 75% of its total sand
volume below low water level.
- 12. Profile Nourishment
- 13. Dune Nourishment Dune nourishment is particularly effective
in protecting upland development against storm waves. The placement
of material high above the waterline does not expand the width of
the dry beach, However, and therefore is not appropriate when the
enhancement of recreational opportunities is an important project
objective
- 14. Dune Nourishment
- 15. Before Nourishment After Nourishment
- 16. Advantages : 1. It widens the bed 2. Structures behind
beach are protected as long as the added sand remains. 3. Most
importantly, beach nourishment reduces the detrimental impacts of
coastal erosion by providing additional sediment which satisfies
erosional forces.
- 17. DISADVANTAGES : 1.Beach nourishment sand may erode .
2.Beach nourishment is expensive, and must be repeated
periodically. 3.The beach turns into a construction zone during
nourishment.
- 18. Alternatives to nourishment Nourishment is not the only
technique used to address eroding beaches. Others can be used
singly or in combination with nourishment, considering economic,
environmental conditions Structural approach is one alternative to
nourishment . It is divided into two types :- 1) Hard structures ,
which includes , wood and rock groins, seawalls, revetments and
breakwaters . 2) Soft structures , which includes sand bags
,geotubes ,planting vegetation .
- 19. Seawalls :- Seawalls are normally constructed of rock and
concrete . Seawalls protect property and infrastructure from wave
assault . Results in no sandy beach and requires long- term
maintenance .
- 20. Groines :- It runs perpendicular to the shore . It lowers
or breaks the energy of wave . Thus it prevent the shore from
erosion .
- 21. Soft Structures Sand Bags Sand bags are kept one on another
as shown in figure . They are more of a temporary emergency
feature
- 22. Geo-tubes :- Geotubes consists of sacks made by geotextile
that are filled with sand or gravel . Geotubes are more durable
emergency protection features which serve as dune cores . . This
anchors the sand and sediment,It is not recommended for continuous
exposure to high wave energy environments . Planting Vegetation :-
This is also called as soft stabilization , because it does not use
a structure . This anchors the sand and sediment, which slows
erosion caused by wind and waves. Because these methods use only
organic materials, the aesthetics and natural habitats of the beach
are maintained .
- 23. Beachface Dewatering Beachface dewatering basically
consists of continuously pumping water away from the beachface. Wet
beaches tend to lose sand. Waves infiltrate dry beaches easily and
deposit sandy sediment. Beach drainage (beach dewatering) uses
Pressure Equalizing Modules (PEMs) allow the beach to drain more
effectively during tide. Fewer hours of wet beach translate to less
erosion. Permeable PEM tubes inserted vertically into the foreshore
connect the different layers of groundwater. The groundwater enters
the PEM tube allowing gravity to conduct it to a coarser sand
layer, where it can drain more quickly .
- 24. New techniques Rainbowing technique - Rainbowing technique
is getting famous nowadays . In rainbowing technique , sand from
the nearby seabed , and discharges the sand to needed shore . The
process of rainbowing begins with the excavation of sediment,
typically sand, from the seabed by a dredger. Dredgers excavate the
sediment using mechanical or hydraulic methods or a combination of
both. The methodology for beach nourishment by Rainbowing technique
was prepared jointly by DCI and Vizag Port. It consists of filling
up the hopper with sand by stationary dredging in the new sand trap
area. The dredger would hold her positionat this point and
discharge the mixture to a distance of approx 100 m so that the
material falls within the shore zone .
- 25. On completion of the discharge within about 1.5 hrs the
dredger returns to the new sand trap area and positions for the
next load. At least 5 loads were pumped every day with cumulative
quantities ranging from 20000 22000 cu.m. per day. Direct
Rainbowing onto the beach resulted in savings in time due to
reduced discharge time and time loss on account of positioning with
anchors. There is also an advantage of pumping in locations with
greater erosion selectively. Further, there has been no disruption
to container shipping or idle time of the dredger.
- 26. Costs Nourishment is typically a repetitive process, since
nourishment does not remove the physical forces that cause erosion;
it simply mitigates their effects. A benign environment increases
the interval between nourishment projects, reducing costs.
Conversely, high erosion rates may render nourishment financially
impractical In many coastal areas, the economic impacts of a wide
beach can be substantial. The 10 miles (16 km)long shoreline
fronting Miami Beach, Florida was replenished over the period
19761981. The project cost approximately $64,000,000 and
revitalized the area's economy.
- 27. Conclusion After considering all the aspects of beach
nourishment , we came to know some important things .Beach
nourishment is not permanent solution for eroding beaches . It is
very costly and have some demerits and some environmental issues .
Whereas, The soft stabilizing methods like sand bags , geotubes ,
planting vegetation dont have any adverse effect on environment .
But they dont restore the eroded beach , they just prevent the
beach from further erosion . On the other hand ,beach nourishment
has been very successful , even on highly eroded beaches .
Nourishment provides us with widened beach that used for various
recreational purposes . Even if it is somewhat costly , it proved
to be very useful . After studying various aspects , I would
conclude that BEACH NOURISHMENT is very beneficial and to protect
and restore our beautiful beaches it is the best option .
- 28. References :- www.wikipedia.com Beach stabilization
:-structure & beach nourishment alternatives .(Paper presented
by Steven Hafner ) Beach and Dune Restoration by Karl Nordstrom
(Book) www.beachapedia.com
- 29. THANK YOU