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This building block covers the spatially concentrated placement of (relatively) large sand volumes for coastal development. Such nourishments are placed at a specific location with the aim to gradually feed the surrounding coast. Wind, waves and currents will spread the sediments along the coast, which is a typical example of 'building with nature'. Such a nourishment will contribute to the coastal safety in the long-term while creating more opportunities for nature and recreation.

An emerged concentrated nourishment along a sandy shore, whereby part of the nourishment is dry, provides more space for recreation, water sports and beach lovers. In addition, new dunes and vegetation could develop, increasing nature value. In case of an unprotected nourishment, the shape and bathymetry of the nourishment will however change continuously under the forcing of tide, wind and waves. This requires an adaptive management strategy to anticipate on unforeseen developments. The Sand Engine Delfland is a good example of an integrated solution providing safety against flooding while facilitating nature development and recreation.

    General Building Block Description

    This building block presents an innovative Building with Nature solution for coastal development through the application of feeder beaches: a spatially concentrated nourishment which is placed at a specific location with the aim to gradually feed the surrounding coast. Wind, waves and currents will spread the nourished sediments along the coast thereby contributing to the coastal safety on the longer term while creating more opportunities for nature and recreation.

    In the past, erosive coasts were protected by man-made, hard structures like dikes and dams. It was soon realised that these defences often induce erosion down-drift and so softer engineering options were introduced. Structures were built that worked with the natural depositional processes occurring at the coast. Groins and breakwaters were seen as the preferred option to build up beach and dune levels in order to offer a natural barrier to the sea. In the last 15 years alternative but nowadays quite common solutions of soft nourishments were applied. Sand was placed at the location where it was directly needed, and slowly dispersing in time, while interacting with the hard structures.

    Related pages

    Required skills

    With this manual, anyone having a basic level of knowledge and/or working experience in sandy coastal systems can make a first-order assessment. To fully assess the suitability for feeder beaches one should have additional expertise on nourishments, local coastal processes and the functionality of the area at the moment.

    BwN Interest

    The added value of this Building Block to Building with Nature (BwN) type projects is that it enables creating natural coastal barriers while enhancing other ecosystem services such as recreation. Furthermore, nature does part of the work spreading the sand.

    Tip: In the figure below the light blue boxes show the advantages of feeder beaches. In the black boxes some of the main necessities for creating a mangrove forest are depicted. Clicking on the image will give you more in depth information about feeder beaches nourishments.

    This Building Block is mainly applicable in the initiation and planning and design phase.

     

    Advantages

    • Concentrated nourishments feeding the surrounding coastal area can facilitate more simultaneous (eco-system) services, like safety against flooding, nature development and recreation.
    • The area to be nourished will be disturbed once in a long period while nature does the work, this can have ecological advantages.
    • Tide, winds and waves transport the sediments and spread it along the coast. This distribution of sand occurs gradually at rates that nature can keep up with. This enables nature and species to adapt.
    • A larger fresh watervolume can be held in the dune area.
    • The price of the large volume of sand for a feeder beach might be lower than the costs of the smaller volumes of sand summed up for regular nourishments.
    • Mobilisation of the dredging equipment is required only once instead of regularly in the case of disposing smaller volumes regularly. This allows for optimization in construction methods.

    Disadvantages

    • The evolution of the nourishment depends on the tides, wind and waves and can therefore not be fully predicted. This may lead to unforeseen or poorly predictable situations which should be managed in an adaptive manner.
    • The initial sand volume of the nourishment of a feeder beach will be much larger than for a regular nourishment. Therefore, benthic species will be buried under a larger amount of sand
    • Eventually the nourishment should be repeated. 

     

    How to Use

    To determine the feasibility and design of a concentrated nourishment for coastal development, guidance is presented below. First, the feasibility of a concentrated nourishment for coastal development is assessed using a rule-of-thumb method. Subsequently, a preliminary design of the concentrated nourishment is determined using simple (interactive design) tools including parameterizations. For appropriate detailing and a geometric design more advanced tools (like process-based models) are available to be applied.

