Difference between revisions of "Shore nourishment"

Revision as of 11:35, 18 January 2022

The application of coastal nourishments requires insight into the processes that shape the coastal profile. For an introduction to these processes, the reader is referred to the article Shoreface profile and other articles mentioned herein.

Definition of Shore nourishment:

Shore nourishments are projects where the coastal system is fed with sediments (sand) from a source (borrow area) at a sufficient distance from the project area so that coastal hydrodynamics remain unaffected.

This is the common definition for Shore nourishment, other definitions can be discussed in the article

Other examples of projects where the coastal system is fed, are large scale land reclamation projects and the construction of an artificial island in the open sea. In these cases often huge volumes of sand are required; typically several hundreds of millions m³ per project. Shore nourishment projects involve moderate volumes, typically in the order of 1-5 million m³ and rarely more than 10 or 20 million m³.

Nourishment concept

Shore nourishments can be regarded as a 'natural' way of combating dune erosion and beach erosion as it artificially replaces a deficit in the sediment budget over a certain coastal stretch with a corresponding volume of sand. However, as the cause of erosion is not eliminated, erosion will continue and carry away the nourished sand. It is thus inherent in the nourishment concept that the nourished sand is gradually sacrificed. This means that nourishment as a stand-alone method normally requires an ongoing maintenance effort. In general, nourishment is only suited for shoreline sections of substantial length; otherwise the loss of sand to neighbouring sections will be too large. Regular nourishment requires a permanent well-functioning organisation, which makes nourishment as a stand-alone solution unsuitable for privately owned coastlines.

Fig. 1. Generally practiced nourishment methods. Pipe discharge on the beach for beach nourishment, over the bow pumping (rainbowing) for nearshore nourishment and split barge for nourishment in the outer part of the upper shoreface.

The design of a nourishment scheme depends very much on the grain size of the nourished sand, the so-called borrow material, relative to the grain size of the native sand. As described in Shoreface profile, the characteristics of the sand determine the overall shape of the coastal profile expressed in the equilibrium profile concept. Furthermore, natural hydrodynamic processes tend to sort the sediments in the profile so that the grain size decreases with increasing water depth. Borrow material is generally mined from the seabed sufficiently far offshore to minimize any influence on the hydrodynamics of the coastal zone. Placement in onshore nourishment sites makes use of pipes; for offshore sites, sand is dumped by split barges or by rainbowing (Fig. 1). For small nourishments, land sources are sometimes used.

Nourishment applications

In the following, a short introduction is given to various different nourishment methods.

Inner dune nourishment

Inner dune nourishment is the strengthening of the dune belt to prevent breaching by an extreme storm surge; it is not intended to prevent shoreline retreat. This measure can be applied when a single dune row that protects low-lying hinterland from flooding is not strong enough to withstand extreme storm surges. Sand is placed at the landward side of the front dune to increase the dune volume and/or to raise the dune crest. Beach morphodynamic processes are not affected by this measure. The amount of sand needed to achieve the desired protection level can be estimated with the methods described in Dune erosion. Inner dune nourishment is particularly effective if the dune foot location is stable i.e., no structural retreat due to ongoing erosion. In this case, a one-off intervention is sufficient, so that the additional costs for applying the sand on the land side are also a one-off investment. Recovery of dune vegetation can be promoted by depositing the top layer of the area to be nourished and later applying it as a cover layer over the nourishment.

Backshore nourishment

Backshore nourishment is the strengthening of the upper part of the beach by placing the nourishment on the backshore or at the foot of the dunes. The material is stockpiled in front of the dunes and acts as a buffer, which is sacrificed during extreme events. The main objective of backshore nourishment is to strengthen the backshore/dune against erosion and breaching during extreme events. This kind of nourishment works more by volume than by trying to restore a natural wide beach. The loss is normally large during extreme events, whereby steep scarps are formed. Backshore nourishment can be characterised as a kind of emergency measure against dune setback/breach; it cannot, therefore, be characterised as a sustainable way of performing nourishment and it does not normally look very natural.

