FEASIBILITY STUDY OF AN ARTIFICAL SANDY BEACH AT BATUMI, GEORGIA ARCADIS/TU DELFT : MSc Report FEASIBILITY STUDY OF AN ARTIFICAL SANDY BEACH AT BATUMI, GEORGIA Date May 2012 Graduate C. Pepping Educational Institution Delft University of Technology, Faculty Civil Engineering & Geosciences Section Hydraulic Engineering, Chair of Coastal Engineering MSc Thesis committee Prof. dr. ir. M.J.F. Stive Delft University of Technology Dr. ir. M. Zijlema Delft University of Technology Ir. J. van Overeem Delft University of Technology Ir. M.C. Onderwater ARCADIS Nederland BV Company ARCADIS Nederland BV, Division Water PREFACE Preface This Master thesis is the final part of the Master program Hydraulic Engineering of the chair Coastal Engineering at the faculty Civil Engineering & Geosciences of the Delft University of Technology. This research is done in cooperation with ARCADIS Nederland BV. The report represents the work done from July 2011 until May 2012. I would like to thank Jan van Overeem and Martijn Onderwater for the opportunity to perform this research at ARCADIS and the opportunity to graduate on such an interesting subject with many different aspects. I would also like to thank Robbin van Santen for all his help and assistance for the XBeach model. Furthermore I owe a special thanks to my graduation committee for the valuable input and feedback: Prof. dr. ir. M.J.F. Stive (Delft University of Technology) for his support and interest in my graduation work; Dr. ir. M. Zijlema (Delft University of Technology) for his support and reviewing the report; ir. J. van Overeem (Delft University of Technology ) for his supervisions, useful feedback and help, support and for reviewing the report; and ir. M.C. Onderwater (ARCADIS Nederland BV) for his technical help, his knowledge of Batumi and support. Besides my graduation committee I would like to thank all my colle agues at ARCADIS for the pleasant time. And last but not least I would like to show my gratitude to all my friends and family for their support during my years as a student. I would like to give a special thanks to Eelco Bijl for all his help, motivation and support. Corine Pepping, Delft, May 2012 MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia i SUMMARY Summary Introduction Batumi is a city located on the coast of the Black Sea in the southwest of Georgia, see Figure a. The coastline south of Batumi is affected by serious erosion problems. South of Batumi the Chorokhi River discharges into the Black Sea. In front of the river a submarine canyon is located as well as in front of Batumi Cape in the north of Batumi. The main driving mechanisms behind the coastal morphological changes in the Batumi area are gradients in the longshore sediment transport, induced by obliquely incident waves. In front of the Chorokhi River, the direction of the waves changes due to wave refraction over the canyon bathymetry. Just north of the submarine canyon wave energy converges due to refraction, causing an increase in wave energy at this location. This induces an increase in sediment transport towards the north, resulting locally in coastal erosion. Additionally, various aspects contribute to the erosion. The beach of Batumi is fed with sediment from the river. The river sediment balance of the Chorokhi River is changing due to mining activities and the construction of power dams on the Turkish side of the river. Based on observations along the coast and the predictions with respect to availability of sediment from the Chorokhi River, it has been concluded in previous studies (Pre-feasibility study, 1999-2000) that in time, the sediment load through the river will decrease and sediment becomes scarce. At that time, more permanent protective measures should be installed in order to prevent high maintenance costs. Figure a Batumi, Georgia Research goals and objectives In one of the previous studies done by ARCADIS (River and coastal protection Adjara, Georgia, 2009), alternatives have been designed to protect the coastal stretch between the port in the north and the Chorokhi River south of Batumi. The final design proposed in 2010 (Alkyon/ARCADIS, 2010) consists of a groyne system along the entire coast, with local revetment along the stretches where groynes are not applicable due to presence of MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia iii SUMMARY submarine canyons. The beaches of Batumi originally consist of pebble. To develop sandy beaches along the northern coast of Batumi, which was requested by the client, pocket beaches have been envisaged here in the 2010 design. These pocket beaches consist of detached breakwaters with landward of these breakwaters a curved shape beach. The beach consists of pebbles up to a level of MSL +3m and a layer of sand above MSL +3m. In the present study an alternative design for the pocket beaches along the Old Boulevard (see Figure