Beach nourishment,a practical method of erosion control

Artificial beach nourishment, the placing of sand onto eroded beaches, is increasingly employed by coastal engineers as an alternative to structural control of shoreline erosion. Man-made beaches approximating natural forms and processes offer greater protection against storms than eroded beaches and provide increased recreational opportunities. It is hoped that maintenance nourishment will keep pace with subsidence and eustatic rise in sea level, primary causes of beach erosion. Even though negative impacts of beach restoration may be short-lived and limited in scope, sound ecological engineering practices require careful monitoring of dredging operations.     

Evaluation of the physical process controlling beach changes adjacent to nearshore dredge pits

Numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots. A process-based numerical model, Delft3D, is used for this purpose. The analysis is based on the modification of existing bathymetry to simulate “what if” scenarios with/without the bathymetric features of interest. Borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots. It was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces (roller force or alongshore component of the radiation stress), pressure gradients due to differentials in wave set-up/set-down and bed shear stress. Modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion.     

The effects of beach replenishment on the benthos of a sub-tropical Florida beach

Changes in the benthic fauna of the near-shore zone were examined before and after a beach replenishment project on the central Florida east coast. Results indicated that the near-shore sand beach community is relatively species rich, although abundance is dominated by only two species of bivalves, the coquina clams Donax variabilis and Donax parvula. Strong gradients of increased species richness and abundance were found, with values increasing at the more seaward sites for both control and nourishment locations. This distributional pattern was unchanged by beach nourishment. Comparison of mean number of individuals per core across dates and among transects (two-way analysis of variance) showed no indication of significant negative effects of beach nourishment. Similar analysis for mean number of species per core also failed to show significant negative effects. Negative biological effects of beach nourishment may have been minimized in the present case due to a seasonal offshore movement of the dominant coquina clams. The close match of mean fill grain size to ambient grain size and an apparent lack of substantial fill movement into the biologically more diverse offshore areas may also have diminished biological damage.     

不同补沙方案对海滩剖面影响的数值模拟对比分析

大量工程实践表明,海滩养护是当前抵御海岸侵蚀的常见措施。通过人为地向海滩补充沙源,以达到海岸防护、修复沙滩等目的。本文建立了XBeach一维海滩剖面演变数值模型,并与物理模型试验结果进行对比验证;计算常浪条件下不同方案补沙后海滩剖面达到平衡状态的速率;通过对比补沙工况与未补沙工况的风暴后剖面,分析风暴作用下的防护效果。结果发现,补沙量较大时,沙坝向海侧位置补沙在常浪条件下补沙效率高于滩肩补沙,在风暴条件下防护效果优于滩肩补沙。此次研究对于在实际海滩养护过程中节约施工成本、提高施工效率有着重要意义,同时对于评估沙滩养护工程效果有一定的参考价值。     

Multigrain sedimentation/erosion model based on cross-shore equilibrium sediment distribution: Application to nourishment design

In the light of global warming and sea level rise there are many coastal beaches that suffer from erosion. Beach nourishment has become a common practice to maintain the sediment balance on a shore-face. In this paper, a three-dimensional numerical model for evaluating long-term impact of beach nourishment projects has been developed. The model addresses the longstanding complex issue of coastal morphology and sediment grain size distribution from an unconventional angle, which exploits the strong links between grain size distribution and the prevailing transport direction of each sediment constituent under ‘average’ wave and storm action. The present model predicts the redistribution of nourished sediment according to the subtle clues implied by equilibrium distribution curves and latest coastal wave transformation theories. After verification against recent field observations in Terschelling, The Netherlands, the model was used to predict long-term effects of different beach nourishment strategies. It was found that: (a) given the source sediment available in Terschelling the tactics of large volume and less frequent implementation are better than otherwise; and (b) from a pure engineering point of view, waterline nourishment outperforms offshore trough nourishment.The model offers an additional tool for coastal engineers to evaluate the feasibility, effectiveness and the optimization of dumping locations for beach nourishment projects. It is also a useful tool for stratigraphic modelling of shallow-marine sedimentation in conjunction with sea level changes.     