Backshore nourishment can be performed by hydraulic pumping sand through pipes discharging at the foot of the dunes and later adjusted using a bulldozer (Fig. 1). The sand source can be either an offshore supply via a cross-profile pipeline, floating or buried, or it can be supplied along the shore from, for example, a sand bypassing plant. The sand can also be supplied via land transport by dumpers.

Beach nourishment

Beach nourishment is the supply of sand to the shore to increase the recreational value and/or to secure the beach against shore erosion by feeding sand on the beach. It is not a protection measure against flooding, as the beach is normally submerged during extreme events. However, it enhances the protection function of the dune belt or other backshore flood defences. The sand is usually supplied via a cross-profile pipeline and adjusted with bulldozers to the natural beach profile. It is therefore necessary that the borrow sand has grain size similar to the native sand. It may be an advantage to use slightly coarser sand than the natural beach sand, as this will enhance the stability of the resulting slightly steeper profile. Finer sand will very quickly be transferred to deeper water and will thus not contribute directly to a wider beach. However, the fine sand will help building up the outer part of the profile. See also Beach nourishment and Experiences with beach nourishments in Portugal.

Shoreface nourishment

Shoreface nourishment is the supply of sand to the subtidal part of the coastal profile. It will strengthen the coastal profile and add sediment to the littoral budget in general. This type of nourishment is used in areas where coastal protection measures have steepened the coastal profile or in areas with a long-term sediment deficit. Shoreface nourishment is sometimes used in combination with beach nourishment, thus creating a nourished profile close to the equilibrium over the entire active coastal zone. See Shoreface nourishment for further details.

Shoreface nourishment is often performed using split barges (Fig. 1). The unloading is fast and the unit price therefore low. Shoreface nourishment can profitably be used in connection with large beach nourishment schemes, in which borrow material, which does not fulfil the requirements for beach nourishment, can be used in the outer part of the profile where it naturally belongs.

Beach Scraping

A beach berm consisting of coarse sand or gravel is sometimes formed during relatively mild summer wave conditions, which tend to transport seabed material towards the beach. This coarse material can be brought to the upper part of the beach to protect the dune foot or the foot of the cliff against erosion by storm surges. This practice is called beach scraping and is normally performed using front loaders.

This method can be used for beaches which are mainly exposed to seasonal erosion, whereas it is probably not feasible for locations exposed to long-term erosion. One disadvantage of the method is that the material used for strengthening the upper part of the beach profile is taken from the lower part of the same profile, which means that the method contributes insignificantly to the overall stability of the beach profile. Another issue is that equipment operated during late summer may disturb recreational activities.

Creation of a new beach

Figure 2. Correlation between sediment grainsize and related beach slope from 78 field studies, adapted from Bujan et al. (2019)^[1]. The violet area indicates the scatter of the data points.

In many places (e.g. along the Mediterranean coast) the coast is rocky with few wide sandy beaches. A beach can be created by artificial sand nourishment if this is desired for recreational purposes. There are two main differences with maintenance nourishment of an existing beach: (1) an entire equilibrium beach profile has to be created, up to the closure depth, to minimize sand loss to deep water; (2) the new beach is subject to strong gradients in longshore sand transport that redistribute the nourishment alongshore. Additional measures are necessary to keep the nourished sand in place, such as confining the artificial beach between groynes or breakwaters. However, such structures must be carefully designed to ensure proper functioning, as explained in the articles Groynes and Detached breakwaters. The sand volume needed to create a stable beach strongly depends on the grain size. The equilibrium profile of a coarse sandy beach is much steeper than the equilibrium profile of a fine sandy beach (Fig. 2). With coarse sand smaller nourishment volumes are needed and longshore sand losses will be smaller.

Channel wall nourishment

At places where the coast is interrupted by tidal inlets, channels of the ebb tidal delta may run some distance along the adjacent shores. The landward migration of these tidal channels can cause erosion of the beaches along these shores. In this case channel wall nourishments can be applied to counteract this landward migration, even when large nourishment volumes are required. However, because lateral channel migration is usually a rather slow process, the lifetime of the nourishment is generally longer than the lifetime of beach or shoreface nourishments. Channel wall nourishments therefore can be a good option to prevent beach erosion by onshore migrating channels. Extensive experience with channel wall nourishments has been gained at tidal inlets along the Dutch coast ^[2].

