BEACH NOURISHMENT PROJECTS IN CARBONATE MATERIAL BEACH

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1 Submitted February, 2006 BEACH NOURISHMENT PROJECTS IN CARBONATE MATERIAL BEACH Ryuichiro Nishi 1, Robert G. Dean 2 and Mario P. de Leon 1 1 Department of Ocean Civil Engineering, Kagoshima University, Japan 2 Department of Civil and Coastal Engineering, University of Florida, USA Abstract Hard engineering approaches such as seawalls, groins, detached and submerged breakwaters to stabilize or restore beaches are used to counteract beach erosion. However, none of these shore protection structures adds more sand to the beach system to compensate for natural and artificial erosion. Thus, beach nourishment, also called artificial nourishment, replenishment, beach fill, and restoration involves the addition of sand in designed contours to extend a beach. In the United States, Europe and Australia, beach nourishment has grown in acceptance as major shore protection and beach restoration measure for more than fifty years. In Japan, hard structures are also commonly used but after a new coastal law was approved in April 2000, beach nourishment as a legal shore protection work was accepted. However, at present, beach nourishment is not yet widely used as shore protection method in Japan. Specifically, this paper deals with beach nourishment projects in carbonate material (coral reef) beach in Okinawa, Japan and in Florida, USA. Data on beach fill length, volume, nourishment volume density, frequency of beach fill, borrow source and cost of beach fill material from different beach nourishment projects were reviewed, assessed, analyzed and consolidated.range of values and mean values of nourishment project parameters were calculated and then were used as basis for the comparative analysis of beach nourishment in normal sandy and coral sandy beaches. The consolidated results will serve as database for implementing future restoration projects in coral sandy beaches in tropical and subtropical countries like the Philippines. Keywords: Beach nourishment, carbonate material (coral reef) beach, beach erosion, shore protection Introduction Beach nourishment involves the placement of sediment on a typically eroding beach to advance the shoreline seaward for the promotion of storm protection, recreation, and natural habitat. Its design process determines the quantity, configuration, source and distribution of the sediment to be placed along a specific section of the coast. Nourishment projects are designed as a series of sequential fill placements over time to account for the long-term erosion process. For design purposes, the fill placed on a beach comprises of two components: 1. The design cross-section which achieves the project purpose (storm protection and recreational area) 2. Advanced-fill amount which erodes between nourishment events. Figure 1. Typical beach nourishment in Okinawa, Japan It is a standard practice to provide sufficient sand to nourish the entire profile, from the dune to the depth of

2 significant sand movement, D C. Therefore, the total volume, V T, somehow independent of profile shape since the shape of the renourished profile will be parallel and similar to the existing natural profile, can be estimated by VT = ( DB + Dc ) LW (1) where D B is the elevation of the berm, L is the length of the nourishment project, and W is the desired amount of beach widening. The geomorphologic characteristic of the beach area significantly affects the amount of nourished sand. For coral sandy beach, the amount of nourished sand is lesser compared to normal sandy beach. Thus, the presence of hard coral cover compensates the volume of nourished sand requirement. The quantity and the distribution of advanced fill can be determined by analyzing the historical erosion and shoreline changes of a beach and estimating how the project fill will affect coastal processes. The procedures used include the historical shoreline change method (USACE, 1991b) or analytical (Campbell et al., 1990) or numerical methods (Hanson and Kraus, 1989). For normal sandy beach, the sediment transport (both for erosion and accretion) is greater compared to coral sandy beach as a result of current and waves impact with beach sand. Source of nourished sand may be located offshore or at an onshore area called borrow area or borrow pit at a relatively short distance seaward or tens of kilometers from the beach to be nourished. Typical plan areas of the borrow pit are on the order of 1 km 2 to 10 km 2 and typical excavated depths on the order of 2m to 10 m. Grain size distribution of the borrow material affects how a beach