Beach nourishment
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Beach nourishment is a complimentary term that describes a process by which sediment (usually sand) lost through longshore drift or erosion is replaced on a beach. It involves the transport of the nourishment material from one area to the affected area. This process is often expensive (minimum of $1 million/mile), depending upon the source (and thus the cost) of the sand. Beach nourishment is almost always used as part of a coastal defense scheme. A poorly-designed and/or executed beach nourishment project can result in a severely impacted ecosystem, regardless of how much care is taken to deal with the sustainability of the littoral environment. Once a beach is nourished, it almost always is necessary to regularly renourish it since nourished beaches tend to erode faster than natural beaches. The economic activity generated through beach tourism may compensate for the cost of both capital and maintenance beach nourishment works, but only in a small number of heavily urbanized areas.
Primary functions:
- to provide protection to backshore property
- to increase the recreational space along the shore
- May replicate natural coastal processes by augmenting coastal sand budgets
- Sediment texture (grain size and sorting) is critical for success. Sand fill must be compatible with native beach sand.
Environmental issues:
- dredging may cause short-term direct mortality to sessile organisms, modifies seafloor habitats and sedimentary character
- burial of plants and organisms (SAV, shellfish)
- blockage of light in water (coral reefs, SAV)
- toxicity of sediments
- dredging too close to shore can cause erosion
- changes critical habitat for nesting sea turtles and birds
- provides a false sense of security that increase development pressure
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[edit] Assessing beach erosion
There are two different ways that a sandy beach can become eroded. The first type of erosion is the natural response of a beach to storms and calm weather. During storms, sand from the visible beach submerges below the water to form storm bars that protect the beach from further damage. During calm weather smaller waves return sand from the storm bar back onto the visible recreational beach surface. The term 'erosion' always sounds bad and conjours up the idea of environmental damage so the term submersion is often used for the natural erosion processes of a healthy sandy beach to distinguish this process from the more serious type of erosion described below.
Another type of erosion is a more serious problem for beach health. Some beaches do not have enough sand available to coastal processes to respond naturally to storms. Reasons can include:
- a seawall locking up sand dunes under urban areas or
- coastal structures like Ports and Harbours that prevent longshore drift
- river management structures like dams
- some coastlines are naturally eroding due to processes like continental drift
- climate change impacts like sea level rise, increased storminess or changes to the pattern of ocean currents
When there is not enough sand left available on a beach, then there is no recovery of the beach following storms.
The submersion/erosion distinction between total sand in a beach (erosion scale) and its position above or below the waterline (submersion) - is an important aspect when considering beach nourishment proposals. The response to coastal erosion should be different between a situation of extreme erosion and one of extreme submersion - even though the visible portion of the beach erosion will appear the same to observers. An eroded beach in a healthy environment may fully recover with no assistance through beach nourishment. There are beaches that are eroding due to natural processes like longshore drift but the majority of problems for beach health are anthropogenic. Addressing the anthropogenic cause of the beach erosion problem is often a better response to beach erosion than beach nourishment.
A common problem with poorly designed beach nourishment schemes, is that sand is dredged only to the visible portion of the beach above the waterline. Like an iceberg, only a small portion of the entire beach system exists above the waterline. If beach nourishment only occurs upon the upper visible beach above the waterline, then the beach becomes unstable and the sand is quickly eroded to fill the lower portions of the beach. A lot of communities have lost faith in the ability for beach nourishment to improve beach health due to poor design of the nourishment program. Politicians go out and have their photos taken on the newly nourished wide upper beach, but when the first storm arrives most of the sand disappears to fill the lower portions of the beach profile and the overall project is declared a failure. Beach Profile Nourishment is a term that suggests that the full beach profile is nourished, not just the upper visible portion. For beach profile nourishment schemes for the Gold Coast, 75% of the total sand volume is placed below low water level. Some coastal authorities are even overnourishing the lower parts of the active beach profile (nearshore nourishment) so that in the months and years following the investment, the natural beach increases in size. Nearshore nourishment and beach profile nourishment schemes tend to increase the community's confidence that beach nourishment is a worthwhile investment.
[edit] Beach nourishment projects
Beach nourishment projects are usually constructed along shorelines where an erosional trend is present that could be either natural or a result of human activities. In those cases where this trend is due to human activities, the project will perform much better if the cause of the erosional trend can be minimized or eliminated in conjunction with construction of the beach nourishment project. The setting of a beach nourishment project is key to design and potential performance. Possible settings include a long straight beach, a project adjacent to an inlet that may be either a natural or modified inlet and a pocket beach. Projects constructed on rocky or seawalled shorelines, that otherwise have no sediment, present unique problems.
