Beach nourishment

Description

Beach nourishment (also known as “replenishment”) is the artificial placement of sand/gravel on an eroded shore in order to maintain the amount of deposit on the coast, and thus compensate for erosion and protect the area against storm surges. Besides fighting erosion and flooding, it most often aims at maintaining or expanding beach width for tourism and recreational purposes (more details on this are covered in Raising and extending coastal land).

Beach nourishment is a standard practice that is constantly being implemented both in Croatia and Italy, but also around the world (the technique has been used in the United States since the 1920s and in Europe since the early 1950s). It was often categorized as a “soft” option in shoreline management, next to hard shoreline management options.

The process involves dredging material (sand, gravel) from a source area (offshore, nearshore or inland) to feed the beach where erosion is occurring, usually by depositing it near the shoreline, on the dry beach or on its submerged part. Although sometimes considered a green measure (although not fully) for the destination area, it is surely grey for the quarry site, the transport route and potential impact of new imported material on coastal and marine habitats (see Limiting factors in Chapter 3). That is why nourishment activities need to be carefully planned.

The embankment material should, considering most of its characteristics (colour, mineral composition, grain size, etc.), correspond to the local natural features of the shore. Sediments with the same grain-size distribution, mineral composition, colour etc. as the native one are not expected to modify the quality of the beach because the profile shifts offshore maintaining the same slope. On beaches with originally finer sediments most of the sand will deposit nearshore, with limited benefit to the dry beach. If finer material is easily accessible, its higher longshore and offshore dispersion can be compensated by more frequent fills, which is more relevant to the Italian side of Adriatic considering the type of the beaches there. Such fills need to be carried out with care, considering that finer sediments can lead to smothering of marine habitats by silt and increased turbidity. However, not all material will deposit nearshore; some of it will float and “feed” the adjacent beaches. Conversely, coarser sediments are more stable under higher wave energy and produce a steeper profile, so most of the fill will remain ashore. Because of that, at parity of volume, the dry beach will be larger. Special considerations need to be taken into account here as well, due to potential environmental impacts, mainly in nearshore areas (see Limiting factors).

Sediment sizes that are finer or coarser than the native one are sometimes used when more suitable ones are not available or are notably more expensive.

In the past, most of the sediment for nourishment was quarried on the river beds, thus reducing the natural fluvial input. This has a strong impact on the environment, and if large quantities are required by the market (like in certain cases in Italy), price of aggregates increases, which can impact housing costs. In addition, the environmental impact of transport of aggregates must be considered.

Aggregates produced by crashed rocks are used as well, although immediate use of the beach in that case can be uncomfortable for walking and lying due to rough grains. However, depending on the material roughness, with time the sea will round off this material and make it more acceptable.

In the Adriatic beach nourishment is carried out at different levels, from large projects promoted by public entities, to small nourishments, sometimes carried out without any authorization: e.g. private people defending their properties or increasing the beach surface.

On the western side of the Adriatic Sea, having long sandy beaches and high erosion rates, large projects can be carried out, using sand and/or gravel since both are easily accessible there. In Marche a significant part of the nourishment has been done with gravel, whereas in Abruzzo, Emilia-Romagna and Veneto almost exclusively sand was deposited.

On the eastern side, beaches are smaller with slower retreat, so deep-sea aggregates are not accessible due to the naturally reduced flow of material by rivers into the sea, unless several small projects are performed at the same time, with difficult technical and administrative coordination. Here, gravel is the most frequent material, also because more similar to the native beach sediments.

Costs and benefits

Beach nourishment typically needs regular application. Rising sea levels and extreme weather events can lead to shortening of the expected duration of the nourishment projects. It is advised to take into account all social and environmental aspects of nourishment, but also to compare the costs (which also depend on the availability of material) with the costs of hard constructions and their maintenance, to ensure an optimal choice. Unitary cost (€/m³) is inversely proportional to the total dredged volume, since mobilization/demobilization cost is roughly the same for any project. In beach nourishment there are certain limiting factors (“costs”), and success factors (“benefits”).