erodes and how the nourished beach responds to storms. Thus, the borrow sand is judged to be compatible if the nourishment grain size distribution is similar to that of the native sand. Various methods of quantifying compatibility include mean and median diameters, sorting and equilibrium beach profiles. Approaches which are commonly used for the placement of nourished sand on the beach include: (1) placing all of the sand as a dune behind the active beach, (2) using the nourished sand to build a wider and higher berm above the mean water level, (3) distributing the added sand over the entire beach profile, and (4) placing the sand offshore to form an artificial bar. For the past 44 years, the United States has spent about $ 15 million per year to help protect the nation s beaches while a number of countries, notably Spain, Germany, Japan and the Netherlands, spend proportionally from twice the dollars in the Netherlands to 100 times in Japan (Houston, 1995). Design of beach nourishment projects in the United States has evolved as knowledge of physical beach processes has increased with the inclusion of design volume, design of advanced fill and analysis of sand compatibility as areas for improvement. Verhagen (1990) described the beach nourishment design method employed in the Netherlands with substantial reliance on historical data and design assumptions. Dette et al (1994) described the method employed in Germany to represent the volumetric losses over time from a beach nourishment project using the assumption that the volume decays exponentially with time. Nishi et al (2004) reviewed the status of beach nourishment projects in Japan and Florida and concluded that average beach nourishment project in Japan is nearly on the order of 1/19 of average beach nourishment in Florida in terms of volume. In addition, average length of beach nourishment projects in Japan is nearly 1/17 of an average length of beach nourishment projects in Florida. On the borrow area (source of sediment), only 10 % of beach nourishment projects use the sediment in the same regional sediment transport system. Because of this, it is encouraged that Japanese researchers need to conduct more studies on borrow site. Hamm et al`s (1998) comparative results in beach fill study in five European countries indicated the big differences in nourishment fill rates and volumes. Spain and the Netherlands are by far the biggest nourishing countries in Europe each at 110 x 10 6 m 3 in volume. Annual fill rates for selected countries are the following; France, 0.7 x 10 6 m 3, Italy, 1x 10 6 m 3, Germany, 3 x 10 6 m 3, Netherlands, 6 x 10 6 m 3, Spain, 10 x 10 6 m 3, Denmark 3 x 10 6 m 3, Great Britain, 4 x 10 6 m 3, Japan, 0.5 x 10 6 m 3, South Africa, 0.5 x 10 6 m 3, Australia, 1 x 10 6 m 3, and USA, 30 x 10 6 m 3. Bird (1990) conducted a review of beach nourishment projects in Australia from Results showed that the average cost of beach nourishment per km is $A 232,902 ( 19,316,855 and $179,960) based from a total of eighteen beach nourishment areas with a total beach length of 19.3 km amounting to a total cost of $A 4,495,000 ( 372,814,588 and $3,473,221). Consolidated data of beach nourishment projects from 1984 to 2000 in Australia indicated a total volume of beach fill equal to 372,000 m 3. According to Massel et al (2000), the increased economic pressure for development, increased impact from land-based and marine industries, and increase access to coral reef areas have all lead to the demands to provide a sound engineering and environmental basis for infrastructure developments in coral reef areas. Such can only

3 be achieved through comprehensive understanding of the physical processes which shape the reef environment and control its ecology. Thus, beach nourishment is a viable engineering alternative for shore protection and is a principal technique for beach restoration. In the Philippines, beach nourishment has been considered specifically for the development of beaches for recreation purposes. Of the 7,107 islands surrounded by bodies of water, major tourism developments are continuously expanding in coral beaches of Mactan, Cebu, Bohol, Palawan, Boracay and many other islands where location of hotels and resorts are well set back from the shoreline. The absence of any hard structures in the coastal zone permeates white sand beaches to extend further. In the efforts to achieve wider and longer white sand beach front in the potential area for resorts and hotels, beach developers usually manage to import white sand as nourished fill from neighboring islands within the region. Materials and Methods Beach nourishment project