Beach nourishments at Coolangatta Bay over the period 1987–2005: Impacts and lessons

Erosion of the southern Gold Coast beaches (SE Queensland, Australia) was exacerbated after the extension of the Tweed River training walls in the early 1960s. To achieve the objective of restoring and maintaining beach amenity, significant nourishment works have been undertaken in Coolangatta Bay over the past 30 years. Particularly, under the Tweed River Entrance Sand Bypassing Project (TRESBP) since 1995, a number of nourishment campaigns and the implementation of a permanent sand bypass system in 2001 have resulted in significant changes of Coolangatta Bay morphology. The present case study investigates the influence of both wave climate and nourishment works on the area extending from the updrift Snapper Rocks area to downdrift Kirra Beach. SWAN spectral wave model is implemented at Coolangatta Bay area and forced by the global wave model WW3 to estimate wave forcing and the potential natural longshore drift entering in Coolangatta. Specific transects extracted from accurate bathymetric surveys are used to investigate and quantify Coolangatta Bay sedimentation for the period 1987–2005. A network of Argus video stations provides high sample rate information on the shoreline evolution. Results show that, over the past 10 years, Coolangatta Bay has infilled rapidly. Sedimentation reached up to 6 m in some areas between 1995 and 2005, with beach width increasing by 200 m at Kirra Beach. Rapid seaward shoreline migration is consistent with the intense over-pumping of sand relative to the natural potential to move sand alongshore. The nourishment strategy used during this project has successfully delivered large amounts of sand to the southern Gold Coast embayment, although it has been up to now controversial from many community perspectives. The artificial sand bypassing process proved to be much more efficient than depositing the dredged sand in the nearshore area which requires a significant period of low energy condition in order for the deposited sediment to migrate shoreward and weld to the shore. This case study confirms that, when carefully undertaken, sand bypassing is a sustainable and flexible soft engineering approach which can work in concert with natural processes.     

Verification of sediment transport rate parameter on cross-shore sediment transport analysis

The sediment transport parameter helps determining the amount of sediment transport in cross-shore direction. The sediment transport parameter therefore, should represent the effect of necessary environmental factors involved in cross-shore beach profile formation. However, all the previous studies carried out for defining shape parameter consider the parameter as a calibration value. The aim of this study is to add the effect of wave climate and grain size characteristics in the definition of transport rate parameter and thus witness their influence on the parameter. This is achieved by taking the difference in between “the equilibrium wave energy dissipation rate” and “the wave energy dissipation rate” to generate a definition for the bulk of sediment, dislocating within a given time interval until the beach tends reach an equilibrium conditions. The result yields that empirical definition of transport rate parameter primarily governs the time response of the beach profile. Smaller transport rate value gives a longer elapsed time before equilibrium is attained on the beach profile. It is shown that any significant change in sediment diameter or wave climate proportionally increases the value of the shape parameter. However, the effect of change in wave height or period on sediment transport parameter is not as credit to as mean sediment characteristics.     

Chronic offshore loss of nourishment on Nice beach,French Riviera: A case of over-nourishment of a steep beach?