a) will be proposed. Along the Old Boulevard most of the tourist activity takes place; therefore this part is most important for tourism and recreation, with the presence of hotels, restaurants and other facilities. This master thesis aims to determine the best design option and the feasibility of an artificial sandy beach along the Old Boulevard of Batumi. This design should contain more sand and less visual structures, opposed to the pocket beaches proposed in the previous study. The objectives of this study are to: . Define measures in order to create and preserve an artificial sandy beach; . Investigate the feasibility and stability of an artificial sandy beach; . Generate design alternatives in order to create a sandy beach along the Old Boulevard of Batumi and assess these alternatives based on qualitative aspects and costs; . Prepare a preliminary design for one of the most promising design alternatives; . Compare the final design alternative with the pocket beaches as de signed in the previous study (Alkyon/ARCADIS, 2010). Approach With the use of a literature study the site conditions have been drawn up and the coastal processes which play an important role in the present study have been defined. The coastal processes are dominated by the wave induced longshore currents, resulting in a longshore sediment drift towards the north. After studying the area of interest, a study is performed on the initial concepts and possible measures in order to design and preserve an artificial sandy beach. The main issues to design an artificial sandy beach are the large amount of sand which is required, the loss of sediment due to longshore transport and the loss of sediment due to cross-shore transport. These issues can be optimised by the following: . using coarser sand; . applying coastal protection works like breakwaters and groynes; . making use of a bypass system; . introducing isolated segments with sand; . applying sand only above the waterline. A potential application of a breakwater is a perched beach. A perched beach combines a low breakwater or sill and a beach fill perched, or elevated above the normal level. By making use of a perched beach the amount of required sand is limited considerably. The perched beach also provides a broad buffer against wave action while offering a potentially excellent recreational site. Perched beaches have the appearance of natural beaches and the submerged sill does not intrude on the view of the waterfront. In order to determine suitable measures and alternatives, the morphological impact of the measures and the corresponding sediment transports should be considered. The sediment transport rates have been computed with the use of numerical models. The models used in MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia iv SUMMARY the present study are UNIBEST-LT and XBeach. UNIBEST-LT is applied to determine the average annual longshore sediment transport and the equilibrium angle of the coast. The cross shore losses of sediment are determined with the use of the XBeach model. UNIBEST modelling results show that the longshore sediment transport is mainly towards the north and only a small share of the net sediment transport is transported towards the south. This means that by placing the sandy beach under the equilibrium angle a more or less stable coast can be created. From the XBeach model results follows that a part of the eroded sand in front of the breakwater is transported over the breakwater in off-shore direction and will be lost, when applying a submerged breakwater. The relation between the amount of sand which is transported over the breakwater and the total amount of erosion at the beachside of the breakwater seems to depend on the height difference between the crest of the breakwater and the sandy profile at the breakwater. The larger the height difference between the crest of the structure and the sandy beach profile at the structure, the less percentage of sand is lost over the breakwater. Alternatives Using the so far gained information, 7 alternatives are proposed for the design of an artificial sandy beach along the Old Boulevard. The first alternative is a fully sandy beach, placed under the equilibrium angle. In the second alternative this fully sandy beach is divided into 3 segments in order to reduce the required amount of sand. In the third alternative a fully sandy beach is placed parallel to the boulevard. This results in less required sand, but introduces a gradient in longshore sediment transports. In alternative 4, 5, 6 and 7 perched beaches are applied, which shortens the beach profiles considerably and with this the total required amount of sand. In alternative 4 the perched beaches are placed under the equilibrium angle and the beach is divided into 4 segments. The breakwater is placed parallel to the boulevard at a distance of approximately 250 meter.