data in coral reef areas from Okinawa, Japan and Florida, USA were obtained from Department of Civil Engineering, Okinawa Prefectural Government and through literature review. The data included; (1) length of nourishment project, (2) volume, (3) nourishment volume density, (4) borrow source, and (5) project cost of beach fill material. Range of values and mean values of the nourishment project parameters were calculated and used as basis for the comparative analysis to provide estimates and basis for future implementation of nourishment projects. Data/Results and Discussion Twenty-four (24) beach nourishment projects in carbonate beach for the periods from are recorded in Okinawa, Japan where six million tourists annually visit and 60 % of them enjoy marine leisure on a white beach. Figure 1 shows typical beach nourishment in Okinawa, Japan. The same with Florida, white sandy beach is a valuable resource to attract more tourists. As of 2003, twenty (20) projects were already completed, two (2) are still partially completed, and two (2) have not been started yet. Data on beach fill length, volume, cost of beach fill material, frequency of beach fill and borrow source are presented in the following figures. Length of beach fill (m) Mean length (m) Volume of beach fill (m3) Mean volume (m3) 1,200m 250,000m3 Length of beach fill (m) 1,000m 800m 600m 400m 200m 00m Beach project areas in Okinawa, Japan Figure 2. Length of beach fill project Volume of beach fill (m 3 ) 200,000m3 150,000m3 100,000m3 50,000m3 00m Beach project areas in Okinawa, Japan Figure 3. Volume of beach fill Figure 2 represents the various nourishment lengths of beach fill projects. The length of beach nourishment is the most important parameter for longevity of the project in general. Beach fill length ranges from 150 m to 1,000 m with a mean of 441 m. In contrast, the average length of artificial beaches in Japan was on the order of 600 m in Figure 3 indicates the range of volume of beach fill. Beach fill volume ranges from 3,930 m 3 to 193,350 m 3 having a mean of 41,581 m 3. Nourishment volume density refers to the nourishment volume per unit length of the beach and is a significant parameter to the actual and/or perceived performance of the project. For coral sandy beaches, typical volume density ranges from 80 to 100 m 3 /m. In the case of beach nourishment projects

4 in Okinawa, the volume density ranges from 20 to 322 m 3 /m with a mean volume density of 94 m 3 /m which is about 38% of the recommended volume density for normal sandy beach in the United States. Volume of beach fill is a function of berm(d B )and critical water (D C ) depths. Thus, the critical water depth in normal sandy beach is larger compared to carbonate beach due to the presence of coral cover which compensates for the volume of nourished sand required (Figures 4 and 5). In general, critical water depth in Japan ranges from 6 to 12 m. D B D B fill fill D CO D C Coral cover where D B D CO = berm depth = critical water depth over a coral reef where D B = berm depth D C = critical water depth Thus, D C >> D CO Figure 4. Typical cross-sectional view of beach Figure 5. Typical cross-sectional view of beach nourishment in carbonate beach nourishment in normal sandy beach Figure 6 represents the cost of beach fill material per unit volume. The actual cost incurred in the projects ranges from 0 to 5,150 JPY/m 3 (0 to 44 USD/m 3 or 0 to 2,266 PHP/m 3 ). Dredged material from other coastal projects is an economical factor in nourishment projects. Thus, information such as port dredging should be properly circulated among multi-government agencies. In general, estimated average cost is 2,564 JPY/m 3 (22 USD/m 3 or 1,128 PHP/m 3 ). Cost of beach fill material per unit volume (JPY/m 3 ) Cost of beach fill material per unit volume (JPY/m3) 6,000 円 5,000 円 4,000 円 3,000 円 2,000 円 1,000 円 00 円 Mean cost (JPY/m3) Beach project areas in Okinawa, Japan Figure 6. Cost of beach fill material Figure 7 indicates the frequency of beach fill with reference to the volume of nourished sand per year. The annual average volume of beach fill is 18,000 m 3. Of the twenty-four projects, 16 (67%) had beach nourishment less than 18,000 m 3 /yr while 8 (33%) had beach fill greater than the annual mean. Figure 8 contains information of two borrow sources from which the twenty-four (24) beach projects got the nourished sand. Twenty-three (95.8%) beach fill projects obtained the borrow sand from the same borrow source area and only one (4.2%) project got a different borrow source, from a dredged area adjacent to the coast of which dredged material was donated to the project legally.