The 4.5 km-long gravel beach fronting the exclusive resort of the city of Nice, on the French Riviera, in southeastern France, was artificially nourished from 1976 to 2005 to the tune of 558,000 m³, making this long-term operation one of the most significant for gravel beaches in the world. Nourishment has ranged from nil in certain years (1979, 1980, 1983–85, and 2001–2002) to a peak of over 97,000 m³ in 2000. Analyses of 50 transects covering the beach highlight no significant change in net beach width over this 30-year period of massive gravel nourishment. A Principal Components Analysis and a Cluster Analysis used to detect patterns in the 87 beach-width measurement dataset show no clear spatial trends in transect groups that can be interpreted in terms of the morphology of the beach and the steep inner shoreface. Significant wave height off Nice shows no change over the period 1979–2005. Since there is no possibility for alongshore gravel leakage on the strongly embayed Nice beach, the relative stability in beach width clearly implies loss of recharged gravel offshore. Gravel loss following nourishment is favoured by: (1) the steep inner shoreface inherited from the geological context of Nice beach at the flanks of the southern Alps, and (2) the practise of artificial beach widening through flattening, in summer, of a narrow (5–15 m-wide) mobile zone of the profile in order to enhance the ‘carrying’ capacity of this highly touristic beach. Beach widening and flattening following nourishment bring close to the very steep inner shoreface zone several cubic metres of gravel for each metre of beach that may be permanently lost downslope during autumn and winter storms. Recharged gravel is redistributed alongshore and offshore leakage is probably enhanced where small narrow submarine canyon heads impinge on the beach, resulting in a very narrow shoreface. Mean beach width shows an oscillating alongshore pattern that may be due to the influence of these canyons as pathways of gravel loss offshore. However, there is no correlation between mean beach width and distance to the 10-m isobath, used as a surrogate for inner shoreface width. Storms are associated with plunging waves that are particularly effective and concentrated, on this almost tideless shore, over the narrow mobile zone of the beach profile where a series of steep reflective berms are built during storms. The high dynamic pressures associated with this narrow zone of concentrated wave breaking, and energy reflection from the steepened profile, are deemed to contribute to the permanent downslope loss of gravel. This situation of long-term gravel loss is probably accepted by the beach management authority because of the low cost of obtaining nourishment material and the advantages derived from a temporarily wider beach in terms of recreational space.     

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.     

Appraisal of storm beach buffer width for cyclonic waves

The loss of beach sand from berm and dune due to high waves and surge is a universal phenomenon associated with sporadic storm activities. To protect the development in a coastal hazard zone, hard structures or coastal setback have been established in many countries around the world. In this paper, the requirement of a storm beach buffer, being a lesser extent landward comparing with the coastal setback to ensure the safety of infrastructures, is numerically assessed using the SBEACH model for three categories of wave conditions in terms of storm return period, median sand grain size, berm width, and design water level. Two of the key outputs from the numerical calculations, berm retreat and bar formation offshore, are then analysed, as well as beach profile change. After having performed a series of numerical studies on selected large wave tank (LWT) test results with monochromatic waves using SBEACH, we may conclude that: (1) Berm erosion increases and submerged bar develops further offshore as the storm return period increases for beach with a specific sand grain size, or as the sand grain reduces on a beach under the action of identical wave condition; (2) Higher storm waves yield a large bar to form quicker and subsequently cause wave breaking on the bar crest, which can reduce the wave energy and limit the extent of the eroding berm; (3) A larger buffer width is required for a beach comprising small sand grain, in order to effectively absorb storm wave energy; and (4) Empirical relationships can be tentatively proposed to estimate the storm beach buffer width, from the input of wave conditions and sediment grain size. These results would benefit a beach nourishment project for shore protection or design of a recreational beach.     

On the design of beach nourishment projects using static equilibrium concepts: Application to the Spanish coast

The concept of equilibrium plan form and equilibrium profile has been widely used as an engineering tool in order to design beach nourishment projects. The scope of this paper is to further explore this “equilibrium beach” concept in crenulated bays, as a long-term tool for beach nourishment projects. The proposed methodology is based on González and Medina (2001) and combines the static equilibrium plan and profile for long-term analysis. This methodology includes a modified equilibrium plan form, which is able to define the orientation of the local wave front in the diffracting point, and also to locate the downcoast starting point of the static equilibrium beach from which the parabolic plan form of Hsu and Evans (1989) is valid. This methodology permits the application of any equilibrium profile formulation. An example of the application of this methodology and long-term formulations to the design of the Spanish nourishment project of Poniente Beach (Gijón) is presented. Ten years after its construction, the beach has still got a static equilibrium and remains pretty close to the predicted equilibrium beach in plan and profile.     