Macrofaunal sediment selectivity considerations for beach nourishment programmes

Nowadays, beach nourishment is widely considered as a better alternative compared to the construction of hard structures to protect a sandy coast against detrimental erosive effects, both from an ecological and an engineering perspective. The rare studies conducted on the ecological impact of beach nourishment are short-term, post hoc monitoring investigations of the benthic macrofauna. Little is known of the biological processes during and after nourishment. To allow swift recolonization after nourishment, the characteristics of the nourished beach have to match the habitat demands of the benthic macrofauna. The sediment preference of the key intertidal species Scolelepis squamata, Eurydice pulchra, Bathyporeia pilosa and Bathyporeia sarsi, which dominate many West European sandy beaches, was investigated through laboratory experiments, both in single-species as well as combined-species treatments. While the former aimed at developing guidelines for impact mitigation of beach nourishment, the latter aimed at elucidating the role of biotic interactions in sediment preference. Results of the experiments indicated that B. pilosa and E. pulchra prefer the finest sediment, while B. sarsi had a broader preference and also occurred in medium-coarse sediments. However, the sediment preference of E. pulchra for fine sediments was not confirmed by other field and experimental studies. The polychaete S. squamata had the broadest preference and even showed a high occurrence in coarse sediments that are not naturally occurring on the sandy beaches where the animals were caught for this experiment. However, this polychaete is a cosmopolitan species, not only occurring on fine-grained beaches, but also on coarse-grained beaches worldwide. The preferences imply that beach nourishment with coarse sediment will have a major effect on B. pilosa while effects of coarse sediments on S. squamata will be minor. Finally, interspecific competition with the sympatrically occurring amphipod B. sarsi was found to change the sediment selection of the amphipod B. pilosa towards the coarser sediments where B. sarsi occurred in lower frequencies.     

Ecological effects of coastal armoring on sandy beaches

Use of coastal armoring is expected to escalate in response to the combination of expanding human populations, beach erosion, and sea level rise along the coasts. To provide a conceptual framework, we developed hypotheses concerning the ecological effects of beach habitat loss associated with coastal armoring. As beaches narrow in response to armoring, dry upper intertidal zones should be lost disproportionately, reducing the habitat types available and the diversity and abundance of macroinvertebrates. Predators, such as shorebirds, could respond to a combination of (i) habitat loss; (ii) decreased accessibility at high tides; and (iii) reduced prey availability on armored beaches. To examine those predictions, zone widths and the distribution and abundance of macroinvertebrates and birds were compared on paired armored and unarmored segments of narrow bluff-backed beaches in southern California. Our results supported the predictions and revealed some unexpected effects of armoring on birds. Dry upper beach zones were lacking and mid-beach zones were narrower (>2 times) year-round on armored segments compared to adjacent unarmored segments. The abundance, biomass and size of upper intertidal macroinvertebrates were also significantly lower on armored segments. Shorebirds, most of which were foraging, responded predictably with significantly lower species richness (two times) and abundance (>3 times) on armored segments. Gulls and other birds (including seabirds), which use beaches primarily for roosting, were also significantly lower in abundance (>4 times and >7 times respectively) on armored segments, an important unexpected result. Given the accelerating pressures on sandy beaches from coastal development, erosion and rising sea levels, our results indicate that further investigation of ecological responses to coastal armoring is needed for the management and conservation of these ecosystems.     

