The setting of a beach nourishment project is key to design and potential performance. Possible settings include a long straight beach, an inlet that may be either natural or modified and a
pocket beach. Rocky or
seawalled shorelines, that otherwise have no sediment, present unique problems.
Cancun, Mexico Hurricane Wilma hit the beaches of Cancun and the
Riviera Maya in 2005. The initial nourishment project was unsuccessful at a cost of $19 million, leading to a second round that began in September 2009 and was scheduled to complete in early 2010 with a cost of $70 million. The project designers and the government committed to invest in beach maintenance to address future erosion. Project designers considered factors such as the time of year and sand characteristics such as density. Restoration in Cancun was expected to deliver of sand to replenish of coastline.
Northern Gold Coast, Queensland, Australia Gold Coast beaches in
Queensland,
Australia have experienced periods of severe 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 the Netherlands to advise them. The 1971 Delft Report outlined a series of works for Gold Coast Beaches, including beach nourishment and an artificial reef. By 2005 most of the recommendations had been implemented. The Northern Gold Coast Beach Protection Strategy (NGCBPS) was an A$10 million investment. NGCBPS was implemented between 1992 and 1999 and the works were completed between 1999 and 2003. The project included dredging of compatible sand from the
Gold Coast Broadwater and delivering it through a pipeline to nourish of beach between
Surfers Paradise and
Main Beach. The new sand was stabilized by an
artificial reef constructed at
Narrowneck out of huge
geotextile sand bags. The new reef was designed to improve wave conditions for surfing. A key monitoring program for the NGCBPS is the ARGUS coastal camera system.
Netherlands Background More than one-quarter of the
Netherlands is below sea level. The shoreline is closely monitored by yearly recording of the
cross section at points apart, to ensure adequate protection. Where long-term erosion is identified, beach nourishment using high-capacity suction dredgers is deployed. In 1990 the Dutch government has decided to compensate in principle all coastal erosion by nourishment. This policy is still ongoing and successful. All costs are covered by the National Budget. • Determine the location of the dune foot • The height of the average low water (glw) is determined • The height h of the dune foot above average low water is calculated • The sand volume A is calculated; A is the volume of sand seaward of the dune foot and above the level (glw-h) • The position of the momentary coastline (SKL) is defined in relation to the national beach pile line as: (A/2h) - Xdv The background of this method is that the thickness of the sand layer to be taken must be a function of the measuring wave height; however, it is unknown. But because the elevation of the dune foot is also a function of the measuring wave height, the value h is a good representation of the effect of both tide and wave influences. For the determination of the beach profiles, the so-called JarKus profiles are measured along the coastline. These profiles are roughly 250 metres apart and are measured annually from around 800 meters in the sea to just behind the dunes. These measurements are available throughout the coast from 1965 onwards. From the period from about 1850 there are also profile soundings available in some places, but these are often slightly shifted compared to the jarkus rowing and are therefore more difficult to analyse. In the case of groynes, the sounding is carried out exactly in the middle between the groynes.
The Basic Coastline (BKL) The Basic Coastline is by definition the coastline of 1 January 1990. But of course there are no measurements made on exactly that date, moreover, there are always variations in the measurements. The BKL is therefore determined by taking the beach measurements of the approximately 10 years prior to 1990 and by determining the MKL for each of those years. These values are placed in a graph, a
regression line is determined. Where this regression line cuts the date 1-1-1990 lies the basic coastline BKL. In principle, the location of the BKL is immutable. In very special cases, where the coast is substantially altered by a work, it can be decided to shift the BKL. This is not based on a technical or morphological calculation, but actually a political decision. An example of this is the Hondsbossche Zeewering, as sea dike near the village of
Petten, where the BKL was actually on the toe of the dike. Due to the construction of a new artificial dune in front of this dike (the Hondsbossche Duinen), a piece of dune was added, of which the intention is to preserve it. So there is the BKL shifted seaward.