    This Building Block is mainly applicable in the initiation and planning and design phase.

    Guidelines for feasibility of concentrated nourishments

    To be able to determine the feasibility of a concentrated nourishment for coastal development the following systematic approach is recommended. 

    Step 1: Project initiation 

    In the initiation phase of the project the next items need to be considered:

    • determine the need for nourishment
    • determine the goal of the nourishment: safety, nature, recreation, or other, or a combination
    • determine possible locations of the concentrated nourishment; the location does not have to be the optimal location from coastal management perspective, but can be a location which balances well all other considerations
    • determine the timing of the nourishment in the year: the period of constructing the nourishment should be carefully chosen with respect to breeding season of species (seals, birds, etc.) and nursery habitats of fish and shrimps

    Step 2: Analyse present situation

    • determine the characteristics of the area such as hydrodynamics, wind, waves, sediment characteristics (grain size, bed composition, cross-shore profile shape), ecology, annual sediment transports, morpho-dynamics, etc.
    • make inventory of stakeholders within project related area

    Step 3: Asses impact of desired intervention

    To assess the impact of the intervention and to investigate whether impacts are acceptable or desirable, or that certain impacts need to be mended, it is advised to:

    • assess the temporal impact of the desired intervention to its surrounding environment; involve experts (like consultants and knowledge institutes) to predict and evaluate the temporal impact. Besides the standard design aspects it is suggested to consider the BwN design aspects listed in the table below:

      Standard design aspects

      Extra BwN design aspects

      Hydrodynamic climate

      Sustainability

      Annual transports

      Dune development

      Profile shape

      Habitat development

      Sand composition

      Recreation

      Sand losses

      Groundwater

      Protection structures

      Diversity in ecological conditions

      Recurrence interval

      Local burial of benthic species

      Costs

      Indirect impact on foreshore
      as proxy for juvenile fish

      Functionality

       

    • In this step the typical design parameters can be varied, such as the nourishment volume, alongshore length, nourishment frequency, and for some case sediment grain size. If the intervention is very different from previous cases, predictive shoreline modelling is required. The same holds for a first nourishment along an unstudied coast. 

    Designing tools for concentrated nourishments

    Step 4: First order designing (conceptual)

    A first design step is to optimise the location of the concentrated nourishment w.r.t. goal,  long-term strategies, stakeholder involvement. For this purpose a design tool has been developed:

    Interactive design tool
    This design tool can be used for 1D shoreline modelling for long-term coastal evolution (up to ~50 yrs). It includes development of coastlines and a parameterized development of dunes and habitat factors related to the coastline dynamics. Interventions can be soft (nourishments) or hard (e.g. groynes) or a combination. Multiple interventions can be evaluated (including interaction). The design variables for nourishments are locations, volumes, and frequency. After a scenario, a scorecard is generated including all kind of relevant (temporal) information including costs. Other information can be displayed (bathymetry, topographic data, etc). The Interactive Design Tool Holland Coast facilitates a user to explore different strategies, climate change scenarios, and optimizing the nourishment location(s). This design tool is a dedicated tool, with an attached calculation module applying the Unibest model.

    Step 5: Appropriate detailing

    Once the location and general size and contours of the concentrated nourishment have been determined, further detailing of the nourishment and its development over time, has to be made. For this purpose several tools are made available increasing the level of detail and accuracy.

    Delft Dashboard
    Delft Dashboard is a standalone Matlab based graphical user interface developed by Deltares supporting modellers to quickly set-up new or existing coastal models anywhere in the world. The large number of coupled toolboxes allow for fast and easy model input generation. With Delft Dashboard setting-up a (coastal) model wherever on earth is a matter of minutes, which used to take days or weeks before! 

    Delft Dashboard can be used to rapidly assess the impact of a nourishment on the local hydrodynamics e.g. currents along the coast.

    Delft3D
    Detailed assessments of the processes around a nourishment can be carried out using the process-based, open source model Delft3D. The state-of-the-art model can combine hydrodynamics (2D or 3D) with waves, sediment transport, morphology, interaction ecology and morphology.

    This model can be used to study the temporal evolution of the nourishment, sediment losses (long- and cross-shore), operational system for predicting swimming conditions, etc.

    It is noted that other well reputed knowledge institutes offer comparable model suites. 

    Step 6: Construction and Monitoring

    When a suitable design has demonstrated to be feasible, a dedicated construction and monitoring program needs to be initiated and maintained.

    • During and after construction
    • Bathymetry, currents, waves, vegetation, topography, benthos, seals, fish, dune development and birds
    • Predicting swimming conditions

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    Practical Applications

    Below a number of field cases are presented providing some application experiences that can be used as inspiration for future designs.

    Sand Engine Delfland

    A surplus of sand (about 21 million m³) is put into the natural system and will  be re-distributed alongshore and into the dunes, through the continuous natural action of waves, tides and wind. In this way mega-nourishments gradually induce dune formation along a larger stretch of coastline over a period of one or more decades, thus contributing to the preservation and increase of safety against flooding over a longer period.

    The coast of Delfland, defined as a coastal stretch of about 14 km between Hook of Holland and The Hague (Netherlands), is characterized by dunes and a net northward transport of sand, driven by predominantly southwestern winds. To maintain this part of the coast regular nourishments have been carried out of about 1 million m³ per year on average. As an alternative nourishment method, now the Sand Engine has been placed based on principle of spatially concentrated nourishment for coastal development. It concerns a pilot experiment which will be extensively monitored and investigated. The findings after one year show that the Sand Engine does already distribute the sand along the coast feeding the adjacent coasts, while it has become a popular recreation area for beach and nature lovers, water sporting, especially surfing. In the first year already rare fauna species have been found at the Sand Engine and primary dunes are forming... read more

    Surfing beach at Scheveningen

    In winter 2010 a beach nourishment was conducted between the port of Scheveningen and the jetty (pier). A volume of 1.5 Mm³ of sand was placed on the beach. The sand was borrowed beyond the 20 m depth contour line at a distance of about 15km. The sand was pumped through a floating pipeline of 2 km long and disposed near the beach. The nourishment resulted in a shift of the shoreline of 40 - 70 m as the area close to the port breakwater was not nourished. This 'jump' in the shoreline caused the waves from the northwest to nicely refract and create great surfing conditions.

    Sand groynes Delfland

    In October and November of the year 2009, a pilot project was executed at the coast of Ter Heijde, a small village along the Holland Coast. The project comprises the construction of three so called sand groynes. Sand groynes are concentrated nourishments, constructed from the shoreline in seaward direction appearing in the form of small peninsulas. The groynes contain about 200.000 m³ of sand and serve as an input of sand in the coastal system. The sand in the groynes is anticipated to be uniformly redistributed over a stretch of coast of about 2.5km by the impact of waves and currents. The pilot project was executed as a part of the reinforcement program of the Delfland Coast as one of the Zwakke Schakels (in English: Weak Links) along the Dutch coast.

    Nourishments at Sylt island, Germany

    Sylt (Germany) is a sandy barrier island in the North Sea. It is the most northern of the German Wadden Sea islands. The coastal zone is characterised by sand dunes, by sand dune cliffs at the west coast (up to 35 m high, flattening towards the south) and by sand beaches in front of the cliffs, that break some of the oncoming wave energy. Nonetheless, the 40 km west coast is very vulnerable to erosion.  
    Sand nourishment started in 1972 and has been repeated at irregular or regular intervals. Hard structure protection of the west coast has been found ineffective in the long run. Even some negative effects have been noticed. Partly because of the hard measures taken, the central part of Sylt is reasonably stable. However, the hard measures on the long run will fail. Nourishments are now needed to protect these hard coastal constructions. Furthermore, the nourishments are effective in stopping the coastline from receding. At Westerland, the nourishments have to be repeated every six years. See the EUROSION report for more details.