References

↑ Bujan, N., Cox, R. and Masselink, G. 2019. From fine sand to boulders: Examining the relationship between beach-face slope and sediment size. Marine Geology 417, 106012
↑ Brand, E., Ramaekers, G. and Lodder, Q. 2022. Dutch experience with sand nourishments for dynamic coastline conservation – An operational overview. Ocean and Coastal Management 217, 106008

The main authors of this article are {{{AuthorFullName1}}}, Jan van de Graaff, Anna Kroon and Job Dronkers
Please note that others may also have edited the contents of this article.

For other articles by this author see [[:Category:Articles by {{{AuthorFullName1}}}]]
For other articles by this author see Category:Articles by Jan van de Graaff
For other articles by this author see Category:Articles by Anna Kroon
For other articles by this author see Category:Articles by Job Dronkers

[[Category:Articles by {{{AuthorFullName1}}}]]

[Bu-1] Bujan, N., Cox, R. and Masselink, G. 2019. From fine sand to boulders: Examining the relationship between beach-face slope and sediment size. Marine Geology 417, 106012

[2] Brand, E., Ramaekers, G. and Lodder, Q. 2022. Dutch experience with sand nourishments for dynamic coastline conservation – An operational overview. Ocean and Coastal Management 217, 106008

[1]

[2]