5 Frequency of beach fill Volume of beach fill per year (m3/yr) Volume of beach fill per year (m 3 /yr) x 1000 m 3 Number of beach fill projects using the same borrow source Number of beach fill projects using the same borrow source Figure 7. Frequency of annual beach fill volume Figure 8. Source of borrow material Conclusion The continuous implementation of beach nourishment in the US, European countries, Australia, Japan is a significant index and a concrete evaluation that beach nourishment is a viable engineering alternative for shore protection and is therefore a principal technique for beach erosion. Thus, beach nourishment is still a favorable shore protection method in developed countries. However, beach fill can also be the best solution in carbonate beaches in tropical and subtropical countries for tourism and economic purposes. Following are the conclusions generated from the review, assessment, analysis and compilation of nourishment projects in carbonate beaches in Okinawa, Japan, to wit; 1. Nourishment length, width, berm and critical water depths are functions of volume of beach fill. In the carbonate beaches considered, mean length is 441 m in contrast to 600 m in artificial beaches in 1990 while volume is on the order of 41,581 m 3 which is 7% lower compared to 44,800 m 3 in normal sandy beaches in Japan. 2. Volume density of beach fill is 94 m 3 /m which is within the range for typical coral sandy beach from 80 to 100 m 3 /m and is about 38% of the recommended density in normal sandy beaches in the United States. 3. Cost of beach fill material is dependent upon the borrow source. Dredged material from ports and harbors dredging works is an economical means for beach fill provided that compatibility of grain size is satisfied. Moreover, geomorphologic characteristic of sandy beaches is a significant factor in the overall cost of beach fill both in the nourishment and re-nourishment stages. Therefore, project scale and cost of beach nourishment are mainly dependent on the need and magnitude for shore protection vis-à-vis availability of resources and environmental impacts. It is further recommended that regular monitoring of beach nourishment projects should be conducted for continuous assessment of performance efficiency and effectiveness as shore protection method. Acknowledgement: The original beach nourishment data was provided by Department of Civil Engineering, Okinawa Prefectural Government Office. Thus, authors would like to extend their special acknowledgement. References Beach nourishment data in Florida (Original data is downloaded from the (super) beach nourishment homepage; Bird, E.C.F.. Artificial beach nourishment on the shores of Port Phillip Bay, Australia, Journal of Coastal Research Special issue No. 6, 1990 pp Campbell, T.G., R.G. Dean, A.J. Mehta, and H. Wang Short Course on Principles and Application of Beach Nourishment. Organized by the Florida Shore and Beach Preservation Association and Coastal and Oceanographic Engineering Department, University of Florida. Dean, Robert G.. Beach Nourishment Theory and Practice, World Scientific, Advanced Series on Ocean Engineering Volume 18, Dette, H., A. Fuhrboter, and A.J. Raudiv Interdedependence of beach fill volumes and repetition intervals, Journal of Waterway, Port, Coastal and Ocean Engineering 120(6): Chibishi By other project Borrow source

6 Hamm, L., H. Hanson, M. Capobianco, H. H. Dette, A. Lechuga, and R. Spanhoff., Beach fills in European projects, practices, and objectives, Proceedings of ICCE 1998, pp Hanson, H., and N.C. Kraus GENESIS: Generalized model for simulating Shoreline change. Report 1: Reference Manual and Users Guide. Technical report No. CERC Vicksburg, Miss.: Coastal Engineering Research center, U.S. Army Waterways Experiment Station, U.S. Army Corps of Engineers. Houston, J.R., Beach nourishment. Shore and Beach 63(1):23-24 Leonard, L. A., Dixon, K. L. and Pilkey, O. H. A comparison of beach nourishment on the U.S. Atlantic, Pacific, and Gulf Coasts, Journal of Coastal Research Special Issue No. 6, pp Massel, S.R. and Gourlay, M.R. On the modeling of wave breaking and set-up on coral reefs, Coastal Engineering, An international journal for coastal, harbour and offshore engineers, Volume 39, N0.1, Elsevier, National Research Council. Beach Nourishment and Protection. National Academy Press, Nishi, R., Dean, R.G., Tanaka, R. Project scale and cost of beach nourishment in Japan, Annul Journal of Civil Engineering in the Ocean. Volume 2, 2005 pp USACE. 1991b. National economic Development Procedures Manaul Coastal Storm Drainage and Erosion. Institute of Water Resources Report No. 91-R-6. Fort Belvoir, Va.: Institute for Water resources, Water Resourcces Support center, U.S. Army of Engineers. Verhagen, H.J Coastal protection and dune management in the Netherlands, Journal of Coastal Research 6: