Download Citation on ResearchGate | On Jan 1, , R.G. Dean and others published Beach nourishment theory and practice. Beach Nourishment. Theory and Practice Biological and economic aspects of beach nourishment are addressed. Sample Chapter(s) Foreword ( KB). Beach Nourishment: Theory And Practice (Advanced Series On Ocean Engineering (Hardcover)) ENGINEERING (HARDCOVER)) BY ROBERT G DEAN PDF.
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Thus, two of the most powerful scientific tools are routinely overlooked in favor of purely observational monitoring. Inferences reached by comparing results of separate monitoring studies are particularly tenuous, because in none of these contrasts does only a single factor differ among studies. The physical habitat and biological response variables commonly monitored in beach nourishment projects tables 2 , 3 include many of relevance.
Among those that monitored habitat condition, varying percentages of studies measured turbidity; mean grain size; sediment grain-size distribution; surface cover by hard substrata shells, limestone, etc.
The biological responses assessed included total abundance of the entire biotic assemblage, abundance of component taxa, total biomass, biomass of selected taxa, size—frequency distribution of selected taxa, various species diversity indices, community composition, and some measure of physiological status of an important species table 4.
Nevertheless, disturbingly high percentages of assessment studies 25 to 38 percent for dredging and 17 to 80 percent for filling failed to measure any habitat variable tables 2 , 3. Despite the need for dredging contractors to monitor topography as a permit condition and as a measure of performance, this important habitat characterization was not routinely reported in the impact assessment documents. Its complete omission from dredge sites table 2 is especially critical because creation of deeper pits induces fine sedimentation, which can inhibit recovery of the natural benthic invertebrate community for years Rakocinski et al.
Although studies frequently measured relevant aspects of physical habitat condition, only sedimentation rate, out of many potentially important physical processes, was estimated with any appreciable frequency tables 2 , 3.
Sediment transport, erosion of fine sediments off the beach face, dynamics of turbidity plumes, concentration of large shells, and other physical processes likely to influence the biota and affect recovery went without evaluation in any impact study. Few studies measured changes in body size within species, which can indicate mode of recolonization larval transport and settlement versus migration of older stages; table 4.
Measurements of biological processes such as burrowing and predation rates have been reported from only one study Manning and recruitment rate from one other Lindeman and Snyder Gut contents of fish were only occasionally measured as an indication of feeding success included in physiological status; table 4. Despite the scientifically compelling advice of Nelson to avoid use and risky interpretation of diversity indices, this practice is still common in beach nourishment studies table 4 and still without rigorous conceptual support Hurlbert When the simple, more readily interpretable species richness is measured matching current usage in basic ecology , the necessary adjustments for statistical dependency on abundance Hurlbert are missing.
Sampling design Our synthesis of sampling designs reveals numerous inadequacies that seriously compromise the studies' results and conclusions box 1.
Researchers engaged in field sampling to estimate biotic abundances usually used appropriate devices, but the 39 percent incidence of failure to employ the least biased gear would be viewed as unacceptably high for any scientific granting agency. The most frequent violation came from the use of grab samplers instead of cores to sample soft-sediment invertebrates.
This results in failure to sample to the full depth of occupation of the sediment column. Furthermore, those sedimentary strata that are included in a grab sample are not sampled equally in contrast to a core, which projects its surface area downward , making it impossible to estimate density accurately. Grab samples also include varying amounts of sediments per sample, depending on bottom hardness and on obstructions such as shells. A serious shortcoming in the sampling designs of most studies was the failure to consider both natural spatial variation and natural temporal variation on multiple scales so as to craft a sampling design that minimized unexplained error variance and prevented confounding of sources of variation Green , Underwood Although 26 percent of the studies included sampling in a spatially nested and 30 percent in a temporally nested design, not one incorporated this information into a nested analysis so as to partition out scales of natural variability.
Hard coastal protection structures
Few of the monitoring studies of beach nourishment employed a priori power analyses of any sort 9 of 46 contained inappropriate power analyses, and only 1 contained an appropriate analysis to help determine how much replication was required to detect an effect of biologically meaningful magnitude.