@@ Line 1: / Line 1: @@
-Nourishment can be divided into [[backshore]] nourishment, beach nourishment and shoreface nourishment.
+<div style="border:1px solid #000000; text-align:center; align=center; padding=5px ; margin-right:20px; margin-left:20px">
+The application of coastal nourishments requires insight into the processes that shape the coastal profile. For an introduction to these processes, the reader is referred to the article [[Shoreface profile]] and other articles mentioned herein.
+</div>
-==What is nourishment?==
-Nourishment can be regarded as a very natural way of combating coastal erosion and shore erosion as it artificially replaces a deficit in the sediment budget over a certain stretch with a corresponding volume of sand. However, as the cause of the erosion is not eliminated, erosion will continue in the nourished sand. It is thus inherent in the nourishment concept that the nourished sand is gradually sacrificed. This means that nourishment as a stand-alone method normally requires a long-term maintenance effort. In general, nourishment is only suited for major sections of shoreline; otherwise the loss of sand to neighbouring sections will be too large. Regular nourishment requires a permanent well-functioning organisation, which makes nourishment as a stand-alone solution unsuitable for privately owned coastlines.
-The success of a nourishment scheme depends very much on the grain size of the nourished sand, the so-called borrow material, relative to the grain size of the native sand. As described in [[Coastal Hydrodynamics And Transport Processes#Onshore and Offshore Transport and Equilibrium Coastal Profile|Onshore and Offshore Transport and Equilibrium Coastal Profile]], the characteristics of the sand determine the overall shape of the coastal profile expressed in the equilibrium profile concept. Furthermore, in nature the hydrodynamic processes tend to sort the sediments in the profile so that the grain size decreases with increasing water depth.
-==Methods, functional characteristics and applicability==
+{{Definition|title=Shore nourishment
-The three different nourishment methods will be discussed briefly in the following (Fig. 1).
+|definition=Shore nourishments are projects where the coastal system is fed with sediments (sand) from a source (borrow area) at a sufficient distance from the project area so that coastal hydrodynamics remain unaffected.
+}}
-[[Image:backshore nourishment.jpg|250px|right|thumb|<small>Fig. 1. Principles in backshore nourishment, beach nourishment and shoreface nourishment. </small>]]
+Other examples of projects where the coastal system is fed, are large scale land reclamation projects and the construction of an artificial island in the open sea. In these cases often huge volumes of sand are required; typically several hundreds of millions m<sup>3</sup> per project. Shore nourishment projects involve moderate volumes, typically in the order of 1-5 million m<sup>3</sup> and rarely more than 10 or 20 million m<sup>3</sup>.
-====Backshore nourishment====
-[[Backshore]] nourishment is the strengthening of the upper part of the beach by placing nourishment on the [[backshore]] or at the foot of the dunes.
-The main objective of [[backshore]] nourishment is to strengthen the [[backshore]]/dune against erosion and [[breaching]] during extreme events.  The material is stockpiled in front of the dunes and acts as a buffer, which is sacrificed during extreme events. This kind of nourishment works more by volume than by trying to restore the natural wide beach. The loss is normally large during extreme events, whereby steep scarps are formed. [[Backshore]] nourishment can be characterised as a kind of emergency measure against dune setback/breach; it cannot, therefore, be characterised as a sustainable way of performing nourishment and it does not normally look very natural.
-[[Backshore]] nourishment can be performed by hydraulic pumping sand through pipes discharging at the foot of the dunes and later adjusted using a bulldozer (Fig. 2). The sand source can be either an offshore supply via a cross-profile pipeline, floating or buried, or it can be supplied along the shore from, for example, a sand [[bypassing]] plant. The sand can also be supplied via land transport by dumpers.
-====Beach nourishment====
-Beach nourishment is the supply of sand to the shore to increase the recreational value and/or to secure the beach against shore erosion by feeding sand on the beach. It is not a coastal protection measure, as the beach will normally be flooded during extreme events, but it will support possible coastal protection measures. When performing beach nourishment, the borrow sand must be similar to the native sand to adjust smoothly to the natural profile. It may be an advantage to use slightly coarser sand than the natural beach sand, as this will enhance the stability of the resulting slightly steeper profile.  Finer sand will very quickly be transferred to deeper water and will thus not contribute directly to a wider beach. However, the fine sand will help building up the outer part of the profile. See also [[experiences with beach nourishments in Portugal]].
-====Shoreface nourishment====
+==Nourishment concept==
-[[Image:nourishment methods.gif|thumb|<small>Fig. 2. Generally practiced nourishment methods. Pipe discharge on the beach for beach nourishment, over the bow pumping (rainbowing) for nearshore nourishment and split barge for nourishment in the outer part of the upper shoreface. </small>]]
-Shoreface nourishment is the supply of sand to the outer part of the coastal profile, typically on the seaside of the bar. It will strengthen the coastal profile and add sediment to the littoral budget in general. This type of nourishment is used in areas where coastal protection measures have steepened the coastal profile or in areas with a long-term sediment deficit. Shoreface nourishment is sometimes used with beach nourishment in order to strengthen the entire coastal profile. It is recommended for obtaining a nourished profile close to the equilibrium profile.
+Shore nourishments can be regarded as a 'natural' way of combating dune erosion and beach erosion as it artificially replaces a deficit in the sediment budget over a certain coastal stretch with a corresponding volume of sand. However, as the cause of erosion is not eliminated, erosion will continue and carry away the nourished sand. It is thus inherent in the nourishment concept that the nourished sand is gradually sacrificed. This means that nourishment as a stand-alone method normally requires an ongoing maintenance effort. In general, nourishment is only suited for shoreline sections of substantial length; otherwise the loss of sand to neighbouring sections will be too large. Regular nourishment requires a permanent well-functioning organisation, which makes nourishment as a stand-alone solution unsuitable for privately owned coastlines.
-Shoreface nourishment is often performed using split barges (Fig. 2). The unloading is fast and the unit price therefore low. Shoreface nourishment can profitably be used in connection with large beach nourishment schemes, in which borrow material, which does not fulfil the requirements for beach nourishment, can be used in the outer part of the profile where it naturally belongs.
+[[Image:nourishment methods.gif|thumb|left|300px|<small>Fig. 1. Generally practiced nourishment methods. Pipe discharge on the beach for beach nourishment, over the bow pumping (rainbowing) for nearshore nourishment and split barge for nourishment in the outer part of the upper shoreface. </small>]]
-====Beach Scraping====
-=====Method=====
-A [[beach berm]] consisting of coarse sand or gravel is sometimes formed during relatively mild summer wave conditions, which tend to transport seabed material towards the beach. Beach scraping is normally performed using front loaders.
-=====Functional characteristics=====
-The purpose of beach scraping is to strengthen the upper part of the beach profile and the foot of the cliff. The material is placed in a position that reduces the erosion occurring during storm surge conditions.
-=====Applicability=====
+The design of a nourishment scheme depends very much on the grain size of the nourished sand, the so-called borrow material, relative to the grain size of the native sand. As described in [[Shoreface profile]], the characteristics of the sand determine the overall shape of the coastal profile expressed in the equilibrium profile concept. Furthermore, natural hydrodynamic processes tend to sort the sediments in the profile so that the grain size decreases with increasing water depth. Borrow material is generally mined from the seabed sufficiently far offshore to minimize any influence on the hydrodynamics of the coastal zone. Placement in onshore nourishment sites makes use of pipes; for offshore sites, sand is dumped by split barges or by rainbowing (Fig. 1). For small nourishments, land sources are sometimes used.
-This method can be used for beaches, which are mainly exposed to seasonal erosion, whereas it is probably not feasible for locations, which are exposed to long-term erosion. One disadvantage of the method is that the material used for strengthening the upper part of the beach profile is taken from the lower part of the same profile, which means that the method only contributes insignificantly to the overall stability of the beach profile. Another issue is that equipment operated during late summer may disturb recreational activities.
+<br clear=all>
+==Nourishment applications==
+In the following, a short introduction is given to various different nourishment methods.
-==Beach nourishment==
+====Inner dune nourishment====
-When borrow sand is placed in a coastal profile, neither the profile nor the grain size distribution will match the equilibrium conditions. Nature will attempt to re-establish a new equilibrium profile so changes will always occur in the nourished profile. There will also be changes caused by the continued long-term erosion trend and the profile response to individual events. This means that in practice it is neither possible to perform a short-term nor a long-term stable nourishment at an eroding coast. It is inherently unstable on eroding shorelines. These are the basic realities, which the public, the politicians and those who fund the projects, find it hard to accept. On the other hand, as environmental concerns and requirements for sustainability are gaining in importance, nourishment has gradually increased its share of shoreline management schemes over the last decades.
+[[File:DuneNourishment.jpg|thumb|right]]
