Luijendijk, Arjen

Ouwerkerk, Sonja

Penning, Ellis

Steetzel, Henk

Van Eekelen, Erik

English

Hydraulic Engineering Repository

Article, Published VersionVan Eekelen, Erik; Luijendijk, Arjen; Ouwerkerk, Sonja; Steetzel, Henk;Penning, EllisSandy strategies for resilience - lessons learned from BWNHydrolinkVerfügbar unter/Available at: https://hdl.handle.net/20.500.11970/109468Vorgeschlagene Zitierweise/Suggested citation:Van Eekelen, Erik; Luijendijk, Arjen; Ouwerkerk, Sonja; Steetzel, Henk; Penning, Ellis (2019):Sandy strategies for resilience - lessons learned from BWN. In: Hydrolink 2019/4. Madrid:International Association for Hydro-Environment Engineering and Research (IAHR). S.106-109. http://iahr.oss-accelerate.aliyuncs.com/library/HydroLink/HydroLink2019_04_a9d9sas0das9f.pdf.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.106 hydrolink number 4/2019Introduction of sandy solutions andpilotsA substantial part of the world’s coastlinesconsists of sandy beaches and dunes that forma natural water defense protecting thehinterland from flooding while at the same timeproviding valuable space for recreational activities and nature development. More than75,000 km of sandy shorelines are experiencingpersistent sand losses which on the longer termresults in a setback of the coastline, negativelyinfluencing the functions and values of theseareas[1]. To mitigate these effects, coastalmanagers implement mitigating measures,which can either be hard constructions (i.e. seawalls or revetments) or soft (sandy) strategies.Sandy strategies are based on the availability ofsand in the system and, when necessary, on thesupply of additional sand via sand nourish-ments (soft solutions) instead of altering thesystem (hard solutions). Sandy strategies are widely applied on workingcoastal systems such as beaches and dunes,with various potential mechanisms to conductthe nourishments. The construction of newsandy solutions is however less common, butalso seems a logical response in light of thevaluable functions that these solutions offer interms of provision of habitats and supportingbiodiversity and providing space for valuablelandscape and recreational functions. Withinthis article three projects are described: alocalized mega-nourishment, the Delfland SandMotor, a newly created dune landscape, theHondsbossche Dunes and a sandy foreshore infront of a dike in a lake environment, theHoutribdijk. All three of them comprise sandysolutions, but they work in different systemsbased on different principles. Still, their lessonslearned are applicable to sandy solutions andNBS in wider context. Sand MotorThe Sand Motor is a large sandy peninsula,constructed in 2011 on the Dutch North Seacoast near The Hague. This unprecedented pilotproject involved placing 21.5 million m3 of sandon and in front of the beach with the aim that itwould spread along the coast. The Sand Motoris a unique beach nourishment due to its size(about five times that of an averagenourishment), the design philosophy behind it,and its multifunctionality. The Sand Motor isintended to feed the adjacent coasts by usingthe natural forces of tides, waves and wind; in away, it is built to “disappear”. Another uniqueaspect of the Sand Motor is that it combines theprimary function of coastal protection with thecreation of a new natural landscape that alsoprovides new leisure opportunities. From theoutset, “learning by doing” has been a crucialpart of the project.A key question was how the morphologicalbehavior would influence the various functions inSANDY STRATEGIES FOR RESILIENCE – LESSONS LEARNED FROM BWNBY ERIK VAN EEKELEN, ARJEN LUIJENDIJK, SONJA OUWERKERK, HENK STEETZEL & ELLIS PENNINGAmongst the various Nature-Based Solutions (NBS) for flood defenses, sandy strategies are well-known andapplied regularly in sandy coastline systems to counter or compensate erosion. However, this is only part of thepossibilities that sandy strategies offer as they provide additional benefits by bringing new habitats and supportingbiodiversity and recreational areas through the active development of ecosystems ranging from new dunes toforeshores. Several sandy strategies have been piloted in the Netherlands by the EcoShape consortium, a Dutchconsortium on NBS knowledge development termed Building with Nature, in order to establish a knowledge baseregarding the full palette of opportunities for sandy strategies. It was found that although the studied cases operatevery differently and have inherent differences in supplying and using (ecosystem) functions, and that their feasibilityis strengthened by the availability of sand and an appreciation for the strategy’s long term flexibility and contributionto (coastal) resilience.Figure 1. Execution of sand nourishmentsGREEN COASTALINFRASTRUCTURE107hydrolink number 4/2019space and time. For example, measurementsshow that the model simulations upfrontoverpredicted growth of the dune area by 500%after four years[2]. Furthermore, the observederosion volume in the first years is significantlyhigher than predicted upfront[2] (reference). Thehigh resolution and frequency of the measure-ments facilitated a unique ’numerical living lab’,where the relevance of a range of environmentalforcing and processes have been analyzed indetail. This has