Feasibility Study of an Artifical Sandy Beach at Batumi, Georgia

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. The crest is located at MSL -0.5m. In alternative 5 not only the beach is placed under the equilibrium angle, but also the breakwaters. A constant distance between the waterline and the breakwater is derived. By doing this the relatively small distances between the waterline and the breakwater, as at some parts of the beach in alternative 4, are avoided. In alternative 6 the breakwater as well as the sandy beach are placed parallel to the boulevard. By doing this the beach does not have to be divided into segments, but it will result in redistribution of sediment along the beach due to longshore transports. In alternative 7 the breakwater is lowered and shifted in shoreward direction. By doing this the total required amount of material for the construction of the breakwater is lowered, but the cross-shore and longshore transports increase.

Multi-Criteria analysis All these 7 alternatives are compared and assessed with the use of a Multi-Criteria analysis (MCA). The alternatives are rated on the qualitative criteria : spatial quality, tourism/beach recreation, safety, environment, maintenance nuisance and risk. Besides these 6 qualitative criteria the designs are also rated on their costs. A distinction is made between capital costs and maintenance costs. The maintenance costs are calculated using the net present value for a period of 50 years. Note that the maintenance costs presented in Table a are based on the soft measures only; the maintenance costs are estimated using the determined sediment transports. The results of the MCA can be found in the table below.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia v

SUMMARY

Table a MCA results Qualitative criteria Costs [M€] Spatial Tourism/ Safety Environ- Mainte- Risk Capital Mainte- Total quality beach ment nance costs nance costs recre- nui- (NPV, ation sance 50 yrs) Alternative 1 Sand, equilibrium ++ + ++ - ++ ++ 272.7 0 272.7 angle

Alternative 2 ± + + ± ++ + 123.1 0 123.1 Sand, segments Alternative 3 + ++ ++ ± - ++ 74.5 12.5 87.0 Sand, parallel Alternative 4 Perched beach, - - - - + + - - 46.9 10.4 57.3 equilibrium angle Alternative 5 Perched beach, - ± - + + - 60.0 1.5 61.5 oblique breakw aters Alternative 6 Perched beach, + + ± + ± ± 42.9 3.3 46.2 parallel Alternative 7 Perched beach 2, + ± - + - - ± 28.1 208.4 236.5 parallel

Alternative 1 scores best on the qualitative criteria, but the costs are very high compared to the other alternatives. Alternative 3 has also a very good rating for the qualitative criteria, but involves much lower costs than alternative 1. Alternative 6 is the cheapest solution and has a relatively good rating for the qualitative criteria. It can be concluded that alternative 3 and 6 will be the most promising alternatives. Whether alternative 3 or 6 is preferred depends on which criteria is valued to be leading.

Results The most promising alternative should be worked out on a preliminary level. Because of the small differences between alternative 3 and 6 in the rates for the qualitative criteria, but a noticeable differences in the total costs, it is decided to select alternative 6 as most promising alternative in this study and to prepare a preliminary design for this alternative. The selected alternative is shown in Figure b.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia vi

SUMMARY

Figure b Design perched beach

The beach profile is studied in more detail and it is decided to adjust the beach profile of the selected alternative to derive a more stable beach. At the level of the boulevard the beach is horizontal with a width of 50 meter. From here the beach profile starts and another 85 meter of beach is present until the profile reaches the waterline. The crest of the breakwater is located at a distance of approximately 180 meter from the waterline.

The basic features of the breakwater are: − The crest height of the submerged breakwater is MSL -0.5m, the crest width is 5 meter and the slope is 1:2; − The armour layer consists of 10-15 ton rock, for the filter layer 1-3 ton rock is applied and the core consists of 60-300 kg rock.

The basic features of the groynes are: − The crest width of the northern and southern groyne is 5m and the slope is 1:2; − The northern groyne is an extension of the revetment and the crest height of the first part is MSL+2.0m, the crest height of the middle part of the groyne is MSL +1.0m and the crest height finally decreases to MSL-0.5m. The armour layer consists of 10-15 ton rock, for the filter layer 1-3 ton rock is applied and the core consists of 60-300 kg rock; − The southern groyne is an extension of the most northern groyne of the groyne system and the crest height of the first part is MSL+2.0m, the crest height of the middle part of the groyne is MSL +0.5m and the crest height finally decreases to MSL- 0.5m. The armour layer of the first part consists of 6-10 ton rock, at the other parts of the groyne 10-15 ton rock is applied for the armour layer. The filter layer of the groyne consists of 1-3 ton rock and the core of 60-300 rock.

Based on unit prices of the required material the capital costs for the perched beach area is estimated at 52.1 M€. The net present value for 50 years of maintenance is estimated to be 4.5 M€. These costs are based on the preliminary design and higher than the presented values in Table a due to the updated beach profile.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia vii

SUMMARY

Final conclusions The pocket beaches as designed in the previous study (Alkyon/ARCADIS, 2010) and the preliminary design of the perched beach as designed in the present study are finally compared. The main characteristics of the options are listed below. Table b Comparison betw een the Pocket beaches Perched beach designs Partly sand Fully sandy beach Visual structures Almost no visual structures Almost no maintenance Maintenance every few years 25.5 M€ 56.6 M€

The pocket beaches have a partly sandy beach, but contain some undesirable visual structures. The perched beach fulfils the wish of a sandy beach with almost no visual structures, the costs are however considerably higher than for the pocket beaches.

It can be concluded that both options have their own benefits and drawbacks. The preference depends on which aspect is valued as most important and/or which aspect is valued as least important. Selection of the most preferred option is subjective and therefore no preferences will be made in this study.

Recommendations In order to make a better decision between the promising alternatives 3 and 6, it is recommended to also make a preliminary design for alternative 3. This alternative could be optimised by, for example, filling a part of the new beach profile (under the upper layer of 2 meter) with pebbles instead of sand. Also the groynes a t the northern and southern end might be shortened. These adjustments could lead to a lowering of the costs and might result in a preference for alternative 3.

Mastic asphalt is suggested as a solution to make the breakwater sand-impermeable. This solution, but also other solutions in order to make a s tructure sand-impermeable, should be investigated.

In this study the XBeach model is used to estimate the yearly average cross-shore sediment transports. The XBeach model is however developed to simulate the beach processes during storms and not to simulate yearly average transports. With this the behaviour of a beach profile behind a submerged structure is rather complex and it should be investigated to which extend the XBeach model is applicable in case of the presence of a submerged breakwater. Because of the doubtful applicability of the XBeach model and the conservative approach in order to estimate the cross-shore transport, it is highly recommended to check the cross-shore sediment losses with a different, more suitable model.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia viii

CONTENTS

Contents

Preface ______i Summary ______iii Contents ______ix

1 Introduction ______1 1.1 General introduction ______1 1.2 Erosion problem ______2 1.3 Problem definition ______3 1.4 Objectives ______4 1.5 Research approach and report structure ______4

2 Previous related studies and projects ______7 2.1 Pre-feasibility study ______7 2.2 Feasibility study 2009 ______7 2.2.1 Numerical modelling ______8 2.2.2 Conclusions______8 2.3 Detailed design 2010 ______9 2.3.1 Final Design ______9

3 Site conditions ______11 3.1 General______11 3.1.1 Economic structure ______11 3.1.2 Climate ______11 3.1.3 Reference level ______12 3.2 The Chorokhi River ______12 3.2.1 General ______12 3.2.2 River regime ______13 3.2.3 Dams ______13 3.2.4 Sediment mining ______14 3.3 Canyons ______14 3.4 Bathymetry ______16 3.5 Water level ______19 3.5.1 Tide ______19 3.5.2 Seasonal fluctuations ______19 3.5.3 Sea level rise ______19 3.5.4 Atmospheric pressure ______20 3.5.5 Wind set-up / storm surge ______20 3.6 Wind______20 3.7 Waves______20 3.7.1 Offshore wave climate ______20 3.7.2 Nearshore wave climate ______21 3.7.2.1. Yearly average conditions ______21 3.7.2.2. Extreme conditions______23

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia ix

CONTENTS

3.8 Currents ______25 3.9 Sediment properties______25

4 Coastal processes ______29 4.1 Sediment transport processes______29 4.1.1 Longshore processes ______29 4.1.2 Cross-shore processes ______30 4.2 Coastline development ______30 4.2.1 Historical overview ______30 4.3 Sediment transport analysis ______32 4.3.1 Wave energy in the coastal zone ______32 4.3.2 Transport capacities and S-φ-curve ______34 4.3.3 Conclusions and discussion cause of erosion/accretion______36

5 Concepts and tools for design sandy beach ______39 5.1 Beach profile ______39 5.1.1 Equilibrium profile ______40 5.1.2 Closure depth ______41 5.1.3 Sandy beach profile along the coast of Batumi ______42 5.2 Design concepts of an artificial sandy beach ______43 5.2.1 Optimisation design sandy beach ______44 5.2.1.1. Lowering amount of required sand______44 5.2.1.2. Limit the loss of sediment due to longshore transports ______46 5.2.1.3. Limit the loss of sediment due to cross-shore transports ______47 5.2.2 Overview of measures to optimise the design of the sandy beach ______47 5.3 Sediment transport modelling ______48 5.3.1 UNIBEST-LT ______48 5.3.1.1. Model set up UNIBEST-LT ______49 5.3.2 XBeach ______50 5.3.2.1. XBeach 2D ______50 5.3.2.1. Model set up XBeach 1D ______51 5.4 Requirements ______53

6 Alternatives______55 6.1 Introduction ______55 6.2 Alternative 1: Sandy beach ______55 6.2.1 Design Sandy beach______55 6.2.2 Overview______58 6.3 Alternative 2: Sandy beach with segments______59 6.3.1 Design Sandy beach with segments ______59 6.3.2 Overview______62 6.4 Alternative 3: Sandy beach, parallel to the boulevard ______62 6.4.1 Design Sandy beach, parallel to the boulevard ______62 6.4.2 Overview______64 6.5 Alternative 4: Perched beach ______65 6.5.1 Design Perched beach ______65 6.5.2 Overview______68 6.6 Alternative 5: Perched beach, oblique submerged breakwater______68

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia x

CONTENTS

6.6.1 Design Perched beach, obllique submerged breakwaters ______68 6.6.2 Overview______71 6.7 Alternative 6: Perched beach, parallel to the boulevard ______71 6.7.1 Designed Perched beach, parallel to the boulevard ______71 6.7.2 Overview______73 6.8 Alternative 7: Perched beach 2, parallel to the boulevard ______74 6.8.1 Design Perched beach 2, parallel to the boulevard______74 6.8.2 Overview______76

7 Selection of alternatives ______79 7.1 MCA criteria ______79 7.2 Rating of the alternatives ______80 7.2.1 Spatial quality______80 7.2.2 Tourism/Beach recreation______81 7.2.3 Safety ______82 7.2.4 Environment ______83 7.2.5 Maintenance nuisance ______84 7.2.6 Risk______85 7.2.7 Captital costs ______86 7.2.8 Maintenance costs ______89 7.3 Result MCA______90

8 Preliminary design ______91 8.1 Introduction ______91 8.2 Beach design ______91 8.3 Design Breakwater ______92 8.3.1 Armour design ______94 8.3.1.1. Filter design criteria ______95 8.3.1.2. Core material______96 8.3.1.3. Transition to seabed ______96 8.3.1.4. Permeability of the armour layer ______97 8.3.2 Design Groynes ______98 8.4 Costs ______99 8.4.1 Bill of quantities ______99 8.4.2 Costs______100

9 Review final proposal ______103 9.1 Design Pocket Beach ______103 9.2 Design Perched Beach ______104 9.3 Comparison______105

10 Conclusions and recommendations ______107 10.1 Conclusions ______107 10.2 Recommendations ______111

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia xi

CONTENTS

Bibliography ______113 List of figures ______115 List of tables______117

Annexes ______119

1 Yearly wave conditions ______121

2 SWAN wave modelling ______123

3 Sandy beach profile ______126

4 Longshore transport ______128

5 XBeach 2D ______140

6 Cross-shore transport ______150

7 Storm conditions ______159

8 Calculations alternatives ______178

9 Maintenance costs preliminary design ______181

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia xii

CHAPTER 1: Introduction

1 Introduction

1.1 GENERAL INTRODUCTION

Batumi is a city on the coast of the Black Sea in the southwest of Georgia. Georgia is bounded to the north by Russia, to the southeast by Azerbaijan, to the south by Armenia, to the southwest by Turkey and to the west by the Black Sea, see Figure 1. Figure 1 Georgia, Adjara

Batumi is the capital of the autonomous republic of Adjara and has approximately 130,000 inhabitants. The Batumi Area is one of the most important tourists’ sites along the Georgian Black Sea coast, attracting a growing number of national and international tourists. The beaches of Batumi consist of pebble and were in the Sovjet time beloved beaches by the Sovjet civilians, also because of its mild subtropical climate. After the collapse of the Sovjet Union (1991) the sea side resorts became deserted. At this moment there is a good investment climate in the tourism development. It is expected that in the coming years the number of tourists that will visit Adjara will grow up to 1,000,000 visitors. A large number of new hotels are built, the infrastructure is being improved and the construction of a large number of new hotels and resorts has been planned.

In Figure 2 some relevant features of Batumi are shown; In the north of Batumi lies the Batumi harbour. The port is of importance with respect to employment, an estimated 1400 people are employed in the port facility. In May 2007 an international airport is reopened. The airport lies south of Batumi. South of the airport, the river Chorokhi discharges into the Black Sea. The Chorokhi River emerges from the mountains in north-eastern Turkey and reaches the Black Sea just south of Batumi a few kilometres from the Turkish-Georgian border.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 1

CHAPTER 1: Introduction

Figure 2 Adjara, Batumi

1.2 EROSION PROBLEM

The coastline south of Batumi is affected by serious erosion problems. Along the coastal stretch south of Batumi already a number of houses and cultivated land has been lost. Without adequate protection measures coastal erosion will continue and the runway of the airport is endangered by coastal erosion and eventually the erosion will affect the beaches and the coastline of Batumi. This could negatively affect the investment climate for tourism development.

The main driving mechanism behind coastal changes in Adjara region are gradients in the longshore sediment transport, induced by obliquely incident waves. Additional there are various aspects contributing to the erosion. The coastal stretch south of Batumi is fed with sediment from the river. The river sediment balance of the Chorokhi River is influenced by sediment mining at large extents. The sediment is mined for construction purposes. Furthermore the total sediment balance of the river is influenced due to the building of dams in the Chorokhi River on the Turkish side of the river.

Finally it should be noticed that in front of the harbour in the north and in front of the river mouth in the south, submarine canyons are located. These submarine canyons trap a lot of sediment.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 2

CHAPTER 1: Introduction

1.3 PROBLEM DEFINITION

Several studies have already been performed on the coast of Georgia. In one of the previous studies done by ARCADIS (River and coastal protection Adjara, Georgia, 2010), alternatives have been designed to protect the coastal stretch between the harbour in the north and the river in the south of Batumi. The detailed design consists of a groyne system along the entire coast, with local revetment along the stretches where groynes are not applicable due to presence of submarine canyons. The beaches of Batumi originally consist of pebble (see Figure 3). 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 a curved shape beach. The beach consists of pebbles up to a level of MSL +3m and a layer of sand above MSL +3m. Figure 3 Pebble beach Batumi

The main goal of the previous study wa s to protect the current coastline. The government of Adjara would like an alternative design, which focuses on tourism. Most of the tourist activity takes place along the Old Boulevard of Batumi, see Figure 4. This northern part is important for tourism and recreation, with hotels, restaurants and other facilities. There is a strong desire for attractive sandy beaches, instead of the current pebble beach, along this part of the coastline. The main point of discussion of the design from the previous study is the lack of sand and the visual pollution by the structures. Therefore the new design should contain more sand and less visual structures. The main focus in this study will be on creating a sandy beach on top of the current pebble beach along the Old Boulevard. Possible alternatives on creating sandy beaches will be investigated and there will be worked towards an optimum combination of costs, feasibility and serviceability. The final design should create a (more or less) stable coast between the Chorokhi River mouth and Batumi Cape, sandy beaches along the Old Boulevard and provide an attractive setting for tourism.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 3

CHAPTER 1: Introduction

Figure 4 Old Boulevard of Batumi

1.4 OBJECTIVES

This master thesis aims to determine the best design option and the feasibility of an artificial sandy beach along the Old Boulevard of Batumi. 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 designed in the previous study (Alkyon/ARCADIS, 2010).

1.5 RESEARCH APPROACH AND REPORT STRUCTURE

To generate a final design for the beaches of Batumi first of all insight into the area of interest should be gained. For this purpose, a literature study has been performed. Different studies have already been carried out on the area of interest; these existing documents are reviewed. The literature study leads to a collection of data of the research area and give insight into the morphological system of the research area. These previous studies are treated in Chapter 2, the collection of the data of the research area will lead to the site conditions which are treated in Chapter 3 and the coastal processes which play an important role in this study are treated in Chapter 4.

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. In order to determine suitable measures and alternatives, information should be gained on the morphological impact of the measures and the corresponding sediment transports. These sediment transport rates will be computed with the use of numerical models. The models in the present study to be applied will be 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 annual losses of sediment are determined with the use of the XBeach model. This study on designing artificial sandy beaches and the morphological behaviour of certain measures is described in Chapter 5. Based on this study, alternatives for

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 4

CHAPTER 1: Introduction

an artificial sandy beach along the Old Boulevard of Batumi are generated. The generated alternatives are proposed in Chapter 6.

In Chapter 7 the alternatives generated in Chapter 6, are assessed using a Multi-Criteria analysis (MCA). The criteria and the rating of the alternatives are treated. With the results of the MCA conclusions are made and one of the alternatives is selected to be worked out on a preliminary level in Chapter 8.

Finally the design as prepared in Chapter 8 is compared with the pocket beaches in Chapter 9 and conclusions and recommendations are treated in Chapter 10.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 5

CHAPTER 2: Previous related studies and projects

CHAPTER 2 Previous related studies and projects

The following chapter describes the previous related studies and projects. In this chapter mainly the objectives and conclusions of the studies are treated. During the remainder of this report several times will be referred to the previous studies as described below.

2.1 PRE-FEASIBILITY STUDY

In 1999-2000 ARCADIS, Alkyon and HKV consultant carried out a pre -feasibility study; IMWM Project in Georgia, Coastal protection study for Batumi. The objectives of the study for the area of Batumi were to:

. Analyse the existing coastal and river system; . Identify the erosion problems; . Define possible coastal protection alternatives for the entire coastline of the study-area; . Assess the impact of those alternatives by using computer models; . Evaluate the protection alternatives by means of a cost-benefit analysis.

The “Batumi area” is defined as the area between the delta of the Chorokhi River and Kobuleti (north of Batumi). The coastline of Batumi was studied in detail; the coastline north of Batumi was only studied in a qualitative way. The system analysis as well as the definition of mitigation measures was studied on a conceptual level only.

Impact of river dams on erosion problem At the time of the feasibility study a few large dams were (being) constructed in the Chorokhi River. After completion of the se Turkish dams, the river discharge of the Chorokhi was expected to change. The changes in the river discharge will have its effect on the sediment supply to the coastline section north of the river mouth. In the present situation approximately 50,000 m3/yr is transported into northern direction from the river delta. After completion of the Turkish dams the amount of sediment which is transported to the north will decrease to almost zero, while the northern transport continues. This will result in erosion of the river delta.

2.2 FEASIBILITY STUDY 2009

In 2009 a feasibility study ‘River and Coastal Protection Adjara, Georgia’ was performed by Alkyon, ARCADIS and HKV consultants. In this feasibility study, various protection scenarios were studied and a preference for the most suitable protection alternative was expressed. The final results of this study were presented in a workshop in November 2009 organised in Batumi.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 7

CHAPTER 2: Previous related studies and projects

Two technical studies of the coastal area and the Chorokhi River were conducted in order to analyse the morphological system. In these studies the development of the coastal- and river- morphological systems was investigated and several alternatives were defined to protect the coastline between the Chorokhi River mouth and Batumi Cape and manage the sediment balance in the Chorokhi River.

A Multi-Criteria Analysis was carried out together with the stakeholders to determine the feasibility of the alternatives. Suitable combinations of coastal- and river alternatives were defined. These combined alternatives were assessed from an environmental and financial perspective.

The overall project objectives were: 1. Analyse the causes of the coastal erosion (and the contribution of the respective causes) along the coast of Batumi; 2. Define sustainable protection measures in order to stop the erosion along the coast and to validate the measures from both an environmental as well as financial point of view; 3. Develop an approach which can be applied to other areas suffering from coastal erosion; 4. Contribute to technical discussions between river and coastal experts of Georgia and Turkey; 5. Training of Georgian counterpart on the Dutch approach on coastal and river engineering and protection and Environmental Impact Assessment; 6. Support the on-going process for reforms of water resources management in Georgia.

2.2.1 NUMERICAL MODELLING

A full analysis of the coastal morphological system was not possible with only the available data. Computer modelling was applied in order to verify the hypotheses with respect to coastal behaviour. By means of computer modelling, the yearly average extreme wave conditions have been translated to nearshore wave climates at various positions a long the coast. Based on numerical modelling, the sediment transport capacity along the coast is computed. A quantitative description of the coastal morphological system is given based on the available data and the results from the computer modelling. Based on this description, a numerical model is made, which simulated the coastline changes as a function of time. This model is calibrated by means of available data.

Some of the results of this numerical modelling, like the derived nearshore wave climate, are used during this thesis. The background of some of these models and results are presented in Chapter 3. When modelling results are used, reference will be made to this study.

2.2.2 CONCLUSIONS

Based on observations along the coast and the predictions with re spect to availability of sediment from the Chorokhi it is in this report of 2009 proposed to implement the following measures in time:

1. In the last two years, accumulation of sediment along the coastline south of Adlia has been observed. Though the exact cause of the accumulation is not known, we expect that

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 8

CHAPTER 2: Previous related studies and projects

the current bathymetry near the river mouth determines the accumulation and that the accumulation is only a temporary event. It is recommended to study the bathymetry near the river mouth in detail by means of frequent monitoring and to keep the “corridor of sediment from the Chorokhi River” open as long as possible. 2. In time, the sediment load through the river will decrease and sediment becomes scarce. Eventually, also the erosion along the coast will increase. At that time (which could already be in several years from now), more permanent protective measures should be installed. Based on coastal, financial and ecological aspects, a series of groynes from the Chorokhi River mouth up to Batumi Cape would then be the most appropriate alternative. 3. It is recommended to start searching for funding as soon as possible, because this will likely take some time to implement.

2.3 DETAILED DESIGN 2010

In 2010 a new study was performed as the follow-up of the feasibility study presented in December of 2009. The study is a detailed design of the coastal protection works along the coast of Batumi. In this detailed design, some of the aspects of the study presented in December 2009 are elaborated in more detailed and some new items are introduced.

