RECOMMENDED BEACH NOURISHMENT GUIDELINES FOR THE STATE OF FLORIDA AND UNRESOLVED RELATED ISSUES
Robert G. Dean and
Thomas J. Campbell
November 5, 1999
Results from a Workshop on Beach Nourishment Held Under the Auspices of:
Office of Beaches and Coastal Systems Department of Environmental Protection State of Florida
Workshop Held on August 3 and 4, 1999 Atlantic Beach, FL
RECOMMENDED BEACH NOURISHMENT GUIDELINES
FOR THE STATE OF FLORIDA AND UNRESOLVED RELATED ISSUES
Results from a Workshop on Beach Nourishment Held Under the Auspices of.Office of Beaches and Coastal Systems
Department of Environmental Protection State of Florida
Workshop Held on
Atlantic Beach, FL August 3 and 4, 1999
Robert G. Dean and Thomas J. Campbell Through a Contract With the Department of Coastal and Oceanographic Engineering University of Florida Gainesville, Florida 32611
A workshop, sponsored by the Office of Beaches and Coastal Systems of the Florida Department of Environmental Protection, was held on August 3 and 4, 1999 to develop beach nourishment guidelines. The main results developed during this workshop are presented below.
Background Erosion: Should be represented in calculating project performance prediction, and could be represented directly based on historical data or as background transport. There is a question of whether the state of the art is sufficiently advanced to calibrate numerical models to represent background erosion in cases where large perturbations (such as a littoral barrier) have not been introduced into the system.
Sediment Sizes: Equilibrium beach profile (EBP) methodology should be used to account for nourishment sediments that differ in size from native beach sediment sizes. If the pre-nourished beach profile does not agree well with EBP methodology, modifications may be required. Other more conventional approaches, such as the overfill method may be considered also. Volume Densities: A nominal minimum nourishment volumetric density of 80 yd'/ft is recommended in cases where the native and nourishment sand sizes are compatible in size. For cases in which the nourishment sand is coarser and finer than the native less and greater densities are recommended, respectively. If these recommended densities are not possible, less than desirable performance should be anticipated.
Project Monitoring: Recommendations for project monitoring are presented which include preand post-project monitoring and annual monitoring for three years for the initial nourishment and for one year for renourishments. Thereafter the monitoring would be on a biennial basis. Additionally, monitoring after severe storms is recommended. Monitoring to address specific design needs is addressed.
End Losses: End losses should be estimated in the design phase through both simple and detailed numerical models which account for the "diffusive" nature of beach nourishment evolution.
ISSUES PRECLUDING GUIDELINE DEVELOPMENT
Issues were identified which preclude guideline development at this stage of understanding. Approaches to reducing uncertainty in design were developed for each such issue. Issues identified are: (1) Poorly sorted nourishment sediments, (2) Sand color, (3) Profile equilibration time, and (4) Erosional hot spots. Recommendations for Minimum design Measures to identify many types of common erosional hot spots are presented.
NEED FOR A FOLLOW UP WORKSHOP
The general consensus was that the Workshop was productive but that a number of significant design issues remain requiring development of additional design guidance, including: (1) Risk and uncertainty, (2) Optimization of renourishment intervals, (3) Project performance, (4) Mining of ebb tidal shoals, and (5) Further refinement of monitoring protocols.
TABLE OF CONTENTS
EXECUTIVE SUM M ARY ..................................................... i
1 INTRODUCTION ...................................................... 1
2 RECOMMENDED GUIDELINES FOR DESIGN ISSUES .................... 1
2.1 Design Issues for which Recommendations Are Developed ............... 1
2.2 Methodology for Representing Background Erosion .................... 2
2.3 Accounting for Sediment Sizes in Situations in which the Sand Is
Reasonably W ell Sorted ........................................... 2
2.4 Nourishment Volume Density ....................................... 3
2.5 Monitoring and Presentation of Monitoring Results .................... 4
2.5.1 Monitoring to Document Project Performance ................... 5
2.5.2 Monitoring for Generic Purposes to Improve
Design Characteristics ....................................... 5
2.6 Accounting for End Losses in Preliminary Design ...................... 5
3 ISSUES WHICH PRECLUDE GUIDELINE DEVELOPMENT ................ 6
3.1 Poorly Sorted Nourishment Sediments ............................... 6
3.2 Sedim ent Color ................................................... 6
3.3 Profile Equilibration Time ......................................... 7
3.4 Erosional H ot Spots ............................................... 7
4 RECOMMENDATIONS FOR IMPROVING UNDERSTANDING OF ISSUES
IN SECTIO N 3 ......................................................... 7
4.1 Poorly Sorted Nourishment Sediments ............................... 7
4.2 Sedim ent Color ................................................... 8
4.3 Profile Equilibration Time ......................................... 8
4.4 Erosional H ot Spots ............................................... 8
5 RECOMMENDED IMPROVEMENTS IN MONITORING PROTOCOL ....... 9
6 NEED FOR FOLLOW UP BY THIS OR ANOTHER GROUP ................. 9
7 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ................. 9
7.1 Sum m ary ........................................................ 9
7.2 C onclusions ..................................................... 10
8 REFEREN CES ........................................................ 10
A WORKSHOP PARTICIPANTS..................................... A-i
B RESULTS FROM VARIOUS WORKING GROUPS ......................B-1
DESIGN CONSIDERATIONS FOR "HOT-SPOTS"............... EHS-1
BEACH NOURISHMENT PROJECT MONITORING ............PM-i
POORLY SORTED SEDIMENTS ............................ PSS-i
SAND COLOR............................................ SC-i
DEPTH OF CLOSURE .................................... DOC-1
PROFILE EQUILIBRATION TIME........................... PE-i
C EXAMPLES OF A FORMAT TO BE INCLUDED IN MONITORING
LIST OF FIGURES
1 Proportion of Material Remaining in Region Places........................... 6
RECOMMENDED BEACH NOURISHMENT GUIDELINES
FOR THE STATE OF FLORIDA AND UNRESOLVED RELATED ISSUES
Beach nourishment technology is a fairly recent field and includes several significant design variables. Although these variables are generally known, their quantitative roles in the performance of beach nourishment projects are not adequately understood. This has resulted in a divergence of design methodologies and less than optimal performance in some instances. In the interest of advancing the technology such that future beach nourishment projects constructed along Florida's shoreline provide the best possible performance, the Office of Beaches and Coastal Systems (OBCS) of the Department of Environmental Protection (DEP) initiated a workshop to: (1) Recommend design guidelines for those issues in which the technology is considered adequately understood, (2) Identify those issues for which the technology is not sufficiently advanced, and (3) Recommend courses of action to improve design methodology for those issues where the understanding is not adequate and the associated impact on the performance of projects is considered substantial. The results of the Workshop are documented in this report.
Sixteen individuals with design and related experience in beach nourishment participated in the workshop. A preliminary draft, formulated by the authors, was furnished prior to the Workshop as a basis for discussion. A final draft, revised by the authors, was furnished subsequent to the Workshop for review and comment by the Participants.
This report is not intended as a primer on beach nourishment. Rather, it is intended for use and application by coastal engineers who are familiar with at least the basics of beach nourishment. Also, this report addresses only the physical performance of beach nourishment projects. It is anticipated that issues related to biology including sea turtles will be the subjects of one or more workshops to follow.
Appendix A provides a list of the Workshop Participants. Appendix B presents the results of Working Groups on the following six design and performance issues: (1) Erosional hot spots, (2) Monitoring, (3) Poorly sorted sediments, (4) Sand color, (5) Depth of closure, and (6) Profile equilibration time. Appendix C provides a recommended format for presenting some of the more significant monitoring results.
2 RECOMMENDED GUIDELINES FOR DESIGN ISSUES
2.1 Design Issues for which Recommendations Are Developed
Five design issues were considered to be of both sufficient magnitude and at a stage where design recommendations were appropriate: (1) Methodology for representing background erosion, (2) Methodology for accounting for sizes of well sorted nourishment sediments, (3) Recommended nourishment volume densities, (4) Monitoring of completed projects, and (5) Accounting for end losses in preliminary design.
2.2 Methodology for Representing Background Erosion
Beach nourishment projects are usually carried out along beach segments where a background erosion persists. A reasonable design consideration is that the processes which have caused the background erosion will continue after project construction and thus it is important that the background erosion be accounted for in the design and prediction of performance.
There are two methods by which background erosion can be accounted for in design. In applying both methods, it is essential to use long-term rates if the background erosion is based on shoreline changes. If volume changes and the associated wave climate are used, shorter time periods are appropriate. One method to account for background erosion is to attempt to calibrate the numerical model used in the design to replicate the background erosion. The second is to consider the historical background erosion rates to apply after project construction and to simply apply them directly or as background transport. For projects constructed in areas where the processes are not affected by littoral obstructions (jetties, inlets, shoreline armoring, etc) the second approach is applicable and will replicate the background erosion exactly, see Dean and Grant, 1989. There was concern that in most cases, the causes of the background erosion were so subtle that the present state of modeling does notjustify calibrating to changes. However, a second position expressed was that it is possible to calibrate numerical models to background erosion. Thus, at this stage of understanding, either method is considered warranted depending on the experience and judgment of the designer. For those locations where a substantial effect has occurred, thereby changing the littoral regime (such as a littoral barrier at an inlet or where the pre-project shoreline is over-eroded such as along an armored shoreline), the background erosion rates would underestimate the post-project rates since the shoreline alignment after construction would induce greater transport gradients and thus erosion rates. It is noted that in some of these situations, the quantification of a reasonable wave direction is much more critical than for projects that are not affected by a littoral obstruction.
2.3 Accounting for Sediment Sizes in Situations in which the Sand Is Reasonably Well Sorted
It is well known that beaches composed of finer sediments are generally milder in slope than beaches composed of coarser sediments. It is unusual for sand available for nourishment to be of the same size characteristics as the native. Thus, in design, it is important to account for sand sizes that are different than the native. The methodology recommended below is for nourishment sediments that are reasonably well sorted and is generally consistent with that recommended in the draft U. S. Army Corps of Engineers Engineering manual "Design of Beach Fills" (1994).
It is recommended that sediment size characteristics be accounted for through equilibrium beach profile (EBP) concepts and methodology. Here, we will not attempt to specify the details too strictly, but rather to illustrate two of several possibilities.
Possibility 1: The pre-nourishment profile is in reasonable agreement with the equilibrium form h =Ay 2/3 where h is the water depth at a distance, y seaward of the mean water line and A is the socalled "sediment scale parameter" which increases with sediment size. In this case, a reasonable approach would be to develop a best-fit of this form to an average pre-nourishment profile and to compare the determined A with published A values which are a function of the median grain size. If the two A values are in reasonable agreement, then the equilibrated profile can be based on
equilibrium profile methodology using the median grain size and published A vs D50,7, relationships. If the published A and best-fit A values are not in reasonable agreement, one possible approach would be to develop a ratio between the determined and published A values and apply this ratio to the published A value for the nourishment sand.
Possibility 2. The pre-nourishment profile is not in reasonable agreement with the equilibrium form. In this case, it is recommended that the total volume density, VT, be the sum of two components with the first component, V1, be based on the Profile Translation Method (Eq. (1)) as if the sediments were compatible
A V, = A y(h. + B)
where AV, is the volume density (volume of sand added per unit length), Ay is the associated shoreline change, B is the berm height and h. is the depth of closure. The second volume component, V21 should be determined based on EBP methodology and is the volume difference for the two sediment sizes without a shoreline advancement. This second component could be positive or negative.
Use of the overfill factor method may be considered in addition to the above recommendations.
2.4 Nourishment Volume Density
A nourished beach will erode at least as fast as the historic or background erosion of the project beach. Additional net erosion will be caused by end losses as nourished sand spreads to adjacent unnourished beaches. Fill needs will also be increased by uneven erosion or hot spots along the project length. An example of end losses is at Delray Beach, Florida which was first nourished in 1973. The pre-nourishment background erosion rate of the project was in the range of 20,000 cubic yards/year. The post-nourishment erosion rate averaged in the range of 100,000 cubic yards/year primarily because of end losses. Two examples of hot spot erosion are Captiva Island and Longboat Key, Florida. Captive has a net (erosion less accretion) erosion of about 50,000 cubic yards/year but was renourished in 1996 with 800,000 cubic yards after 7-1/2 years since initial nourishment. In this case, hot spot erosion areas doubled nourishment needs. On Longboat Key the net erosion since 1993 has averaged 60,000 cubic yards per year. Hot spot erosion has increased gross erosion and the annual nourishment needs to 200,000 cubic yards/year.