+Inner dune nourishment is the strengthening of the dune belt to prevent breaching by an extreme storm surge; it is not intended to prevent shoreline retreat. This measure can be applied when a single dune row that protects low-lying hinterland from flooding is not strong enough to withstand extreme storm surges. Sand is placed at the landward side of the front dune to increase the dune volume and/or to raise the dune crest. Beach morphodynamic processes are not affected by this measure. The amount of sand needed to achieve the desired protection level can be estimated with the methods described in [[Dune erosion]]. Inner dune nourishment is particularly effective if the dune foot location is stable i.e., no structural retreat due to ongoing erosion. In this case, a one-off intervention is sufficient, so that the additional costs for applying the sand on the land side are also a one-off investment. Recovery of dune vegetation can be promoted by depositing the top layer of the area to be nourished and later applying it as a cover layer over the nourishment.
-===Grain size===
-[[Image:nourished beaches equilibrium.jpg|350px|right|thumb|<small>Fig. 3. Equilibrium conditions for nourished beaches required to obtain an additional beach width of &delta;w with borrow sand, which is finer and coarser than the native sand (upper and lower, respectively). </small>]]
-As mentioned above, the performance of a nourishment scheme very much depends on the grain size of the borrow material relative to the grain size of the native material; see the discussion on [[Coastal Hydrodynamics And Transport Processes#Onshore and Offshore Transport and Equilibrium Coastal Profile|equilibrium profiles]].
+====Backshore nourishment====
+[[File:BackshoreNourishment.jpg|thumb|right]]
+[[Backshore]] nourishment is the strengthening of the upper part of the beach by placing the nourishment on the [[backshore]] or at the foot of the dunes. The material is stockpiled in front of the dunes and acts as a buffer, which is sacrificed during extreme events.
+The main objective of [[backshore]] nourishment is to strengthen the [[backshore]]/dune against erosion and [[breaching]] during extreme events.  This kind of nourishment works more by volume than by trying to restore a natural wide beach. The loss is normally large during extreme events, whereby steep scarps are formed. [[Backshore]] nourishment can be characterised as a kind of emergency measure against dune setback/breach; it cannot, therefore, be characterised as a sustainable way of performing nourishment and it does not normally look very natural.
-[[Image:nourish grain size.jpg|300px|thumb|right|<small>Fig. 4. Relation between Nourishment Efficiency and the Grain Size Ratio for Nourishment<ref name="Vestkysten"/></small>]]
+[[Backshore]] nourishment can be performed by hydraulic pumping sand through pipes discharging at the foot of the dunes and later adjusted using a bulldozer (Fig. 1). The sand source can be either an offshore supply via a cross-profile pipeline, floating or buried, or it can be supplied along the shore from, for example, a sand [[bypassing]] plant. The sand can also be supplied via land transport by dumpers.
+====Beach nourishment====
+[[File:BeachNourishment.jpg|thumb|right]]
+[[Beach nourishment]] is the supply of sand to the shore to increase the recreational value and/or to secure the beach against shore erosion by feeding sand on the beach. It is not a protection measure against flooding, as the beach is normally submerged during extreme events. However, it enhances the protection function of the dune belt or other backshore flood defences. The sand is usually supplied via a cross-profile pipeline and adjusted with bulldozers to the natural beach profile. It is therefore necessary that the borrow sand has grain size similar to the native sand. It may be an advantage to use slightly coarser sand than the natural beach sand, as this will enhance the stability of the resulting slightly steeper profile.  Finer sand will very quickly be transferred to deeper water and will thus not contribute directly to a wider beach. However, the fine sand will help building up the outer part of the profile. See also [[Beach nourishment]] and  [[Experiences with beach nourishments in Portugal]].
-If the borrow sand is finer than the native sand, it will tend to form a flatter profile than the natural one. The equilibrium reshaping of the nourished sand will reach out to the closure depth. If the objective of the nourishment is to obtain a wider beach, this will require very large volumes of sand, as illustrated in the upper part of Fig. 3.
+====Shoreface nourishment====
+[[File:OuterBarNourishment.jpg|thumb|right]]
-It is evident that the volume of sand needed to obtain a certain beach width increases drastically with the decreasing grain size of the nourished sand. Most coastal authorities realise this and some of them have introduced special bonuses for their nourishment contractors when they provide coarse sand.
+[[Shoreface nourishment]] is the supply of sand to the subtidal part of the coastal profile. It will strengthen the coastal profile and add sediment to the littoral budget in general. This type of nourishment is used in areas where coastal protection measures have steepened the coastal profile or in areas with a long-term sediment deficit. Shoreface nourishment is sometimes used in combination with beach nourishment, thus creating a nourished profile close to the equilibrium over the entire [[active coastal zone]]. See [[Shoreface nourishment]] for further details.