The study of ARCADIS, 2010, consists of three reports: Basis of design, Functional design and Detailed design. In ‘Basis of design’, the available information at the start of the project is described along with the hydraulic boundary conditions and the design strategy. In the ‘Functional Design’ , various options with respect to the layout, the construction material and the construction method have been investigated. The most detailed design principle has been selected based on spatial aspect as well as financial aspects. In the ‘Detailed Design’, the final design for the chosen coastal protection scheme is presented.

2.3.1 FINAL DESIGN

Based on findings as presented in the Functional Design and discussions with the client, the detailed design of various coastal protection works has been prepared. The detailed design is described below and is shown in Figure 6. The locations of the reference points to which is referred in this description can be found in Figure 5. Figure 5 Locations of the reference points

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 9

CHAPTER 2: Previous related studies and projects

. A revetment will be applied along the most northern coastline section between Kp0.000 and Kp0.600; . Pocket beaches, protected by breakwaters will be applied along the coastline section where currently all large hotels are situated (Kp0.600 to Kp2.400); . Further to the south, a series of 29 groynes is applied (Kp2.400 to Kp7.400); South of the groynes, no coastal protection works are foreseen. Once the sediment discharge of the Chorokhi River decreases to a minimum, the coast along this section will erode. The most important infrastructural feature (waste water treatment plant) will however be safe from coastal erosion.

Figure 6 Detailed design of the coastal protection Batumi, Adjara

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 10

CHAPTER 3: Site conditions

CHAPTER 3 Site conditions

Chapter 3 describes the site conditions of the coastal area of Batumi. Section 3.1 provides general information like the economic structure and climate. In Section 3.2 the Chorokhi River will be treated. Section 3.3 gives some information about the canyons and the bathymetry is presented in Section 3.4. The water level is treated in Section 3.5. Section 3.6 and 3.7 present the wind- and wave conditions. And in the final Section 3.8 and 3.9 the currents and sediment properties are presented.

3.1 GENERAL

3.1.1 ECONOMIC STRUCTURE

In Adjara the most significant sectors of activity are agriculture, forestry and fishing, trade and repair services, transport and communications and tourism.

The focus of the government is on improving the economy by attracting investment and developing tourism. Other major sectors with development potential are transport, agriculture and construction. Transport can be considered an important sector for Adjara as Batumi is the only major Georgian seaport apart from Poti, as well as a transition route for goods to and from Turkey.

As for agriculture, Adjara used to be one of the main producers of citrus fruits, tea, nuts and tobacco in the Sovjet Union. Accordingly a high number of food processing factories were situated in Adjara which are currently mostly dysfunctional or producing very little. Currently the main source of income for the rural population is subsistence-type agriculture in small land plots an cattle -farming.

While in the medium term prospects for economic development are good in coastal region due to tourism industry, it can be expected that the mountainous district remain characterized by small scale agriculture (Concept Development for Reforms of the Water Sector, Financial Cooperation with Georgia, 2006).

3.1.2 CLIMATE

Batumi lies at the northern periphery of the humid subtropical zone. The city’s climate is heavily influenced by the onshore flow from the Black Sea and is subject to the orographic effect of the nearby hills and mountains, resulting in significant rainfall throughout most of the year, making Batumi the wettest city in both Georgia and the entire Caucasus Region.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 11

CHAPTER 3: Site conditions

The average annual temperature in Batumi is approximately 14 °C. January is the coldest month with an average temperature of 7 °C. August is the hottest month with an average temperature of 22 °C. The city receives 1958 hours of sunshine per year.

Batumi's average annual precipitation is 2,718 mm. September is the wettest month with an average of 335 mm of precipitation, while May is the driest, averaging 92 mm. Batumi generally does not receive significant amounts of snow (accumulating snowfall of more than 30 cm.), and the number of days with snow cover for the year is 12. The average level of relative humidity ranges from 70-80%.

3.1.3 REFERENCE LEVEL

The reference level in Georgia is officially Baltic Zero. However, in previous studies the Mean Sea Level (MSL) is used as the vertical reference level. The reason for this is that the control points of the Baltic Zero have not been checked since the 1960’s, which makes this reference level uncertain. It is decided to use in this thesis also the Mean Sea Level as the vertical reference level.

3.2 THE CHOROKHI RIVER

3.2.1 GENERAL

The Chorokhi River originates in the mountainous region of Anatolia, Turkey. It has a catchment area of 22,100 km2 of which approximately 9% is located in Georgia. From the total length of 438 km, only the last 26 km of the river lies in Georgia. Here it flows into the Black Sea, approximately 7 km south of Batumi.

Historically the main branch of Chorokhi River reached the Black Sea near Magine, some 3-4 km north of the present river mouth. A smaller southern branch reached the coast approximately 2 km South of the present river mouth. In the 19th century the main northern branch was abandoned and the river mouth shifted towa rds its present position. The location of the mouth has been fixed by dikes and revetments.

The Chorokhi river pattern is governed by multiple variables. Typically, a large discharge and sediment load as well as a wide river bed leads to a breading pattern. In the upstream part the presence of rigid surrounding, the foothills of the Lesser Caucasus, leads to a meandering pattern. Further downstream, more lateral space allows the development of a more braiding pattern with multiple channels. With the introduction of a new discharge regime, regulated by dams, and a decreasing sediment load, the Chorokhi River will develop towards a more meandering pattern. Already visible near the mouth of the river, see Figure 7.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 12

CHAPTER 3: Site conditions

Figure 7 Meander development near the mouth of the Chorokhi River, (left: 2004, right: 2007)

3.2.2 RIVER REGIME

Based on the water levels and discharges at Erge station some hydrological characteristics are derived in the pre-feasibility study. The annual average discharge at Erge is about 275 m3/s. Rain accounts for 39% of the discharge, groundwater 32% and snow melt for 29%. In Figure 8 the average annual river regime at Erge is given based on monthly average discharges from 1930 to 1991. It is clear that the peak discharge of the Chorokhi River occurs in May (Alkyon/ARCADIS/HKV, 2000). Figure 8 Monthly average discharge at Erge (Alkyon/ARCADIS/HKV, 2000)

3.2.3 DAMS

In June 2005 the first and most downstream of a series of dams in the Turkish part of Chorokhi River became operational. In April 2007 a second dam became operational. Some more dams are currently under construction and plans are made for even more.

The dams block the flow of sediment through the Chorokhi and influence the discharge regime. The expected changes in discharge regime is a decrease in the period in which the maximum discharge occur after 2 dams are operational (narrower peak) and the maximum

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 13

CHAPTER 3: Site conditions

discharge itself decrease (lower peak) when 2 additional dams become operational. The average discharge in high flow season approaches the critical discharge needed to transport beach-forming material which is estimated to be 400 m 3/s (Alkyon/ARCADIS/HKV, 2009).

3.2.4 SEDIMENT MINING

Since 1975 sediments have been mined from the Chorokhi river to be used for the purpose of construction. In Table 1 the amounts of mined sediments are shown. In 2007 the mining have temporarily been stopped because of likely detrimental effects on coastal erosion. Sediment mining is a relevant source of input for the Adjara construction sector with not many alternatives at hand. To provide the construction sector of sufficient material, mining has been permitted further upstream the Chorokhi river and in its tributaries. The yearly amount of licensed sediment mining is 400-500K m3 excluding extra sediment for large projects. Table 1 1982 1983 1984 1985 1986 1987 1988 1989 1990 Total Amounts of removed Place of removal sediment from Chorokhi By crane from - 219.3 543.2 341.5 698.1 634.8 858.3 803.0 245.2 4343.4 River and the Batumi Cape close to (*1000 m3) Chorokhi River Mouth

From further 128.0 168.0 138.4 208.2 179.9 135.4 68.0 139.0 99.1 1264.0 upstream of the Chorokhi River From the river 128.0 387.3 683.6 549.7 878.0 770.2 926.3 942.0 344.3 5609.4 mouth area By crane from 27.0 - 20.0 20.0 30.0 63.0 20.0 24.0 14.0 218.0 the Batumi Cape Total 283.0 774.6 1385.2 119.4 1786.0 1603.4 1872.6 1908.0 702.6 11434.8

The mining campaigns had a significant impact on the sediment characteristics. Due to the mining the average grain size in the river has reduced with almost factor 3 over 27 years. The explanation for this is that especially the coarse material was mined at a much faster rate than it is transported through the river.

3.3 CANYONS

In front of the mouth of the Chorokhi river and in front of Batumi Cape, submarine canyons are located. These submarine canyons had a large impact on the coastal development in the past. The submarine canyons are shown in Figure 9.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 14

CHAPTER 3: Site conditions

Figure 9 left: Submarine canyon in front of Chorokhi River. right: Submarine canyon in front Batumi Cape

Most large rivers along the eastern part of the Black Sea have a submarine canyon near its mouth. The slopes of the canyon consist of sandy material. An explanation for this phenomenon could be the rise of the sea level of the Black Sea. It is believed that the sea level in the Black Sea was much lower in the past (thousands years ago). Also in that time rivers have flown into the sea. At some stage the Black Sea and the Mediterranean Sea were connected by a channel near Turkey and the sea level in the Black Sea increased rapidly. The current present submarine canyons could be the riverbeds from the past. The fact that the slope of the submarine canyon consist of sandy material makes the canyon vulnerable.

In the present situation the canyon in front of the Chorokhi mouth seems to be stable. The submarine canyon at the Batumi Cape is however still moving in landward direction

The cause of this movements is schematically shown in Figure 10. Due to longshore and cross-shore transport, the sediment is transported into the canyon. This sediment deposits along the slope of the canyon. During this process it looks like the canyon is moving into seaward direction. When a large amount of sediment has deposited, geotechnical instabilities could occur because of the large weight and steep slopes of the recently deposited sediment. This will then cause the sediment to slide down further into the canyon. This means that in only a short period of time the canyon is able to move over a large distance into landward direction.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 15

CHAPTER 3: Site conditions

Figure 10 Active canyon

3.4 BATHYMETRY

Measured bathymetrical data is available for the years 1999, 2003, 2007 and 2009. The bathymetries of these years are similar and indicate that the overall bathymetry did not change much over the period between 1999 and 2009. The most recent survey was performed in 2009, but the bathymetry of 2009 does not cover the entire coastal project site and therefore the bathymetry of 2007 is used in the previous detailed design study and will also be used in this study. The survey of 2003 contains however more detailed information of the slopes of submarine canyons in front of the Chorokhi River mouth. Therefore the nearshore bathymetry of 2003 is used as input for the applied numerical models in the feasibility study in 2009. Depth contours at water depths larger than 25 m were digitized from Admiralty Charts. The bathymetry of 2007 of the area just south of the Chorokhi river up to Batumi Cape is presented in Figure 11.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 16

CHAPTER 3: Site conditions

Figure 11 Bathymetry, 2007

In 2008 additional bathymetrical surveys took place. Based on these recent surveys, the cross-shore profiles are determined at various locations along the coast. The locations of the cross-shore profiles are presented in Figure 12 and the profiles are shown in Figure 13.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 17

CHAPTER 3: Site conditions

Figure 12 Locations of a number of selected cross-sections

Figure 13 Cross-shore profiles based 2 on bathymetrical surveys, B-06 B-08 2008 0 B-10

B-12 B-14 -2 B-16 B-18

-4 Bed Bed level (m) -6

-8

-10 -800 -700 -600 -500 -400 -300 -200 -100 0 Distance along reference line (m)

Based on the cross-shore profiles it can be seen that the bed slopes are relatively steep up to a depth of CD -4 to CD -5m; the slopes are in the order of 1 in 20. Seaward of the CD -5m depth contour, the bed slope is more gentle and in the order of 1 in 100. This indicates that the pebble beach extends to a depth of approximately CD -5m.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 18

CHAPTER 3: Site conditions

3.5 WATER LEVEL

The design water level is set by the following phenomena: sea level rise, tide, atmospheric pressure, seasonal fluctuation and wind setup. All these phenomena will be discussed in the following subsections.

The lifetime of coastal structures along the coast of Batumi is 50 years. For this reason the design water level is the water level which may occur in a period of 50 years. The water level over 50 years for different future scenarios is given in Table 2. Table 2 Contribution Minimum Average Maximum Sea level after 50 years for Sea level rise 0.1 m 0.2 m 0.5 m different scenarios Tide 0.1 m 0.1 m 0.1 m Atmospheric pressure 0.3 m 0.3 m 0.3 m Seasonal fluctuation 0.2 m 0.4 m 0.5 m Wind setup at MSL-5m 0.0 m 0.0 m 0.0 m Total 0.7 m 1.0 m 1.4 m

3.5.1 TIDE

The tides of the Black Sea are of semidiurnal type. The Black Sea tidal movement originates from the Bosporus, which is the connection between the Black Sea, the Sea of Marmara and eventually the Mediterranean Sea. The effect of the tide on the water levels is small. The maximum amplitude is 12 cm and the period is about 12 hours and 25 minutes.

3.5.2 SEASONAL FLUCTUATIONS

The water level in the Black Sea fluctuates 0.25 to 0.5 meters (based on measured Sea levels, just south of Batumi Cape, 1925-1996).

The main input of water to the Black Sea is coming from the rivers. The most important is the Danube (Germany to Romania), and is responsible for 54% of the runoff in the Black Sea by rivers.

Another important way of water entering the Black Sea is the Mediterranean Sea through the Bosporus. On average 824.4 km3/year water flows into the Black Sea, on average 824.4 km 3/year water is lost out of the Black Sea. The maximum sea level is reached in March, April and May. From June till October the sea level drops. From then on the level rises again due to precipitation and discharge due to melting snow and ice .

3.5.3 SEA LEVEL RISE

The most likely scenario of the Mean Sea Level rise in 50 year will be around 0.2 meter, according to predictions in a Georgian report. In a maximum scenario, the sea level rise elevation will be around 0.5 meter and in the minimum scenario the sea level will rise around 0.1 meters (Giginelshvilii, Metreveli, Gzirishvili, & Beritashvili, 1999).

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 19

CHAPTER 3: Site conditions

3.5.4 ATMOSPHERIC PRESSURE

The Black Sea is influenced by several streams of air from all wind directions. Severe storms are mainly caused by low atmospheric pressure areas. The most important air streams for Batumi are the Mediterranean Low and the Icelandic Low. These streams mainly occur during winter and beginning of the spring. A depression of the water level is caused by high atmospheric level, and elevation is caused under low atmospheric pressure.

Because the Black Sea is a basin with large depths the elevation due to these pressures will be limited. During a long severe storm the low atmospheric pressure can cause elevation of the water level of 0.3 meters (Sing & Aung, 2005).

3.5.5 WIND SET-UP / STORM SURGE

Wind and barometric pressure may locally affect the water level. Westerly winds raise the water level while easterly winds lower the water lever especially during summer.

Computations from the previous study by ARCADIS in 2010, show that in a 1/100 yr storm, the surge is not higher than 0.02 to 0.05 m. This is negligible small compared to other values.

3.6 WIND

The wind speed is determined for various return periods and directional classes. The resulting wind speeds are given in Table 3. These return periods of the design wind speed are based on 40 years of measurements at the port of Poti (Alkyon/ARCADIS, 2010). Table 3 Extreme w ind speeds for Direction class different return periods in Return -22.5 22.5 67.5 112.5 157.5 202.5 247.5 292.5 Period m/s 22.5 67.5 112.5 157.5 202.5 247.5 292.5 337.5 Omni 1 16.60 25.78 15.21 19.18 19.61 20.45 18.44 23.93 5 18.76 28.52 17.04 21.51 21.52 22.79 20.93 26.06

10 19.60 29.61 17.74 22.43 22.28 23.71 21.90 26.91 No fit 25 possible 20.66 30.99 18.62 23.57 23.22 24.88 23.12 28.00 50 21.42 32.00 19.25 24.38 23.91 25.72 24.00 28.79 100 22.15 32.97 19.85 25.17 24.56 26.53 24.85 29.56 200 22.85 33.91 20.43 25.92 25.19 27.31 25.66 30.30

Based on the analysis of the wind speeds it was found that the maximum wind speed is coming from the west (between 247.5 and 292.5°N).

3.7 WAVES

3.7.1 OFFSHORE WAVE CLIMATE

The data source for the offshore wave climate is the Argoss hindcast model calibrated using satellite observations. This data is compared with data from Alkyon’s in-house database of ship’s observations and offshore wave data received from the National Environmental

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 20

CHAPTER 3: Site conditions

Agency of Ministry of Environment Protection and Natural Resources of Georgia, containing offshore wave data which is extracted from the Atlas of Wave of the Black Sea (1969 and 1972 or 1974). Based on the comparison of the three sources of offshore wave data it can be concluded that the Argoss hindcast model is a reliable resource. Therefore the Argoss hindcast model is used as data source in the present study.

During Unibest calculations in the feasibility study of 2009, it turned out that the resulting transports along the coast of Batumi did not correspond with the orientation of the coast and the changes of the coastline during the last decades. It was concluded that the directions of wind and waves are not reliable. The offshore climate was therefore rotated in order to get a nearshore wave climate which resulted in transports corresponding to the observed changes of the coastline. A modification of 30 degrees in clockwise direction provided the best results.

In this present study the same modification of the offshore wave data of 30 degrees in clockwise direction is used in order to get the nearshore wave climate and to determine transport capacities along the coast, unless mentioned differently.

3.7.2 NEARSHORE WAVE CLIMATE

The SWAN model has been used to compute the wave propagation from offshore to the nearshore area along the Adjara coastline. The SWAN model accounts for all important physical phenomena, including 2D-refraction, shoaling, dissipation by bottom friction, depth-induced breaking and generation of wave energy by wind. The entrance boundary condition of the SWAN model was specified uniformly on the open sides of the domain as a JONSWAP spectrum.

Computing the nearshore wave climate, a distinction is made between the yearly average conditions and the extreme conditions. The yearly average wave condition are required to clarify observed coastline changes, to compute wave induce sediment transport and to simulate the effect of mitigation measures. The extreme wave heights are required for engineering purposes such as the structural design of the constructions in the coastal zone.

3.7.2.1. YEARLY AVERAGE CONDITIONS

For the yearly average nearshore wave conditions the SWAN results of the feasibility study of 2009 are used.

Input To compute the nearshore normal wave climate , the following values for the parameters wave height, steepness, direction and water level are used as boundary conditions in SWAN, see Table 4.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 21

CHAPTER 3: Site conditions

Table 4 Range of values for Parameter Range of values for boundary conditions boundary condition for Hs [m] 0.5 1 2 3 4 5 6.5 average w ave climate s0 [-] 0.015 0.035 0.0055 Dir [°N] 195 225 255 285 315 345 375 L [m] 0.0 2.0

The relation between wind speed and wave height was derived for each directional sector by correlating the probabilities of exceedance of the wave heights to the probability of exceedance of the wind speed offshore. This relation was then used to determine the wind speed for each wave height applied into SWAN model. The relation betwe en the wave height and wind speed is shown in Table 5. Table 5 Relation w ave height and Wave height [m] Wind speed [m/s] w ind speed for average 0.5 1 w ave climate 1 7 (Alkyon/ARCADIS/HKV, 2 11 2009) 3 14.4 4 17.7 5 20.5 6.5 24

Output The offshore wave climate was transformed using transformation matrix to nearshore wave climates. This was done at a large number of locations along the coast of Batumi.

For several output points the probability of occurrence per wave height are given in so called occurrence tables. Table 6 shows the occurrence table for the northern location B_08 at a 10m depth. For location of point B_08 see Figure 12.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 22

CHAPTER 3: Site conditions

Table 6 H (m) Wave direction (deg) Probability of occurrence s per w ave height for output -15 15 45 75 105 135 165 195 225 255 285 315 point B_08 Lower Upper 15 45 75 105 135 165 195 225 255 285 315 345 Total

< 0.25 .84 .94 .81 1.61 5.40 5.12 3.79 1.58 2.56 3.33 10.54 6.94 43.47 0.25 0.75 .68 .08 . . . .00 .47 .75 1.85 7.82 15.38 6.50 33.53 0.75 1.25 .07 ...... 00 .12 2.23 8.66 1.90 12.98 1.25 1.75 .01 ...... 00 .29 4.25 .98 5.53 1.75 2.25 ...... 06 1.90 .32 2.28 2.25 2.75 ...... 01 .90 .18 1.08 2.75 3.25 ...... 44 .11 .55 3.25 3.75 ...... 25 .05 .30 3.75 4.25 ...... 14 .02 .16 4.25 4.75 ...... 05 .03 .08 4.75 5.25 ...... 01 .02 .03 5.25 5.75 ...... 00 .01 5.75 6.25 ...... 6.25 > ...... Total 1.60 1.02 .81 1.61 5.40 5.13 4.26 2.33 4.53 13.73 42.52 17.05 100.00

3.7.2.2. EXTREME CONDITIONS

For the extreme conditions the SWAN calculations made in the detailed design study of 2010 are used.

Input As mentioned earlier the offshore wave climate is rotated in order to correspond well with the local coastal system. In order to account for uncertainties with respect to offshore wave direction, simulations for the design conditions are made for a rotation of the offshore wave climate of 15°, 25° and 35° into clockwise direction. Besides the different clockwise rotations of the offshore wave climate, simulations are performed for various return periods, for different direction classes and for 3 different scenarios for the sea level. The range of values for the boundary conditions for simulations for computing the extreme wave climate are shown in Table 7. Table 7 Parameter Range of values for boundary conditions Range of vaules for Dir [°N] 210 240 270 300 330 boundary conditions for extreme w ave climate R [yrs] 1 5 10 25 50 100 200 CWR [°] 15 25 35 L [m] 0.7 1.0 1.4

Within the computation, accompanying extreme wind speed were applied, see Table 5. Within the computation, the wind direction was set the same as the wave direction.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 23

CHAPTER 3: Site conditions

Output Following the computational results, the design wave conditions are known at a large number of locations along the coastline. It is known that the SWAN-model does not compute wave energy dissipation on steep slopes correctly. Therefore, the waves as computed with the SWAN-model were corrected afterwards with formulations as given by D.P. Hurdle and G. van Vledder, 2000. The correction generally results in somewhat higher waves.

In Figure 15, the design wave conditions (for various return periods) are shown along the Kp-values reference line. The locations of the Kp-values on the horizontal axe is shown in Figure 14. The wave conditions are given at the MSL-5m depth contour. Figure 14 Indication points along the reference line, referred to as Kp-values

Figure 15 Computed extreme w ave conditions along the MSL- 5m depth contour

The following can be seen from the figure: . Relatively high waves occur in the north (around Kp1.000) and the wave height gradually reduces towards the south; . South of Kp7.400, the wave height suddenly increases significantly. This is caused by the configuration of the submarine canyon in front of the Chorokhi River. Along this coastal section, the submarine canyon lies relatively close to the coast and secondly the shape of the canyon causes focussing of wave energy; . Especially along the central part of the coast, the differences between 1/1 year storm conditions and 1/200 year storm conditions is small. This means that the wave height is mainly determined by the local water depth.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 24

CHAPTER 3: Site conditions

3.8 CURRENTS

The global feature of current in the Black Sea is counter clockwise with an almost constant flow of water from the Black Sea to the Mediterranean. Offshore the coast of Batumi the velocities are 0.25 to 0.35 m/s which may change due to river runoff, wind and other meteorological effects. Flow velocities, other than wave induced, are relatively low and therefore it is expected that currents do not have effect on the coastal morphological processes.