Limiting factors:

• Beach nourishment can have different impacts on marine ecosystems, causing modifications on inhabiting organisms, from small interstitial organisms to large mobile organisms, at various trophic levels. Negative impacts on benthic (macro-, meio- and micro-) organisms can be recorded in form of important changes in community composition, abundance and biodiversity. Moreover, direct and indirect impacts of nourishment are also recorded on commercial fishery species (such as bivalves, crustaceans, sponges, demersal fish, etc.).
• Certain negative effects on foreshore ecosystem are expected: there can be burial of biota and the loss of habitats in nearshore sandbars and nearshore seafloor. Care needs to be taken also with finer sediments due to turbidity and smothering with slit: clogging of fish gills, adverse impacts on planktonic larvae, molluscs, etc. According to some research, particles smaller than 0.063 mm that float and cover a wide area around the beach have significant harmful effects.
• Nourishment activities should be limited in areas where they can have severe impacts on protected species (such as Pinna nobilis) and important marine habitats (such as Posidonia oceanica meadows).
• Proper timing of nourishment is also important – nourishment is usually carried out in spring time, after the winter storms (which erode the beach), and before the summer season. In addition, if in future there will be areas where nesting of marine turtles takes place, nourishment should be avoided during nesting periods.
• Being an ongoing process, nourishment leads to higher costs over time and repeated disturbance of the ecosystem. Nourishment does not stop the erosion; it only provides additional sediments on which erosion will continue.
• Finding a source with sufficient quantities and good-quality material can be challenging. The material for nourishment should match the native material in terms of size, colour, and composition. Practice has shown that many times using finer sediments led to a need for more frequent fills, which impacts the overall costs. Using a similar type of material is also important for public acceptance of beach nourishment interventions. In addition, the source site should be close enough to the nourishment site to keep costs reasonable, but also impacts on the environment.
• Sediment availability can be an issue if the demand for nourishment projects rises. Offshore sand deposits may be a limited resource, e.g. it is the case in the eastern side of Adriatic Sea. Beach nourishment, in a long-term perspective, must be integrated within a wider approach, e.g. including managed retreat, setback definition, re-planning and zoning of coastal areas, etc.

Success factors:

• Beach nourishment is a flexible and fast erosion protection method compared to hard construction, and it is adaptable to changing conditions.
• It is a relatively cheap measure to prepare, since long-term design criteria are usually not taken into account (unlike for hard construction): if conditions change in a negative way, additional nourishment can be added.
• It can complement other grey measures, such as seawalls or groynes, and green measures, such as dune reinforcement. Dune construction/reinforcement can even act as sand reservoir, thus improving effectiveness of beach nourishment.
• Besides flood and erosion protection, beach nourishment provides benefits for coastal tourism and recreation activities.
• In some cases, beach nourishment can use material extracted for another purpose, allowing material reuse. Special care is needed in that case, as the use of such material to reduce costs is relatively frequent, but often such material can be contaminated or inadequate in some other way for nourishment and beach expansion in general.

It is difficult to estimate the costs of beach nourishment in Italy and Croatia since it depends on many factors (e.g. pre-nourishment survey costs, the size of nourished area, transport costs, etc.). There are some estimations saying that for recent large nourishment in Emilia Romagna the costs were around 10-15€/m³.

The UK AVOID report (2010) estimated nourishment costs at US$ 4.6 to 46.4 (3.5-35€)/m³ for UK. In the Netherlands, lower estimates were found, around US$ 3 to 8 (2-6€) per m³. However, prices there have recently risen due to the lack of contractors available to undertake nourishment works. Among other costs, one should take into consideration transportation costs, research costs, and the frequency of fills. 

Implementation time and lifetime

Implementation time is 1-5 years. Nourishment of beaches can remain in place for intervals that vary from 2 to 10 years. Beach nourishment is a continuous process and the beach erosion won’t be fully stopped with this option. SLR and increase in extreme events will probably reduce the lifetime of such projects, i.e. increase the need and frequency of supplementary nourishment if a project relies exclusively on this measure

The tourism sector asks for beach nourishment, but this is a strategy of no return, that is, once the nourishment begins, one should count on the continuity of such practice.

Source for more detailed information

https://climate-adapt.eea.europa.eu/metadata/adaptation-options/beach-and-shoreface-nourishment

Greene, K. (2002) Beach Nourishment: A Review of the Biological and Physical Impacts. Washington (DC): Atlantic States Marine Fisheries Commission. ASMFC Habitat

Linham, M.M. and Nicholls, R.J. (2010) Technologies for climate change adaptation: coastal erosion and flooding (TNA Guidebook Series) New Delhi, IN.Management Series no. 7.

PAP/RAC (2021) Handbook on coastal resilience for the Adriatic, INTERREG AdriAdapt project, Split.

MEASAURING THE BEACH TO MANAGE THE COAST – https://www.youtube.com/watch?v=lL4uvCtVGK0

We kindly thank Prof. Enzo Pranzini from University of Florence, the Beachex project team (Prof. Dalibor Carević and Tonko Bogovac from Faculty of Civil Engineering in Zagreb, Dr. Kristina Pikelj for Faculty of Science of Zagreb University) and Dr. Maja Krželj from University of Split, for all the help and support in preparation of this text.