The coastline to be tested (TKL) Within the framework of the coastal policy is determined annually whether nourishment is required in a given coastal sector. This is done by determining the coastline (TKL) to be tested before the reference date. This is determined in the same way as the BKL, namely by a regression analysis of the MKL values of the previous years. See the attached graph. In this example, a supplementation was carried out in 1990, causing the MKL to shift far seawards. The number of years over which the regression analysis can be carried out is therefore somewhat limited. If there are too few years available, a regression line is usually adopted parallel to the previous regression line (so it is assumed that the erosion before and after supplementation is approximately the same). By the way, the first year after supplementation is often more than average due to adjustment effects. In this case, it appears that the TKL is still just satisfactory for 1995 and is no longer satisfactory for 1996. In principle, a supplement at this location would be required in the course of 1995. Now the decision to supplement does not depend on a single BKL exceedance, but only if multiple profiles are threatened to become negative. In order to assess this, coastal maps are issued annually by Rijkswaterstaat. These maps indicate whether the coast is growing or eroding with a dark green or light green block. A red block indicates that in that place the TKL has exceeded the BKL, and that something has to happen there. A red hatched indicator means that the TKL has exceeded the BKL, but this coastal section has an accreting tendency, so no urgent works are needed
Beach nourishment design A beach nourishment to broaden the beach and maintain the coastline can be designed using mathematical calculation models or on the basis of beach measurements. In the Netherlands, Belgium and Germany, a nourishment design is mainly based on measurement, while mathematical models are mainly used elsewhere. A nourishment design for coastal maintenance and beach widening can be made much more reliable based on measurement data, provided that they are present. If there are no good, long-term series of measurements of the beach profile, one must make the design using calculation models. In the Netherlands, the coast has been measured annually for years (JarKus measurements) and therefore the very reliable method based on measurements is used in the Netherlands for the design of supplements to prevent erosion.
Use of measurements for nourishment design To compensate for coastal erosion, the design of a supplementation is actually very simple, every year the same amount of sand has to be applied as erosion disappears annually. The assumption is that there is no significant change in the wave climate and the orientation of the coastline. With most nourishments, this is a correct assumption. In case of substantial changes in the coastal orientation, this method is therefore not always usable (e.g. in the design of the sand engine). In practice, the length of the nourishment must be 20-40 times the width in order to apply this method. In short, the method consists of the following steps: • Make sure there are enough measured profiles (at least 10 years). • Use these profiles to calculate the annual sand loss (in m3/year) for a coastal section. • Multiply this amount by an appropriate lifetime (e.g. 5 years). • Add a loss factor (order 40%). • Place this amount of sand somewhere on the beach between the low water line and the dune foot. To determine the amount of sand in the profile, the same method can be used as used for the basic Coastline. Given the fact that the instantaneous coastline has been measured for the necessary years and thus the decline of this coastline, determining the loss of sand is quite simple. Suppose the decline of the MKL is 5 m/year, then the annual sand loss is 5*(2h) m3 per year per linear meter of coastline. Here is 2h the height of the active beach profile. Along the Dutch coast, h is near Hoek van Holland in the order of 4 m, so in the above example the erosion would be 40 m3 per year per linear meter of coast. For a nourishment with a length of 4 km and a lifespan of 5 years is therefore 40*4000*5 = 80 000 m3. Because there is extra sand loss immediately after construction, a good amount is 1.4 *80000 = 112 000 m3. This is a seaward shift of 1.4*5*5= 35 m. In the practice of beach nourishments (from 1990 onwards), this method appears to work very well. Analyses of nourishments in northern Germany also show that this is a reliable method. The starting point is that the grain size of the nourishment sand is equal to the original beach sand. If this is not the case, it must be corrected. In case of finer sand in the win area, the volume of the nourishment will need to increase.
Use of mathematical models for nourishment design Single line model For relatively wide and short nourishment (such as the sand motor), a single-line model can be used. In this model, the coast is represented by a single line (e.g. the instantaneous coastline) and a constant profile along the entire coastline. For each profile, the orientation of the coast is given, and in each profile the sand transport is calculated by the surf induced current. If in a profile 1 the sand transport is larger than in a profile 2, there will be between profile 1 and 2 sedimentation, for details about the model. As there is sedimentation, the coastal orientation will change, and thus also the transport of sand. This makes it possible to calculate the coastline change. A classic example is the calculation of a relatively short and wide supplementation with straight waves. The single-line model can very well predict how such supplementation can develop over time. The Unibest calculation model of Deltares is an example of a single-line model.