In the Black Sea there is hardly any tide. Also the wind set-up near Batumi is negligible. This means that there is basically no force, which could induce relevant currents along the coast of Batumi.

3.9 SEDIMENT PROPERTIES

In November 2008 bed samples were taken at the beach and at 10 m water depth at several locations along the coastline during a field survey. The locations are given Figure 16 and the sieve analysis are presented in Table 8.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 25

CHAPTER 3: Site conditions

Figure 16 Locations of bed samples taken in 2008

Table 8 D (mm) at 10m D (mm) at D (mm) at D (mm) high up Sieve analysis for different Profile 50 50 50 50 depth w aterline middle of beach the beach profiles 1 0.11 17.19 16.19 2.77

12 0.09 78.84 49.94 25.23 18 0.08 19.42 28.83 47.59 21 0.08 22.64 30.31 49.78 25 0.09 18.94 21.55 21.55 29 0.09 38.36 18.29 44.18 34 0.09 26.72 16.18 9.20 40 0.10 15.50 6.83 30.90 Average 0.09 29.45 23.52 28.90

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 26

CHAPTER 3: Site conditions

From the sieve analysis it is concluded that the beach mainly consist of gravel (2-50mm) with small amounts of course sand (0.3-2mm) and some cobbles (>50mm). The seabed material is much finer compared to the beach material and mainly consists of fine sand.

In the study carried out by Alkyon in 2000, sieve curves are given of sediment samples taken near the waterline. The resulting D50 varied between 10 mm and 45 mm. These values correspond with the results of the measurements carried out in 2008.

In the computations in previous studies the applied gravel settings were based on the sieve analysis, a Dn50 of 2.5 cm was used. The density of pebbles was taken as 2650 kg/m3. The applied roughness length was 0.06 m.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 27

CHAPTER 4: Coastal processes

CHAPTER 4 Coastal processes

In this chapter the processes driving the erosion in Batumi is treated. First of all the sediment transport processes will be treated in Section 4.1. In Section 4.2 an overview is given of the observed coastal changes in the last approximately 150 years. In Section 4.3 the erosion and accretion rates are discussed and finally some conclusions are given.

4.1 SEDIMENT TRANSPORT PROCESSES

4.1.1 LONGSHORE PROCESSES

The main processes that contribute to the longshore sediment transports are: . Wave induced longshore currents . Tide driven longshore currents

Wave induced longshore currents The longshore sediment transport at the coast of Batumi is dominated by the wave induced longshore currents. The longshore current is generated by the shore-parallel component of the stress associated with the breaking process for oblique incoming waves, the so-called radiation stresses, and by surplus water which is carried across the breaker zone toward the coastline. These longshore currents can be observed mainly inside the breaker zone but extend to a small area outside the breaker zone.

From the feasibility study by ARCADIS in 2009, follows that the peak of the longshore transport of the pebbles at the coast of Batumi lies at around MSL -2,0 m. The total width of the transport zone (the breaker zone) is about 100 m. Only less than five per cent of the total yearly transport occurs below a depth of MSL -5 m, see Figure 17. Figure 17 Distribution of annual alongshore transports, pebbles (about 4 km north of the Chorokhi River)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 29

CHAPTER 4: Coastal processes

Tide driven longshore currents Sediment transport can be distinguished in bottom transport and transport in suspension. Material that comes into suspension, for instance in the breaker zone under the influence of breaking waves, can be transported parallel to the coast unde r influence of tidal currents along the shore, even if this current is too weak to cause bottom transport.

Along the coast of Batumi tidal currents are small and the longshore currents are therefore dominated by the wave induced currents.

4.1.2 CROSS-SHORE PROCESSES

Wave induced cross-shore currents causes fluctuations of the beach profile. In case of a sandy beach, sediment will be transported from the upper part of the profile to the lower part during severe wave conditions. Where the average coastal profile is in equilibrium, the sediment will be transported back to the upper part during mild wave conditions. If the average profile is not in equilibrium, a net cross-shore loss (or gain) affects the sediment balance.

Along the coast of Batumi cross-shore transports are assumed to be minimal. This assumption is based on the composition of the cross-shore profiles. To a depth of approximately MSL -5m the profile consists of pebbles. At larger depths the seabed consists of much finer sands. The energy of the waves that approach the coast will be dissipated on the pebble shore. The wave return current will flow through the stones back in offshore direction. Due to the size of the pebbles and the magnitude of the current, transport is minimal. However, if present, finer sediment particles will be washed out almost instantly from the highly energetic breaker zone and are transported outside the breaker zone where the seabed consists of much finer sands.

4.2 COASTLINE DEVELOPMENT

In this section, an overview is given of the observed coastal changes in the last approximately 150 years.

4.2.1 HISTORICAL OVERVIEW

From old charts it can be seen that the Chorokhi River consisted of two major branches, at least until 1830. The most southern branch was at the same position as the current river mouth. The northern branch was situated just north of Adlia. In front of the northern branch there is a coastal plain with depths up to CD -20m. In Figure 18 the coastline from 1830 is drawn together with the existing coastline position. From the figure it can be seen that the delta formation of the northern branch reached up to approximately 450 m seaward of the existing coastline.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 30

CHAPTER 4: Coastal processes

Figure 18 Observed coastline changes after 1830. (pink: measured coastline1830, blue: measured coastline 2008)

In front of the southern branch there is no delta present. This is because there is a submarine canyon with depths up to several hundreds of meter present right in front of the river mouth. Most of the sediment is transported directly into this canyon and does not benefit the coastal system.

Between 1830 and 1880 two major changes have occurred along the coastal stretch between the southern branch of the Chorokhi River and the city of Batumi. Firstly, the northern branch of the river was closed (that exact date of closure is unknown) and secondly, a port was constructed just north of Batumi. The port was constructed in combination with a long breakwater just south of Batumi Cape. The impact of these two measures can be seen in Figure 18. Just south of Batumi Cape accumulation of sediment can be seen due to blockage of sediment by the breakwater. At the position of the former northern branch of the Chorokhi River erosion of the coastline can be seen. Because of closure, there is no longer a supply of sediment into the coastal system. There is however longshore sediment transport due to waves, which means that there is a deficit of sediment and the delta is gradually eroded.

Just north of the southern branch of the Chorokhi River accumulation of sediment has occurred. When comparing the coastline of 1830 and the existing coastline, it can be seen that the coastline has shifted seaward for approximately 120m. The accumulation of sediment did not proceed because the coastal profile reached the slope of the submarine canyon.

Between 1880 and 1913 the coastline of Adlia has eroded rapidly due to closure of the northern branch. On average, the erosion was 6 to 8 m/y at the location of the former delta. Further to the north, a seaward shift of the coastline can be seen due to blockage of sediment by the breakwater at Batumi Cape. Near the mouth of the Chorokhi River, the coastline position is fixed because the coastline cannot extend further seaward and the input of sediment from the river is large enough to prevent erosion of the coast.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 31

CHAPTER 4: Coastal processes

From 1913 up to 1983, the erosion of the coastline gradually reduced. This happens because the orientation of the coastline becomes closer to its equilibrium.

During the period 1982-1992 sediment was dredged from the Chorokhi River and near Batumi cape. The dredged material was used for nourishments along the coastline just north of the airport. In Table 9 the nourishment volumes are presented. In total approximately 1.3 Mm3 of beach forming sediment was mined. According to the table, the yearly averaged volume for nourishments is 130,000 m3/year. From 1992, nourishments were stopped due to lack of funding. Erosion took over again. Table 9 Year 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 Volume of nourished 3 3 sediment along the coast Volume (10 m ) 88 130 100 108 160 115 141 239 131 53.8 1.5 near Adlia From 2001 to 2007 the coastal changes were mainly restricted to the area from the Chorokhi River to just north of Batumi airport. Further to the north, the coastline is more or less stable.

Between 2007-2008 high rates of accretion (seawards movement of shoreline) were noticed near Batumi airport. The reason for this is discussed later on in Section 4.3.3.

4.3 SEDIMENT TRANSPORT ANALYSIS

4.3.1 WAVE ENERGY IN THE COASTAL ZONE

As the waves propagate towards the shore, energy is lost due to bottom friction and wave breaking. Also the wave direction is changing due to refraction. The yearly average wave energy and the direction of this energy determine the sediment transports and with that the erosion and accumulation pattern along the coastline. The direction of the annual averaged wave energy flux is used to analyse a coastal system as it gives an indication of the direction of the literal drift and the equilibrium orientations of shoreline sections.

The wave energy flux and the yearly average direction of the wave energy have been computed for several locations along the Batumi coast in previous studies. In Figure 19 the yearly averaged direction of the wave energy flux is graphical presented along the coastline.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 32

CHAPTER 4: Coastal processes

Figure 19 Graphical presentation of averaged direction of w ave energy fluxes along the Adjara coast (Alkyon/ARCADIS/HKV, 2009)

From Figure 19 it can be seen that from location 0, located in front of the Chorokhi River mouth, the wave energy increases towards the north. This induces an increase in the sediment transport towards the north, resulting in coastal erosion. From the location just north of Batumi airport the wave energy decreases continuously towards Batumi cape. This results in a decreasing sediment transport and thus accretion of the coastline.

It can also be seen that the yearly average angle of the wave energy flux is in the order of 30° (i.r.t. the coastal normal). Further to the north, the angle reduces to approximately 15° and stays approximately 15° along the rest of the coast up to Batumi Cape.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 33

CHAPTER 4: Coastal processes

4.3.2 TRANSPORT CAPACITIES AND S-Φ-CURVE

With the use of the UNIBEST-LT model the longshore transport is computed for several locations along the coastline in the previous feasibility study by Alkyon, ARCADIS and HKV, 2009. The model has been calibrated using observed changes in coastline.

In the table below the computed transport capacities are shown. It can be seen that the computed net transport capacity is between 70,000 and 150,000 m3/y in a northerly direction. This results from the two gross southward (3,000 to 18,000 m 3/y) and northward (84,000 to 153,000 m3/y) contributions respectively. Table 10 Profile Orientation X Alongshore transport rates integrated over full year Computed alongshore 3 (°N) (m) (m /y) sediment transport Gross southwards Gross northwards Net capacities B04 (Batumi 321 7782 -16,229 84,979 68,750 (Alkyon/ARCADIS/HKV, Cape) 2009) B06 323 7419 -11,985 104,884 92,899 B07 319 7140 -18,104 108,910 90,806 B09 316 6545 -17,198 133,125 115,927 B11 315 6019 -10,740 105,689 94,941 B15 307 4619 -8,135 87,984 79,850 B18 304 3748 -6,622 103,315 96,693 B19 307 3276 -4,938 134,909 129,972 C01 309 2375 -3,212 153,414 150,202 C03 292 1236 -10,354 100,288 89,934

Longshore sediment transport rates can usually not be computed within accuracy ranges less than a factor two. An uncertainty factor of 2 is therefore applied. This is indicated in Figure 20, which show the longshore transports, by the vertical lines.

Figure 20 Longshore transports Adjara coast (Alkyon/ARCADIS/HKV, 2009)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 34

CHAPTER 4: Coastal processes

The effect of the orientation of the shoreline on the transport rates is presented by the so- called S-ϕ-curve. Here, S stands for the longshore transport and ϕ for the orientation of the shoreline. The S-ϕ-curves for gravel computed in previous pre-feasibility study with the Pilaczyk formula, is shown in Figure 21. The location of the profiles are shown in Figure 22.

Figure 21 S-φ curves for different profiles along the coast (Alkyon/ARCADIS/HKV, 2000)

Figure 22 Locations profiles

From the figure can be seen that the equilibrium coastline angle hardly changes along the central part of the Batumi coastline. A re-orientation of the shoreline by some degrees to 290°N leads to zero-transport for profile 10, 14 and 21. At the Batumi Cape the equilibrium coastline suddenly changes, this is caused by the presence of the canyon. Along the slope of the canyon refraction of waves will occur and therefore the yearly average wave direction differs in this area from the direction along the rest of the coastline at Batumi.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 35

CHAPTER 4: Coastal processes

4.3.3 CONCLUSIONS AND DISCUSSION CAUSE OF EROSION/ACCRETION

Summary In the previous section an overview is given of the observed coastal processes since 1830. The observed large-scale morphological processes are clarified by two activities, which took place in the end of the 19th century:

. Construction of the breakwater near the port of Batumi; . Closure of the northern branch of the Chorokhi River. After closure, the supply of sediment towards the coast has stopped, but the longshore sediment transport due to waves along the coast has continued. In about 180 years, the coastline has retreated over approximately 450 m.

Besides this, there are features along the coastline which determine the small-scale morphological processes. These are mainly the Chorokhi River mouth and the shape of the submarine canyon. Near the canyon the direction of the waves changes due to wave refraction. Wave refraction causes convergence of the waves just north of the submarine canyon and hence an increase in wave energy at this location. This induces an increase in the sediment transport towards the north, resulting in coastal erosion.

The influence of the canyon can be seen up to Adlia. Even further to the north, wave energy reduces and the angle of approach of waves in relation with the coastline orientation remains constant. A reduction of wave energy results in a reduction in the longshore sediment transport. This would imply accumulation along the coast. The coastline position is however constant in time (for decades).

Discussion of coastline position north of the airport As explained above, accumulation is to be expected along this coastal stretch, but the coastline is however constant in time. By Georgian experts it is believed that pebbles are transported both along the beach profile as well as along a submarine bar. This submarine bar is expected to move in shoreward direction. It will finally reach the coast and lead to temporary accretion. In a few years a new bar will develop and this bar will then also move to the shore and this will again lead to accretion near the waterline.

The theory is supported by numerical wave models, but from a physical point of view it is not realistic because the bar is located at a relative large water depth where the sediment transport capacity is only minimal.

Although the explanation of the Georgian experts is questionable, the reason for no accumulation will not further be verified in this thesis.

Discussion of temporary accretion Recently (2007-2008) high rates of accretion were noticed near Batumi airport. This phenomenon is presumably caused by the breach of the dike along the southern bank of the Chorokhi River. The most downstream meander of the Chorokhi currently caused erosion of the southern bank, which led to a dike breach. With this the sediment load increases and this may result in an increased sediment supply towards the coast, causing a temporary accretion near Batumi airport.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 36

CHAPTER 4: Coastal processes

Other possible phenomena for the natural accumulation of sediment along the coast should be found in either one of the following processes or a combination of these: 1. Additional sediment due to cross-shore transports; Due to wave action, sediment is transported into a cross-shore direction. Relative low conditions tend to generate shoreward directed transport, while high waves (during storm conditions) are more destructive and result in seaward directed transport of pebble. In the last few years, hardly any severe storm condition has occurred and large volumes of pebble have been transported towards the coast. 2. Additional sediment due to (lack of) longshore transports; 3. More effective pass-through of sediment from the Chorokhi River towards the coast. It is believed that the pass-through of sediment from the Chorokhi River towards the coast may be more effective due to some changes near the river mouth. These changes could either be: − The most downstream meander of the Chorokhi River, which results in a northerly directed discharge of water and sediment (towards the coast instead of directly into the canyon); − Reduced river discharges which cause more deposition of sediment north and south of the river mouth inste ad of being transported directly into the canyon due to high flow velocities ; − Changes in the local bathymetry of the Chorokhi River mouth, which forms some sort of corridor for sediment from the Chorokhi River towards the coast. A change in the local bathymetry, which could cause this, is a slide (avalanche) of pebbles, which (temporarily) cause a milder beach profile;

Acceleration erosion processes The erosion processes north of the Chorokhi River mouth are recently accelerated due to human interference: 1. Starting around 1975, large scale mining of sediment from the Chorokhi River takes place. Currently in the order of 300,000 m3/y of beach forming sediment is mined. The impact along the coast can be seen in a smaller average grain size; 2. In 2005 the first power dam in Turkish side of the Chorokhi River became operative. More dams will follow. The impact of these power dams is twofold. First of all, the sediment is blocked completely by the dams. On downstream side of the dam, there is now deficit of sediment. This can be seen in erosion of the river bed. Secondly, the water discharge is regulated and due to this, less sediment is transported through the river towards the river mouth.

The morphology of the Chorokhi River is changing due to mining activities and the hydro dams on the Turkish side of the river. Based on the latest observations along the coast and the predictions with respect to availability of sediment from the Chorokhi River, it is concluded that in time, the sediment load through the river will decrease and sediment becomes scarce. At that time (which could already be in several years from now), more permanent protective measures should be installed in order to prevent high maintenance costs.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 37

CHAPTER 5: Concepts and tools for design sandy beach

5 Concepts and tools for design sandy beach

In this chapter the information and theories which are used to generate the alternatives as proposed in Chapter 6, are treated. This chapter is the preliminary study of possible measures in order to create and preserve a sandy beach along the Old Boulevard of Batumi. First of all the characteristics of a beach profile and corresponding theories are treated in Section 5.1. The main issues of creating a sandy beach, possible measures to solve or limit these issues and possible measures to preserve the created sandy beach are discussed in Section 5.2. In order to determine suitable measures and alternatives information should be gained on the morphological impact of the measures and the corresponding sediment transports. For this purpose numerical models are applied, namely UNIBEST-LT and XBeach. These models are treated in Section 5.3. At least also the requirements should be known before design alternatives can be defined. These requirements for the sandy beach along the Old Boulevard of Batumi are treated in Section 5.4. With the use of the executed study treated in this chapter, the different alternatives which are proposed in Chapter 6 are generated.

5.1 BEACH PROFILE

Sandy beaches are in constant motion, continually changing shape and shifting position in response to winds, waves, tides relative sea level, and human activities. Concurrent reshaping of the beach owing to wave -induced sediment transport takes place both in the on-/offshore directions and in the alongshore direction.

Beach profile data are important for an understanding and quantification of the coastal zone processes and the related interaction of coastal structures with these processes. The total seasonal envelope of profile change must be defined, for the design of coastal structures as well as for the establishment of coastal boundaries and the design of beach nourishment. A typical coastal profile and how the various depth zones are often referred to is shown in Figure 23. Figure 23 Profile schematisation and indication of different zones

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 39

CHAPTER 5: Concepts and tools for design sandy beach

After a relatively long period of calm wave action sediment is slowly transported landward to build the beach face in the foreshore zone and to extend the berm seaward, thus causing a steeper beach face profile. With the appearance of higher and steeper waves, common during a period of storm activity, sediment is transported seaward. The beach profile in the vicinity of the mean water level is thus cut back and the slope is flattened. The sand transported offshore will build a larger offshore bar around the point of wave breaking. At most locations, storm waves predominate during winter months and calmer waves occur during the summer. Thus the terms winter and summer profile are often used to define the two types of beach profile.

The beach slope, which varies with the steepness of the incident waves as discussed above, also depends on the sand size that constitutes the beach face. For the same incide nt wave energy level, a beach made of coarser sand will have a steeper beach face slope. Conversely, for a given sand size, beaches exposed to higher wave energy will have a flatter beach slope (as discussed above), see Figure 24. Figure 24 Beach face slope versus median sand grain diameter for high and low energy exposure (Modified from Wiegel, 1964) (Sorensen, 2006)

In addition to wind wave-induces beach profile changes, there will be a recession in the beach profile if there is a relative rise in mean sea level as has been historically happening along most of the coastlines of the world. Besides the flooding of a profile caused by relatives rise in MSL, there will be an adjustment of the profiles as sediment is transported offshore and the MSL position on the beach face is shifted landward. This produces a recession of shoreline. Bruun (1962) discussed this process and presented a procedure to analyse the distance a shoreline will retreat owing to a given rise in MSL.

5.1.1 EQUILIBRIUM PROFILE

As discussed above, as the wave and water level conditions vary, the beach profile will respond by changing. An useful concept, however, is the equilibrium beach profile. This is the mean profile that would occur when profiles are measured over a period of several years. This concept is useful for a variety of coastal engineering analysis and design purposes as the computations of beach nourishment volumes and analysis of the impact of coastal structures on the resulting beach profile.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 40

CHAPTER 5: Concepts and tools for design sandy beach

The most common form of an equation to define the equilibrium beach profile is

with: h = depth below mean water level for a given distance y offshore [m] y = offshore distance from the shoreline [m] A = sediment scale parameter m = profile shape factor

This equilibrium beach profile equation defines a profile that is concave and has an increasing slope at given point of increasing sand grain diameters. However, it also predicts an infinite slope at the shoreline so it should not be applied very close to the shoreline. Other more complex profile form equation have been proposed that overcome this problem.

Bruun (1954) and Dean (1987) concluded, based on empirical data, that profile shape factor m may be considered constant and equals 2/3.

Moore (1982) and Dean (1987b) have provided empirical correlations between the sediment

scale parameter A as a function of sediment size D and fall velocity wf as shown below.

and

( ) for D < 0.0001

for 0.0001 < D < 0.001

for D > 0.001 with:

= fall velocity [m/s] D = grain diameter [m]

5.1.2 CLOSURE DEPTH

Seaward of some point along the beach profile in the offshore direction there will be insignificant sediment transport for a given wave condition. This point will be further offshore for higher and longer period waves. However, for coastal engineering design, it is desirable to define a profile closure depth at some offshore point where there is negligible profile change for some significant level of wave action. Definition of this profile closure depth is useful for establishment the seaward limit of placement of beach sand during a beach nourishment.

When nourishing a beach, the entire nearshore profile down to an approximate closure depth must be nourished. Hallermeier (1981b) used laboratory data and limited field data from the Pacific Ocean and the Gulf of Mexico to de velop a formula for computing closure depth. Birkemeier (1985), used an extensive data set measured at the Coastal Engineering Research Center’s ( CERC) Field Research Facility (FRF) located along the Atlantic Ocean in northeastern North Carolina to develop the following modification of Hallermeier’s formula:

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 41

CHAPTER 5: Concepts and tools for design sandy beach

( )

where:

hc = closure depth in meters

Hs0.137 = extreme nearshore significant wave height exceeded 12 hrs per year in meters (i.e.,0.137% of the year)

Ts = period associated with Hs0.137

It should be noted that the depth of closure is a morphodynamic boundary, not a sediment transport boundary. Sediment transport occurs seaward of the closure depth, especially during storms. However, the closure depth is a good empirical indicator of an increasing capacity for shoreward sediment transport at any point within the limits of closure.

5.1.3 SANDY BEACH PROFILE ALONG THE COAST OF BATUMI

The coastal area at Batumi consists of both sand and pebble. Above approximately CD-4m, the coastal profile consist of pebble. Beneath this level, the sediment gradually changes into sand. The shape of the beach profile will significantly change when sand is applied.