Development of a medium–long term beach evolution model

A new medium–long term beach evolution model is proposed. This model is based on an analytically integrated sediment conservation equation and on a beach profile evolution model. The sediment conservation equation provides the sediment supplies or losses. The beach profile evolution model redistributes the sediment supplies or losses along the beach profile. In the beach profile evolution model, the definition of the complete profile is incorporated (breaking zone, transition zone, exterior zone and geological zone). The proposed model has been applied to several theoretical cases and to field data, showing the advantages of this model compared to classical “one-line models”.     

Experimental simulation of shoreface nourishments under storm events: A morphological,hydrodynamic, and sediment grain size analysis

This study focuses on barred beach shoreface nourishments physically simulated in a wave flume. The attack of a schematic storm on three different nourishments is analysed. The apex and waning storm phases lead respectively to offshore and onshore sediment transports. Nourishments in the trough and on the outer bar feed the bar and increase wave dissipation offshore. The bar acts as a wave filter and reduces shore erosion (lee effect). In contrast, nourishment on the beach face leads mostly to shore feeding and reconstruction (feeder effect). With successive nourishments, the beach face clearly becomes steeper and onshore sediment transport is reduced during moderate wave climates. The surface grain size analysis reveals marked variations. Coarser sediments are sorted on the bar and the upper beach face. These locations correspond to large wave dissipation zones during the storm apex.     

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.     

Statistical simulation of wave climate and extreme beach erosion

Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion.     

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.     

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。     

Reduction of sand demand for shore protection

Beach nourishment is an environmentally preferred method of shore protection, but the annual sand requirement may lead to substantial maintenance costs. The shoreline processes, involving the surf zone, beach and dune, are reviewed with the aim of reducing the annual sand requirement of eroding shorelines. It is shown that surf zones with equilibrium profiles, on which the wave energy conversion is evenly distributed across the surf zone, from experience for given conditions indicate least loss of sand. On steep, eroding shorelines it may be difficult to establish an equilibrium profile. For such cases, the use of perched surf zones is recommended, which are supported at the seaward limit by an underwater sill. For reduction of littoral transport, the use of pervious pile groynes is recommended. These are arguably more efficient than impervious groynes. The sand loss from a usually dry beach by raised water levels is shown to be a function of the beach slope and is least when the storm waves at raised water levels do not cut an erosion escarpment. The loss of sand from a dune by infrequent severe storm tides can be prevented with the aid of a built-in membrane. These sand losses are usually large and constitute an uneconomic use of this sand resource. The proposed concepts and measures are linked to existing knowledge, augmented by data from the large wave flume (LWF) in Germany and field data from the North and Baltic Sea coasts.     

莺歌海三莺村岸段人工沙滩工程岸线数值模拟以及模型的验证方

以乐东莺歌海三莺村岸段人工沙滩工程为例,其完工1年后的岸线监测结果,表明需要进一步对人工沙滩后的海滩岸线演变进行研究分析。通过GENESIS岸线演变模型模拟人工沙滩后的岸线变化,并尝试采用3种方法对模型进行验证。经过验证后,对人工沙滩工程后1年、3年、5年岸线变化进行了模拟分析。研究结果表明:GENESIS岸线演变模型对于包围型(拦沙堤和离岸堤结合方式)人工沙滩工程是适用的。工程完工1年后,补沙岸线形成了侵淤变化的凹凸弯曲岸线,侵淤幅度不大,5年后侵淤幅度变缓,开始逐渐趋于平衡。据此,也为人工沙滩后期的养护、补沙防护工作起到重要的参考作用。     

Analysis of submerged bar nourishment strategies in a wave-dominated environment using a 2DV process-based model

The present study aims to analyze the effects of different submerged bars nourishment strategies using a 2DV process-based morphodynamical model. A two-barred beach profile typical of the French Mediterranean micro-tidal storm-dominated coastline is chosen as a reference profile. Two different kinds of modified beach profiles are considered. (i) Only the outer bar is nourished, the inner bar being unchanged (ii) both bars are nourished. Three typical wave forcing regimes are considered. The behavior of the natural profile is first investigated under the 3 wave forcing regimes. Then the behavior of the various nourished profiles is analyzed in terms of wave dynamics and bars behavior. On the basis of the model results, the outer bar only nourishment strategy appears to be preferable.     