resulted in greatly improvedinterdisciplinary knowledge on the behavior ofsuch sandy solutions [3]. Extended modelcapabilities for predicting its decadal behaviornow allow for landscape designing of sandysolutions elsewhere in the world.Hondsbossche dunesThe Hondsbossche and Pettemer sea dike nolonger met current safety standards. Therefore,the dike was reinforced in 2015 with a soft,natural barrier of 30 million m3 of sand on theseaside of the dike. It was renamed'Hondsbossche Dunes'.The design consists of a soft shallow foreshore(the beach) and a varied artificial dunelandscape that has the potential to develop invaluable Natura 2000 habitats. Together, theseconnected systems make up the primary flooddefense and provide the desired spatial quality. In order to get more insight in how the design ofsuch a new dune can influence landscapeforming processes, an innovation project wasstarted, including the following themes:• Optimizing design and morphologicalevolution• Predictability in the development ofengineered habitats• Perception of local community and visitorsMonitoring showed us that the morphologicaldevelopment of the dunes was relatively wellpredicted [4]. The development of theengineered habitats is more difficult: it is a slowprocess and it takes (more) time to be able toconclude whether valuable Natura2000 habitatsare created [4]. The perception of localcommunity and visitors is merely positive: theamount of hinder by sand being transportedover the dike (one of the biggest fears beforeconstruction started) is limited [4].Furthermore, the Hondsbossche Dunescombine water safety, recreational value andnature value.[4] In several occasions one has tochoose which function prevails.Different coastal solutionsAlthough at first glance the large-scale sandyinterventions of the Hondsbossche dunes andthe Sand Motor seem much alike, their conceptand their design are very different. Whereas theHondsbossche dunes created a new beach-dune system that is designed andcreated to stay in place and protect thehinterland, the design of the Sand Motor hasbeen such that it disappears. Morphologicallong-shore transport is part of the working of theSand Motor, as long as the sand is brought toother parts of the beach or foreshore of theDutch coast, but this transport was to beminimized for the goals of the Hondsbosschedunes. Despite their differences, the similaritiesregarding the additional values created by bothprojects are also striking; both areas are nowrenown landscape features that have anenormous ecological and natural value, but also attract recreation. Aeolian development ofyoung dunes and associated habitats is takingplace at both sites.IAHRErik van Eekelen is Lead Engineerof the environmental engineeringdepartment of Van Oord. He is partof the Management Team of theEcoShape-consortium, thatdevelops knowledge via pilots andresearch on the topic of Buildingwith Nature.Arjen Luijendijk is an expert in thefield of modelling morpho-logicalimpacts of coastal developments atDeltares. For EcoShape he wasproject manager for theNatureCoast project, studyingdevelopment, behaviour and widerapplicability of the Sand Motor.Sonja Ouwerkerk is head of thedepartment Rivers, Coasts andEstuaries at HKV Consultants. ForEcoShape she was projectmanager of the innovation projecton the Hondsbossche Dunes,learning from its development.Henk Steetzel is senior advisor coastal morphology, safetyissues and building with natureconcepts at ARCADIS NederlandBV. For EcoShape, he was projectmanager of the Houtribdijk pilotproject, a test with sandyreinforcement of the dike.Ellis Penning is a senior ecologistat Deltares and leads the researchprogram on Nature BasedSolutions. She specializes inecohydraulics with a focus on theinteraction between vegetation andhydro-morphological processesand its application in daily watermanagement. Figure 2. Aerial view on the Sand Motor Figure 3. Aerial overview of the Hondsbossche DunesGREEN COASTALINFRASTRUCTURE109hydrolink number 4/2019IAHRHoutribdijkA conventional dike reinforcement is usually thefirst option to be considered when an existingdike does not meet the required safetystandards. An alternative solution is to constructa foreshore which consists of a large quantity ofsand that is capable to dissipate the incomingwaves, thereby reducing or even eliminating thewave loads on the dike. For the strengthening ofthe Houtribdijk the latter was considered, butrequired further insights in the behavior of suchforeshore in its lake environment.In order to gather such insight, a researchproject was established with the objective todemonstrate the feasibility and the limitations ofthis approach, and answer research questionson, for example, the effect of waves on theforeshore and beach and the influence ofvegetation growth on the stability of the sandbody. Results have been used to supportdecision making and enable the design of futureforeshores for other locations and environ-ments [5]. As part of the project, a large-scale pilot studywas carried out. The research plot was locatedalong the Houtribdijk between the citiesEnkhuizen and Lelystad in a large shallow lakecalled Markermeer in the Netherlands. Theforeshore test section was monitored intensivelyduring four years, from 2014 to 2018. Thismonitoring