美国东海岸海滩养护工程对中国砂质海滩旅游资源开发与保护的启示

借鉴美国长期以来东部海岸的海滩养护工程投入大量资金物力所取得的显著成效，提出了中国砂质海滩资源开发面临的问题，如海岸侵蚀造成砂质海滩资源丧失、砂质海滩旅游资源面临严重的污染、砂质海滩旅游资源的利用程度差异悬殊、砂质海滩旅游资源的人为破坏严重等，预见到中国实施海滩养护工程将是大势所趋，该工程将会被纳入国家或地方海岸综合规划管理与相关法律中。     

人工岛影响下的海滩修复对策研究——以海口西海岸为例

人工岛建设在缓解滨海人地矛盾的同时带来新的环境问题。本研究聚焦人工岛建设引起的岸滩侵蚀与泥沙分配失衡问题,以海口西海岸为例,建立GENESIS岸线演变模型,探讨人工岛影响下的海滩地貌演化机制,并在此基础上提出“循环养护”的海滩修复对策。主要研究结论为:①海口湾南海明珠人工岛对邻近海滩的影响以“岛后方淤积、两侧侵蚀”为显著特征,且两侧侵蚀热点区的响应幅度存在明显差异。五源河口至新国宾馆岸段侵蚀更为强烈的主导因素为物源匮乏与岸线形态外凸。②通过人工补沙与循环养护相结合的生态修复措施,可实现岸滩泥沙的合理分配与地貌的动态平衡,有效缓解人工岛引起的海岸侵蚀问题。本研究成果可为国内相似类型海岸的岸滩修复提供良好的借鉴意义。     

Eco-environmental impact assessment of pre-leisure beach nourishment on the benthic invertebrate community at Anping coast

In recent years,owing to global warming and the rising sea levels,beach nourishment and groin building have been increasingly employed to protect coastal land from shoreline erosion.These actions may degrade beach habitats and reduce biomass and invertebrate density at sites where they were employed.We conducted an eco-environmental evaluation at the Anping artificial beach-nourishment project area.At this site,sand piles within a semi-enclosed spur groin have been enforced by use of eco-engineering concepts since 2003.Four sampling sites were monitored during the study period from July 2002 to September 2008.The environmental impact assessment and biological investigations that we conducted are presented here.The results from this study indicate that both biotic(number of species,number of individual organisms,and Shannon-Wiener diversity) and abiotic parameters(suspended solids,biological oxygen demand,chemical oxygen demand,dissolved inorganic nitrogen,dissolved inorganic phosphorus,total phosphorus,total organic carbon,median diameter,and water content) showed significant differences before and after beach engineering construction.Biological conditions became worse in the beginning stages of the engineering but improved after the restoration work completion.This study reveals that the composition of benthic invertebrates changed over the study period,and two groups of organisms,Bivalvia and Gastropoda,seemed to be particularly suitable to this habitat after the semi-enclosed artificial structures completion.     

Cost of beach maintenance in the Gulf of Cadiz (SW Spain)

Beach erosion problems have been solved by adding sand to the beaches along the Gulf of Cadiz. The Gulf is located in SW Spain between the Portuguese border and the Strait of Gibraltar. During the last decade, more than 12×10⁶ m³ of sand have been nourished in 38 restoration operations carried out on 28 beaches. The main characteristics of the nourishment campaigns (year, volume, budget, transport method, sand data, etc.) are presented. Location of sand borrow sites and distance to the beaches are also shown. Monitoring programs have been performed in order to calculate sediment loss rates. These results have been related to the beach length, the berm width and the budget in order to obtain a variety of relationships for maintenance cost as, for example, the total annual cost for each beach. This information is very useful when developing a strategy in coastal zone management. Furthermore, at least in reef-protected beaches, small yearly renourishments similar to the yearly losses, instead of greater nourishments performed with a periodicity of many years, lead to an economical saving, as well as to a better use of the natural resources.     

人工海滩研究进展

海滩是激浪作用下泥沙在激浪带的堆积,是海岸带最活跃的地貌单元。近年来,由于世纪性的海平面上升,侵蚀型海滩范围扩大,侵蚀加重,海滩宽度变窄、坡度变陡和滩面物质粗化等问题日益严重,引起了广泛关注,亦成为海岸工程研究的热点课题之一。几十年的工程实践表明,海滩喂养与人工海滩是当前防护海滩侵蚀最有效的措施,并已为欧、美、日等国广泛应用。利用海岸地貌学原理方法,借鉴模拟环境条件类似的周边自然海滩的形成和演变规律,合理的设计海滩物质的颗粒大小和组成,海滩的坡度、高度、宽度以及填砂范围等关键参数,能够有效地使人工海滩更快的达到平衡状态并维持其稳定。在海滩的娱乐休闲功能在国际范围内日益受到重视的今天,这一方法在海岸工程应用上具有重要的现实意义。     