There are models that can be used to help predict end losses and hot spot erosion. The GENESIS shoreline model is the generally accepted design tool that uses the CERC sediment transport formula to predict movement of sand along the project beach. The GENESIS model has been used with limited success because of difficulties in replicating the background erosion rates. Spatial changes in background erosion along the project are difficult to replicate with the model. The model is necessarily calibrated over limited time frames for which known shorelines and wave climate exist. The selected shorelines may not be representative of actual volumetric changes of the beach because seasonal variability typically exceeds the expected change over these short time periods. As described in greater detail later in this report, diffusion estimates can be used to predict end losses from a non-contained project. Dean and Grant (1989) have computed diffusion coefficients for all sections of the State of Florida which can be readily applied to compute end losses and when added
to background rates to predict total net project losses. Both the spatial distribution and total quantity of advanced fill should be estimated by the designer. The total quantity of advanced fill should be based on the background erosion rates, end losses and estimated hot spots erosion quantities.
For the examples given the required advanced fill ranged from double the net erosion (Captiva) to five times the background erosion rates (Delray Beach). Using the annual net background erosion rate (a common practice) to predict nourishment needs can seriously underpredict renourishment quantities.
With the above as background, specific recommendations are in order relating to the nourishment "volume density". The term "volume density" as used here refers to the volume of material placed per unit length of beach, for example cubic yards per foot of beach (yd3/ft) The volume density is one of the most significant design variables in beach nourishment projects. The volume densities of beach nourishment projects in Florida have ranged from less than 40 yd3/ft to greater than 100 yd3/ft. There is a "rule of thumb" that states that 1 yd3/ft is required to advance the equilibrated shoreline seaward 1 ft. The origin of this rule of thumb can be seen for cases in which the design is with compatible sand. Thus, it is reasonable to expect profiles to be of the same form before and after nourishment and if, say, the depth of closure, h., is 19 feet and the berm height, B, is 8 feet, then according to Equation (1), 27 cubic feet per foot of beach length (or 1 yd3 per foot of beach length) is required to advance the beach one foot.
A related and important issue arises because beach nourishment projects do not perform uniformly in the alongshore direction. Some portions of the project may perform better than indicated by design methodology, whereas others may underperform. Through placement of a sufficient volume density, the locations of additional erosional stress which may be erosional hot spots, can be accommodated by the project without the necessity of early renourishment.
It is recommended that if compatible sand is being used in the project, an attempt be made to place at least 80 yd3/ft. If a lesser density is placed, areas should be anticipated where underperformance of the project will be evident. Somewhat smaller placement densities may be warranted along those portions of the west coast of Florida where the wave heights are generally lower.
If sands smaller or larger than the native are used, greater and less volume densities will be required, respectively to achieve the design objectives. As noted, the use of EBP procedures is recommended to account for nourishment sediment sizes different than the native.
2.5 Monitoring and Presentation of Monitoring Results
There are at least two separate reasons for monitoring beach nourishment projects: (1) To monitor the performance of the specific project, possibly to assist in determining when renourishment will be required, and (2) To address generic issues that will improve and lead to more effective design procedures which can be applied to a wide range of projects. Additional discussion on monitoring protocol detail is presented in Appendix B and recommended formats for reporting monitoring results are provided in Appendix C.
2.5.1 Monitoring to Document Project Performance
After the initial nourishment of a project, it is recommended that the project be surveyed prior to, immediately after and at one-year, two-years and three years post-construction periods and biennially thereafter. For renourishment projects, monitoring surveys would be conducted one year after renourishment and biennially thereafter. Project monitoring should also include sand sizes of the native beach, immediately after nourishment and at the times of surveying with the minimum interval being yearly. Project monitoring subsequent to severe storms is recommended.
In order to provide an improved basis for assessing design capabilities, it is recommended that during the design phase, the predicted performance be documented. This documentation would provide the basis for later comparison with monitoring results with differences providing focus for needed improvement in design methodology.
It was noted that with the increasing nourishment construction and related monitoring activities along Florida's coastline, the prospects for duplication in monitoring efforts are increasing and some Participants noted instances of duplicate surveys, aerial photography flown, etc. It was recommended that a Web page be developed on which the planned monitoring efforts would be listed to minimize duplication of efforts. Those planning on conducting monitoring could list their plans as far in advance as possible and those interested in monitoring results would know of data which would soon be available. All would benefit. It would seem reasonable for the Office of Beaches and Coastal Systems to host the Web page.
2.5.2 Monitoring for Generic Purposes to Improve Design Capabilities
Project monitoring could be carried out to improve understanding of specific design issues, some of which will be discussed subsequently. Without specifying the particular design issue, it is impossible to establish monitoring plans. However, in most situations, it would probably not be efficient to monitor for one design issue since some of the same instrumentation (for example wave gages) would be required for all design issues. Thus, if plans are developed to conduct monitoring of a beach nourishment project to improve design capabilities for a particular design issue, it would be worthwhile to examine the need and incremental costs of addressing several design issues where needs exist to improve design capabilities.
2.6 Accounting for End Losses in Preliminary Design
Although the final design will probably be based on a numerical model, it is useful in comparing design alternatives at the preliminary design stage, to employ approximate methods of accounting for end losses. For projects that are to be constructed on a long straight beach, it is recommended that the estimated end losses be based on Figure 1 in which G is the so-called longshoree diffusivity", t is time and e is the project length, all in consistent units.
0so 1.0 S 1.0
1,_ ,s .0. .i I I I I I 'a j i i I I I I I I "1 I I i I 1 I '
0 G Alonigshore Diffusivity 1AIMM
U.- O. Ay,,plote p .,o.
_.l J0 .o I I I I I I I I J -1 7l 1 1 I I I
OU 0 1 2 3 4 5 6
Figure 1. Proportion of Material Remaining in Region Placed.
3. ISSUES WHICH PRECLUDE GUIDELINE DEVELOPMENT
There are a number of design issues which at present preclude specific design guidance. Several of these are discussed below and possible design guidance offered; however, it is stressed that additional design guidance development is warranted. Additionally, it is noted that the list below is not all inclusive.