included water levels, as well aswave measurements, morphological changes inthe sandy profile and vegetation development.All the data gathered has been analysed toanswer a series of pre-defined researchquestions, such as how a secure, stable andcost efficient sandy foreshore can be designedin a lake system. Finding a balance betweensecurity and cost-efficiency requires insight inthe physical processes driving the morpho-logical change and the wave damping capacity,as well as quantification of the related uncer-tainties. The results have been applied to designa sandy reinforcement of a large section of theHoutribdijk as shown in Figure 4 [5].The application of a sandy foreshore in a lakeenvironment, demonstrates that sandy solutionsare not only applicable in coastal settings.Vegetation developmentIn all the above examples it is clear thatvegetation and its development play a major rolein sandy solutions. Dune and shorelinevegetation such as marrow grass, reeds andwillows have a strong impact on morphody-namic processes in sandy foreshores. Thepresence of vegetation helps to stabilize thesediments and limits aeolian transport. Also,when vegetation develops along the shorelineand in shallow waters it reduces wave impact onthe shore. Especially in newly created sandyforeshores, vegetation needs several years toestablish itself and mature. Therefore, it can bebeneficial to stimulate the presence ofvegetation to reduce sand drift inland immedi-ately after construction. The success, speed andtype of vegetation development dependsstrongly on the abiotic conditions at the site,such as soil type, average groundwater tableand fluctuations in water levels along the shore.Additionally, the available seed bank and grazingof the vegetation by birds and mammals affectthe final result. Planting the desired vegetationspeeds up the process, as does the applicationof more nutrient rich silty sediments or claysupplied to the top-layer of the sandy foreshore.The additional nutrients stimulate growth and theenriched soil retains water better during dryperiods. Planting should be done in the correctseason depending on the plant species,generally in early spring and if necessary, atemporary irrigation system (e.g. using sprinklers) could be used to aid the solid rootingof the planted vegetation. As vegetationdevelops over time, attention must be payed toits management over the life time of the sandyforeshore. A proper long-time vegetationmanagement plan must be made that addre-sses potential measures to counter undesirabledevelopments, such as the sudden collapse ofthe vegetation due to illness or heavy grazingand the occurrence of undesirable species.Creating such management plans during thedesign phase of a new sandy foreshore alsohelp in the acceptance of concept.   Conclusive remarksDespite the distinct features of the various sandysolutions studied by EcoShape, it is clear that asa palette of solutions, the sandy strategies havedemonstrated their feasibility, both from atechnical perspective as well as from theperspective of created value. For furtherupscaling it is important to recognize keycomponents that have contributed in this feasibility being a) the availability of sand (atrelatively limited costs), b) an appreciation forthe flexibility that the sandy strategy inherentlyoffers and c) the landscape values created andtheir opportunities for recreation. nReferences: [1] Luijendijk, A.P., G. Hagenaars, R. Ranasinghe, F. Baart, G.Donchyts, and S.G.J. Aarninkhof (2018). “The State of the World’sBeaches.” Scientific Reports 8. https://doi.org/10.1038/s41598-018-24630-6, pp. 2045–2322.[2] Taal, M.D., Löffler, M.A.M., Vertegaal, C.T.M., Wijsman, J.W.M., Vander Valk, L. and Tonnon, P.K., 2016. Development of Sand Motor.Concise Report Describing the First Four Years of the Monitoringand Evaluation Programme (MEP). Delft, Netherlands: Deltares.[3] Luijendijk, A.P. and van Oudenhoven, A., 2019. The Sand Motor: ANature-Based Response to Climate Change: Findings andReflections of the Interdisciplinary Research Program NatureCoast.[4] EcoShape (2018), Eindrapportage Innovatieproject HondsbosscheDuinen (in Dutch)., available at:https://www.ecoshape.org/uploads/sites/3/2016/07/Eindrapportage-Innovatieproject-Hondsbossche-Duinen.pdf[5] Steetzel, H., van der Goot, F., Fiselier, J., de Lange, M., Penning, E.,van Santen, R. and Vuik, V., 2017. BUILDING WITH NATURE PILOTSANDY FORESHORE HOUTRIBDIJK DESIGN AND BEHAVIOUROF A SANDY DIKE DEFENCE IN A LAKE SYSTEM. CoastalDynamics: Port of Spain, Trinidad and Tobago.[6] de Lange, H.J., Huiskes, H.P.J., de Groot, G.A., Penning, E.,Steetzel, H.J., Fiselier, J., Ouwerkerk, S. and de Vries, J.V.T., 2016.The role of vegetation in Building with Nature pilot sandy foreshoreHoutribdijk. In Netherlands Annual Ecology Meeting (NAEM) 2016.Figure 4. Execution of sand nourishments Figure 5. Planted section of the sandy foreshoreGREEN COASTALINFRASTRUCTURE

Sandy strategies for resilience - lessons learned from BWN

http://henry.baw.de/bitstream/20.500.11970/109468/1/HydroLink_2019_04_Sandy%20strategies%20for%20resilience%20-%20lessons%20learned%20from%20BWN.pdf

Sandy strategies for resilience - lessons learned from BWN

Abstract

Similar works

Full text

Available Versions

Hydraulic Engineering Repository