The characteristic shape of the sandy profile is determined with the formula of Dean (1977) and the closure depth is calculated using Hallermeier (1981b), resulting in a closure depth of CD-6.2 m. For the determination of the parameters and calculations see Annex 3. The grain diameter of the sand is defined 0.3 mm, as this is locally available.

To create the sandy beach, sand will placed on top of the gravel. To avoid mixing of the gravel and the sand, at the location were the current profile reaches the water line a sand layer of approximately 2 meters will be placed on top of the gravel. In Figure 25 an arbitrary calculated equilibrium profile and the initial profiles are shown. Figure 25 Equilibrium profile sandy 4 beach profile and the initial Sand profile B-P03 profiles 2 B-P04

B-P06 0 B-P08

-2

-4 Bed Bed level (m +CD)

-6

-8

-10 -600 -500 -400 -300 -200 -100 0 Distance from waterline (m)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 42

CHAPTER 5: Concepts and tools for design sandy beach

The emerged profile of the beach depends, among others on the shifting of the waterline in seaward direction. An example of the emerged beach profile is given in the following. The slopes as presented in this example are used as an indication for the slopes of the emerged profiles of the different type of beaches in the remainder of the report.

The sand profile will run up from the water line to the 2.5 meter height under a slope of 1:20. At the height of 2.5 meter the beach profile will run up to +3.5m under a slope of 1:10. From here the slope of the beach will be much flatter with a slope of 1:50, till it will reach the height of the boulevard. The emerged sandy beach profile and the current profiles of the pebble beach are shown in the figure below. Figure 26 Emerged sandy beach 4 profile and initial pebble Sand profile 3 B-P03 profiles B-P04

2 B-P06 B-P08

1 Bed Bed level (m +CD)

0 -60 -40 -20 0 20 40 60 80 Distance from waterline (m)

Combining the emerged and submerged profile of the sandy beach results in the cross-shore profile at location B_P06 as shown in Figure 27. Figure 27 Sandy beach profile at 4 location B_P06 2

-2

-4

-6 Bed Bed level (m +CD)

-8 Beach profile Initial profile -10 Waterline

-12 -500 -400 -300 -200 -100 0 100 Distance (m)

5.2 DESIGN CONCEPTS OF AN ARTIFICIAL SANDY BEACH

In this section the issues of creating and preserving a sandy beach along the coastal stretch of Batumi are discussed. This will be done by using the most straight forward solution as a starting point. The objective is to create a sandy beach along a part of the coastal stretch of Batumi. So the starting point will be an e ntire sandy beach along this coastal stretch, by simply putting sand along this stretch, without using any protection measures like structures. From this starting point the problems will be analysed and possible solutions to

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 43

CHAPTER 5: Concepts and tools for design sandy beach

optimise the design of the sandy beach will be treated. This approach will finally lead to different type of possibilities to realize successful sandy beaches along the coast of Batumi.

5.2.1 OPTIMISATION DESIGN SANDY BEACH

To main issues of a fully sandy beach are: . Large quantity of sand required . Loss of sediment due to longshore transport . Loss of sediment due to cross-shore transport

These issues and ways to solve these issues will be treated in the following sections.

5.2.1.1. LOWERING AMOUNT OF REQUIRED SAND

One of the main issues is the large quantity of sand that is required. The first optimisation is lowering the amount of sand that is required. Possibilities to optimise the required amount of sand are: . Steeper slope - Coarser sand - Lower wave height . Lower closure depth - Coarser sand - Lower wave height . Transition of sandy profile and initial profile at lower depth - Perched beach

Steeper slope and lower closure depth The equilibrium profile and the closure depth are determined for the case of a lower wave height and/or coarser sand by a factor 2, see Figure 28. From the figure follows that a lower wave height results in a lower closure depth. Coarser sand results in a much steeper slope as well as in a lower closure depth. Figure 28 4 Equilibrium profiles, Dean Representative profile 2 Sand profile, Dean H/2, Dean 0 D50*2 H/2 & D50*2, Dean -2

-4

-6 Bed Bed level (m +CD) -8

-10

-12 0 100 200 300 400 500 600 Distance from waterline (m)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 44

CHAPTER 5: Concepts and tools for design sandy beach

The initial sand profile is determined for a grain diameter of 2mm and . A wave height half of the wave height in the initial situation results in less than the half of the needed amount of sand. A sand diameter twice the diameter of the initial situation results also in a decrease of the total needed amount of sand by a factor 2. If the wave height is lowered as well as an increase in the grain diameter, the total needed amount of sand will decrease by a factor larger than 4 as in the initial situation.

Lowering wave height By lowering the wave heights the closure depth reduces. The wave height can be lowered by creating a sheltered area. A sheltered area can be created with the help of a breakwater. A possible alternative is a floating breakwater.

Perched beach By placing a structure in front of the ne w nourished beach a transition can be made between the new profile and the old profile at a much lower water depth.

This can be done by creating a perched beach. A perched beach combines a low breakwater or sill and a beach fill perched, or elevated above the normal level, see Figure 29. This alternative provides a broad buffer against wave action while offering a potentially excellent recreational site. Perched beaches have many of the same qualities as natural beaches, and the submerged sill does not intrude on the view of the waterfront. With this alternative a fully sandy beach is created. Figure 29 Sketch of a perched beach

Another possibility is creating a protected sandy beach, with in front of the sandy beach a pebble beach. The sandy beach is protected by a structure in front of the sandy beach, and in front of the structure a pebble beach will be created. This variant is shown in Figure 30. Figure 30 Sketch of a sandy beach w ith in the front a pebble beach

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 45

CHAPTER 5: Concepts and tools for design sandy beach

5.2.1.2. LIMIT THE LOSS OF SEDIMENT DUE TO LONGSHORE TRANSPORTS

Another issue is the large loss of sand due to longshore transport. To limit this loss of sand one could focus on the following: . No transport of sediment out of the system; . New input of sediment into the system; . Reduction of longshore transport.

No transport of sediment out of the system By placing groynes it can be prevented that sediment will be lost out of the system. A groyne is a coastal structure which is constructed perpendicular to the coastline from the shore into the sea, to trap longshore sediment transport or control longshore currents.

New input of sediment into the system New input of sediment into the system can be accomplished by nourishing frequently.

Another solution can be found by combining new input of sediment into the system and not losing sediment out of the system. This can be done with the use of a sand bypass system. A sand bypass system is a permanent solution to sand erosion and littoral drift problems. The system consist of a pump that removes sand from the beach face in the north at the end of the sandy beach, and a discharge line that discharges the sand onto the beach in the south at the beginning of the sandy beach.

Reduction of the longshore transport A way to limit the longshore transport is by creating a stable coast. This can be done by placing groynes. In between these groynes the sediment transport can be made zero by orientating the shoreline in such a way that it equals the equilibrium coastline angle.

Another way to limit the longshore transport is by protecting the beach against the waves. By creating a sheltered area, the transport in this area will be limited. Examples of alternatives are given below.

Beaches between detached breakwaters are called pocket beaches, see Figure 31. Detached breakwaters are straight shore-parallel structures, which partly provide shelter in their lee thus protecting the coast and decreasing the littoral transport between the structure and the shoreline. This decrease in transport results in trapping sand in the lee zone and some distance upstream. Figure 31 Sketch of pocket beaches

By construction a cove a sheltered area is gained. A cove is a semi protected sandy bay, formed by two curved shore connected breakwaters at a coastline, which is otherwise protected by revetments, see Figure 32.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 46

CHAPTER 5: Concepts and tools for design sandy beach

Figure 32 Sketch cove

By constructing a kind of se parated segment like in Figure 33, the coast is protected and a sheltered area is gained at which a sandy beach can be created. Figure 33 Sketch of constructed segment

A sheltered area can also be gained by using groynes. Groynes can have different shapes. By using these different shapes, the lee side area can be influenced. In Figure 34 a different shape of groyne is used, creating a sheltered area. Figure 34 Sketch of groynes

5.2.1.3. LIMIT THE LOSS OF SEDIMENT DUE TO CROSS-SHORE TRANSPORTS

Ways to limit the losses due to cross-shore transports are: . Using coarser sand . Limit the wave attack

Limiting of the wave attack can be done by creating a sheltered area. Some examples to create a sheltered area are already treated and can be found in the previous section.

5.2.2 OVERVIEW OF MEASURES TO OPTIMISE THE DESIGN OF THE SANDY BEACH

From the different issues and the different ways to solve these issues follow some main measures.

Coarser sand Coarser sand will decrease the required amount of sand considerable, it increases the slope as well as it decreases the closure depth. Coarser sand will also limit the cross-shore transports and also in some extend the longshore transport.

Breakwaters A breakwater is designed to provide protection from wave action. Protection from wave action will result in less sediment transport in longshore as well as cross-shore direction. Less wave action will also result in a lower closure dept.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 47

CHAPTER 5: Concepts and tools for design sandy beach

Two interesting applications of breakwaters are: . Pocket beaches The beaches between detached breakwaters are called pocket beaches. Detached breakwaters are straight shore-parallel structures, which partly provide shelter in their lee thus protecting the coast and decreasing the littoral transport between the structure and the shoreline. This decrease in transport results in trapping sand in the lee zone and some distance upstream. . Perched beach A perched beach combines a low breakwater or sill and a beach fill perched, or elevated above the normal level. A perched beach will decrease the required amount of sand enormously. A perched beach will also provide a broad buffer against wave action.

Groynes A groyne is a coastal structure which is constructed perpendicular to the coastline from the shore into the sea, to trap longshore sediment transport or control longshore currents. By using the different shapes, the lee side area can be influenced.

Other variants Besides the main measures above there are also some other measures that could be a good solution for the problem. Some of these variants are: . Bypass system . Segments of sand . Sand only applied above the water level

5.3 SEDIMENT TRANSPORT MODELLING

In this study, different alternatives will be investigated in order to create a sandy beach which is attractive for tourists. To validate the alternatives and to design these alternatives in more detail, it is necessary to know the effects of the measures. The morphological effects of the measures will be determined with the help of numerical models. Two computer models are applied in the present study. The computer models used in the present study are UNIBEST-LT for longshore transport and XBeach for cross-shore transport. In this section the models are introduced. The more detailed model set-up and calculations can be found in Annex 4, 5, 6 and 7. The modelling results will be used to assess the morphological effects of the different alternatives which are proposed in the following chapter.

5.3.1 UNIBEST-LT

UNIBEST-LT is an acronym for "Uniform Beach Sediment Transport - Longshore Transport". The module has been developed to compute tide - and wave-induced longshore currents and sediment transports on a beach for arbitrary profiles. The surfzone dynamics are derived from a built-in random wave propagation and decay model, which transforms offshore wave data to the coast, taking into account the principal processes of linear refraction and non-linear dissipation by wave breaking and bottom friction. The longshore sediment transports and cross-shore distribution can be evaluated on the basis of different transport formulae (Bijker, Van Rijn, Bailard, Engelund-Hanssen, CERC).

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 48

CHAPTER 5: Concepts and tools for design sandy beach

5.3.1.1. MODEL SET UP UNIBEST-LT

The main input for the UNIBEST-LT model is the wave climate, the local coastal profile and the sediment characteristics (and if relevant local tidal currents, not used in this study). The wave climate is derived from the table of occurrence as obtained in the feasibility study of 2009 (see Section 3.7.2.1) for the locations B_P04, B_P06 and B_P08 at 10 meter depth. The corresponding cross-shore profiles at these locations are determined from the bathymetrical

survey in 2008. In this present study medium fine sand with D50 = 300μm is used. The transport computations are carried out for mean sea level. More details about the model input can be found in Annex 4.

The formula of Bijker is used. This formula is based on a transport formula for rivers proposed by Kalinkske-Frijlink (Frijlink, 1952). Bijker distinguishes between bed load and suspended load, where the bed load transport depends on the total bottom stress by waves and currents. The suspended load is obtained by integrating the product of the concentration and velocity profiles along the vertical, where the reference concentration for the suspended sediment is expressed as a function of the bed load trans port.

To calculate the sediment transport of gravel, a different formula is used: the formula of van Hijum and Pilarczyk (1982). This formula aimed specifically at coarse-grained transport rates and was derived from the laboratory experiments of van Hijum (1976) and van Hijum and Pilarczyk (1982).

Yearly average longshore sediment transport The yearly average longshore sediment transports are calculated at 3 locations along the Old Boulevard; B_P03, B_P06 and B_P08, see Figure 35. With the computed yearly average longshore sediment transports, the maintenance costs of the sandy beach for different alternatives can be determined. Figure 35 Location of B_P04, B_P06, B_P08 along the Old Boulevard

To calculate the sediment transport in case of a perched beach, two different approaches are used. In the first approach the breakwater is not included in the profile. The transports are calculated behind the breakwater using transmitted wave heights. In the second approach the breakwater is included in the profile and the transports are calculated using the normal wave climate, for calculations and results see Annex 4.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 49

CHAPTER 5: Concepts and tools for design sandy beach

Equilibrium angle With the use of the UNIBEST LT model also the longshore sediment transport (S) is assessed for a range of orientations of the shoreline (ф). The relationship between the net alongshore transport (S) and the coast orientation (ф) is presented in the so-called S-ф curve. With the use of the S-ф curve the orientation of the coastline for which S=0 can be found. In this study the equilibrium angle refers to the coastline angle for which S=0. The equilibrium angle will be used for the design of the sandy beaches. For example, the net longshore sediment transport for a sandy beach placed under the equilibrium angle will be more or less equal to zero.

5.3.2 XBEACH

XBeach is a two-dimensional model for wave propagation, long waves and mean flow, sediment transport and morphological changes of the nearshore area, beaches, dunes and backbarrier during storms. It is a public-domain model that has been developed with funding and support by the US Army Corps of Engineers, by a consortium of UNESCO - IHE, Deltares (Delft Hydraulics), Delft University of Technology and the University of Miami. XBeach solves the time -dependent short wave action balance, the roller energy equation, the nonlinear shallow water equations of mass momentum, sediment transport formulations and bed update on the scale of wave groups (Roelvink et al., 2009).

The default approach in the XBeach model for hydrodynamics is the surf beat approach. In a given wave or water level signal the surf beat approach makes a distinction between high and low frequency waves. The propagation of high frequency waves is simulated with a wave action balance on the scale of short wave groups. In the surf zone the wave energy dissipation by breaking is input to the roller energy balance. For a more detailed description of the wave action balance, see Roelvink et al, 2009. The low frequency wave motions are solved using nonlinear shallow water equations (NSWE) for continuity and conservation of momentum.

The sediment transport is predicted in XBeach using a depth-averaged advection diffusion equation, given by (Galapatti, 1983). The concept of the advection diffusion equation is that sediment will be picked up from the bottom when the local concentration is lower than the equilibrium concentration (underload condition), and sediment will be deposited when local concentration is higher than the equilibrium concentration (overload condition). The more sediment is in suspension, the more can be transported. The equilibrium sediment concentration depends on the grain characteristics and the flow conditions. The Van Rijn (2007) formula is used in the present study to calculate the equilibrium sediment concentration. Bed level changes are computed from sediment transport gradients and take account of avalanching when slope gradients exceed pre -defined treshholds. XBeach accounts for feedback between evolving bathymetry and the hydrodynamics at each time step or a given morphological time step.

5.3.2.1. XBEACH 2D

At the start of the present study it was decided to calculate the cross-shore sediment transports with the use of the 2D XBeach model. After modelling the effects of some

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 50

CHAPTER 5: Concepts and tools for design sandy beach

preliminary alternatives in XBeach it was concluded that the coastal morphology did not vary a lot along the Old Boulevard. To limit the calculation time and to acquire less complex model results it was decided to switch to a 1D- XBeach model. Some of the 2D XBeach model set-ups and computational results can be found in Annex 5.

5.3.2.1. MODEL SET UP XBEACH 1D

The yearly average cross-shore loss of sediments for the different proposed alternatives elaborated in Chapter 6 are calculated with the 1D XBeach model.

Input In this study XBeach is configured such that all relevant processes for coastal erosion are enabled: short waves, long waves, flow, sediment transport and morphology. Non- hydrostatic flow, groundwater flow and quasi-3D flow are disabled. Most of the (simulation-independent) parameters in the model are set to default.

The initial bathymetry is provided by using the cross-shore profile at location B_P08 and the sand profiles as designed for the different alternatives. The extent of the profiles in seaward direction should be sufficiently long to model a reliable development of the wave field before reaching the shore.

Water level variations, caused by tide and storm are assumed to be negligible for yearly conditions. The mean sea level is used as the water level throughout the computational domain. Additional variations by wave group effects and coastal set-up are calculated by XBeach.

In this study the sediment characteristics are kept constant for all considered locations. The sediment properties D50 and D90 are set to 300 μm and 400 μm respectively.

XBeach has several options to impose wave boundary conditions. In this study the standard JONSWAP spectrum, based on user-input spectrum coefficients is used. XBeach computes a spectrum from provided JONSWAP parameters. The used JONSWAP parameters in this study are: . peak enhancement factor in the JONSWAP expression, gammajsp = 3.3; . directional spreading coefficient, s = 10000 . the highest frequency used to create JONSWAP spectrum, fnyq = 1.

The parameters wave height, peak frequency and main angle a re derived from the wave occurrence tables (see Section 3.7.2.1).

In some of the alternatives a structure is present. This structure is defined in XBeach as an impermeable object, which cannot be eroded.

To decrease computational time, a morphological acceleration factor (MORFAC) can be applied. MORFAC is the factor that is multiplied with the hydrodynamic time step to obtain the morphological time step. For example a simulation over 10 min with a MORFAC of 6 effectively simulates morphological development for 1hr. The applied MORFAC differs for the various simulations and can be found in Annex 6.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 51

CHAPTER 5: Concepts and tools for design sandy beach

Method of calculation To estimate the yearly averaged amount of sand which will be lost in cross -shore direction over the submerged breakwater, the XBeach 1D model and the wave occurrence table of B_P08 are used. The occurrence table is converted to combinations of wave height and direction with a yearly occurrence in seconds. The medial of the directional bin and wave height bin are defined as values for these parameters, e.g. the value for the directional bin between 15 and 45 degrees is defined as 30 degrees. Each combination of wave height and direction and corresponding duration is used separately as input for the 1D XBeach model. The sum of the sediment losses for each condition gives an estimate of the yearly sediment loss over the submerged breakwater. The approach, input and results of the calculations can be found in Annex 6. With this yearly average cross-shore loss of sediment, the maintenance costs of the sandy beach for different alternatives can be determined.

The XBeach model is not developed to simulate processes behind submerged structures and this raises the question whether the model is applicable for this study. In order to get some insight into the simulation of these processes by the XBeach model, the relation between the erosion at the beachside of the breakwater and the loss of sand over the breakwater are compared. A relation can be found between the loss of sand over the breakwater in relation with the erosion at the beachside of the breakwater and the height difference between the crest of the breakwater and the sandy profile at breakwater. The greater the height difference between the crest of the structure and the sandy beach profile at the structure, the less sand is lost over the structure in relation with the erosion at the beachside of the structure. The relation can be found in Figure 36. The realization of this graph can be found in Annex 6. Figure 36 4 Relation loss of sand over breakw ater and height 3.5 difference between crest breakw ater and sandy 3 profile

2.5

1.5

1 Height difference between crest difference Height between sand (m) profile and

0.5 0 10 20 30 40 50 60 70 80 90 100 Loss of sand over the breakwater (%)

The relation between the percentage of sand lost over the submerged breakwater and the difference in height between the crest of the breakwater and the sandy profile seems to be likely and the calculated losses over the submerged breakwater seems to be plausible. It is therefore assumed that the outcome of the simulated processes is reasonable and can be used to get a rough estimate of the losses of sand over the submerged breakwater and the behaviour of the beach profile in front of the breakwater.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 52

CHAPTER 5: Concepts and tools for design sandy beach

Storm conditions To determine the behaviour of the sandy beaches during storm conditions also the cross- shore transports in case of a storm are calculated. The input and calculations can be found in Annex 7. The results show that for various alternatives during a 50 year storm condition a beach width of 60 meter is not sufficient to protect the boulevard from damage by erosion. The results have not been taken into account in the rating of the alternatives due to a shortage of time, but are enclosed as an extra note which should be taken into account if the regarded alternative is selected.

5.4 REQUIREMENTS

The requirements for the protection measures along the coastal stretch of Batumi are listed below.

. The protection measures should prevent further erosion along the coastal stretch between Batumi Cape and the mouth of the Chorokhi; . A sandy beach should be created along the old boulevard. . The appearance of the protection measures should be such that the works will not have a negative impact on tourism. It is favourable to create a structure which is not seen from the boulevard; . The coastal protection measures should not be affected by possible slide events of the submarine canyon. And the coastal protection measures should not create or reinforce instable slopes of the submarine canyon; . The design lifetime of all coastal structures is set to 50 years; . Accepted damage level: − During 1/5 year storm conditions, no damage is allowed. This corresponds with S=2 Van der Meer, 1988; − During 1/100 year storm conditions, some damage is allowed. This corresponds with S=5; − Large damage, but not failure is allowed during 1/200 year storm. This corresponds with S=8; . Tourists should be able to enter the sea safely; . It should be safe at the lee side of the structure during operational condition, but also during 1/1 year storm conditions; . The water quality along the sandy beaches should be guaranteed; . Along the boulevard (at the seaward side of the existing path) a rail track is foreseen, which connects the port with the airport. A stretch with a width of 10m should be reserved for this; . There are plans for constructing a restaurant on piles (like San Remo) along the northern section of the coast. In the functional design it should be determined if it is possible to incorporate the restaurant with the coastal protection works. The design of the restaurant is not part of the scope of the study; . Besides the beach, also other recreational facilities should be possible (bars, restaurants, sports, ..); . The protection measures should be in line with the city development plan.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 53

CHAPTER 6: Alternatives

CHAPTER 6 Alternatives

In the previous study (Alkyon/ARCADIS, 2010) a detailed design of various coastal protection works has been prepared; in the north a revetment, pocket beaches along the Old Boulevard and a series of groynes along the southern section of the coast. In this chapter alternatives for the pocket beach along the Old Boulevard are presented. In these new alternatives sand must be the main coverage of the beaches and visible hard constructions should be avoided. The alternatives treated in this chapter are generated us ing the study of possible solutions and morphological behaviour as treated in Chapter 5. All generated alternatives are illustrated with a sketch and an overview is given from the main characteristics and the main advantages and disadvantages.

6.1 INTRODUCTION

In the following, 7 generated alternatives are described. For each alternative some main characteristics are listed. The definition of some of these characteristics can be found in the appendices; the estimations of the required volumes for the breakwate rs and groynes can be found in Annex 8; the estimated longshore sediment transports and the equilibrium angle of the coastline can be found in Annex 4; and the estimated cross-shore sediment transports can be found in Annex 6.

6.2 ALTERNATIVE 1: SANDY BEACH

In this alternative the sandy beach along the Old Boulevard will be created by placing sand on top of the original profile. To create a more or less stable beach, the beach will be constructed under a so called equilibrium angle. On the north and south side of this artificial sandy beach the sediment transport is defined zero to avoid mixing from sand and gravel. In order to achieve zero sediment transport, there will be an interference at the northern and southern boundary in the form of a groyne. At the southern boundary the most northern groyne from the coastal protection works in the south can be used, but this groyne should be extended.

6.2.1 DESIGN SANDY BEACH

In this alternative the sand is placed under the equilibrium angle. With the use of UNIBEST- LT the equilibrium angle is calculated (see Annex 4). The results can be found in Table 11. Table 11 Longshore sediment Location Equilibrium orientation w.r.t. the coastal normal transports along the Old B_P06 13.79 ° Boulevard (sandy beach) B_P08 13.86 °

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 55

CHAPTER 6: Alternatives

Applying a rotation of 13.8° of the sandy beach w.r.t. tot the coastal normal, results in a beach width of approximately 60m at the most southern end of the beach and a beach width of approximately 540m at the northern end. The artificial sandy beach profile extends to a large depth, especially in the north. This results in large amount of required sand. The required amount of sand is approximately 11Mm3. Also a lot of material to construct the northern groyne is required. There are however no other structures used besides the structure at the northern and southern boundary. The total amount of required material for the groynes is approximately 1,065,000 m3. The design of this alternative is shown in Figure 37. In Figure 38 the cross section at location A is displayed.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 56

CHAPTER 6: Alternatives

Figure 37 Alternative 1

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 57

CHAPTER 6: Alternatives

Figure 38 Cross section at location A, alternative 1

Transport capacities The sandy beach profile is designed with the use of the equilibrium beach profile (Dean) and the closure depth (Hallermeier). This will result in enough available sand in order to reshape the beach during different wave circumstances, resulting in a net cross-shore transports more or less equal to zero.

The longshore transports for the present coastline are mainly towards the north, the transport towards the south is only a small percentage of the net transport. By placing the artificial sandy beach under the equilibrium angle, the net longshore sediment transport will be more or less equal to zero.

6.2.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 11,000,000 m3 . Beach width: ± 60-540 m

Structures . 2 groynes: − Required volume: ~ 1,065,000 m3

Sediment transport . Average annual longshore sediment transport: Equilibrium angle (~ 0 m3/y) . Average annual sediment losses due to cross-shore transport: Dean profile (~ 0 m3/y)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 58

CHAPTER 6: Alternatives

Advantages and disadvantages Advantages . No structures needed (except at the boundaries in the north and south) . Large swimming area . Almost no maintenance required

Disadvantages . Large amount of sand required . Large amount of material required to construct the groynes

6.3 ALTERNATIVE 2: SANDY BEACH WITH SEGMENTS

The sandy beach will in this alternative also be constructed under the equilibrium angle, but to limit the required amount of sand, the sandy beach will be divided into three segments by 2 extra groynes.

6.3.1 DESIGN SANDY BEACH WITH SEGMENTS

In this alternative the sand is also placed under the equilibrium angle, but this time the beach is divided into 3 segments to limit the required amount of sand. The equilibrium angle differs slightly along the 3 segments, but also the coastal normal differs slightly. To segment the beach, 2 extra groynes have to be constructed besides the groynes at the northern and southern boundary. The beach width will vary from 60 meters north of the groynes to 250 meters south of the groynes. For this alternative less sand and material to construct the groynes are required than for the previous alternative, but there is still a lot of material required. The required amount of sand will be approximately 4.9 Mm 3 and the required amount of material for the 4 groynes will in total be 508,000 m3. The design of this alternative is shown in Figure 39. In Figure 40 the cross section at location A, south of the groyne is displayed and in Figure 41 the cross section north of the groyne at location B is shown.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 59

CHAPTER 6: Alternatives

Figure 39 Alternative 2

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 60

CHAPTER 6: Alternatives

Figure 40 Cross section at location A, alternative 2

Figure 41 Cross section at location B, alternative 2

The longshore transports for the present coastline are mainly towards the north, the transport towards the south is only a small percentage of the net transport. By placing the artificial sandy beach under the equilibrium angle, the net longshore s ediment transport will be more or less equal to zero.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 61

CHAPTER 6: Alternatives

6.3.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 4,900,000 m3 . Beach width: ± 60-250 m

Structures . 4 groynes: − Required volume: ~ 508,000 m3

Sediment transport . Average annual longshore sediment transport: Equilibrium angle (~ 0 m3/y) . Average annual sediment losses due to cross-shore transport: Dean profile (~ 0 m3/y)

Advantages and disadvantages Advantages . Large swimming area . Almost no maintenance required

Disadvantages . Structures needed to segment the beach . Large amount of sand required . Large amount of material required to construct the groynes

6.4 ALTERNATIVE 3: SANDY BEACH, PARALLEL TO THE BOULEVARD

Also in this alternative the sandy beach along the Old Boulevard will be created by placing sand on top of the original profile. This time however, the sandy beach is not placed under the angle of equilibrium but placed parallel to the boulevard.

6.4.1 DESIGN SANDY BEACH, PARALLEL TO THE BOULEVARD

By not constructing the beach under the equilibrium angle a nice constant beach width is created and the required amount of sand is reduced. This will however mean that a lot of maintenance is needed in order to retain a sandy beach in the southern part. The beach width will approximately be 100 meter along the entire coastal stretch. The required amount of sand is reduced to 3.3 Mm3. There are only groynes required at the northern and southern boundary. The total amount of material required for the groynes is 172,000 m3. The design of this alternative is shown in Figure 42. In Figure 43 the cross section at location A is displayed.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 62

CHAPTER 6: Alternatives

Figure 42 Alternative 3

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 63

CHAPTER 6: Alternatives

Figure 43 Cross section at location A, alternative 3

The artificial sandy beach is not placed under the equilibrium angle , resulting in a gradient in the longshore transport of sediment. With UNIBEST-LT the longshore transports are calculated for several points along the artificial sandy beach, resulting in an average annual longshore transport of approximately 130,000 m3/y, for calculations see Annex 4.

6.4.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 3,300,000 m3 . Beach width: ± 100 m

Structures . 2 groynes: − Required volume: ~ 172,000 m3

Sediment transport . Average annual longshore sediment transport: ~ 130,000 m3/y . Average annual sediment losses due to cross-shore transport: Dean profile (~ 0 m3/y)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 64

CHAPTER 6: Alternatives

Advantages and disadvantages Advantages . No structures needed to segment the beach . Large swimming area . Nice constant beach width . Relatively small volume required for the structures

Disadvantages . Still a large amount of sand required . High maintenance

6.5 ALTERNATIVE 4: PERCHED BEACH

By applying a perched beach the depths to which the beach profiles should extend can be lowered considerably. With this the total amount of required sand is lowered. In this alternative the submerged breakwater will be placed a t a distance of approximately 250 meter from the boulevard and will have a submergence of 0.5 meter.

6.5.1 DESIGN PERCHED BEACH

In this alternative a perched beach is applied in order to reduce the amount of required sand. The required amount of sand will be reduced to 1 Mm3. The sandy beach will in this design be placed under the equilibrium angle. The distance between the emerged beach profile and the submerged breakwater should at least be 60 meter in order to avoid dangerous currents and enormous losses of sand. The beach has to be divided into 4 segments in order to be placed under the equilibrium angle, this means that 3 extra groynes have to be constructed. The lengths of the groynes, including the northern and southern groynes, are however relatively short. The submerged breakwater has a submergence of 0.5 meter and will therefore not negatively affect the view. The distance in-between the submerged breakwater and the waterline varies from 200 meter north of the groynes to 60 meter south of the groynes. The swimming area of the beach visitors will by this submerged breakwater unfortunately be restricted. The total required amount of material for the groynes and the submerged breakwater will approximately be 442,000 m3. The design of this alternative is shown in Figure 44. In Figure 45 the cross section at location A south of the groyne is displayed. In Figure 46 the cross section north of the groyne at location B is displayed.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 65

CHAPTER 6: Alternatives

Figure 44 Alternative 4

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 66

CHAPTER 6: Alternatives

Figure 45 Cross section at location A, alternative 4

Figure 46 Cross section at location B, alternative 4

Transport capacities The characteristic shape of the sandy profile is determined with the formula of Dean (1977), but is interrupted by the submerged breakwater. The breaking of waves at the submerged breakwater will result in a turbulent area behind the breakwater which lead to cross -shore losses of sediment over the breakwater. With the use of XBeach the amount of sediment which will be transported over the submerged breakwater and by this be lost is calculated. For the approach and calculations see Annex 6. The average sediment losses due to cross- shore transport is for this alternative approximately 27,000 m3/y.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 67

CHAPTER 6: Alternatives

6.5.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 1,000,000 m3 . Beach width: ± 60-200 m

Structures . 5 groynes: − Required volume: ~ 121,000 m3 . Submerged breakwater: − Freeboard submerged breakwater: - 0.5 m − Distance from waterline: ± 60-200 m − Required volume: ~ 321,000 m3

Sediment transport . Average annual longshore sediment transport: equilibrium angle (~ 0 m3/y) . Average annual sediment losses due to cross-shore transport: ~ 27,000 m3/y

Advantages and disadvantages Advantages . Relatively small amount of sand required

Disadvantages . Structures needed to segment the beach . A submerged breakwater needed . Small swimming area . Cross-shore loss of sediment

6.6 ALTERNATIVE 5: PERCHED BEACH, OBLIQUE SUBMERGED BREAKWATER

In this alternative also a perched beach with a beach under the equilibrium angle is applied. However, in this alternative the submerged breakwater is also constructed under the equilibrium angle. By doing this the swimming area will be enlarged.

6.6.1 DESIGN PERCHED BEACH, OBLLIQUE SUBMERGED BREAKWATERS

In this alternative the distance between the waterline and the submerged breakwater is enlarged, compared with previous alternative. This results in a larger swimming area, but also avoids dangerous currents near the waterline and reduces the losses of sediment in cross-shore direction over the submerged breakwater. There is however a little more sand and material to construct the groynes and submerged breakwaters required. The total required amount of material for the construction of the groynes and the breakwaters will be approximately 545,00 m3. The total required amount of sand will be 1.4 Mm 3. The design of this alternative is shown in Figure 47. In Figure 48 the cross section at location A south of the groyne is displayed. In Figure 49 the cross section north of the groyne at location B is displayed.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 68

CHAPTER 6: Alternatives

Figure 47 Alternative 5

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 69

CHAPTER 6: Alternatives

Figure 48 Cross section at location A, alternative 5

Figure 49 Cross section at location B, alternative 5

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 70

CHAPTER 6: Alternatives

6.6.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 1,400,000 m3 . Beach width: ± 60-235 m

Structures . 5 groynes: − Required volume: ~ 222,000 m3 . Submerged breakwater: − Freeboard submerged breakwater: - 0.5 m − Distance from waterline: ± 150 m − Required volume: ~ 323,000 m3

Sediment transport . Average annual longshore sediment transport: equilibrium angle (~ 0 m3/y) . Average annual sediment losses due to cross-shore transport: ~ 4,000 m3/y

Advantages and disadvantages Advantages . Relatively small amount of sand required

Disadvantages . Structures needed to segment the beach . Submerged breakwaters needed . Cross-shore loss of sediment

6.7 ALTERNATIVE 6: PERCHED BEACH, PARALLEL TO THE BOULEVARD

Also in this alternative a perched beach will be created with a submerged breakwater. This time however, the sandy beach is not placed under the angle of equilibrium but placed parallel to the boulevard.

6.7.1 DESIGNED PERCHED BEACH, PARALLEL TO THE BOULEVARD

By placing the beach parallel to the boulevard the swimming area increases, a nice constant beach width is created and the amount of groynes and the required material to construct the groynes is reduced. Placing the beach parallel to the boulevard means on the other hand that maintenance is needed in order to retain a sandy beach in the southern part. The beach width will approximately be 100 meter. The total amount of required sand is 1Mm 3. The total amount of required material for the two groynes and the submerged breakwater will approximately be 362,000 m3. The design of this alternative is shown in Figure 50. In Figure 51 the cross section at location A is displayed.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 71

CHAPTER 6: Alternatives

Figure 50 Alternative 6

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 72

CHAPTER 6: Alternatives

Figure 51 Cross section at location A, alternative 6

Transport capacities With the use of XBeach the amount of sediment which will be transported over the submerged breakwater and by this be lost, is calculated. For the approach and calculations see Annex 6. The average sediment losses due to cross-shore transport is for this alternative approximately 6,000 m3/y.

The artificial sandy beach is not placed under the equilibrium angle, resulting in a gradient in the longshore transport of sediment. With UNIBEST the longshore transports are calculated for several points along the artificial sandy beach, resulting in an average annual longshore transport of approximately 10,000 m3/y, for calculations see Annex 4.

6.7.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 1,000,000 m3 . Beach width: ± 100 m

Structures . 2 groynes: − Required volume: ~ 41,000 m3 . Submerged breakwater: − Freeboard submerged breakwater: - 0.5 m − Distance from waterline: ± 150 m − Required volume: ~ 321,000 m3

Sediment transport . Average annual long-shore sediment transport: ~ 10,000 m3/y . Average annual sediment losses due to cross-shore transport: ~ 6,000 m3/y

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 73

CHAPTER 6: Alternatives

Advantages and disadvantages Advantages . No structures needed to segment the beach . Nice constant beach width . Relatively small amount of sand required

Disadvantages . A submerged breakwater needed . Maintenance required

6.8 ALTERNATIVE 7: PERCHED BEACH 2, PARALLEL TO THE BOULEVARD

This alternative is also a perched beach parallel to the boulevard, however in this alternative the submerged breakwater will be lowered and placed closer to the beach, in order to reduce the construction costs of the submerged breakwater. The breakwater will be placed at a distance of approximately 200 meters from the boulevard instead of 250 meter and will have a submergence of 1.5 meter instead of 0.5 meter.

6.8.1 DESIGN PERCHED BEACH 2, PARALLEL TO THE BOULEVARD

By placing the structure closer to the boulevard and lowering the height of the submerged breakwater, the required amount of sand reduces and the required amount of material to construct the submerged breakwater and the groynes reduces. Resulting in 700,000 m3 required amount of sand and a total required of material for the 2 groynes and submerged breakwater of approximately 184,000 m3. Because the submerged breakwater is situated closer to the boulevard the swimming area is reduced, the currents near the waterline will increase and the sediment transport will increase resulting in high maintenance costs. This alternative will however result in a nice constant beach width of 100 meter with low capital costs. The design of this alternative is shown in Figure 52. In Figure 53 the cross section at location A is displayed.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 74

CHAPTER 6: Alternatives

Figure 52 Alternative 7

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 75

CHAPTER 6: Alternatives

Cross section at location A: Figure 53 Cross section at location A, alternative 7

6.8.2 OVERVIEW

Characteristics Beach . Required amount of sand: ~ 700,000 m3 . Beach width: ± 100 m

Structures . 2 groynes: − Required volume: ~ 36,000 m3 . Submerged breakwater: − Freeboard submerged breakwater: - 1.5 m − Distance from waterline: ± 100 m − Required volume: ~ 148,000 m3

Sediment transport . Average annual longshore sediment transport: ~ 45,000 m3/y . Average annual sediment losses due to cross-shore transport: ~ 532,000 m3/y

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 76

CHAPTER 6: Alternatives

Advantages and disadvantages Advantages . No structures needed to segment the beach . Nice constant beach width . Relatively small amount of sand required . Relatively small volume required for the structures

Disadvantages . Small swimming area . A submerged breakwater needed . High maintenance

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 77

CHAPTER 7: Selection of alternatives

CHAPTER 7 Selection of alternatives

In this chapter the alternatives as treated in Chapter 6 will be validated using a Multi- Criteria analysis (MCA). In Section 7.1 the selection criteria will be treated. In Section 7.2 all the alternatives will be rated for the drawn-up criteria. In Section 7.3 the alternatives will be assessed with the help of the MCA and the most promising alternative(s) will be selected.

7.1 MCA CRITERIA

The alternatives as described in Chapter 6 will be assessed on the following criteria.

. Spatial quality One of the intentions of this study is to make a design with as little undesirable visual structures as possible. The alternatives are rated on this requirement by the criterion spatial quality. The visual pollution but also the spatial quality, i.e. the beach width and corresponding possibilities for hotels and restaurants are taken into account.

. Tourism/beach recreation The main goal of this study is to make an alternative design which focusses more on tourism by making attractive sandy beaches for tourism and beach recreation. At the criterion tourism/beach recreaction the focus will be on how user-friendly the beach design is. The beach shape and the possibilities for beach recreation, like swimming will be reviewed.

. Safety Structures like submerged breakwaters could cause a safety risk due to their impact on currents by wave breaking etc. For each alternative, possible dangerous currents will be evaluated and rated at the criterion safety. Besides the dangerous currents also the risk of collision for swimmers with structures is taken into account.

. Environment To take the impact on the environment into account the area of influence by the design of the sandy beach will be de termined. The area which will be influenced by the design is presumed to be the total area which will be covered with sand or constructions. In other words, the area which is directly affected will determine the impact of the environment and be rated at the criterion environment.

. Maintenance nuisance Maintaining the beach can cause some nuisance for the beach visitors. The maintenance will probably be carried out before the summer season starts so the nuisance will be minimal. But it might be the case for some of the alternatives that during the season an extra maintenance should be carried out. This nuisance for beach tourists by maintenance is rated at the criterion maintenance nuisance.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 79

CHAPTER 7: Selection of alternatives

. Risk Some of the alternatives cause complex coastal processes. This makes it difficult to compute the sediment transports. Therefore the results will have an uncertainty. This degree of uncertainties of the designs on the coastal processes are rated at the criterion risk.

. Capital costs A distinction is made between the costs for sand nourishment and the costs for construction of the structures, which is then separated into groynes and submerged breakwaters.

. Maintenance costs The maintenance costs will mostly be determined by the sediment losses in both longshore and cross-shore direction. A distinction is made between costs for redistributing sand and for adding new sand. The maintenance costs will be calculated using the net present value for a period of 50 years.

The above criteria will be evaluated for each alternative and will be given a score. The score of the first 5 criteria will be expressed as follows: 1. - - very negative 2. - negative 3. ± neutral 4. + positive 5. ++ very positive

The two remaining criteria, capital costs and maintenance costs, will be expressed in M€.

7.2 RATING OF THE ALTERNATIVES

The alternatives have been rated for each of the criteria as described above. The criteria will be treated one by one in the following. The resulting score for the a lternatives will be treated in Section 7.3.

7.2.1 SPATIAL QUALITY

Alternative 1; Sandy Beach, equilibrium angle: There are no extra structures besides the groynes at the northern and southern boundary. This results in a nice view towards the sea, without visual pollution by structures. The beach is wide, mainly in the north, which gives great opportunities for example for new hotels and restaurants to settle at this part of the beach. Alternative 2; Sandy Beach, segments: To segment the beach, two extra groynes are needed besides the groynes at the northern and southern boundary. This will negatively affect the view. Alternative 3; Sandy Beach, parallel to boulevard: There are no extra structures needed, resulting in a nice view. Alternative 4; Perched Beach, equilibrium angle: To segment the beach, three extra groynes are needed, which will negatively affect the view. Alternative 5; Perched Beach, oblique submerged breakwaters: To segment the beach, three extra groynes are needed, which will negatively affect the view.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 80

CHAPTER 7: Selection of alternatives

Alternative 6; Perched Beach, parallel to boulevard: There are no extra groynes needed besides the groynes at the northern and southern boundary, resulting in a nice view. Alternative7; Perched Beach 2, parallel to boulevard: There are no extra groynes needed besides the groynes a t the northern and southern boundary, resulting in a nice view. Table 12 Rating spatial quality Alternative Spatial quality Alternative 1 ++ Sand, equilibrium angle Alternative 2 ± Sand, segments Alternative 3 + Sand, parallel Alternative 4 - Perched beach, equilibrium angle Alternative 5 - Perched beach, oblique breakw aters Alternative 6 + Perched beach, parallel Alternative 7 + Perched beach 2, parallel

7.2.2 TOURISM/BEACH RECREATION

Alternative 1; Sandy Beach, equilibrium angle: The swimming area is only restricted by the northern and southern boundary and there is no restriction in seaward direction, resulting in a large swimming area. The distance between the sea and the boulevard in the northern part is however quite large, which will make the beach less attractive. Alternative 2; Sandy Beach, segments: The swimming area is not restricted in seaward direction. It is limited a bit sideward due to the segmentation; however the swimming area is still large. Alternative 3; Sandy Beach, parallel to boulevard: The swimming area is only restricted at the northern and southern boundary, resulting in a large swimming area. The beach is attractive, due to its pleasant width along the entire coastal stretch. Alternative 4; Perched Beach, equilibrium angle: The swimming area is restricted by the submerged breakwater, resulting in a small swimming area. There is also a sideward restriction due to the segmentation. Alternative 5; Perched Beach, oblique submerged breakwaters: The swimming area is restricted by the submerged breakwater, resulting in a small swimming area. There is also a sideward restriction due to the segmentation. Due to the oblique placement of the breakwaters, the swimming area is enlarged at most of the parts, but also decreased at some parts. Overall the swimming area is made more attractive. Alternative 6; Perched Beach, parallel to boulevard: The swimming area is restricted by the submerged breakwater, resulting in a small swimming area. Due to the parallel shape of the beach the swimming area is enlarged and made more attractive compared to alternative A4. There is no sideward restriction except at

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 81

CHAPTER 7: Selection of alternatives

the northern and southern boundary. The beach width is pleasant and makes the beach attractive. Alternative 7; Perched Beach 2, parallel to boulevard: The swimming area is restricted by the submerged breakwater, resulting in a small swimming area. The submerged breakwater is placed closer to the beach resulting in an even smaller swimming area. The beach width is however pleasant. Table 13 Rating tourism/beach Alternative Tourism/Beach recreation recreation Alternative 1 + Sand, equilibrium angle

Alternative 2 + Sand, segments Alternative 3 ++ Sand, parallel Alternative 4 - Perched beach, equilibrium angle Alternative 5 ± Perched beach, oblique breakw aters Alternative 6 + Perched beach, parallel Alternative 7 ± Perched beach 2, parallel

7.2.3 SAFETY

Alternative 1: Sandy Beach, equilibrium angle: There will be some currents at the end of the groynes at the northern and southern boundary. These are however situated at a large distance from the beach so the swimmers will practically not be affected. Alternative 2; Sandy Beach, segments: The beach is segmented by 2 extra groynes. These groynes will cause extra currents. Because the end of the groynes are situated at a large distance from the beach, the swimmers will be less affected. Besides the dangerous currents, the groynes itself are also dangerous because they are an obstruction which causes risk of collision for swimmers. Alternative 3; Sandy Beach, parallel to boulevard: There will be some currents at the end of the groynes at the northern and southern boundary. These are however situated at a large distance from the beach that the swimmers will hardly be affected. Alternative 4; Perched Beach, equilibrium angle: The submerged breakwater can cause dangerous currents under certain circumstances. The shoreline is at some parts at only 60 meters from the submerged breakwater, and therefore the currents can become dangerous for beach visitors. The 3 extra groynes in this alternative cause some additional currents, resulting in a dangerous situation. The submerged breakwater and the groynes cause a risk of collision for swimmers. Alternative 5; Perched Beach, oblique submerged breakwaters: The submerged breakwater can cause dangerous currents under certain circumstances. The distance between the beach and the submerged breakwater is in this alternative 150 meter. Close to the beach the currents will be tolerable. The 3 extra groynes in this alternative cause

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 82

CHAPTER 7: Selection of alternatives

some additional currents. The submerged breakwater and the groynes cause a risk of collision for swimmers. Alternative 6; Perched Beach, parallel to boulevard: The submerged breakwater can cause dangerous currents under certain circumstances. The distance between the beach and the submerged breakwater is in this alternative 150 meter. Close to the beach the currents will be tolerable. The submerged breakwater cause a risk of collision for swimmers. Alternative 7; Perched Beach 2, parallel to boulevard: The submerged breakwater in this alternative has a submergence of 1,5 meter, which will result in less currents than in the previous three alternatives. The submerged breakwater is however closer to the beach, which will result in less reduction of the currents close to the beach, and with this a dangerous situation. The submerged breakwater cause a risk of collision for swimmers. Table 14 Rating safety Alternative Safety Alternative 1 ++ Sand, equilibrium angle Alternative 2 + Sand, segments Alternative 3 ++ Sand, parallel Alternative 4 - - Perched beach, equilibrium angle Alternative 5 - Perched beach, oblique breakw aters Alternative 6 ± Perched beach, parallel Alternative 7 - Perched beach 2, parallel

7.2.4 ENVIRONMENT

To take the impact on the environment into account the area of influence by the design of the sandy beach will be determined. The environment will mainly be influenced by the area which is directly affected by the designs. In other words, the total area which will be covered by the design and directly be affected will be used as a parameter for the environmental impact. The area which is interfered by the designs are shown in the table below. Alternative 1 will affect a large area and is therefore rated negatively, alternative 4, 5, 6 and 7 will cover a relative small area and are therefore rated positive.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 83

CHAPTER 7: Selection of alternatives

Table 15 Alternative Interference area [m2] Environment Rating environment Alternative 1 1,390,000 - Sand, equilibrium angle Alternative 2 1,050,000 ± Sand, segments Alternative 3 970,000 ± Sand, parallel Alternative 4 510,000 + Perched beach, equilibrium angle Alternative 5 510,000 + Perched beach, oblique breakw aters Alternative 6 510,000 + Perched beach, parallel Alternative 7 400,000 + Perched beach 2, parallel

7.2.5 MAINTENANCE NUISANCE

In order to determine the maintenance nuisance, the quantities of longshore and cross-shore sediment transport are evaluated. These transport rates can be found in Table 16. It should be noted that high rates of longshore transport will result in more maintenance than high rates of cross-shore transport. The reason for this is that the retrieve of the coastline due to longshore transport will mainly take place over a few hundred meters of the beach, while the retrieve of the coastline due to cross-shore transport is distributed over the entire beach.