3.1 Poorly Sorted Nourishment Sediments
Limited methodology exists for predicting post nourishment profiles for sediments that are poorly sorted. However, these methods are relatively untested and, as discussed in Section 2.3, it appears that the most appropriate method at present is to base the estimate of the resulting equilibrium beach profile on the median grain size of the composite sediment. The effect of sediment size on longshore sediment transport is not adequately understood to recommend design guidance for this variable.
3.2 Sediment Color
In most cases, the color of the nourishment sediment will be discernibly different from the native material. With time, the color within the project area will usually approach that of the native material. In some cases, it may not be possible to distinguish color differences after a few years whereas in other cases, the color may remain distinctly different for many years. One reason for color change after nourishment is "bleaching" due to exposure to the sun, rain and other elements. The other reason is intermixing with native sediments due to longshore and cross-shore sediment transport. This difference in color will be regarded by some as unfavorable. It would be useful to develop methods for predicting in advance any long-term differences in color between the nourishment and native sands.
3.3 Profile Equilibration Time
Nourished material is usually placed at slopes which are significantly steeper that the equilibrated profiles. The equilibration process usually occurs rapidly at first and then more slowly later. During the equilibrium process, the additional dry beach width is available for recreation and undoubtedly provides more storm protection than after equilibration. Methodology to predict equilibration times would allow conveying this information to the various stakeholders and would provide a rational basis for including the benefits of the wider beach during the equilibration process.
3.4 Erosional Hot Spots
Erosional hot spots are regions of higher erosion relative to the rest of the project area and/or regions where design expectations are not met. Hot spots can be "real" or "Perceived." Real hot-spots result from natural forces such as wave transformation over irregular bathymetry, etc. Perceived hot spots are regions where the beach is perceived to exhibit accelerated erosion because of the seaward location of development, insufficient or irregular beach fill design, lack of consideration of a known process in design, etc.
In many cases, preemptive identification of hot spots is possible before project construction. The engineer should preliminarily identify potential hot spots in the beach nourishment area during the project design process by examining the following:
a.) aerial photography,
b.) comparative rates of beach volume change alongshore,
c.) comparative rates of shoreline change alongshore,
d.) anecdotal information.
When hot spots are possible in the project area, the designer should use a high quality nearshore wave propagation model coupled to the primitive equations of sediment transport to resolve local details of project performance. Note that a simple diffusion equation method to infer beach fill evolution is generally not adequate to resolve most hot spots.
Before construction, all project stakeholders must be educated on the anticipated overall and local project performance. The potential for hot spots and the need for mitigation should be emphasized. Depending on the cause and type of hot spot, mitigation would be either sacrificial (overnourishment, high frequency sand transfer, etc.) or corrective (bathymetric alterations, structures, etc.). Additional discussion is presented, in outline form in Appendix B.
4. RECOMMENDATIONS FOR IMPROVING UNDERSTANDING OF ISSUES IN
4.1 Poorly Sorted Nourishment Sediments
It is recommended that if data of adequate quality are available, they be analyzed to determine whether the use of the median grain size of the nourishment material provides reasonable estimates
of the equilibrated post-nourishment profiles. Additionally, the use of two grain sizes of the nourishment material could be considered to represent the range in sediment sizes. If available data are not of adequate quality or if the results are not supportive of use of the approaches described above, the monitoring and analysis program described in the following paragraph is recommended.
Monitoring of a beach nourishment project should be conducted to document: (1) the native sediment size characteristics, (2) the sediment size characteristics in the borrow area, (3) the longshore distribution of sediment size characteristics of the placed material, and (4) the profile evolution during the cross-shore equilibration process. The analysis should compare available methodology for the predicted profiles with the measured profiles. Depending on the results of this comparison, it may be appropriate to develop improved methodology.
4.2 Sediment Color
It is recommended that each nourishment project include documentation of the color characteristics of the native and nourishment materials. The color of the nourishment material should be documented immediately after placement and at the same intervals recommended for the surveys. Additionally, "pan tests" should be developed to determine whether this technique will provide guidance on the color changes to be anticipated subsequent to the nourishment project. These pan tests would include placing small quantities of material taken directly from the borrow area and exposing the samples to the atmospheric elements and documenting color change. It is anticipated that results from pan tests would be conservative, that is, through mixing with native sands, the color of the beach at some future time would be closer to that of the native beach than indicated by the pan tests.
4.3 Profile Equilibration Time
Very little information exists on which to base estimates of equilibration times. This is important in developing predictions of available dry beach area with time since this is the area that the public sees and evaluates the relative success of the project. In previous studies of the Miami Beach and Anna Maria Key beach nourishment projects, the surprising preliminary results have been found that approximately 9 years are required for the profile to accomplish 50% of its equilibration. This is longer than is usually estimated and certainly more evaluations based on field data are required.
The approach to improving our present design basis on this issue would be to evaluate the adequacy of existing monitoring data for this purpose and if appropriate data exist, to proceed with the necessary analysis and recommendations. Lacking suitable monitoring results, a program for the required monitoring should be established and carried out followed by the analysis and recommendations.
4.4 Erosional Hot Spots
As described in Section 3.4 and Appendix B, methodology exists to predict some types of erosional hot spots. It is recommended that during design of future nourishment projects, the most advanced methodology be applied and if unanticipated erosional hot spots develop, they be examined in detail
and an attempt be made to identify their cause(s) and to develop appropriate methodology for their prediction.
5. RECOMMENDED IMPROVEMENTS IN MONITORING PROTOCOL
See Sections 2.4.1, 2.4.2, and all of Section 4 and Appendix B. Additionally, the subject of monitoring appears to justify being included in or as the focus of a future workshop.
6. NEED FOR FOLLOW UP BY THIS OR ANOTHER GROUP
The general sense was that the Workshop was beneficial to all Participants and that the opportunity to discuss design issues resulted in improved consensus as expressed in the design guidelines presented in this report. Much of the methodology used in beach nourishment design has been developed somewhat independently by the various practitioners and the Workshop was the first opportunity for the Participants to discuss the merits of the various approaches used. There was considerable discussion relating to procedures with general agreement on some issues and differences remaining on others.
There appeared to be unanimous agreement on the benefits of the Workshop and the value of future workshops on beach nourishment technology. Issues identified as appropriate topics for workshops are (in no special order): (1) Risk and uncertainty, (2) Optimization of renourishment intervals, (3) Project performance (understanding where sand goes), (4) Use of ebb shoals as a borrow site, and
(5) Further refine the monitoring protocol recommended herein.
7. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
This brief report is based on the deliberations in preparation for, during and subsequent to the Workshop on Beach Nourishment Technology sponsored by the Office of Beaches and Coastal Systems of the Department of Environmental Protection of the State of Florida. The overall purposes of the Workshop were to develop design guidelines where appropriate, to identify issues where the available knowledge did not support the development of guidelines at this time and to suggest, in broad terms, programs to reduce the uncertainty in design.
Guidelines have been recommended for five specific design issues: (1) Accounting for background erosion rate, (2) Accounting for nourishment sediment sizes in cases where the sediments are reasonably well sorted, (3) Recommended nourishment volume densities, (4) Monitoring of completed projects, and (5) Procedures for accounting for project end losses in preliminary design.
Significant design issues for which it was felt that the available information did not justify the development of guidelines included: (1) Accounting for the effects of poorly sorted sediments, (2) Predicting sediment color after the project had been in place for a considerable length of time, (3) Prediction of profile equilibration time, and (4) Erosional hot spots. Programs are outlined to
improve design technology for these issues. The assessments and recommendations of Working Groups on these and other design issues are presented in Appendix B.
The implementation of the recommendations formalized as a result of this workshop will contribute to improved performance of beach nourishment projects and to the capability to predict project performance and thus inform the general public more effectively of the anticipated performance. Additionally, for the design issues that were left unresolved due to a present lack of understanding and/or data, it is considered worthwhile to implement monitoring and other appropriate programs to improve design capabilities.
It would be appropriate for the Office of Beaches and Coastal Systems to host a Web page listing all known future coastal monitoring efforts. Those entities planning monitoring efforts would post the scope and timing of the monitoring thereby providing the basis for minimizing duplication of effort. The posting of efforts partially or completely funded by public funds would be mandatory.
Dean, R. G. and J. Grant (1989) "Development of Methodology for Thirty-Year Shoreline Projections in the Vicinity of Beach Nourishment Projects", UFLICOEL-891026, Coastal and Oceanographic Engineering, University of Florida.
U. S. Army Corps of Engineers (1994) "Design of Beach Fills", EM 1110-2-3301, Department of the Army, Washington, D. C.
7785 Baymeadows Way, Suite 202
Jacksonville, FL 32256
Office of Beaches and Coastal Systems
Florida Department of Environmental Protection
Marjorie Stoneman Douglas Building
Tallahassee, FL 32399
U. S. Army Corps of Engineers
400 West Bay Street
P. O Box 4970
Jacksonville, FL 32232-0019
Office of Beaches and Coastal Systems
Florida Department of Environmental Protection
Marjorie Stoneman Douglas Building
Tallahassee, FL 32399
Coastal Systems International
464 South Dixie Highway Coral Gables, FL 33146
Olsen and Associates, Inc.
4438 Herschel Street
Jacksonville, FL 32210
Coastal Planning and Engineering 2481 NW Boca Raton Boulevard
Boca Raton, FL 33431
Coastal and Hydraulics Laboratory Waterways Experiment Station Vicksburg, MS 39180
Humiston and Moore Engineers 10661 Airport Road N., Suite 14
Naples, FL 34109
U. S. Army Corps of Engineers 400 West Bay Street
P. 0 Box 4970
Jacksonville, FL 32232-0019
U. S. Army Corps of Engineers
400 West Bay Street
P. O Box 4970
Jacksonville, FL 32232-0019
Coastal and Hydraulics Laboratory Waterways Experiment Station
Vicksburg, MS 39180
Taylor Engineering, Inc.
9000 Cypress Green Drive, Suite 200
Jacksonville, FL 32256
Taylor Engineering, Inc.
9000 Cypress Green Drive, Suite 200
Jacksonville, FL 32256
Coastal Engineering Consultants, Inc.
3106 South Horseshoe Drive
Naples, FL 34104
Department of Coastal and Oceanographic
University of Florida
Gainesville, FL 32611-6580
RESULTS FROM VARIOUS WORKING GROUPS
1. Working Group on Design Considerations for "Hot Spots"
2. Working Group on Beach Nourishment Project Monitoring
3. Working Group on Poorly Sorted Sediments
4. Working Group on Sand Color
5. Working Group on Depth of Closure
6. Working Group on Profile Equilibration Time
Note: With few minor exceptions, the reports from the six Working Groups are presented here verbatim.
DESIGN CONSIDERATIONS FOR "HOT-SPOTS"
Working Group Participants:
So-called beach "hot spots" are regions of higher erosion relative to the rest of the project area, and/or regions where design expectations are not met. Hot spots can be "real" or "perceived." Real hot-spots result from natural forces such as wave transformation over irregular bathymetry, offshore canyons, etc. Perceived hot spots are regions where the beach is perceived to exhibit accelerated erosion because of the seaward location of development, insufficient or irregular beach fill design, etc. As such, perceived hot spots can be created by:
- failure to define the project's anticipated performance in local detail,
- failure to educate the sponsor and property owners of anticipated performance, and failure to acknowledge that project protection (or post-equilibration width) will not
In many cases, the potential for the development of hot spots within a given beach nourishment project reach can be preemptively identified during the project design process if the analyses described below are performed. To the extent that a predicted hot-spot cannot be mitigated through design, the sponsor/public must be educated as to the anticipated performance of the hotspot and the possible need for interim action at the hot-spot before the next project renourishment.
B. INITIAL RECONNAISSANCE INVESTIGATION
The engineer should examine and/or develop the following data to preliminarily identify possible or historical hot-spots.
1.) aerial photography
2.) comparative rates of beach volume change alongshore
3.) comparative rates of shoreline change alongshore
4.) anecdotal information
Prior, or potential hot-spots, identified through these means can be investigated through, or may be traced to, one or more of the phenomena listed below. Additional hot-spots, or hot-spots not otherwise evident from historical observation, may be elucidated by the investigations listed below.