Numerical study of shoreline changes by emergency beach nourishment project at the Middle Beach of Beidaihe, China

Beach nourishment is a common coastal management strategy used to protect beach from erosion along the sandy coastlines. This method has been successfully applied to an emergency project at the West Beach of Beidaihe in the summer of 2008 and the full West Beach nourishment project in 2009-2010, which is the direct base of this study. Some basic information about the emergency engineering area at the Middle Beach is firstly described. The shoreline change of this area, including the analysis of beach width in five monitoring profiles in the bathing places of Middle Beach, is then discussed. After that a numerical model based on one-line theory is established and the numerical results agree well with the measured shorelines, which indicates that the model is appropriate and is qualified to predict the shoreline change of the Middle Beach. With the same model and parameters, long-term performance of the project is predicted, and the result shows that without follow-up nourishment and project, the bathing places can remain suitable for bathing for about 10 a. It is suggested to nourish the beach in time and carry out the beach nourishment project for the full Middle Beach in Beidaihe.     

工程养护海滩对"803"风暴潮的响应过程研究

研究养护海滩对风暴潮的响应过程在人工养滩工程设计与施工中具有重要意义。老龙头养护海滩在竣工半个月后遭遇“803”风暴潮,导致岸滩滩肩最大蚀退 6.5 m,沙坝坝顶最大下蚀 1.2 m。在现场测量的基础上,利用 XBeach 建立风暴潮过程 的老龙头海滩海床演变模型,研究结果表明： （1） XBeach 模拟结果与实际地形变化侵淤趋势一致,风暴潮期间人工沙坝均向岸移动,但模拟结果的侵蚀程度更大,海滩响应更加剧烈; （2） 强浪条件下人工沙坝的透射系数为 0.29~0.42,常浪条件下透射系数为 0.45~0.95,因而人工沙坝在大浪条件下掩护作用更佳; （3） 风暴潮期间人工沙坝附近破波显著,坝顶流速明显增大,最大可达 1.21 m/s,是无人工沙坝情况下的 2.3 倍,而在人工沙坝向岸侧,因波能提前耗散,流速减为 0.28 m/s,是无人工沙坝时的 0.4 倍,且没有产生离岸流。老龙头养护工程整体泥沙损失较少,易于恢复.     

Stability of an artificially nourished beach,Balaena Bay,Wellington Harbour,New Zealand

Balaena Bay, Wellington Harbour, New Zealand, has a small pocket beach that was covered originally by pebbles and cobbles. In February and October 1982, the beach was nourished with sandy granular gravel, the stability of which was monitored until February 1984. Although isolated from oceanic swell, the new beach readily responded to locally generated wind waves which induced both northwards and southwards longshore drift. The net effect was erosion of the southern beach, aggradation over the central beach, and minor fluctuations at the northern end. Yet despite this mobility nearly all the nourishment sediment was retained in the littoral zone. Beach volumes, calculated for each survey, varied little and sediment distribution patterns revealed negligable transport of nourishment sediment to adjacent beaches and offshore areas. Stability is further confirmed by compositional data which record no preferential loss of the sandstone, argillite, and quartz components. The only compositional changes were the incorporation into the new beach of small (< 10%) quantities of sediment derived from the old beach surface and from biogenic productivity.     