Only one study Wilber et al.
This power analysis showed that the design could detect only threefold or greater differences in surf fish abundance, which obviously did not provide much resolution. A large fraction 62 percent of past assessments of ecological impacts of beach nourishment possessed sampling designs without adequate power to detect effects of importance defined as an ability to detect with 80 percent probability a decline of approximately 50 percent or an increase of approximately percent.
Most, but not all, studies included sampling of control sites, but there was a relatively high incidence of potential violations of the basic principle of independent controls box 1.
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Few beach nourishment studies followed the sound statistical advice Hurlbert of interspersing treatments and controls to avoid spatial interdependence.
This is due, in part, to the lack of replication of fill sites in most projects, because sediments are typically deposited along a continuous stretch of the shoreline Nelson Despite the common practice of extracting sediments for nourishment from multiple dredge sites, interspersion of treatments and controls to determine the impacts of sediment mining is also rare.
Where the lack of replication of disturbed sites prevents a fully interspersed design, bracketing of the disturbed site with controls on both sides is the next best option. This was done in 11 of 35 controlled studies examining the impacts of filling. Often, however, the putative control site was located too near the fill site, so that impacts transported by physical along-shore processes probably modified the control at least at one end of the beach Hayden and Dolan Absent a gradient design that spaces sites at varying distances away from the fill site, rigorously identifying when a putative control has been compromised and quantifying the spatial extent of impact is difficult or even impossible.
A gradient design has been employed in only one assessment of fill impacts Hayden and Dolan In some studies, sites that had been recently nourished were then used to represent controls for subsequent nourishment Burlas et al.
Such a design violates the concept of a control and should be avoided to prevent the bias of underestimation of impacts of nourishment. The duration of monitoring in these studies was frequently insufficient to characterize the biota before nourishment or to demonstrate the duration of habitat and biological impacts afterward. Sampling before the disturbance occurs should be sufficient to characterize natural preexisting differences between treatment and control sites in physical habitat and biotic systems Stewart-Oaten et al.
Frequently, studies did not adequately anticipate the nourishment project, and permit-granting agencies failed to delay the project to allow initial biotic characterization during relevant productive seasons.
Eighty-seven percent of monitoring studies, with an average duration of 1. Statistical analyses The statistical analyses done on the monitoring data to test for biological impacts suffer from critical flaws in the basic sampling design; from improper analyses that do not match the sampling design; from failure to fully explain, justify, and report on the analyses; and from unjustified interpretations box 1. A disappointing 27 percent of the beach nourishment studies conducted no formal statistical tests of significance.
Many studies 70 percent of the 33 studies that employed formal statistical testing failed to include all appropriate independent factors or did not test for significance of all the measured response variables.
The most serious analytic deficiency was the almost universal failure in 41 of 46 studies to isolate estimates of impact from confounding contributions of natural spatial and temporal variation by using a BACI before—after, control—impact type of analysis Green , Stewart-Oaten et al. The tests for biological impacts generally used either a spatial contrast among control and disturbed sites or a temporal contrast across time at sites before and after dredging or filling.
Use of only spatial contrasts requires that no natural spatial variation exists between control and disturbed sites, a generally flawed assumption, since the structure of macrobenthic assemblages varies according to the morphology of beaches at scales of tens to hundreds of meters Barros et al. Using a temporal contrast to evaluate the impacts of nourishment requires the assumption that the response variable typically organism density would remain constant over time in the absence of any impact.
This assumption is violated by benthic invertebrate populations, whose seasonal variation is quite dramatic on sandy beaches Manning Even if season is controlled, interannual differences can be large, confounding the ability to use temporal contrasts to infer impacts.
Interestingly, 50 percent of the studies of beach nourishment were designed with the potential for BACI-type analysis, yet failed to conduct this most appropriate and rigorous analysis of variance to reach conclusions unbiased by natural spatial and temporal change. Despite the emergence of powerful methods of multivariate statistical analysis of community responses to perturbations Clarke , few studies of impacts of beach nourishment went beyond tests on separate taxa or totals of taxa.