Field models In highly two-dimensional situations, e.g. at a tidal inlet or the mouth of an estuary, or if the nourishment itself has a strong two-dimensional character (as with the Sand Engine), an approach with profile measurements is not possible. A single-line model is often inappropriate. In these cases, a two-dimensional sand transport model is made (usually with models such as Delft3D from Deltares in the Netherlands or
Mike 21 of
DHI in Denmark). In such a model, the bed of the area is introduced as a depth map. Then there is a tidal flow calculation and a wave penetration calculation. After that, the sand transport is calculated at each mesh-point and from the difference in sand transport between the different mesh-points, the sedimentation and erosion is calculated in all boxes. It can then be assessed whether a nourishment behaves as intended. The problem with this type of model is that (apart from the fairly long computation times for the computer) the results are rather sensitive to inaccuracies in the input. For example, at the edge of the model, the water levels and flow rates must be properly entered, and the wave climate must be well known. Also variations in the sand composition (grain size) have a great influence.
Channel wall nourishment At some places along the Dutch coast tidal channels are very near to the beach. In the years from around 1990 these beaches were also nourished in the classical way, but the problem was that the width of the beach is small. So the amount of sand to be placed is limited, resulting in a short lifetime of the nourishment. It was found that in such cases it is more effective to nourish the landward wall of the channel, and in some cases uses sand from the seaward side of the channel as borrow area. This is in fact moving the tidal channel further from the coastline In the period 1990–2020 in total 236 million cubic meters has been nourished, mainly as beach nourishment. However, after 2004 more focus has been on foreshore nourishment. In 2006 the costs of some nourishment were analysed in detail. This resulted in: F= Foreshore, B= Beach nourishment, B+F is combination; Price level 2006, excluding VAT.
Maui Maui, Hawaii illustrated the complexities of even small-scale nourishment projects. A project at Sugar Cove transported upland sand to the beach. The sand allegedly was finer than the original sand and contained excess silt that enveloped coral, smothering it and killing the small animals that lived in and around it. As in other projects, on-shore sand availability was limited, forcing consideration of more expensive offshore sources. A second project, along Stable Road, that attempted to slow rather than halt erosion, was stopped halfway toward its goal of adding of sand. The beaches had been retreating at a "comparatively fast rate" for half a century. The restoration was complicated by the presence of old seawalls, groins, piles of rocks and other structures. The smooth, cylindrical geotextile tubes could be difficult to climb over before they were covered by sand.
Southern Shores, North Carolina - the estimated costs for the Southern Shores project was approximately $950,000 and was completed in 2017. There is a proposed additional project to widen the beaches in 2022 with an estimated cost of between $9 million and $13.5 million.
Kitty Hawk, North Carolina - the beach nourishment project in Kitty Hawk was completed in 2017 and included 3.58 miles of beaches running from the Southern Shores to Kitty Hawk and cost $18.2 million.
Kill Devil Hills, North Carolina - the beach nourishment project was completed in 2017.
Nags Head, North Carolina - The town's first beach nourishment project took place in 2011 and cost between $36 million and $37 million. The renourishment project in 2019 cost an estimated $25,546,711. Upcoming Projects - the towns of Duck, Southern Shores, Kitty Hawk and Kill Devil Hills have secured a contract with Coastal Protection Engineering for tentative re-nourishment projects scheduled for 2022.
United States Florida - Ninety PEMs (Pressure Equalizing Modules) were installed in February 2008 at
Hillsboro Beach. After 18 months the beach had expanded significantly. Most of the PEMs were removed in 2011. Beach volume expanded by 38,500 cubic yards over 3 years compared to an average annual loss of 21,000.
New Jersey - Over decades, the
U.S. Army Corps of Engineers has pour millions of cubic yards of sand slurry along the
Jersey Shore. Costs for the project are shared by the Army Corps of Engineers, the state, and local municipalities. Justifications for the projects, controversial within New Jersey, have included
flood control, prevention of damage to waterfront residences, and protection of summer tourism along the shore, Critics, such as the
Sierra Club and
Surfrider Foundation, have argued that beach renourishment in the state is wasteful since the sand often washes away quickly; they argue for alternative policies to mitigate the effects of
climate change,
storm surges and
rising sea levels, and argue that renourishment is effectively a subsidy for wealthy homeowners. ==See also==