    Sand Engines IJsselmeer

    Along the Frisian coast of the IJsselmeer a need for strengthening of lake dikes in the light of rising sea levels and the need of adapting lake water levels became apparent. It was decided to explore the application of small sand engines at two locations (see Soft Sand Engine IJsselmeer). The general goal of the two experiments is to gain expertise in creating semi-natural floodplains along shallow lake shores and to fill knowledge gaps concerning sediment dynamics and the role of bioengineers in an environment without tides. Moreover, as the area has a complex ownership and is intensively used, good lessons are learned on governance of this type of shore protection and on recreational embedding. 
    Despite the similarity the two Sand Engines are each focusing on different spatial functions The Workumerwaard, aimed at revitalizing a nature area by inducing new sedimentation. The second, at Oudemirdumerklif, concerns an experimental shallow foreshore to absorb wave energy as alternative to dike reinforcement. The first pilot, at Workumerwaard is in place now and monitoring of ecological and morphological effects is taking place. For more details and figures, see Sand Engine Workumerwaard.

    Natural nourishment - Bornrif at Ameland

    The Bornrif is an attached bar at the northwestern edge of the Wadden Sea barrier island, Ameland. Ameland is located in the northern part of Netherlands and together with another Wadden island, Terschelling, it forms the Amelander inlet. The Bornrif is a dynamic feature influenced by the Ameland estuary dynamics, tides and wave driven currents; however, other aspects as wind, vegetation and bioturbation also play an important role in its development. 
    In 1993 the Bornrif was shaped as a hook (like a plunging wave), which was later copied in the design shape of the Sand Engine Delfland. Furthermore, the eco-morphological evolution of the Bornrif shows large similarities with the numerical model predictions for the Sand Engine. The evolution of the Bornrif was studied in detail (Achete, 2011).

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    Below some characteristic data on the above cases are summarized.

    Location 

    Size 

    Volume per m 

    Alongshore shape 

    Measured period 

    Available Data 

    Nourishments cases 

     

     

     

     

     

    Vlugtenburg 

    2.7 Mm³

    1,500 m³ / m 

    uniform 

    2 years 

    27 monthly surveys 

    Sand groynes Delfland  

    1 Mm³ 

    1,000 m³ / m

    3 humps 100 x 50m size 

    4 months 

    7 surveys (2-5 weeks apart) 

    Surfing beach Scheveningen 

    1.5 Mm³

    500 m³ / m

    straight edge (70m) 

    4 months 

    surveys & aerial photographs 

    Sand Engine Delfland

    18.5 Mm³ 

    4,000 m³ / m

    Peninsula 

     

    monthly surveys & aerial photographs 
    and in future ARGUS video 

    Sand Engines IJsselmeer

    2* 25,000 m³

    100 m³ / m

    Peninsula / longshore reef

     

    regular surveys & Lidar images & fibre optic measurements
    and in future ARGUS video 

    Natural development

     

     

     

     

     

    Bornrif

    20 Mm³

    +4,000 m³ / m+

    Spit formation 

    > 10 years 

    Yearly cross-shore profile measurements & bathy surveys  every 5 years 

    References

    Literature

    • Achete, F. (2011). Morphodynamics of the Ameland Bornrif: An analogue for the Sand Engine. MSc Thesis, TU Delft.
    • Achete, F. and Luijendijk, A.P. (2012). Morphodynamics of the Ameland Bornrif: An analogue for the Sand Engine, ICCE 2012. Conference proceedings.
    • Huisman, B. and Luijendijk, A.P. (2010). Approach for eco-morphological modelling of mega-nourishments along the Holland coast.Assessment of tools and approach for multi-scale modelling. BwN Report HK4.1.
    • Huisman, B. and Luijendijk, A.P. (2011). Evaluation of nourishment strategies Holland Coast. BwN Report HK4.1.
    • Van Rijn, L. (1998). Principles of Coastal Morphology. Aqua publications.

    Images

         

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