Seasonal persistence of a small southern California beach fill

Torrey Pines State Beach, a site with large seasonal fluctuations in sand level, received a small shoreface beach fill (about 160,000 m³) in April 2001. The 600 m-long, flat-topped nourishment pad extended from a highway riprap revetment seaward about 60 m, terminating in a 2 m-tall vertical scarp. A 2.7 km alongshore span, centered on the nourishment region, was monitored prior to the nourishment and biweekly to monthly for the following 2 years. For the first 7 months after the nourishment, through fall 2001, significant wave heights were small, and the elevated beach fill remained in place, with little change near and above Mean Sea Level (MSL). In contrast, the shoreline accreted on nearby control beaches following a seasonal pattern common in southern California, reducing the elevation difference between the nourished and adjacent beaches. During the first winter storm (3 m significant wave height), the shoreline retreated rapidly over the entire 2.7 km survey reach, forming an alongshore-oriented sandbar in 3 to 4 m water depth [Seymour, R.J., Guza, R.T., O'Reilly, W., Elgar, S., 2004. Rapid erosion of a Southern California beach fill. Coastal Engineering 52 (2), 151–158.]. We show that the winter sandbar, most pronounced offshore of the nourishment, moved back onto the beach face during summer 2002 (following the usual seasonal pattern) and formed a wider beach above MSL at the site of the original nourishment than on the control beaches. Thus, the April 2001 shoreline nourishment was detectable until late fall 2002, persisting locally over a full seasonal cycle. In an extended 7-year time series, total sand volumes (summed between the back beach and 8 m water depth, over the entire 2.7 km reach) exhibit multi-year fluctuations of unknown origin that are twice as large as the nourishment volume.     

Monitoring and comparison to predictive models of the Perdido Key beach nourishment project, Florida, USA

This paper summarizes the results of over 8 years of data describing the performance of a large beach nourishment project on Perdido Key, immediately adjacent to Pensacola Pass in Escambia County, FL, USA. As a result of a major excavation of the entrance channel to Pensacola Bay, over 7 million m³ of beach-quality sand were placed along the easternmost 7.5 km of Perdido Key, adjoining the entrance channel at Pensacola Pass. The project included the placement of 4.1 million m³ of sand directly upon the shoreline in 1989–1990, followed by the placement of an additional 3 million m³ as an underwater berm just offshore of the beach nourishment project in water depths of roughly 6 m. Monitoring of the performance of the beach nourishment project and the offshore berm has been conducted since 1989, beginning with a pre-construction survey of the project area. Monitoring surveys have been conducted on an annual or biennial basis since that time, with the most recent survey occurring in July/August, 1998. Over 8 years of monitoring data indicate that the beach nourishment project has retained approximately 56% of the original volume placed within the 7.5-km project length. In addition, according to the latest monitoring survey, the dry beach width of the project, initially constructed as 135 m on average, is still 53 m wider than pre-project conditions. Approximately 41% of the originally placed dry planform area remains as of July 1998. The most recent monitoring surveys in 1995, 1997, and 1998 encompass the effects of two major storm systems, Hurricanes Erin (August 1995) and Opal (October 1995). Monitoring of the offshore berm area indicates only a slight landward migration of the berm, accompanied by a minor decrease in volume, over the entire monitoring period. The performance of both the beach nourishment project and the offshore berm appear to be significantly related to the two storm events, particularly Hurricane Opal, and the proximity of the project to the tidal entrance at Pensacola Pass. Comparison of the documented performance of the beach nourishment project to simple existing analytical models of beach-fill evolution have yielded encouraging results in terms of preliminary design aids for future beach nourishment projects in the vicinity of deep tidal entrances.     

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。     

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.     

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.