-It is evident from this figure that if borrow sand with a larger grain size than that of the native sand is nourished into a coastal profile, it will tend to form a steeper profile than the natural profile. This means that a wider beach will tend to be formed, see the lower part Fig. 3.
+Shoreface nourishment is often performed using split barges (Fig. 1). The unloading is fast and the unit price therefore low. Shoreface nourishment can profitably be used in connection with large beach nourishment schemes, in which borrow material, which does not fulfil the requirements for beach nourishment, can be used in the outer part of the profile where it naturally belongs.
-Furthermore, coarser sand will be more stable in terms of longshore loss. This '''nourishment efficiency''' of the nourished sand has been studied by the Danish Coastal Authority on basis of many years of nourishment along the Danish North Sea Coast<ref name="Vestkysten">Vestkysten 2000 (in Danish) (The West Coast or the Danish North Sea Coast 2000), The Danish Coastal Authority.</ref>. The nourishment efficiency is defined as the ratio between the erosion rate for the natural sand (theoretical) and that of the nourished sand. The nourishment efficiency has been analysed as function of the ratio between the mean grain size of the borrow sand and that of the native sand:
+====Beach Scraping====
+A [[beach berm]] consisting of coarse sand or gravel is sometimes formed during relatively mild summer wave conditions, which tend to transport seabed material towards the beach. This coarse material can be brought to the upper part of the beach to protect the dune foot or the foot of the cliff against erosion by storm surges. This practice is called beach scraping and is normally performed using front loaders.
-:<math>GSR_{Nourishment}=d_{50,Borrow}/d_{50,Native}</math>
+This method can be used for beaches which are mainly exposed to seasonal erosion, whereas it is probably not feasible for locations exposed to long-term erosion. One disadvantage of the method is that the material used for strengthening the upper part of the beach profile is taken from the lower part of the same profile, which means that the method contributes insignificantly to the overall stability of the beach profile. Another issue is that equipment operated during late summer may disturb recreational activities.
-The analysis covers effects of cross shore as well as longshore effects. The results are expressed as a relation between the nourishment efficiency versus the grain size ratio <math>GSR_{Nourishment}</math>. It is evident from the relation shown in Fig. 4. that the Nourishment Efficiency increases considerably with increasing Grain Size Ratio for Nourishment.
+====Creation of a new beach====
-===Steepness of profile===
+[[Image:BeachSlopeGrainSizeData.jpg|thumb|350px|right|<small>Figure 2. Correlation between sediment grainsize and related beach slope from 78 field studies, adapted from Bujan et al. (2019)<ref name=Bu>Bujan, N., Cox, R. and Masselink, G. 2019. From fine sand to boulders: Examining the relationship between beach-face slope and sediment size. Marine Geology 417, 106012</ref>. The violet area indicates the scatter of the data points.</small>]]
-Areas, which for a long time have been protected by hard coastal protection structures, have often developed steepened coastal profiles. Such areas are very far from their cross-shore equilibrium form. If nourishment is introduced in such areas it will require huge volumes of sand to restore the profile to the equilibrium profile, which is required to release the pressure on the coastal structures. In such cases, it is very important to find borrow sand, which is coarser than the native sand.
-==Shoreface nourishment==
+In many places (e.g. along the Mediterranean coast) the coast is rocky with few wide sandy beaches. A beach can be created by artificial sand nourishment if this is desired for recreational purposes. There are two main differences with maintenance nourishment of an existing beach: (1) an entire equilibrium beach profile has to be created, up to the [[closure depth]], to minimize sand loss to deep water; (2) the new beach is subject to strong gradients in longshore sand transport that redistribute the nourishment alongshore. Additional measures are necessary to keep the nourished sand in place, such as confining the artificial beach between groynes or breakwaters. However, such structures must be carefully designed to ensure proper functioning, as explained in the articles [[Groynes]] and [[Detached breakwaters]]. The sand volume needed to create a stable beach strongly depends on the grain size. The equilibrium profile of a coarse sandy beach is much steeper than the equilibrium profile of a fine sandy beach (Fig. 2). With coarse sand smaller nourishment volumes are needed and longshore sand losses will be smaller.
-[[File:CamperduinShorefaceNourishment.jpg|thumb|350px|left|<small>Fig. 5. Shoreface nourishment Camperduin (North Holland coast) in 2002<ref name=SE>Van der Spek, A.F.J. and Elias, E., 2013. The effects of nourishments on autonomous coastal behaviour. Procs. Coastal Dynamics Conf. 2013, pp. 1753-1762</ref>. The figure shows a time stack of coastal profiles at the same Camperduin location with a 5-year interval (observed intermediate annual profiles are left out). The vertical scale of 10 m is equal to the distance between the 5-year interval lines. The migration (on average directed offshore) of the crests of the nearshore bars  is indicated by blue lines. The shoreface nourishment was positioned in 2002 just seaward from the fading outer bar. The nourishment crest location is indicated by the red line. The nourishment was stable (slightly moving offshore) for more than 10 years. After applying the nourishment, the position of the inner bar was also stable and even moved slightly onshore.</small>]]