Alternative 1; Sandy Beach, equilibrium angle: This alternative requires almost no maintenance. The sandy beach is placed under the equilibrium angle and consistent with the Dean equilibrium profile. The sediment transport is therefore negligible small, resulting in hardly any need for maintenance. Alternative 2; Sandy Beach, segments: This alternative requires almost no maintenance. The sandy beach is placed under the equilibrium angle and consistent with the Dean equilibrium profile. The sediment transport is therefore negligible small, resulting in hardly any need for maintenance. Alternative 3; Sandy Beach, parallel to boulevard: In this alternative the sandy beach is not placed under the equilibrium angle and therefore maintenance should be carried out in order to retain the sandy beach in the south. The yearly longshore sediment transport is relatively high and therefore it will be necessary to redistribute the sand several times a year, resulting in nuisance for the beach visitors. Alternative 4; Perched Beach, equilibrium angle: In this alternative a submerged breakwater is applied. There will be cross-shore losses over the submerged breakwater, but beach nourishment to maintain the beach every few years will suffice. Alternative 5; Perched Beach, oblique submerged breakwaters: In this alternative a submerged breakwater is applied. There will be cross-shore losses over the submerged breakwater. The yearly cross-shore losses are relatively low and therefore maintenance every few years will suffice.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 84

CHAPTER 7: Selection of alternatives

Alternative 6; Perched Beach, parallel to boulevard: In this alternative a submerged breakwater is applied and the sandy beach is not placed under the equilibrium angle. There will be cross-shore losses over the submerged breakwater. The yearly cross-shore losses are relatively low and therefore maintenance every few years will suffice. The yearly longshore sediment transport is relatively low and therefore it will take only a few days to prepare the beach for the recreation season. Maintenance every few years will suffice to compensate for the longshore losses, but to maintain a nice constant beach width it is recommended to carry out maintenance every year. Alternative 7; Perched Beach 2, parallel to boulevard: In this alternative a submerged breakwater is applied and the sandy beach is not placed under the equilibrium angle. There will be cross-shore losses over the submerged breakwater. The yearly cross-shore losses are relatively high and therefore maintenance should be carried out several times a year, resulting in a lot of nuisance for beach visitors. To account for the yearly longshore sediment transport the sand should be distributed more than once a year, resulting in nuisance for the beach visitor. Table 16 Rating maintenance Alternative Longshore sediment Cross-shore sediment Maintenance transport (m3/yr) transport (m3/yr) nuisance nuiscance Alternative 1 0 0 ++ Sand, equilibrium angle Alternative 2 0 0 ++ Sand, segments Alternative 3 130,000 0 - Sand, parallel Alternative 4 0 27,000 + Perched beach, equilibrium angle Alternative 5 0 4,000 + Perched beach, oblique breakw aters Alternative 6 10,000 6,000 ± Perched beach, parallel Alternative 7 45,000 532,000 - - Perched beach 2, parallel

7.2.6 RISK

Alternative 1; Sandy Beach, equilibrium angle: This alternative is rather straightforward. It is expected that there will be no noteworthy extra losses of sediment. Alternative 2; Sandy Beach, segments: This alternative contains extra groynes. The groynes cause currents and these currents can cause some sediment transport. This can, to a small extend, result in losses or movement of sediment which are not taken into account. Alternative 3; Sandy Beach, parallel to boulevard: This alternative is rather straightforward. It is expected that there will be no noteworthy extra losses of sediment.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 85

CHAPTER 7: Selection of alternatives

Alternative 4; Perched Beach, equilibrium angle: In this alternative a submerged breakwater is applied. There will be cross-shore losses over the submerged breakwater. The results of the cross-shore losses over the submerged breakwater have an uncertainty. Because the distance between the submerged breakwater and the waterline varies, some unexpected currents can occur which extends the uncertainties. Furthermore the groynes cause currents and the se currents can lead to some additional sediment transports. Consequently the actual losses can deviate from the losses assumed in this study. Alternative 5; Perched Beach, oblique submerged breakwaters: In this alternative a submerged breakwater is applie d. There will be cross-shore losses over the submerged breakwater. The results of the cross-shore losses over the submerged breakwater have an uncertainty. Furthermore the groynes cause currents and these currents can lead to additional sediment transports. Consequently the actual losses can deviate from the losses assumed in this study. Alternative 6; Perched Beach, parallel to boulevard: In this alternative a submerged breakwater is applied. There will be cross-shore losses over the submerged breakwater. The results of the cross-shore losses over the submerged breakwater have an uncertainty. Alternative 7; Perched Beach 2, parallel to boulevard: In this alternative a submerged breakwater is applied. There will be cross-shore losses over the submerged breakwater. The results of the cross-shore losses over the submerged breakwater have an uncertainty. Table 17 Rating risk Alternative Risk Alternative 1 ++ Sand, equilibrium angle Alternative 2 + Sand, segments Alternative 3 ++ Sand, parallel Alternative 4 - - Perched beach, equilibrium angle Alternative 5 - Perched beach, oblique breakw aters Alternative 6 ± Perched beach, parallel Alternative 7 ± Perched beach 2, parallel

7.2.7 CAPTITAL COSTS

Table 18 show the required amount of sand for the different alternatives and corresponding costs.

The unit price for sand used in this report is based on a memo from the government of Adjara, 2010. The unit prices for the submerged breakwater and groynes is based on the unit prices used in the previous study (Detailed design, 2010).

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 86

CHAPTER 7: Selection of alternatives

Table 18 Volume Unit price Costs Costs nourishment nourishment nourishment

Mm3 €/m 3 M€

Alternative 1 11 20 220 Sand, equilibrium angle Alternative 2 4.9 20 98 Sand, segments

Alternative 3 3.3 20 66 Sand, parallel Alternative 4 1.0 20 20 Perched beach, equilibrium angle Alternative 5 1.4 20 28 Perched beach, oblique breakw aters Alternative 6 1.0 20 20 Perched beach, parallel Alternative 7 0.7 20 14 Perched beach 2, parallel

In the previous study (Detailed design, 2010) is stated that for waterborne equipment probably foreign contractors are needed. In order to account for hiring foreign contractors, a multiplier of 1.1 is applied on top of the unit cost based unit prices for waterborne construction. Following this study, for the constructing of almost all of the structures waterborne equipment is needed. Therefore the costs of the submerged breakwater and groynes are multiplied by 1.1. The unit prices shown in Table 19 and Table 20 already include the multiplier. Table 19 Costs groynes Volume groyne Unit price Costs groyne 3 3 m €/m M€ Alternative 1 1,065,000 49.5 52.7 Sand, equilibrium angle Alternative 2 508,000 49.5 25.1 Sand, segments Alternative 3 172,000 49.5 8.5 Sand, parallel

Alternative 4 121,000 49.5 6.0 Perched beach, equilibrium angle Alternative 5 222,000 49.5 11.0 Perched beach, oblique breakw aters Alternative 6 41,000 49.5 2.0 Perched beach, parallel Alternative 7 36,000 49.5 1.8 Perched beach 2, parallel

The breakwater used in some of the alternatives is meant to be sand-impermeable. The upper layer of the breakwater exists however of large rocks. Sand can easily move through the large rock, so the structure will be sand-permeable. The structure should be made sand- impermeable. How this can be realised should be studied in a following, more detailed design stage. For now some extra costs in order to make the structure sand-impermeable are

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 87

CHAPTER 7: Selection of alternatives

taken into account. The costs for the submerged breakwater for the different alternatives are shown in Table 20. Table 20 Costs breakw aters Volume Unit price Additional Costs submerged costs, sand- submerged

breakwater impermeable breakwater m 3 €/m 3 M€ M€ Alternative 1 - - - - Sand, equilibrium angle Alternative 2 - - - - Sand, segments

Alternative 3 - - - - Sand, parallel Alternative 4 Perched beach, equilibrium 321,000 49.5 5 20.9 angle Alternative 5 Perched beach, oblique 323,000 49.5 5 21.0 breakw aters Alternative 6 321,000 49.5 5 20.9 Perched beach, parallel Alternative 7 148,000 49.5 5 12.3 Perched beach 2, parallel

Adding the costs for nourishment, the costs for the groyne and the costs for the breakwater results in the total capital costs as shown in Table 21. Table 21 Costs Costs groynes Costs Total costs Total costs Nourishment submerged breakwater M€ M€ M€ M€

Alternative 1 220.0 52.7 - 272.7 Sand, equilibrium angle Alternative 2 98.0 25.1 - 123.1 Sand, segments Alternative 3 66.0 8.5 - 74.5 Sand, parallel Alternative 4 Perched beach, equilibrium 20.0 6.0 20.9 46.9 angle Alternative 5 Perched beach, oblique 28.0 11.0 21.0 60.0 breakw aters Alternative 6 20.0 2.0 20.9 42.9 Perched beach, parallel Alternative 7 14.0 1.8 12.3 28.1 Perched beach 2, parallel

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 88

CHAPTER 7: Selection of alternatives

7.2.8 MAINTENANCE COSTS

The maintenance costs can be divided into two different types. The loss of sand at the southern part of the beach due to longshore transport, will accumulate at the northern part of the beach. The beach can be restored be redistributing the sand, so the sand at the northern part of the beach can be redistributed at the southern part of the beach. There are however also cross-shore losses. The sediment which is transported over the breakwater in offshore direction will be lost. The lost volume should be nourished. The volumes of sand and corresponding costs for nourishment and redistribution can be found in Table 22. In order to compare the maintenance costs with the capital costs the net present value (NPV) is calculated. The net present value accounts for the time value of money. The net present value of the maintenance costs is determined for a period of 50 years and a discount rate of 5%. The maintenance costs are based on the soft measures for yearly conditions only. Table 22 NPV maintenance costs, Volume Unit Costs Redistri- Unit Costs Total NPV, 50 sand price sand bution price redistri- maintenance yrs 50 years lost of sand bution costs

3 3 3 3 m /yr €/m €/yr m /yr €/m €/yr €/yr M€

Alternative 1 Sand, equilibrium - 20 - - 5 - - - angle

Alternative 2 - 20 - - 5 - - - Sand, segments

Alternative 3 - 20 - 130,000 5 650,000 650,000 12.5 Sand, parallel

Alternative 4 Perched beach, 27,000 20 540,000 - 5 - 540,000 10.4 equilibrium angle

Alternative 5 Perched beach, 4,000 20 80,000 - 5 - 80,000 1.5 oblique breakwaters

Alternative 6 Perched beach, 6,000 20 120,000 10,000 5 50,000 170,000 3.3 parallel

Alternative 7 Perched beach 2, 532,000 20 10,640,000 45,000 5 230,000 10,870,000 208.4 parallel

Please note that in case of an extreme storm event additional maintenance costs will be necessary for both the structures and the soft measures. The impact of a 1/1, 1/5 and 1/50 year storm on the beach profile can be found in Annex 7. For alternative 1, 2, 4 and 5 the boulevard could be damaged in case of a 1/50 year storm. This should be taken into consideration in a more detailed design if one of these alternatives will be selected.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 89

CHAPTER 7: Selection of alternatives

7.3 RESULT MCA

All the scores for the criteria for each of the alternative can be found in the table below. Table 23 Result MCA Qualitative criteria Costs [M€] Spatial Tourism/ Safety Environ- Mainte- Risk Capital Mainte- Total quality beach ment nance costs nance costs recre- nui- (NPV, ation sance 50 yrs) Alternative 1 Sand, equilibrium ++ + ++ - ++ ++ 272.7 0 272.7 angle Alternative 2 ± + + ± ++ + 123.1 0 123.1 Sand, segments Alternative 3 + ++ ++ ± - ++ 74.5 12.5 87.0 Sand, parallel Alternative 4 Perched beach, - - - - + + - - 46.9 10.4 57.3 equilibrium angle Alternative 5 Perched beach, - ± - + + - 60.0 1.5 61.5 oblique breakw aters Alternative 6 Perched beach, + + ± + ± ± 42.9 3.3 46.2 parallel Alternative 7 Perched beach 2, + ± - + - - ± 28.1 208.4 236.5 parallel

Alternative 1 scores best on the qualitative criteria, but the costs are very high compared to the other alternatives. Alternative 3 has also a very good rating for the qualitative criteria, but involves much lower costs as alternative 1. Alternative 2 scores lower and is more expensive than alternative 3, and will therefore not be an interesting alternative. Also alternative 4, 5 and 7 are less interesting, because they score lower on the qualitative criteria than alternative 6 and are more expensive as well. Alternative 6 is the cheapest solution and has a relatively good rating for the qualitative criteria.

It can be concluded that alternative 3 and 6 will be the most promising alternatives. Whether alternative 3 or 6 is preferred depends on which criteria is valued to be leading. Because of the small differences between alternative 3 and 6 in the rates for the qualitative criteria, but a noticeable differences in the total costs, it is decided to select alternative 6 as most promising alternative in this study. The selected alternative 6 is worked out on a preliminary level in Chapter 8.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 90

CHAPTER 8: Preliminary design

CHAPTER 8 Preliminary design

Based on the conclusions of the Multi-Criteria analysis in the previous chapter, alternative 6 was chosen to be worked out in more detail. In this chapter a preliminary design for the perched beach parallel to the boulevard is described. Further research should be done to optimize the final design.

8.1 INTRODUCTION

In this section the conceptual design of the breakwater and groynes at the northern and southern boundary of the perched beach are presented.

The breakwater as defined in Chapter 6 is located 250 meters into seaward direction from the boulevard. The breakwater is positioned parallel to the coast. The breakwater turns in the northern into a revetment construction, which is foreseen along the existing boulevard between Kp0.000 and Kp0.600. At the southern end the breakwater turns into the northern groyne from the groyne system, which is foreseen along the coast between Kp2.400 en Kp7.400.

The filter layer of the constructions consists out of rock. The rock grading that are applied in the design are standard rock grading according to The Rock Manual (CIRIA, CUR, & CETMEF, 2007).

8.2 BEACH DESIGN

The beach profile is studied in more detailed and it is decided to adjust the beach profile as defined in Chapter 6. Near the waterline the slope of the be ach profile is 1:20. After discussion with experts it is concluded that a beach slope of 1:20 near the waterline is quite steep. It is decided to adjust the slope to 1:40 in order to get a more stable beach profile . The new shape of the profile will have a slope of 1:40 from MSL -1.0m to MSL +2.0m. From MSL +2.0m the beach profile will have a slope of 1:4 till it reaches the height of the boulevard. After reaching the height of the boulevard it is preferred to have a coastal stretch of about 50 m for recreation. In order to apply this beach profile shape the beach has to be shifted 50 meter in seaward direction. To avoid an increase in dangerous currents and cross-shore losses over the breakwater, the breakwater will shift along in seaward direction. This will result in the beach profile as shown in Figure 54.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 91

CHAPTER 8: Preliminary design

Figure 54 Cross section preliminary beach design

The beach will be nourished with sand after construction of the breakwater and the groynes. To avoid mixing of the pebble and the sand a minimum layer of 2 meter sand on top of the gravel is to be applied. In order to do so, the pebble at the upper part of the beach should be excavated, see Figure 55. By placing these excavated pebbles at the lower part of the beach profile and by placing some additional gravel at the lower part of the beach profile, less sand is needed to realize the beach profile . This will result in a required amount of sand of approximately 1,350,000 m3 and 430,000 m3 of pebbles.

Figure 55 Redistribution pebbles

8.3 DESIGN BREAKWATER

The breakwater is a submerged structure with a crest level 0.5 m below MSL. Submerged structures have their crest below water, but the depth of the submergence of these structures is such that wave breaking processes affect the stability. Submerged structures are overtopped by all waves and the stability increases considerably if the depth of submergence increases; in the case of non-overtopped structures, waves mainly affect stability of the front slope ,while in case of overtopped structures the waves do not only

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 92

CHAPTER 8: Preliminary design

affect the stability of the front slope, but also the stability of the crest and rear slope. Therefore, the size of the armourstone for these segments is more critical for an overtopped structure than for a non-overtopped structure.

The armour layer of a low-crested breakwater can be divided into different segments; front slope (I), crest (II) and rear slope (III), see Figure 56. Figure 56 Low -crested breakwater

A distinction can be made between statically stable and dynamically stable low-crested structures. Statically stable submerged breakwater can be designed with a broad crest, also called artificial reefs. In tidal environments and when frequent storm surge occur, submerged narrow-crested breakwaters become less effective in reducing the transmitted wave height and more expensive broad-crested breakwaters can be an alternative.

Van der Meer and Pilarczyk (1990) give a stability formula for statically stable submerged structures based on the limited experimental data of van der Meer (1988) and Gilver and Sørensen (1986) and is valid only for side slopes of 1.5 to 2.5. A functional relationship is provided between the relative crest height of a submerged breakwater, the damage level S,

and the spectral stability number Ns*:

hc 0.14N *  (2.1 0.1S)e s h where:

hc = crest height, measured from bottom [m] h = water depth, measured from bottom [m] S = damage level [-]

* H s 1/ 3 N s  s p Dn50 where:

Hs = wave height [m] Δ = relative density [-]

2H s p s = local wave steepness [-]; defined as 2 gTp

Dn50= median nominal diameter [m]

Stability of the submerged breakwater is a function of the relative crest height, the damage level S, and the spectral stability number. For fixed crest height, water level, damage level ,

and wave height and period, the required Dn50 can be calculated. The reliability of the design

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 93

CHAPTER 8: Preliminary design

formula can be described when the factor 2.1 is considered as a stochastic variable. The data gave a standard deviation of 0.35. With this standard deviation, it is possible to calculate the 90% confidence bands, using 2.1 ± 1.64 *0.35.

8.3.1 ARMOUR DESIGN

The calculations for rock are performed by considering the following criteria:

. During 1/5 year storm conditions, no damage is allowed. This corresponds with S=2 in Van der Meer, 1988; . During 1/100 year storm conditions, some damage is allowed. This corresponds with S=5; . Large damage, but no failure is allowed during 1/200 year storm. This corresponds with S=8.

When the damage levels are considered, the groyne has enough stability against short return period storms and is repairable when longer return period storm occurs. For the design of the armour layer the minimum, average and maximum scenario for sea level rise are taken into account The scenario resulting in the largest stones size will be leading.

In the designs, as presented in Chapter 6, the slopes were set to 1:3. Because the structure is submerged the waves will mainly affect the stability of the crest instead of the slope. Therefore the slope can be steeper as assumed in Chapter 6. It is concluded that a slope angle of 1:2 is favourable.

At MSL -9.4 meter water depth the design conditions for different return periods and water level scenarios are given in Table 24. Table 24 Design conditions at MSL Return Period -9.4m 5 years 100 years 200 years

Hs (m) Tp (s) Hs (m) Tp (s) Hs (m) Tp (s) L1 (MSL +0.7m) 5.10 10.40 5.42 11.56 5.48 11.56 L2 (MSL +1.0m) 5.20 10.40 5.54 11.56 5.60 11.56 L3 (MSL +1.4m) 5.34 10.40 5.66 11.56 5.76 11.56

Using the stability formula for statically stable submerged structures by van der Meer and Pilarczyk (1990) gives:

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 94

CHAPTER 8: Preliminary design

Table 25 hc h S H T s D D D Determination nominal s p p n50 n50 n50 (m) (m) (-) (m) (s) (m) -90% +90% stone diameters (m) (m)

L1 8.9 10.1 2 5.10 10.40 0.030 1.53 1.24 2.19 L1 8.9 10.1 5 5.42 11.56 0.026 1.51 1.28 1.97 L1 8.9 10.1 8 5.48 11.56 0.026 1.39 1.20 1.7 L2 8.9 10.4 2 5.20 10.40 0.031 1.50 1.22 2.12 L2 8.9 10.4 5 5.54 11.56 0.027 1.49 1.27 1.3 L2 8.9 10.4 8 5.60 11.56 0.027 1.37 1.19 1.68 L3 8.9 10.8 2 5.34 10.40 0.032 1.47 1.21 2.05 L3 8.9 10.8 5 5.66 11.56 0.027 1.47 1.25 1.88 L3 8.9 10.8 8 5.76 11.56 0.028 1.36 1.18 1.65

Using the formula of van der Meer and Pilarczyk results in a nominal stone diameter of 1.53 meter. Using a confidence band of 90% results in a nominal stone diameter ranging between 1.24 m and 2.19 m. The stone class 6-10 ton corresponds with a nominal stone diameter of 1.4 m and the stone class 10-15 ton corresponds with a nominal diameter of 1.7m. Stones from the class 10-15 ton are applied for the armour layer.