Community and Population Responses of the Macroinfauna to Physical Factors over a Range of Exposed Sandy Beaches in South-central Chile

Ten exposed sandy sites covering a range from reflective to dissipative beaches were sampled in south-central Chile to evaluate: (1) spatial changes in species richness, abundance and biomass of the intertidal macroinfauna in response to changes in mean grain size, beach face slope and beach type, and (2) spatial changes in abundance, biomass and body sizes of the most abundant species in response to changes in the physical factors. The number of species, abundance and biomass per beach in general decreased with increasing particle size and beach face slope (steeper beaches) and increased from reflective to dissipative conditions. The best fit for number of species was with Dean's parameter, a measure of beach type, whereas for abundance and biomass the best fits were found with particle size. The isopod Excirolana braziliensis and the anomuran Emerita analoga increased in abundance and biomass towards dissipative conditions, whereas Excirolana hirsuticauda showed the opposite trend in biomass and was significantly larger in beaches with steeper profiles. It is concluded that responses to changes in beach type are more pronounced at community level than within species populations.     

Numerical modelling of erosion and accretion of plane sloping beaches at different scales

The paper focuses on the numerical simulation of erosion of plane sloping beaches by irregular wave attack in three wave flumes of different scales. One of the prime objectives of the tests was to provide a consistent data set for the improvement of numerical beach profile models. A practical application of this research with wave attack on plane sloping beaches is the erosion of the plane beaches after nourishment. Three models (CROSMOR, UNIBEST-TC and DELFT3D) have been used to simulate the flume experimental results focusing on the wave height distribution and the morphological development (erosion and deposition) along the beach profiles. Overall, the model predictions for wave heights show consistent results. Generally, the computed wave heights (H_rms and H_1/3) are within 10% to 15% of the measured values for all tests (under-prediction of the largest wave heights close to the shore). The three models can simulate the beach erosion of the wave flume tests (erosive tests) reasonably well using default values of the sand transport parameters. The model performance for the accretive tests is less good than that for the erosive tests. A practical field application of this research is the erosion of nourished beaches, as these beaches generally have rather plane beach slopes immediately after nourishment. Various graphs are given to estimate the beach erosion of nourished beaches.     

海滩修复养护技术发展趋势与前景

海岸侵蚀是沿海各国面临的共同问题,海滩养护是当前砂质海岸保护的最佳手段,在全球范围内得到广泛应用。本文回顾了海滩养护技术的发展历程,总结了世界范围的海滩养护实践,分析各国海滩养护理念上存在的差异。以研究文献为基础,总结归纳了平面和横向剖面的补砂方式、辅助工程技术和海滩模型预测等方面的海滩养护技术研究进展,并在此基础上提出了海滩养护的未来发展趋势:①针对复杂海岸的海滩养护应用拓展;②基于沉积物管理的海滩养护修复;③从地貌系统到生态系统全面考虑的海滩养护技术;④全球砂源赤字条件下的海滩保护和修复思路。     

Application of remote sensing video systems to coastline management problems

This contribution evaluates the application of coastal video systems to monitoring and management of coastal stability problems on sandy coastlines. Specifically, video-derived parameters (coastal state indicators or CSIs) are developed which facilitate the measurement of the shoreline evolution (erosion/accretion) and response to storms, seasonal cycles and anthropogenic interventions like beach/shoreface nourishment and dredging. The primary variable which forms the basis for all the CSIs discussed in this contribution is the shoreline position derived from time-averaged video images. These waterlines are used to generate secondary products including shoreline contours at a constant pre-defined level, (intertidal) beach volumes, and momentary shoreline positions which reflect the sand volume in a meter wide section of the intertidal coast. Video-derived coastal state indicators were verified via comparisons with traditional topographical/bathymetric surveying techniques and a good agreement was found in all cases. CSIs were computed for three contrasting sandy coastal environments including an unprotected natural beach, a protected beach and a spit. Firstly, results are presented which demonstrate the advantages of coastal video systems over and above infrequent traditional topographic/bathymetric surveying methods. Namely, the ability of video-derived CSIs to quantify the magnitude, accurate location, precise timing and rates of change associated with individual extreme events and seasonal variability in the wave climate. Secondly, video-derived coastal state indicators were used to monitor two different types of human intervention, including beach nourishments and a dredged pit in a navigation channel. The video-derived datasets of coastal state indicators offered significant improvement to current CZM practices, facilitating better timing of management interventions as well as more effective monitoring of the spatial impact and longevity of these actions.