+<br clear=all>
-Shoreface nourishment is mainly intended to halt shoreline retreat. It is less effective for beach widening. If offshore sand borrow locations are abundant and not far away, the price per m<sup>3</sup> is substantially less compared to beach nourishment. In the Netherlands, of the annual average of 12 Mm<sup>3</sup> nourished sand, about 2/3 is supplied to the shoreface (since 2000). Along the Dutch coast, long-term net shoreline retreat is related to the long-term net offshore migration of [[nearshore sandbars]]. Most nourishments were applied as an artificial bar just seaward of the outer bar; some nourishments were placed in the trough between the outer and inner bar. The lifetime of the artificial nourished bar is the time from nourishment until integration of the artificial bar into the original bar pattern and the resumption of the offshore migration cycle.
+====Channel wall nourishment====
-The evaluation of the nourishments brought forward the following observations about the effects and effectiveness<ref>Ojeda E., Ruessink, B.G. and Guillen, J. 2008. Morphodynamic response of a two-barred beach to a shoreface nourishment. Coastal Engineering 55: 1185-1196</ref><ref name=SE>Van der Spek, A.F.J. and Elias, E., 2013. The effects of nourishments on autonomous coastal behaviour. Procs. Coastal Dynamics Conf. 2013, pp. 1753-1762</ref><ref>Gijsman, R., Visscher, J. and Schlurmann, T. 2019. The lifetime of shoreface nourishments in fields with nearshore sandbar migration. Coastal Engineering 152, 103521</ref><ref>Atkinson, A.L. and Baldock, T.E. 2020. Laboratory investigation of nourishment options to mitigate sea level rise induced erosion. Coastal Engineering 161, 103769</ref>, see also Fig. 5:
+[[File:ChannelWallNourishment.jpg|thumb|right]]
-*The nourishments were effective to stop the offshore bar cycle during the lifetime of the nourishment;
+At places where the coast is interrupted by tidal inlets, channels of the ebb tidal delta may run some distance along the adjacent shores. The landward migration of these tidal channels can cause erosion of the beaches along these shores. In this case channel wall nourishments can be applied to counteract this landward migration, even when large nourishment volumes are required. However, because lateral channel migration is usually a rather slow process, the lifetime of the nourishment is generally longer than the lifetime of beach or shoreface nourishments. Channel wall nourishments therefore can be a good option to prevent beach erosion by onshore migrating channels. Extensive experience with channel wall nourishments has been gained at tidal inlets along the Dutch coast <ref>Brand, E., Ramaekers, G. and Lodder, Q. 2022. Dutch experience with sand nourishments for dynamic coastline conservation – An operational overview. Ocean and Coastal Management 217, 106008</ref>.
-*The lifetime of the nourishments increased with increasing nourishment concentration (the sand volume nourished per meter);
-*The lifetime of the nourishments increased with increasing grainsize;
-*The lifetime of the nourishments increased with increasing placement depth;
-*The lifetime of the nourishments increased with increasing bar cycle period (the time it takes for an offshore moving bar to reach the position of the preceding bar);
-*A more landward position of the nourishment reduced dune erosion during storms;
-*A small fraction (less than 10%) of the nourished sand was lost offshore;
-*The nourishments developed a trough at the shoreward flank;
-*The bar shoreward of the nourishments migrated onshore;
-*Part of the nourished sand was distributed alongshore to neighbouring coastal stretches;
-*The "feeder effect" of the nourishments (sand supply from the nourishment to the beach) did not reach the subaerial beach;
-*Accretion of the subaerial beach occurred in some cases by the "lee effect" of the nourishments – the convergence of longshore sediment transport at the nourishment site due to local reduction of wave heights, with downdrift erosion as a consequence.
 <br clear=all>
 ==Related articles==
-:[[Artificial nourishment]]
+:[[Beach nourishment]]
+:[[Shoreface nourishment]]
+:[[Shoreface profile]]
+:[[Experiences with beach nourishments in Portugal]]
+:[[Dealing with coastal erosion]]
 :[[Nearshore sandbars]]
-:[[Dealing with coastal erosion]]
-:[[Experiences with beach nourishments in Portugal]]
-:[[Shoreface profile]]
@@ Line 107: / Line 90: @@
-{{author
+{{4Authors
 |AuthorID=13331
 |AuthorFullName=Mangor, Karsten
-|AuthorName=Karsten}}
+|AuthorName=Karsten
+|AuthorID2=11540
+|AuthorName2= Jan van de Graaff
+|AuthorFullName2= Jan van de Graaff
+|AuthorID3=16611
+|AuthorName3= AnnaKroon
+|AuthorFullName3= Anna Kroon
+|AuthorID4=120
+|AuthorFullName4=Job Dronkers
+|AuthorName4=Dronkers J
+}}
-{{Review
-|name=Job Dronkers|AuthorID=120|
-}}
 [[Category:Coastal protection]]
 [[Category:Soft coastal interventions]]
 [[Category:Beaches]]

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