[edit] Northern Gold Coast
Gold Coast Beaches have experienced periods of severe beach erosion. In 1967 a series of 11 cyclones removed most of the sand from Gold Coast beaches. The Government of Queensland engaged engineers from Delft University in Holland to advise what to do about the beach erosion. The Delft Report was published in 1971 and outlined a series of works for Gold Coast Beaches, that included beach nourishment and an artificial reef. By 2005 most of the recommendations of the 1971 Delft Report had been implemented. The Northern Gold Coast Beach Protection Strategy (NGBBPS) was a Aus$10 million dollar investment into the health of sandy beaches along the northern Gold Coast in Queensland Australia. The NGCBPS was developed between 1992 and 1999 and the works were completed between 1999 and 2003. The NGCBPS included dredging 3.5 million cubic meters of beach compatible sand from the Gold Coast Broadwater and delivering it through a pipeline to nourish 5 km of sandy beaches along the northern Gold Coast between Surfers Paradise and Main Beach. The new sand nourishment was stabilised by an artificial reef constructed at Narrowneck out of huge geotextile sand bags. The new reef was also designed to be an artificial surfing reef that would improve wave conditions for surfing. A key monitoring program for the NGCBPS is the ARGUS coastal camera system operated by the University of New South Wales.
[edit] Holland
See the National Institute for Coastal and Marine Management for more information.
[edit] Response alternatives on an eroding beach
- Structural - The structural approach is simply to prevent upland loss and can be in the form of: revetments, seawalls, detached breakwaters, or groins, etc. If well designed, armoring in the form of shore parallel structures (seawalls or revetments) is emplaced on an eroding shoreline, it will satisfy its intended function of preventing erosion of the upland; however, with continuing erosion, the beach will narrow and eventually the beach will no longer be present. Groins trap sand from the littoral stream and may impact adjacent shorelines. Recognizing that there are cycles of shoreline advancement and recession superimposed on the long-term shoreline change, the armoring will tend to occur during periods of erosional cycles. The time required before no fronting beach is present may be decades.
- Retreat - A second option is retreat as the shoreline erodes. This option has been exercised very infrequently along the United States shoreline; however, a number of examples exist. Retreat would appear to be the most appropriate option in areas of high erosion and in the presense of small economic revenue base. Many, but not all areas of high erosion are due to human activities. These activities interfere with the natural sediment flows either through dam construction (thereby reducing riverine sediment sources) or construction of littoral barriers such as jetties, or by deepening of inlets; thus preventing longshore transport of sediment across these channels.
- Beach nourishment - A third option for responding to an eroding shoreline is beach nourishment. This process usually consists of the placement of large quantities of good quality sediment along the water’s edge to advance the shoreline seaward. Beach nourishment is the only alternative that addresses the sand deficit directly through the placement of additional sediment. Beach nourishment is usually but not always carried out on an eroding shoreline and is favored by a substantial upland investment and a relatively mild erosion rate. Beach nourishment has a finite lifetime and renourishment is almost always required.
[edit] Benefits of a beach nourishment project
[edit] Storm protection
It has been demonstrated from both field studies and theory that a wide beach provides significant benefits in the form of storm damage reduction. During storms with elevated water levels and high waves, a wide beach performs as an effective energy absorber with the wave energy dissipated across the surf zone and wide beach rather than impacting on the upland structures and infrastructure. The storm damage reduction benefits of beach nourishment projects have been well established.
[edit] Recreational benefits
In many coastal areas, the recreational benefits of a wide beach can be substantial. An excellent example of this is the ten mile long Miami Beach, FL, USA project that was constructed over the period 1976 and 1981, cost approximately $64,000,000 and has revitalized the economy of this area. Prior to nourishment of the Miami Beach project, it was quite difficult to walk along many portions of this beach, especially during periods of high tide.
The benefit cost ratio for the Northern Gold Coast Beach Protection Strategy (NGCBPS) was conservatively estimated at 75:1 for a AUS$10million investment into beach health. The identified benefits were extrapolated from a model of lost visitor nights in hotels following previous beach erosion events. The NGCBPS improved the health of beaches so that recovery of the recreational sandy surface following minor and moderate storms occurred within weeks. Additional unquantafied benefits of the NGCBPS included lifestyle benefits for residents, additional public open space and improved fishing, diving and surfing conditions.
[edit] Potential environmental effects
There are potential environmental costs associated with beach nourishment projects. These include decreased habitat for sea animal nesting such as sea turtles due to the pumping of sand onto nesting site that hardens making the digging of nest very difficult. Decreased foraging areas for sea birds, and burying of beach flora under sand being pumped in. The cost of such projects can have a political environment impact as well when there is no willingness to continue paying for the expensive projects that serve as only a temporary fix for erosion problems. Beach Nourishment can also improve habitat for sea turtles, sea birds and beach flora. Typically an eroded beach removes the habitat for sandy beach creatures and so renourishment can often be a positive contribution. In Florida there was concern that the dredge pipes would suck turtles into the pumps. A special vacuum cleaner grill was designed and added to the dredge pipes that ensured that turtles were not sucked in with the sand.
[edit] Possible settings for beach nourishment projects
There are a number of possible settings for beach nourishment projects.
- Long straight beach
- Beach nourishment adjacent to inlets
- Pocket beaches
- Seawalled beach
[edit] External links
- Beach nourishment /NOAA and NOS / Main Page
- Beach Nourishment with Emphasis on Geological Characteristics Affecting Project Performance
- ARGUS Beach Nourishment Monitoring Program at the University of New South Wales
- Beach Replenishment at Lyme Regis in Dorset, 2006
- USGS assessments and mapping of sand and gravel resources in U.S.offshore environments