C. TYPES, CAUSES AND PREDICTION OF HOT SPOTS
1. Wave Focusing
a.) Causes: Offshore/nearshore bathymnetry and/or shoreline orientation produce alongshore
gradients (acceleration) in longshore transport potential and/or wave energy
b.) Prediction: Compute wave transformation to the point of incipient breaking for various
representative offshore wave conditions; then compute, weight (by occurrence), sum, and plot the alongshore variation in net longshore transport rate and breaking wave energy density. It is noted that direct application of a diffusion model approach to the planform analysis of a beach nourishment project using an effective incident wave condition and an imposed background erosion rate offers the engineer no chance of identifying potential hot spots within the project. If the engineer is to have the opportunity to identify potential hot spots during the project design phase, additional more detailed analyses are required. These include wave transformation models that consider variations in the incident wave climate and nearshore
bathymetry in the vicinity of typical wave breaking.
c.)Correlate the results from "b", above, to observed behavior in item B. Areas of noncorrelation may suggest that the beach behavior is dominated by effects other than
bathymetric wave transformation.
2. Shoreline Orientation
a.) abrupt changes in shoreline orientation,
c.) shoreline declination relative to dominant wave angle,
d.) Prediction: Examination of aerial photographs and charts, and wave transformation
modeling (see above).
a.) Upland development is near, at, or beyond the landward limit of the historical natural
b.) Passive and Active encroachment: upland development does not, and does, interact with
littoral system, respectively.
1. Contrast (locate the seaward line of development with the historical landward limit of the active beach; the latter being described by some stable feature of the beach (e.g.,) vegetation line, elevation contour at which morphologic variability
commences, horizontal-slope offset above the mhwl, etc.).
2. Plot the setback distances, along the shoreline, between the line of development
and the existing or historical mhwl.
4. Offshore Vents, Canyons, Relict Borrow Areas, Rips, Other Sinks
Prediction: Inspection of bathymetry.
5. Sediment Starvation
Example Area downdrift of inlet, etc.
6. Design Deficiencies or Irregularities in Initial (Prior) Beach Fill
a.) Failure to place proper initial fill density (e.g., so as to satisfy pre-project profile deficit,
b.) Irregular project planform that accentuated perturbative nature of beach fill (e.g., failure
to vary alongshore fill density so as to create a quasi-uniform equilibrium shoreline
7. Taper and End Effects
Diffusive losses and/or lack of a fully developed subaqueous fill platform may result in
locally higher (or perceived higher) erosion rates.
8. Rhythmic Topography, Irregular Nearshore Hardbottom, etc.
a.) cyclical variations in erosion/accretion local,
b.) erosion "waves,"
c.) Prediction: difficult to predict and identify, except as revealed by prior trends and
C. METHODS TO ADDRESS HOT SPOTS DURING DESIGN
1. Education. Prior to construction, it is essential to educate the sponsor, public, property owner,
agencies, etc. as to the anticipated presence and performance of a hot spot area, and the degree to which it may need maintenance (if possible) prior to the project's overall renourishment.
2. Overnourish (a/k/a extra advance nourishment). This is a sacrificial fix. There is a practical
upper limit to the advance fill, because loss rates increase with the size of the physical
perturbation posed by the localized advance fill.
3. Alter offshore/nearshore bathymetry where possible or practicable to reduce wave transformation
or convergence effect. Examples include strategic dredging of a borrow source (i.e., to
remove a shoal), channel relocation, etc.
4. Coastal Structures
a.) localized breakwaters, groins
b.) net benefit/applicability is determined by the structures' potential reduction of sand loss
(and future renourishment requirements), and by potential impact to adjacent shores.
5. Internal, high-frequency short-term sand transfer.
b.) maintenance by supplemental fill from upland sources
6. Remove offending encroachment.
a.) purchase and relocation/demolition of encroaching structure
b.) partial demolition of offending structure (pavilion, pool deck, etc.)
7. Avoid project terminations in adverse areas (i.e., areas of accelerating transport gradients,
convergent wave focusing, shoreline declination, etc.)
8. Introduce or increase sand bypassing, (applies to sediment starved areas)
9. Correct design deficiencies or irregularities in prior project
a) ensure that adequate fill density is provided in areas with high profile deficits, etc.
b) vary alongshore fill density so as to create a post-fill, equilibrium shoreline of quasiregular shape with minimum perturbations.
10. General / Other -- The degree to which of these design features apply to various hot spots is a
function of the causative factor(s) of each hot spot. Some hot spots may not allow for
practical mitigative measures. These may include:
a) offshore vents, canyons, etc.
b) rhythmic topography, erosion waves, etc.
In regard to the latter, one might seek to ensure that the width of the advance fill, beyond the equilibrated design profile, is as large or larger than the amplitude of the
erosion "waves" that are anticipated to migrate through the project area.
BEACH NOURISHMENT PROJECT MONITORING Working Group Participants:
A monitoring program should be conducted to evaluate the performance of the beach fill to provide information needed for the operational management of the project. Data collection is limited to these purposes; additional field measurements to verify the analyses that were conducted in the design of the project or for increased understanding of beach nourishment design technology which should be conducted as a supplemental or separate program.
Topographic and Bathymetric Surveys
Topographic and bathymetric profile surveys should be conducted of the beach and offshore zone within the project area and along 3000 feet and 5000 feet of the adjacent updrift and downdrift shorelines, respectively. Profile surveys should be conducted at every EDEP reference monument (approximately 1000-ft spacing) along the same azimuths previously surveyed by the department and extend to a depth of closure or a minimum of 3000 feet seaward of mean high water, whichever is farther. Additional profile surveys should be conducted at intermediate stations adjacent to coastal protection structures or within localized areas of accelerated erosion.
As a project construction element, surveys should be conducted prior to construction and immediately following completion of construction. Monitoring surveys should be conducted annually at one-year, two-year, three-year post-construction intervals and biennially thereafter for initial beach restoration projects. Monitoring surveys for subsequent beach nourishment projects should be conducted biennially beginning with the one-year post-construction survey. The survey should be conducted during the same month of the year for each monitoring event. Poststorm surveys should be conducted upon the recommendation of the project engineer with the concurrence of the local sponsor and FDEP.
As a project construction element, bathymetric surveys of borrow areas should be conducted immediately following complete of construction. Post-construction monitoring surveys of an inlet channel and shoals should be conducted on a biennial basis beginning with the one-year post-construction survey when the ebb shoal is used as a source of borrow material.