The thickness of the armour layer will approximately be 3.4 meter. The crest width is

advised to be 3 x D50 = 5.1 meter. So the 5 meter crest width as set in the design in Chapter 6 is a good assumption.

8.3.1.1. FILTER DESIGN CRITERIA

Based on the Coastal Engineering Manual [US Army Corps of Engineers, 2001, Coastal Engineering Manual], the following criteria have been taken into account for design of under layers.

W50F  7 15 : retention criteria W50B

D15F  4  5 : to prevent material from leaching out D85B

D15F  1 : permeability D15B

D60  10 : internal stability D10

In which

W 50 : the nominal ‘weight’of rock grading (kg);

D15 : the 15% value of the sieve curve (m);

D85 : the 85% value of the sieve curve (m)

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 95

CHAPTER 8: Preliminary design

Because standard grading are used it can be presumed that the last criterion will be fulfilled. Therefore this criterion will in the remainder not be checked. The grading of the armour layer is 10-15 tons. A filter layer of 1-3 tons meets the filter rules as:

F: W50 = 12500 kg W 50F  6.25 D50 = 1.68 m W D15 = 1.62 m 50B B: W50 = 2000 kg D15F  1.64 D50 = 0.91 m D 85B D15 = 0.80 m D 15F  2.03 D85 = 0.99 m D From Detailed design 2010 15B

The thickness of the filter layer is also taken as 2 * Dn50, where Dn50 is the nominal diameter of the rock (equivalent size). A filter layer of 1-3 ton with a layer thickness of 1.8 meter is applied between the armour layer of 6-10 ton and the core material.

8.3.1.2. CORE MATERIAL

Underneath the filter and armour layer the core material is placed. Core material of 60-300 kg will meet the filter rules as:

W F: W50 = 2000 kg 50F  11.11 D50 = 0.91 m W50B D15 = 0.80 m D 15F  1.74 B: W50 = 180 kg D 85B D50 = 0.40 m D D15 = 0.33 15F  2.42 D85 = 0.46 m D15B From Detailed design 2010

A grading of 60-300 kg meets the filter rule requirements and will be applied as core material.

8.3.1.3. TRANSITION TO SEABED

The transition between the toe and the seabed is crucial for the breakwater stability. If the local seabed material are very fine, it is important to prevent seabed material from being washed out through top layers, which leads to scouring of seabed layer and instability of the breakwater.

The seabed material at that location is fine sand with a median diameter of 0.09 mm (Detailed design). In order to create a proper transition between the seabed and the first layer of quarry run it is advised to apply geotextile by using geometrical closed filter rules. The characteristic of the geotextile should be:

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 96

CHAPTER 8: Preliminary design

. Opening size ≤ 200μm (O90 < D90) . Weight ≥ 300 g/m2

The core material (60-300kg) is not to be placed directly on the geotextile as the larger rocks may cause damage to the geotextile. The geotextile need to be covered with smaller material (1-60 kg) before applying the core material.

8.3.1.4. PERMEABILITY OF THE ARMOUR LAYER

The upper layer, consisting of the large stones, will be sand-permeable. In order to make the breakwater sand-impermeable, mastic asphalt can be used. Please note that the following description on the use of mastic asphalt is an example of a possible solution to make the structure sand-impermeable. Further research on mastic asphalt and other possibilities needs to be performed before implementation.

Mastic asphalt is a mixture of mineral aggregate and filler in which voids in the mineral matrix are overfilled with bitumen. The result is an asphalt mix that can be applied by pouring or by hand-floating into place. A typical mastic contains 60% sand, 20% filler, and 20% bitumen (by weight). The mechanical properties of the bitumen are dominant in determining mix behaviour. At ambient temperature, mastic asphalt is highly viscous under long-duration loading. It behaves like an elastic material when subjected to short-duration loading, such as wave forces.

The composition of an asphalt grout dumped under water as well as its mixing is similar to that used above water. The asphalt grout can be dumped into the water or can flow through a steel chute on surfaces not more than one or two meters below the surface of the water. At greater depths the asphalt grout must be lowered in clamshell bucket which is opened near the stone surface. Little grout is lost, if any, because the water will cool the surface of the mass of grout thus forming a protective skin whilst the hot core of the grout will penetrate into the voids and find its way like a mass of hot lava from a volcano.

An extra layer of smaller stones will be placed at the inner slope of the breakwater. This layer of smaller stones will be covered with the mastic asphalt. To determine the size of the stones of this extra layer, the filter criteria are used. Because the stones will be covered with the mastic asphalt after placement, not all the filter criteria have to be fulfilled. The stones should however be prevented from disappearing into the armour layer. Therefor the stability criteria D15F/D85B < 5 should be fulfilled. This results in a stone class of 40-200kg, with a corresponding nominal stone diameter of 34 cm. A layer with a thickness of 68 cm will be applied on top of the armour layer at the inner slope of the breakwater. From a memo of “Rijkswaterstaat” it follows that placing a layer of 40 cm of 5-40 kg stones covered with mastic asphalt will cost 39.25 €/m2 . A layer of 68 cm of 40-200kg stones covered with mastic asphalt is assumed to cost 80 €/m2.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 97

CHAPTER 8: Preliminary design

8.3.2 DESIGN GROYNES

The southern groyne is an extension of the most northern groyne of the groyne system which is foreseen along the coast between Kp2.400 en Kp7.400. In Chapter 6 the slope was preliminary set to 1:3, in this design a slope of 1:2 will be applied.

The most northern groyne of the groyne system, south of the perched beach, has a crest height of MSL+2m. This groyne should turn into the breakwater which has a crest height of MSL -0.5m. So in-between the groyne and the breakwater the crest height will decrease from MSL+2m into MSL -0.5m. The breakwater should however be situated 2 meter above the sandy profile in order to avoid mixing of the sand and pebbles. The groyne will be constructed using waterborne equipment, like crane pontoons and barges. The southern groyne of the perched beach is shown in Figure 57. The head of the breakwater of the most northern groyne of the groyne system should be adjusted, this is not taken into account in the figure.

The crest height at cross section A is MSL+2.0 m. The armour layer exists of 6-10 ton rocks, the crest width is 5 meter and the slope is 1:2. The crest height at cross section B is MSL+0.5 m. The armour layer exists of 10-15 ton rocks, the crest width is 5 meter and the slope is 1:2. The crest height at cross section C is MSL-0.5 m. The armour layer exists of 10-15 ton rocks, the crest width is 5 meter and the slope is 1:2. Figure 57 Cross sections southern groyne

The northern groyne is an extension of the revetment, which is foreseen along the existing boulevard between Kp0.000 and Kp0.600. The revetment has a crest height of MSL +5.0m and a width of 22.36m. The revetment is very wide because of the boulevard on top of it. The extension of the revetment will not contain a boulevard and will therefore be much smaller. The revetment will be extended with a groyne with a crest height of MSL +2.0m and a width of 5 meter. In order to capture the sand which will be transported to the north due to wave induced longshore currents, the crest height of the groyne will only in the last

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 98

CHAPTER 8: Preliminary design

meters turn into a crest height of MSL -0.5m. This northern groyne will also be constructed using waterborne equipment. The northern groyne of the perched beach is shown in Figure 58.

The crest height at cross section D is MSL+2.0 m. The armour layer exists of 10-15 ton rocks, the crest width is 5 meter and the slope is 1:2. The crest height at cross section E is MSL+1.0 m. The armour layer exists of 10-15 ton rocks, the crest width is 5 meter and the slope is 1:2. The crest height at cross section F is MSL-0.5 m. The armour layer exists of 10-15 ton rocks, the crest width is 5 meter and the slope is 1:2. Figure 58 Cross sections northern groyne

Note that the designs are only a sketch. A more detailed design has to be prepared before constructing.

8.4 COSTS

This new design will result in some changes of quantities and costs. These new quantities and costs are summarized in the following.

8.4.1 BILL OF QUANTITIES

Beach design Table 26 Quantities for design Grading Quantity 3 beach Sand 1,350,000 m 3 Excavation 140,000 m Pebbles 430,000 m3

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 99

CHAPTER 8: Preliminary design

Breakwater design Table 27 Quantities for design Grading Quantity 3 breakw ater 10-60 kg 38,000 m 1-300 kg 0 60-300 kg 85,000 m3 300-1000 kg 0 1-3 T 136,000 m3 3-6 T 0 6-10 T 0 10-15 T 115,000 m3 Geotextile 16,000 m3 Mastic asphalt layer 28,000 m2

Southern groyne Table 28 Quantities for design Grading Quantity 3 southern groyne 10-60 kg 3,000 m 1-300 kg 0 60-300 kg 4,000 m3 300-1000 kg 0 1-3 T 7,000 m3 3-6 T 0 6-10 T 2,000 m3 10-15 T 5,000 m3 Geotextile 1,500 m3 Mastic asphalt 800 m3

Northern groyne Table 29 Quantities for design Grading Quantity 3 northern groyne 10-60 kg 4,000 m 1-300 kg 0 60-300 kg 15,000 m3 300-1000 kg 0 1-3 T 13,000 m3 3-6 T 0 6-10 T 0 10-15 T 17,000 m3 Geotextile 2,000 m3 Mastic asphalt 800 m3

8.4.2 COSTS

The costs are determined on the basis of the required amounts of material as determined in Section 8.4.1. The results are presented in Table 30.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 100

CHAPTER 8: Preliminary design

Table 30 Grading Volume Unit price Total price (M€) Total quantities and 3 3 corresponding costs Sand 1,350,000 m 20 €/m 27.0 3 3 Pebbles 430,000 m 2.5 €/m 1.1 10-60 kg 45,000 m3 43 €/m3 1.9 1-300 kg 0 43 €/m3 0 60-300 kg 104,000 m3 43 €/m3 4.5 300-1000 kg 0 43 €/m3 0 1-3 T 156,000 m3 46 €/m3 7.2 3-6 T 0 46 €/m3 0 6-10 T 2,000 m3 49 €/m3 0.1 10-15 T 137,000 m3 52 €/m3 7.1 Geotextile 19,500 m2 20 €/m2 0.4 Excavation 140,000 m3 2.5 €/m3 0.4 Mastic asphalt 29,600 m2 80 €/m2 2.4 Total price 52.1

The annual average transports will differ slightly. The calculations of the annual longshore transports and cross-shore transports for the preliminary design can be found in Annex 9. The calculations of the maintenance costs can be found in Table 31. Table 31 NPV maintenance costs Volume Unit Costs Redistribution Unit Costs Total NPV, sand price sand of sand price redistribution maintenance 50 yrs preliminary design, 50 lost costs years m 3/yr €/m 3 €/yr m 3/yr €/m 3 €/yr €/yr M€

9,000 20 180,000 11,000 5 55,000 235,000 4.5

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 101

CHAPTER 9: Review final proposal

CHAPTER 9 Review final proposal

In this chapter the final proposal of the perched beach will be compared with the proposal of pocket beaches. First the pocket beaches and the perched beach will shortly be treated. Then the advantages and disadvantages of each proposal will be compared to each other.

9.1 DESIGN POCKET BEACH

The pocket beaches consist of four breakwaters with an average length of 300 meter, The breakwaters are positioned parallel to the coast. The most northern breakwater turns into a revetment construction, which is foreseen along the existing boulevard between Kp0.000 and Kp6.000.

The principle of the proposed pocket beaches is that a serie s of protective breakwaters are being constructed along the northern section of the Batumi coast. Landward of these breakwaters, curved shaped beaches will exist. The beach up to a level of MSL+3m will consist of pebbles. The (dynamic) equilibrium shape of these beaches is determined based on empirical formula’s.

Landward of the MSL+3m contour, a layer of sand is placed on top of the pebbles. A layer thickness of 1m is applied. In order to avoid large aeolian transport of the sand, the sand should be relatively coarse. The minimum D50 of the applied sand should be 200 μm. The basic features of the protective breakwaters are: . The armour layer of the head of the breakwaters consist of 7 m3 Xbloc units along the slope. At the crest, 10-15 ton rock is applied; . The armour layer of the trunk of the breakwaters consist of 5 m3 Xbloc units along the slope. At the crest, 10-15 ton rock is applied. The crest height at the middle section is MSL+5m. Towards both ends, the crest height gradually decreased to MSL+3.5m. . The boulevard at the centre of the breakwater need to be closed for public access when a significant wave height of 2.25 m is measured in front of the revetment (<1.4% of the time, mostly in winter time). . The geotechnical stability for the revetment is found to be sufficient. No deep sliding circles are encountered

The design of the pocket beaches is shown in Figure 59. Based on unit prices of the required material and a multiplier of 1.1 for works which need waterborne construction methods (and probably foreign contractors), the total costs for the pocket beach area is estimated at 25.5 M€.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 103

CHAPTER 9: Review final proposal

Figure 59 Design pocket beaches

9.2 DESIGN PERCHED BEACH

The perched beach consist of a submerged breakwater positioned parallel to the coast. At the northern and southern end of the breakwater, the breakwater turns into a groyne. The northern groyne turns into a revetment as designed in the “Detailed design” by Alkyon/ARCADIS in 2010. And the southern groyne turns into the most northern groyne of the designed groyne system in the previous study (Alkyon/ARCADIS, 2010) .

The principle of the perched beach is to create a fully sandy beach along the old boulevard, without undesirable visual structures. A nice wide sandy beach is created and only the groynes in the north and south of the old boulevard will be partly visible. The basic features of the breakwater are: . The crest height of the submerged breakwater is MSL -0.5m, the crest width is 5 meter and the slope is 1:2; . The armour layer consists of 10-15 ton rock, for the filter layer 1-3 ton rock is applied and the core consists of 60-300 kg rock.

The basic features of the groynes are: . The crest width of the northern and southern groyne is 5m and the slope is 1:2; . The northern groyne is an extension of the revetment and the crest height of the first part is MSL+2.0m, the crest height of the middle part of the groyne is MSL +1.0m and the crest height finally decreases to MSL-0.5m. The armour layer consists of 10-15 ton rock, for the filter layer 1-3 ton rock is applied and the core consists of 60-300 kg rock; . The southern groyne is an extension of the most northern groyne of the groyne system. The crest height of the first part is MSL+2.0m, the crest height of the middle part of the groyne is MSL +0.5m and the crest height finally decreases to MSL-0.5m. The armour layer of the first part consists of 6-10 ton rock, at the other parts of the groyne 10-15 ton rock is applied for the armour layer. The filter layer of the groyne consists of 1-3 ton rock and the core of 60-300 rock.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 104

CHAPTER 9: Review final proposal

At the level of the boulevard a horizontal beach with a width of 50 meter is present. From here another 85 meter of beach is presented until the beach profile reaches the wate rline. The crest of the breakwater is located at a distance of approximately 180 meter from the waterline.

The design of the perched beach is shown in Figure 60. Based on unit prices of the required material and a multiplier of 1.1 for works which need waterborne construction methods (and probably foreign contractors), the total costs for the perched beach area is estimated at 52.1 M€. The net present value for 50 years of maintenance is estimated to be 4.5 M€. Figure 60 Design perched beach

9.3 COMPARISON

The main advantages and disadvantages of the two options are listed in the table below. Table 32 Comparison of the main Pocket beaches Perched beach advantages and Partly sand Fully sandy beach disadvantages Visual structures Almost no visual structures Almost no maintenance Maintenance every few years 25.5 M€ 56.6 M€

The pocket beaches has a partly sandy beach, but contain undesirable visual structures. The perched beach fulfils the wish for a sandy beach with almost no visual structures, the costs are however considerably higher than for the pocket beaches. These higher costs might be regained due to additional tourism income.

It can be concluded that both options have their benefits and drawbacks. The preference depends on which aspect is valued as most important and/or which aspect is valued as least important. Selection of the most preferred option is subjective and therefore no preferences will be made in this study.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 105

CHAPTER 10: Conclusions and recommendations

CHAPTER 10 Conclusions and recommendations

The conclusions are presented in Section 10.1 and are discussed on the basis of the objectives of this study (as described in Section 1.4). The recommendations resulting from this master thesis are presented in Section 10.2.

10.1 CONCLUSIONS

. Define measures in order to create and preserve an artificial sandy beach

When a sandy beach is created the main issues are: − Large quantity of sand required − Loss of sediment due to longshore transport − Loss of sediment due to cross-shore transport These issues can be optimised by: − coarser sand − breakwaters − groynes − bypass system − isolated segments with sand − sand only above the water line

A potential application of a breakwater is a perched beach, providing a broa d buffer against wave action while offering a potentially excellent recreational site.

. Investigate the feasibility and stability of an artificial sandy beach

Longshore transport The longshore transports are mainly directed towards the north, only a small share of the net transport is transported towards the south. Therefore placing the beach under the equilibrium angle could be a solution to create a more or les s stable coast. There is however much more sand required if the beach is positioned under an equilibrium angle instead of parallel to the boulevard.

By applying a perched beach with a submerged breakwater with a crest height of MSL -0.5m and a distance of approximately 150m from the waterline, the longshore transport reduces from approximately 130, 000 to approximately 10,000 m3/yr.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 107

CHAPTER 10: Conclusions and recommendations

Cross-shore transport 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 mainly on the height difference between the crest of the breakwater and the sandy profile at the breakwater. The larger the height between the crest of the structure and the sandy beach profile at the structure, the less percentage of sand is lost over the breakwater, see Figure 61.

Figure 61 4 Relation loss of sand over breakw ater and height 3.5 difference between crest breakw ater and sandy 3 profile

2.5

1.5

1 Height difference between crest difference Height between sand (m) profile and

0.5 0 10 20 30 40 50 60 70 80 90 100 Loss of sand over the breakwater (%)

Storm condition After a storm event extra maintenance should be executed. During a 50 year storm condition a beach width of 60 meter may not be sufficient to protect the boulevard from damage by erosion.

. 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

The following 7 alternatives are generated, for a more detailed description see Chapter 6: − Alternative 1: Sandy beach The sandy beach is placed under the equilibrium angle − Alternative 2: Sandy beach with segments The sandy beach is placed under the equilibrium angle and divided into 4 segments − Alternative 3: Sandy beach, parallel to the boulevard − Alternative 4: Perched beach The beach is placed under the equilibrium angle and divided into 4 segments. The breakwater is located ± 250m form the boulevard and has a submergence of MSL - 0.5m. − Alternative 5: Perched beach, oblique submerged breakwater The beach and the breakwaters are placed under the equilibrium angle. The beach is divided into 4 segments, the breakwater is located ± 150 meter form the waterline and has a submergence of MSL -0.5m − Alternative 6: Perched beach, parallel to the boulevard

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 108

CHAPTER 10: Conclusions and recommendations

The breakwater is located ± 150 meter from the water line and has a submergence of MSL -0.5m − Alternative 7: Perched beach 2, parallel to the boulevard The breakwater is located ± 100 meter from the waterline and has a submergence of MSL -1.5m

These alternatives are validated with the use of a Multi-Criteria analysis (MCA). The results are presented in Table 33. Table 33 Result MCA Qualitative criteria Costs [M€] Spatial Tourism/ Safety Environ- Mainte- Risk Capital Mainte- Total quality beach ment nance costs nance costs recre- nui- (NPV, ation sance 50 yrs) Alternative 1 Sand, equilibrium ++ + ++ - ++ ++ 272.7 0 272.7 angle Alternative 2 ± + + ± ++ + 123.1 0 123.1 Sand, segments

Alternative 3 + ++ ++ ± - ++ 74.5 12.5 87.0 Sand, parallel Alternative 4 Perched beach, - - - - + + - - 46.9 10.4 57.3 equilibrium angle Alternative 5 Perched beach, - ± - + + - 60.0 1.5 61.5 oblique breakw aters Alternative 6 Perched beach, + + ± + ± ± 42.9 3.3 46.2 parallel Alternative 7 Perched beach 2, + ± - + - - ± 28.1 208.4 236.5 parallel

It can be concluded that alternative 3 and 6 will be the most promising alternatives. In case the quantitative criteria are valued the most, alternative 3 might be most promising. If the costs are leading, alternative 6 will be the most interesting alternative.

Based on the MCA it can also be concluded that the amount of required sand is governing for the costs. This means that cost savings can be achieved by applying less expensive fill material where possible. Beaches placed under the equilibrium angle require more sand than beaches positioned parallel to the boulevard, as a result of which the beaches positioned parallel to the boulevard are more attractive.

. Prepare a preliminary design for one of the most promising design alternatives

Based on the small differences between alternative 3 and 6 in the rates for the qualitative criteria in the MCA, but noticeable differences in the total costs, it is decided to select alternative 6 as most promising alternative in this study.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 109

CHAPTER 10: Conclusions and recommendations

The preliminary design of the most promising alternative consists of a submerged breakwater positioned parallel to the coast. At the northern and southern end of the submerged breakwater, the breakwater turns into a groyne. The northern groyne turns into a revetment as designed in the “Detailed design” by ARCADIS in 2010. The southern groyne turns into the most northern groyne of the designed groyne system as designed in the “Detailed design”.

Result The main task of the perched beach is to create a fully sandy beach along the Old Boulevard, without undesirable visual structures. A nice wide sandy beach is created and only the groynes in the north and south of the Old Boulevard will be partly visible. The design of the perched beach is shown in Figure 62.

Figure 62 Design perched beach

At the level of the boulevard the beach is horizontal with a width of 50 meter. From here the beach profile starts and another 85 meter of beach is present until the profile reaches the waterline. The crest of the breakwater is located at a distance of approximately 180 meter from the waterline.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 110

CHAPTER 10: Conclusions and recommendations

− The southern groyne is an extension of the most northern groyne of the groyne system and the crest height of the first part is MSL+2.0m, the crest height of the middle part of the groyne is MSL +0.5m and the crest height finally decreases to MSL- 0.5m. The armour layer of the first part consists of 6-10 ton rock, at the other parts of the groyne 10-15 ton rock is applied for the armour layer. The filter layer of the groyne consists of 1-3 ton rock and the core of 60-300 rock.

Based on unit prices of the required material the capital costs for the perched beach area is estimated at 52.1 M€. The net present value for 50 years of maintenance is estimated to be 4.5 M€. The costs are higher than the presented values in Table 33 due to the updated beach profile.