Those few studies that did conduct assessments of community response employed similarity indices to compare nourished and control biotas typically restricted to the soft-sediment invertebrates. No study applied the gold standard of multivariate analysis, nonmetric multidimensional scaling n-MDS , an ordination procedure that has been demonstrated to discriminate ecological patterns with far greater resolution than univariate responses Clarke Most 84 percent studies overlooked formal statistical analysis of how changes in a physical factor or process may have caused a biological response box 1.
This oversight is particularly important in the case of the benthic invertebrates, for which much basic biological research demonstrates that sedimentology can dictate community composition Gray Often the physical factors are monitored by a consultant separate from the one who conducts the biological studies, thereby inhibiting coordinated sampling and joint analyses of sampling results.
Partly as a consequence, no monitoring study of beach nourishment has critically assessed how mismatched sediments continue to serve as a press disturbance Bender et al. Beach nourishment is universally considered a short-term pulse disturbance, inappropriately viewed as analogous to natural sediment movements during a major storm.
Uncharacteristically coarse sediments can be expected to remain for years on intertidal beaches and to become concentrated by wave action in the biologically most important zone, the swash zone, where they can continue to modify natural invertebrate abundance and community composition for years.
Enhancement of the fraction of fine sediment during beach nourishment also has the potential to represent a press disturbance long after filling is completed, as wave energy over time erodes and exposes fill materials into which mud has been embedded and thereby continues to inject biologically deleterious turbidity into the surf zone.
For both methodological and biological reasons, the biological impacts of elevating turbidity during and after beach nourishment are never properly assessed Telesnicki and Goldberg The persistence of a veneer of sediments over a coral reef or hard-bottom habitat constitutes a press perturbation that can last at least as long as the typical 3- to year interval between repeated nourishment projects Lindeman and Snyder Conclusions and interpretations The conclusions of beach nourishment studies are often flawed by lack of compelling support from adequate evidence, analysis, or interpretation box 1.
In our sample, the authors of 73 percent of the studies misinterpreted at least some of their results. Few studies 22 percent included attempts to interpret observed biological responses by appeal to mechanistic processes. The conclusions of 56 percent of studies lacked rigorous support from evidence and analysis, most often because the sampling design, the analyses, or both failed to control for both natural spatial and temporal variation. The failure to address the power of the study design also frequently led to unjustified conclusions of absence of impacts, when capacity to detect even large impacts was compromised by high natural variability and low replication.
The scholarship of the science in these studies was poor. A large fraction 49 percent of beach nourishment studies failed to do more than a superficial job of citing 0 to 10 citations and synthesizing relevant scientific literature. Agency practice and policy implications Our review of studies of impacts of beach nourishment, mostly monitoring studies conducted as a condition for permits, reveals serious deficiencies.
The widespread flaws in design, analysis, and interpretation help explain why so much uncertainty still persists over the ecological consequences of beach nourishment despite four decades of monitoring at substantial expense.
Substandard biological monitoring of beach nourishment persists despite the publication of reviews that provide explicit guidelines for the variables that should be monitored and the spatial and temporal scales to consider Nelson , NRC , Schmitt and Osenberg , Greene Further detailed guidance required to produce a model study design to assess impacts of beach nourishment with rigor is implicit in our descriptions of study flaws box 1.
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Inadequate funding of basic process-oriented science in the beach ecosystem contributes to the prevailing high uncertainty involved in predicting biological impacts of beach nourishment projects. To extrapolate from the demonstration of any given nourishment project's impacts and make reliable predictions about future projects requires a basic understanding of the processes that drive the dynamics of the natural system at 1- to km resolution, a typical length scale of nourishment.
Although many monitoring studies are adequately funded for the narrow goal of assessing impacts, funding for interdisciplinary studies of fundamental processes in the natural beach system, such as coupled physical and biological consequences of relative sea-level rise, waves, currents, and storms, either has not been sufficient or has not been pursued by the basic science community.