All work should be conducted in compliance with the U.S. Army Corps of Engineers' "Technical Requirements for Hydrographic and Topographic Surveying" for Class 11 hydrographic surveys and in accordance with Chapter 6 1G17-6, F.A.C., Minimum Technical Standards established by the Florida Board of Professional Surveyors and Mappers pursuant to Chapter 472, Florida Statutes.
As a project construction task, aerial photography should be taken immediately following complete of construction. Monitoring should include aerial photography conducted on a biennial schedule. The specifications for the photography should be consistent with the standards adopted by the department for its state-wide shoreline monitoring program.
As a project construction element, samples of sediment should be collected immediately prior to construction and immediately following completion of construction. Monitoring samples should be collected concurrently with the three-year post-construction topographic survey. Samples should be taken along shore-normal profiles spaced every 3,000 to 5,000 feet from stations located at the toe of dune, vegetation or bulkhead line, at a mid-berm location, and at the approximate mean high water contour. Collection of samples should comply with applicable USACE guidance and be analyzed for grain size and distribution, shell content and rocks or other foreign matter, in accordance with applicable ASTM standards.
As a project construction task, the engineer of record should prepare a detailed construction completion report on the as-built project. The report should include all pre- and postconstruction monitoring information, including a plan view map and table showing the location and survey control information for the topographic and bathymetric profile surveys. A comparison of the as-built project with the design plans and specifications should be provided for discrete segments of the entire beach fill. All sediment should be accounted for in both the longshore and cross-shore direction and the information summarized in a standard format of tables and figures. The report should include an evaluation of the utilization of the borrow area and a comparison of the sediment characteristics of the borrow material used in the design with the characteristics of the sediment sampled from the native beach and from the constructed beach fill.
An engineering report should be prepared following each post-construction monitoring event. All sediment movement should be accounted for within the monitoring area in both the longshore and cross-shore direction. The volumetric and shoreline position changes, both cumulatively and during the latest monitoring period, should be provided and compared to the design goals of the project. The information should be summarized in standard tables and graphical figures depicting the profile and plan view comparisons with time and the performance expectations. A discussion of the project performance in relation to design expectations should be included along with a prediction of future evolution of the beach fill. Following sediment sampling, a comparison of the sediment characteristics of the native beach sand and the beach fill material should be made and discussed in context of the performance of the beach fill. The report should recommend modifications to the monitoring program to increase or decrease the field data collection effort as appropriate to evaluate the project based on past performance.
Appendix C includes an example of a recommended formats for reporting monitoring data results.
Synoptic physical data for contiguous littoral cells containing multiple beach erosion control projects should be collected on a periodic basis. In the near-term this should be accomplished through comprehensive county-wide surveys using conventional survey techniques. The longterm goal should be regional or comprehensive state-wide surveillance monitoring of the shoreline, which includes beach erosion control projects, utilizing L1DAR or other remotesensing technology as it becomes reliable and cost effective. In the interim, the department should coordinate its current state-wide survey activities with the local sponsors to avoid duplication of efforts. The department should continue to investigate emerging survey technologies and make comparisons between LIDAR, multi-beam acoustic and jet ski/wave runner based equipment.
POORLY SORTED SEDIMENTS Working Group Participants: Peter Grace
Topic 3.1 Variation in Sediment Sizes Problem
How can we predict post-nourishment profiles for sediments that are poorly sorted? What is the effect of sediment size on longshore sediment transport?
Present "Solutions" (How good are they?) 1) Base the estimated equilibrium profile on median grain size.
/ 4Zw-v- 72-55
I~ = WAE:
2) Apply overfill ratio (James, 1975)
(484 + 416)
Standard deviation = a measure of sorting Fill Mean diameter
3) Other methods/sources of information (?)
Dean & Abramian, 1993. CR DRP-93-2 "Rational Techniques for Evaluating the Potential
for Sands for Beach Nourishment".
DRP-1-1 1 Technical Note, 1993. "Size Dependence in Fine Grained Sediment Transport".
Recommendations (To Test Effectiveness of the Existing Estimation Procedures) 1) Compile and analyze data AOM7 CIO~~
2) If data is not adequate or comparisons are not favorable, execute a monitoring program.
a) Establish sediment characteristics at the borrow source (vertical/horizontal variation) //
C: C C.- 0 CLT
b) Establish a beach profile/sediment sampling plan
c) Prior to project construction, collect sediment samples and profile surveys at 1, 2 and
During dredging, keep records that indicate where dredge was operating during each stage of beach/fill placement. After placement and during each monitoring survey, collect samples 1 through 5 at each profile.
Establish a sediment data/beach profile grid.
1--I I EL L' _. L L L Fi LLLv
Compare measured and estimated volumes. Observe/inspect longshore trends as well.
Working Group Participants:
Sand for Florida beaches should be primarily selected based on grain size characteristics and economics. A secondary consideration is color similar to the native beach. Color of sand may be mineralogical or temporary stains.
Color may affect sea turtle nesting and public acceptance. Sea turtle nesting may be affected by the thermal characteristics of the sand. While color may be different, the reflectivity of the material may be more important than color differences.
In selecting borrow materials that are of comparable cost, materials with temporary stains are preferred to materials with more persistent stains.
Where sand quality is variable in the borrow area, provisions should be included in the specifications to enable the project owner to direct the contractor to upgrade sections that fall below minimum project color specifications at additional cost.
With time weathering and mixing with native materials will cause the color of sand to evolve to lighter colors but may not match prenourishment conditions.
When planning for nourishment, project sand sources should be evaluated for color. Information on color should be included in planning reports, permit applications and public meetings. Once an economical sand source is selected, the decision on proceeding with the project should be a local decision.
Predicting color change for temporary staining, by exposing samples to sun for several months.
Establish standards for exposing samples to the sun.
DEPTH OF CLOSURE
Working Group Participants: Don Stauble
This working group was assigned the task of discussing the importance of depth of closure in beach fill design and practice.
The group came up with three main focus areas:
A Does closure exist on beach fill projects?
B Understanding the depth of closure on beach fill projects will provide:
1) Aspects of cross-shore movement of fill material
2) Definition of offshore limit of fill movement
3) Profile volume measurements to calculate fill remaining on profile
4) Fill performance and bar development as fill readjusts
5) Prediction of fill requirements in the design process and renourishment needs
C How does closure impact fill behavior in the vicinity of nearshore hardbottoms and sea grass
To measure and identify a definition of closure requires long profiles using an accurate survey technique (i.e. sled)
To determine depth of closure on profiles on the east coast, profiles need to extend to a depth of at least 6 mn NGVD. The west coast and panhandle were not immediately known but work by Dean and Grant (1989) was identified as a source of closure depths around the State of Florida.
Uniform measurement techniques are needed to be developed for profiles on:
Coarser grained, steeper beach slopes and
Finer grained, flatter sloping beaches.
The finer grained beach may present a more difficult measurement task due to the small changes, possibly within the bounds of survey error, and long distances in offshore survey limits.
Define closure based on beach nourishment needs. Depth of closure may be identified where profile change is equal to survey accuracy (ie. around 0.5 ft of elevation change). Where do the shoreface processes end and the shelf processes start and what effect does each have on fill rearrangement?
The group proposed monitoring two new fill projects or use adequate data from recent fills to address the main concerns of profile closure.
Chose one project that has a coarser, more poorly sorted steeper slope and one that has a finer more well sorted, flat beach slope.
Profile survey requirements need to sample past suspected closure depth.
No hardbottom or sea grass should be associated with the projects to confuse the closure depth. This aspect can be addressed later.
Access to wave gage useful to identify storm events and characterize wave climate for closure calculations.
Grain size data along the entire profile will be needed to characterize influence of grain size in fill closure.
Measure: Pre- and post-fill placement
Post storm events
Over long-term (ie. three years and up)
Does fine-grained fill material move past closure and be lost to system?
Develop methods to predict closure in areas where measurement of closure difficult
Sediment budget approach Calculate end loss
Calculate fill volume change Find: cross-shore volume from what is left.
PROFILE EQUILIBRATION TIME
Working Group Participants:
A) RELEVANCE TO BEACH NOURISHMENT DESIGN
Success or perception of success of a designed beach nourishment project, particularly from the viewpoint of the general public, is directly linked to width and longevity of the dry beach area of the project. Contributing factors to loss of dry beach area include cross-shore adjustments and recession of the nourished berm profile and longshore migrations of the nourishment sand. In terms of cross-shore adjustment of the nourished profile, the concept of equilibrium profile becomes an important design consideration.
The design berm width, notwithstanding advance fill and overfill factors, is usually based on projection of a fully-equilibrated nourished profile. Actual construction templates for nourishment projects usually consist of berm slopes further seaward and much steeper than the native, pre-nourished profile. In most cases, the nourishment sand is similar to or smaller in grain size to the native sand resulting in a berm which is out of equilibrium, and thus, over time, adjusts to a flatter, equilibrated profile. The time for the construction template to reach profile equilibration has been identified as a relevant and important topic for consideration in beach nourishment design. Ability to better predict the time of profile adjustment toward equilibrium could assist in projections of longevity of dry beach area and may, thereby, become a factor in refining projections of project performance and project benefits.
The equilibrium profile concept was initially discussed by Bruun (1954) and further advanced by Dean (1977). The concept has been used extensively in development and formulation of dune erosion predictive modeling (e.g., Kriebel and Dean (1985)). Expanding on Bruun's earlier empirical relationship for the equilibrium profile, Dean analyzed 500 beach profiles along the Atlantic and Gulf coasts and found a general equilibrium profile of the form:
h(y) = y1
Through work by Dean (1977), Hughes (1978), and Moore (1982), an empirical relationship was developed relating A to mean grain size diameter. Dean and Kriebel (1985) derived an expression for offshore transport at any point in the surf zone in terms of difference between actual and equilibrium levels of wave energy dissipation in the surf zone.
Qs = K(D-D* )
The above two expressions and an expression for conservation of sand over the profile shown below form the basis for dune erosion modeling.
Studies have shown (Kriebel and Dean (1985)) that berm recession over time for storm-type conditions occurs in an exponential manner which can be expressed as follows:
R(t) = R, [ 1 exp(-t/T5)]
Berm recession is initially expected to be more rapid and then approaches equilibrium asymptotically. Recession of a beach nourishment berm appears to behave in a similar manner. However, as a result of more random, unpredictable conditions over longer time periods, a more complex change rate could be expected. It does appear from the storm simulation analyses that variations in parameters such as water level, wave height, sediment size and beach slope will affect berm recession rates and thus time of equilibration.
C) INTERIM CONCLUSIONS AND RECOMMENDATIONS
There has been significant research work performed relative to the equilibrium profile concept and profile response to storm events related to development of dune erosion predictive models. However, there is relatively little existing research and design methodology applicable to the time associated with profile equilibration. Existing research regarding the equilibrium profile concept and profile response briefly discussed above can provide some interim direction. Sand grain size data, wave, tide and current data, and profile survey data from the project areas can be used in formulating profile equilibration projections and techniques. However, additional studies to monitor equilibration periods for actual nourishment projects are needed and recommended.
In practice, design engineers have indicated that a high percentage (e.g. 50%) of profile equilibration of a nourished beach occurs over a relatively short time period (1-2 yrs.). However, recent preliminary studies (Robert Dean and Thomas Campbell, personal communication ) of two projects in Florida have shown significantly greater time periods on the order of 9 years to reach 50% of equilibration. A more comprehensive review of past and current project performance to document equilibration on a wider scale and development of methodologies based on empirical information from past projects is needed.
The uncertainty of factors influencing profile equilibration over longer time durations, such as occurrence of storm conditions, add to the complexity of prediction of equilibration time. Until more evolved methodologies are developed, it may be prudent to consider a more conservative (being more rapid) estimate of equilibration time, in light of uncertainties. The most conservative approach would be to assume a rapid adjustment to full (or near-full) equilibration. A conservative approach would reduce the potential of underpredicting adjustment (and loss) of dry beach area, beach width, andi longevity for project sponsors and the general public.
EXAMPLES OF A FORMAT TO BE INCLUDED IN MONITORING REPORTS
The purpose of this provide a sampling of formats for presenting monitoring results of beach nourishment projects. A the time of writing this draft, Only one format has been forwarded.
E4 <6661 I!Jdv
4-4--966 1 lfltV ~-'~-966L 1'!jdV: L66L sn6nV
. L66 IPdV
0 o 96-3 o. r I!j dV
0C) C CD CC) C) CD C) Ci CD
0 z 0
>.C U C
iuu~ewj WnflOA Pue MJV uid 1UMJFd MF- 1