Funding at about twice this level and for the same duration could have created a model study of fundamental beach processes that would improve the generic capacity to predict impacts. Funding agencies for basic science and the scientists who apply for their research grants bear partial responsibility for this poverty of understanding.
The National Science Foundation and NOAA National Oceanic and Atmospheric Administration , through their coastal ocean programs, could provide targeted funding for physical—geological—biological process studies of beaches to enhance the necessary fundamental understanding that is now lacking.
Such interdisciplinary studies, using observation, experimentation, and modeling of the nearshore ecosystem, also provide potential for incorporating the consequences of multiple stressors on a landscape scale and thereby approach the ideal of ecosystem-based management endorsed by the US Commission on Ocean Policy US COP There is a need for more basic and holistic research on process as well as more rigor in project-specific impact analyses. So why do the federal US Army Corps of Engineers and state permit-granting agencies that are responsible for carrying out the mandates of the National Environmental Policy Act NEPA fail to ensure prevailing standards of scientific rigor and thus to discharge their obligation to protect public trust resources?
Partial answers to this critical question come from a consideration of the process by which the monitoring components of beach nourishment permits are developed. Neither the US Army Corps of Engineers nor the state permitting agency employs the anonymous scientific peer-review process that is central to insuring high standards of excellence in basic scientific research NRC A sufficiently substantial beach can accommodate the dynamic changes that are the result of differing climatic conditions.
However, where human life may be at risk and high density, high value conurbations exist, the use of hard elements of a defence may be unavoidable. Conditions for applying hard coastal structures A good understanding of the coastal environment at a site under consideration is an essential prerequisite to assessing the ability of a coastal defence option to perform as it is intended. A complex interaction exists between the various elements defining the coastal environment.
The introduction of coastal protection works will invariably modify nearshore processes in some way and it is important to account for that feedback effect.
Coastal morphology at any location is the result of erosion and accretion patterns which, in turn, depend on the interaction of wave climate, currents and tides with this morphology. The causes and effects of coastal features must always be considered when dealing with works which affect littoral movement. The origin of beach material can be from inland sources brought to the coast by rivers or from the erosion of cliffs in the immediate or adjacent coastlines.
Sometimes there can be shoreward pathways of sediment from offshore sources. In some cases, these processes may no longer be active and the beach may consist of relic materials. Knowledge of the geology underlying the nearshore zone is important because a stratum that is different from the surface material can affect the way in which a beach behaves.
Study on alternatives of sand placement method for beach nourishment project
A thin veneer of loose material on an erodible platform can act as an abrasive and accelerate erosion, whilst its existence on an impermeable base will be inherently unstable and more mobile than an equivalent deep beach.Although 26 percent of the studies included sampling in a spatially nested and 30 percent in a temporally nested design, not one incorporated this information into a nested analysis so as to partition out scales of natural variability.
Google Scholar. Please choose whether or not you want other users to be able to see on your profile that this library is a favorite of yours. Beach nourishment can also be employed in conjunction with other adaptation technologies and can help to address the drawbacks of these hard technologies, which include beach lowering and downdrift sediment starvation.
Appropriate levels of monitoring and mitigation charges could be assessed to each project and paid into a single fund. No study applied the gold standard of multivariate analysis, nonmetric multidimensional scaling n-MDS , an ordination procedure that has been demonstrated to discriminate ecological patterns with far greater resolution than univariate responses Clarke This oversight is particularly important in the case of the benthic invertebrates, for which much basic biological research demonstrates that sedimentology can dictate community composition Gray Assuming that the peer-reviewed, university-examined, and more widely cited gray literature tends to be of higher quality than unpublished reports that are only locally available and not readily accessible, the statistics based on our sample most likely understate the frequencies of study deficiencies.
A review of 46 beach monitoring studies shows that a only 11 percent of the studies controlled for both natural spatial and temporal variation in their analyses, b 56 percent reached conclusions that were not adequately supported, and c 49 percent failed to meet publication standards for citation and synthesis of related work.