. Compare the final design alternative with the pocket beaches as designed in the previous study (Alkyon/ARCADIS, 2010)

The pocket beaches and the preliminary design of the perched beach are compared. The main characteristics are listed below. Table 34 Comparison of the main Pocket beaches Perched beach advantages and Partly sand Fully sandy beach disadvantages Visual structures Almost no visual structures Almost no maintenance Maintenance every few years 25.5 M€ 56.6 M€

It can be concluded that the designs have their own benefits and drawbacks. The preference depends on which aspect is valued as most important and/or which aspect is valued as least important.

10.2 RECOMMENDATIONS

. In order to make a better decision between the promising alternatives 3 and 6, it is recommended to also make a preliminary design for alternative 3. This alternative could be optimised by, for example, filling a part of the new beach profile (under the upper layer of 2 meter) with pebbles instead of sand. Also the groynes at the northern and southern end might be shortened. These adjustments could lead to a lowering of the costs and might result in a preference for alternative 3.

. In this study, mastic asphalt is suggested as a solution to make the breakwater sand- impermeable. This solution, but also other solutions in order to make a structure sand- impermeable, should be investigated.

. The XBeach model is used to estimate the yearly average cross-shore sediment transports. This model is developed to simulate the beach processes during storms and not to simulate yearly average transports. It might be interesting to investigate whether the XBeach model is also applicable for year round conditions.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 111

CHAPTER 10: Conclusions and recommendations

. The behaviour of a beach profile behind a submerged breakwater is rather complex. This behaviour is recommended to be investigated in more detailed. Also the currents at the lee side of the structure need to be taken into consideration as well as the transport of sediment through the (permeable) upper layer of the breakwater. Furthermore it should be investigated to which extend the XBeach is applicable in case of the presence of a submerged breakwater.

. Because of the doubtful applicability of the XBeach model and the conservative approach in order to estimate the cross-shore transports, it is highly recommended to check the cross-shore sediment losses with a different, more suitable model or physical model testing.

. Storm events should be better defined and taken into account. The characteristics of storms along the coast of Batumi, like the storm duration, should be defined based on local meteorological data.

. If alternative 6 is found to be a promising alternative, the layout and geometry of this alternative should be designed and optimised in more detail.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 112

BIBLIOGRAPHY

Bibliography

(2006). Concept Development for Reforms of the Water Sector, Financial Cooperation with Georgia. Alkyon/ARCADIS. (2010). Basis of Design. Alkyon/ARCADIS. (2010). Detailed Design. Alkyon/ARCADIS. (2010). Functional Design. Alkyon/ARCADIS/HKV. (2000). IMWM Project in Georgia, Coastal protection study for Batumi. Alkyon/ARCADIS/HKV. (2009). River and coastal protection Adjara, Georgia. Bernabeu, A., Medina, R., & Vidal, C. (2003). A morphological model of the beach profile integrating wave and tidal influences. Elsevier. Birkemeier, W. (1985). Field Data on Seaward Limit of Profile change. Journal, Waterway, Ports, Coastal and Ocean Division, 589-602. Bosboom, J., Aarninkhof, S., Reniers, A., Roelvink, J., & Walstra, D. (2000). Unibest-TC 2.0, Overview of model formulations. Bruun, P. (1954). Coast Erosion and the Development of Beach Profiles. Technical Memorandum 44. US Army Corps of Engineers Beach Erosion Board. Centre for Civil Engineering Research, Rijkswaterstaat, & Delft Hydraulics. (1987). Manual on artificial beach nourishment. CUR. CIRIA, CUR, & CETMEF. (2007). The Rock Manual. The use of rock in hydraulic engineering. CIRIA. d'Angremond, K. (1996). Wave transmission at low-crested structures. ASCE. d'Angremond, K., Span, H. T., van der Weide, J., & Waestenenk, A. (1970). Use of asphalt in breakwater construction. Proceedings of the Twelth Coastal Engineering Conference (pp. 1601-1627). ASCE. d'Angremond, K., van Roode, F., & Verhagen, H. (2008). Breakwaters and closure dams. Delft: VSSD. de Looff, A., Versluis, A., & Montauban, C. (2002). Technisch rapport Asfalt voor Waterkeren. Rijkswaterstaat, DWW. Dean, R. (1977). Equilibrium beach profiles: characteristics and applications. Journal of Coastal Research, 53-84. Dean, R. (1987). Coastal Sediment Processes: Toward Engineering Solutions. Proceedings of Coastal Sediments '87. ASCE. Dean, R. (2002). Beach nourishment. World Scientific. Dean, R., & Dalrymple, R. (2004). Coastal Processes with Engineering Applications. Cambridge University Press. Giginelshvilii, G., Metreveli, G., Gzirishvili, T., & Beritashvili, B. (1999). The Influence of Contemporary Global Warming On the Coastal Zone of Georgian Sea. González, M., Medina, R., & Losada, M. (1999). Equilibrium beach profile model for perched beaches. Elsevier. Graaff, J. v. (2009). Coastal Morphology&Coastal Protection. Hallermeier, R. (1981). A profile zonation for seasonal sand beaches from wave climate. Coastal Engineering, Vol. 4, 253-277. Holthuijsen, L. (2007). Waves in oceanic and coastal waters. Cambridge University Press.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 113

BIBLIOGRAPHY

Hurdle, D., & van Vledder, G. (2000). Development of a new source term for wave breaking in shallow water. Moore, B. (1982). Beach profile evolution in response to changes in water level and wave height. Pilarczyk, K., & Zeidler, R. (1996). Offshore Breakwater and Shore Evolution Control. A.A. Balkema, Rotterdam. Roelvink, D., Reniers, A., van Dongeren, A., van Thiel de Vries, J., Lescinski, J., & McCall, R. (2010). XBeach Model Description and Manual. Unesco-IHE Institute for Water Education; Deltares; Delft University of Technology. Roelvink, D., Reniers, A., van Dongeren, A., van Thiel de Vries, J., McCall, R., & Lescinski, J. (2009). Modelling storm impacts on beaches, dunes and barrier islands. Elsevier. Schiereck, G. (2004). Introduction to Bed, Bank and shore protection. VSSD. Silvester, R., & Hsu, J. (1997). Coastal stabilization. World Scientific Publishing. Sing, A., & Aung, T. (2005). Effect on barometric pressure on sea level variations in the Pacific Region. The South Pacific Journal of Natural Science, Vol. 23. Sorensen, R. (2006). Basic Coastal Engineering. Springer Science+Business Media, Inc. Swart, D. (2003). Beach nourishment and particle size effects. Elsevier. US Army Corps of Engineers. (1994). Coastal groins and nearshore breakwaters. ASCE. US Army Corps of Engineers, & Coastal Engineering Research Center. (1984). Shore protection manual: Volume I and II. USACE. van der Meer, J. W. (1988). Rock slopes and gravel beaches under wave attack. van der Meer, J., & Daemen, I. (1994). Stability and wave transmission at low crested rubble mound structures. ASCE. van der Meer, J., & Pilarczyk, K. (1987). Dynamic stability of rock slopes and gravel beaches. Proceedings of the Twenthieth Coastal Engineering Conference (pp. 1713-1726). ASCE. van der Meer, J., & Pilarczyk, K. (1990). Stability of low-crested and reef breakwaters. Van Wellen, E., Chadwick, A., & Mason, T. (2000). A review and assessment of longshore sediment transport equations for coarse-grained beaches. Elsevier.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 114

LIST OF FIGURES

List of figures

1) Georgia, Adjara ______1 2) Adjara, Batumi ______2 3) Pebble beach Batumi ______3 4) Old Boulevard of Batumi ______4 5) Locations of the reference points ______9 6) Detailed design of the coastal protection Batumi, Adjara ______10 7) Meander development near the mouth of the Chorokhi River, (left: 2004, right: 2007) _ 13 8) Monthly average discharge at Erge (Alkyon/ARCADIS/HKV, 2000) ______13 9) left: Submarine canyon in front of Chorokhi River. right: Submarine canyon in front Batumi Cape ______15 10) Active canyon ______16 11) Bathymetry, 2007 ______17 12) Locations of a number of selected cross-sections ______18 13) Cross-shore profiles based on bathymetrical surveys, 2008 ______18 14) Indication points along the reference line, referred to as Kp-values ______24 15) Computed extreme wave conditions along the MSL-5m depth contour______24 16) Locations of bed samples taken in 2008 ______26 17) Distribution of annual alongshore transports, pebbles (about 4 km north of the Chorokhi River) ______29 18) Observed coastline changes after 1830. (pink: measured coastline1830, blue: measured coastline 2008) ______31 19) Graphical presentation of averaged direction of wave energy fluxes along the Adjara coast (Alkyon/ARCADIS/HKV, 2009) ______33 20) Longshore transports Adjara coast (Alkyon/ARCADIS/HKV, 2009) ______34 21) S-φ curves for different profiles along the coast (Alkyon/ARCADIS/HKV, 2000) _____ 35 22) Locations profiles ______35 23) Profile schematisation and indication of different zones ______39 24) Beach face slope versus median sand grain diameter for high and low energy exposure (Modified from Wiegel, 1964) (Sorensen, 2006) ______40 25) Equilibrium profile sandy beach profile and the initial profiles ______42 26) Emerged sandy beach profile and initial pebble profiles ______43 27) Sandy beach profile at location B_P06______43 28) Equilibrium profiles, Dean ______44 29) Sketch of a perched beach ______45 30) Sketch of a sandy beach with in the front a pebble beach ______45 31) Sketch of pocket beaches ______46 32) Sketch cove ______47 33) Sketch of constructed segment ______47 34) Sketch of groynes ______47 35) Location of B_P04, B_P06, B_P08 along the Old Boulevard ______49 36) Relation loss of sand over breakwater and height difference between crest breakwater and sandy profile ______52

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 115

LIST OF FIGURES

37) Alternative 1 ______57 38) Cross section at location A, alternative 1 ______58 39) Alternative 2 ______60 40) Cross section at location A, alternative 2 ______61 41) Cross section at location B, alternative 2______61 42) Alternative 3 ______63 43) Cross section at location A, alternative 3 ______64 44) Alternative 4 ______66 45) Cross section at location A, alternative 4 ______67 46) Cross section at location B, alternative 4______67 47) Alternative 5 ______69 48) Cross section at location A, alternative 5 ______70 49) Cross section at location B, alternative 5______70 50) Alternative 6 ______72 51) Cross section at location A, alternative 6 ______73 52) Alternative 7 ______75 53) Cross section at location A, alternative 7 ______76 54) Cross section preliminary beach design ______92 55) Redistribution pebbles ______92 56) Low-crested breakwater ______93 57) Cross sections southern groyne ______98 58) Cross sections northern groyne ______99 59) Design pocket beaches ______104 60) Design perched beach ______105 61) Relation loss of sand over breakwater and height difference between crest breakwater and sandy profile ______108 62) Design perched beach ______110

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 116

LIST OF TABLES

List of tables

1) Amounts of removed sediment from Chorokhi River a nd the Batumi Cape (*1000 m3) 14 2) Sea level after 50 years for different scenarios ______19 3) Extreme wind speeds for different return periods in m/s______20 4) Range of values for boundary condition for average wave climate______22 5) Relation wave height and wind speed for average wave climate (Alkyon/ARCADIS/HKV, 2009) ______22 6) Probability of occurrence per wave height for output point B_08 ______23 7) Range of vaules for boundary conditions for extreme wave climate______23 8) Sieve analysis for different profiles ______26 9) Volume of nourished sediment along the coast near Adlia______32 10) Computed alongshore sediment transport capacities (Alkyon/ARCADIS/HKV, 2009) 34 11) Longshore sediment transports along the Old Boulevard (sandy beach) ______55 12) Rating spatial quality ______81 13) Rating tourism/beach recreation ______82 14) Rating safety ______83 15) Rating environment ______84 16) Rating maintenance nuiscance ______85 17) Rating risk ______86 18) Costs nourishment ______87 19) Costs groynes ______87 20) Costs breakwaters______88 21) Total costs ______88 22) NPV maintenance costs, 50 years______89 23) Result MCA ______90 24) Design conditions at MSL -9.4m ______94 25) Determination nominal stone diameters ______95 26) Quantities for design beach ______99 27) Quantities for design breakwater______100 28) Quantities for design southern groyne ______100 29) Quantities for design northern groyne______100 30) Total quantities and corresponding costs ______101 31) NPV maintenance costs preliminary design, 50 years ______101 32) Comparison of the main advantages and disadvantages______105 33) Result MCA ______109 34) Comparison of the main advantages and disadvantages______111

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 117

ANNEXES

Annexes

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 119

ANNEXES

ANNEX 1 Yearly wave conditions

The probability of occurrence per wave height is given at 3 locations along the Old Boulevard. These locations can be found in Figure A1 and the coastal orientation of these locations are given in Table A1. Figure A1 Location of B_P04, B_P06, B_P08 along the Old Boulevard

Table A1 Location Coastal orientation Coastal orientation B_P04 321° B_P06 323° B_P08 318°

Probability of occurrence per wave height for output locations B_P04, B_P06 and B_P08

Table A2 Table of occurrence, Hs wave direction (Deg) location B_P04 (m) -15 15 45 75 105 135 165 195 225 255 285 315 to to to to to to to to to to to to Total Lower Upper 15 45 75 105 135 165 195 225 255 285 315 345 < .25 .91 .92 .81 1.61 5.40 4.63 4.12 1.70 2.46 2.83 11.00 10.50 46.89 .25 .75 .63 .06 . . . . .12 .37 .83 4.67 18.82 7.24 32.74 .75 1.25 .06 ...... 43 9.80 2.29 12.58 1.25 1.75 .00 ...... 00 3.69 .88 4.57 1.75 2.25 ...... 1.51 .39 1.90 2.25 2.75 ...... 54 .19 .73 2.75 3.25 ...... 18 .15 .33 3.25 3.75 ...... 03 .14 .17 3.75 4.25 ...... 05 .05 4.25 4.75 ...... 03 .03 4.75 5.25 ...... 00 . 5.25 5.75 ...... 00 . 5.75 6.25 ...... 6.25 > ...... Total 1.60 .99 .81 1.61 5.40 4.63 4.24 2.07 3.30 7.93 45.57 21.86 100.00

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 121

ANNEXES

Table A3 Table of occurrence, Hs wave direction (Deg) location B_P06 (m) -15 15 45 75 105 135 165 195 225 255 285 315 to to to to to to to to to to to to Total Lower Upper 15 45 75 105 135 165 195 225 255 285 315 345 < .25 .88 .98 .81 1.61 5.40 4.91 3.97 1.64 2.54 3.10 9.45 8.96 44.25 .25 .75 .67 .07 . . . .00 .29 .56 1.54 6.02 16.79 7.39 33.32 .75 1.25 .07 ...... 02 .98 9.43 2.27 12.76 1.25 1.75 .01 ...... 10 4.13 1.08 5.33 1.75 2.25 ...... 1.79 .41 2.21 2.25 2.75 ...... 83 .20 1.03 2.75 3.25 ...... 40 .14 .54 3.25 3.75 ...... 17 .11 .27 3.75 4.25 ...... 08 .08 .16 4.25 4.75 ...... 01 .07 .08 4.75 5.25 ...... 04 .04 5.25 5.75 ...... 01 .01 5.75 6.25 ...... 01 .01 6.25 > ...... Total 1.63 1.05 .81 1.61 5.40 4.91 4.26 2.20 4.10 10.20 43.07 20.75 100.00

Table A4 Table of occurrence, Hs wave direction (Deg) location B_P08 (m) -15 15 45 75 105 135 165 195 225 255 285 315 to to to to to to to to to to to to Total Lower Upper 15 45 75 105 135 165 195 225 255 285 315 345 < .25 .84 .94 .81 1.61 5.40 5.12 3.79 1.58 2.56 3.33 10.54 6.94 43.47 .25 .75 .68 .08 . . . .00 .47 .75 1.85 7.82 15.38 6.50 33.53 .75 1.25 .07 ...... 00 .12 2.23 8.66 1.90 12.98 1.25 1.75 .01 ...... 00 .29 4.25 .98 5.53 1.75 2.25 ...... 06 1.90 .32 2.28 2.25 2.75 ...... 01 .90 .18 1.08 2.75 3.25 ...... 44 .11 .55 3.25 3.75 ...... 25 .05 .30 3.75 4.25 ...... 14 .02 .16 4.25 4.75 ...... 05 .03 .08 4.75 5.25 ...... 01 .02 .03 5.25 5.75 ...... 00 .01 5.75 6.25 ...... 6.25 > ...... Total 1.60 1.02 .81 1.61 5.40 5.13 4.26 2.33 4.53 13.73 42.52 17.05 100.00

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 122

ANNEXES

ANNEX 2 SWAN wave modelling

The nearshore extreme wave conditions were determined with use of numerical modelling. The 2D-model SWAN was used for this purpose. In this annex the model set-up is presented.

Grid In the wave climate study a coarse grid, reaching up to 35 km into the Black Sea was used to transform the offshore wave conditions towards the nearshore area. In the nearshore area with depths of 0 to 20 m, more detailed computational grids have been applied along the Adjara coastal zone and near the submarine canyons.

An overview of the applied computational grids is given in Figure A2 and Figure A3. The resolutions of the grids are given below.

. A, overall grid − resolution: 200m . B, grid coastal area between Chorokhi River and Batumi Cape − resolution: 40m . C, detailed grid submarine canyon near Chorokhi River − resolution: 15m

Figure A2 SWAN computational grids

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 123

ANNEXES

Figure A3 SWAN computational grids; from left to right: A grid, B grid and C grid

Boundary conditions The entrance boundary condition of the SWAN model was specified uniformly on the open sides of the domain as a JONSWAP spectrum.

To cover the wave climate in the nearshore of Batumi all combinations of the offshore wave conditions as given in the table below have been taken into account. Table A5 Input SWAN, w ave Parameter Values parameters Wave height Hsig (m) 0.5, 1, 2, 3, 4, 5, 6.5 Wave steepness (%) 0.5%, 1.5%, 3.5% Wave direction (◦N) 195, 225, 255, 285, 315, 345, 375

Each possible combination of wave height, wave steepness and wave direction was applied, which means in total, 7x3x7 = 147 simulations have been made. With use of the computational result, a transformation matrix was made, which is a way of giving a parametric relationship between the local wave conditions a nd the governing parameters.

Input normal wave climate . Bathymetry: Nearshore bathymetry of the survey of 2003 is used as input. Depth contours larger than 25m were digitized from Admiralty Charts. . Steepness: S1: 0.015; S2: 0.035; S3: 0.055 . Water levels: L1: 0.0m; L2: 2.0m . Directions: D1: 195°N; D2: 225°N; D3: 255°N; D4: 285°N; D5: 315°N; D6: 345°N; D7: 375°N

Input extreme wave climate . Bathymetry: Depth information from a bathymetrical survey of 2007 is applied. The survey is performed to a depth of approximately 20 m along the coast between Batumi and the Chorokhi River. Water depths further offshore have been taken from Admiralty Charts.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 124

ANNEXES

. Water level: L1: 0.7m; L2: 1.0m; L3: 1.4m . Clockwise rotation: C1: 15°; C2: 25°; C3: 35° . Direction: D1: 210°N; D2: 240°N; D3: 270°N; D4: 300°N; D5: 330°N. . Return period: R1: 1 year; R2: 5 years: R3: 10 years; R4: 25 years; R5: 50 years; R6: 100 years; R7: 200 years.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 125

ANNEXES

ANNEX 3 Sandy beach profile

The sandy beach profile is determined with the use of the formula of Dean (1987b) and the closer depth is calculated using Hallermeier (1981b). the grain diameter of the sand is defined 0.3 mm.

To compute the closure depth, the extreme nearshore significant wave height in meters exceeded 12 hours per year, which corresponds with 0.137 per cent of the year, has to be determined. Using the wave climate occurrence tables, the probability of exceedance of wave heights can be presented in a graph. From this graph the wave height corresponding to a probability of exceedance of 0.137% can be determined. This is done for the locations B_P04, B_P06 and B_P08 along the old boulevard. In Figure A4 an example of the graph at location B_P06 is given. Figure A4 Probability of exceedance, B-P06 6 location B_P06

3 Wave height (m) Wave height 2

0 -2 -1 0 1 2 10 10 10 10 10 Probability of occurence (%)

In the table below the calculated 12 hrs exceeding wave height for the three locations along the old boulevard are given. Table A6 Location H 12 hrs exceeding w ave s0.137 height for given locations B_P04 3.53 m B_P06 4.25 m B_P08 4.12 m

At location B_P06 the wave height that is exceeded 12hrs per day is 4.25m. This wave height will be used to determine the closure depth. The closure depth will by this be overestimated at some part of the coast, but using a lower wave height will result in underestimation at some parts of the coast, which is undesirable. The corresponding wave period T is 9.28 seconds. (T=alpha(=4.5)*sqrt(H))

Using Hs12= 4.25; T=9.28s; d50=0.3mm results in a closure depth of -6.2m. Dean profile and closure depth are calculated with the use of Matlab:

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 126

ANNEXES

Figure A5 Dean profile, output Matlab

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 127

ANNEXES

ANNEX 4 Longshore transport

Input UNIBEST-LT

Initial situation In the initial situation the bed material is gravel. Using the input for gravel as described above, the cross sections B_P04, B_P06 and B_P08 from the bathymetrical survey in 2008 and the wave occurrence tables as given in Annex 1, result in longshore transports as described in table A7 and shown Figure A6. Table A7 Location Net transport Longshore sediment Equilibrium orientation w.r.t. the coastal normal transport and equilibrium B_P04 103,000 m3/y 13.06° angle along the old B_P06 139,000 m3/y 16.62° boulevard; Present situation B_P08 118,000 m3/y 14.86°

Figure A6 Longshore transport for location B_P04, B_P06 and B_P08 respectively; Present situation

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 128

ANNEXES

Sandy beach The beach profile as calculated with the formulas of Dean and Hallermeier is used as input to calculated the longshore sediment transport. The sandy beach will be placed along the old boulevard, along the locations B_P04, B_P06 and B_p08. The bed material consists of sand

with Dn50=300μm. The results of the UNIBEST calculations are given in Table A8 and Figure A7. Table A8 Location Net transport Longshore sediment Northern Southern Equilibrium transport transport orientation w.r.t. the transport and equilibrium coastal normal orientation; Sandy beach B_P04 99,000 m3/y 26,000 m3/y 73,000 m3/y 11.04° B_P06 158,000 m3/y 27,000 m3/y 130,000 m3/y 13.82° B_P08 161,000 m3/y 26,000 m3/y 134,000 m3/y 13.89°

Figure A7 Longshore transport for location B_P04, B_P06 and B_P08 respectively; Sandy beach

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 129

ANNEXES

Perched beach To calculate the sediment transport in case of a perched beach, two different approaches are used. In the first approach the breakwater is not included in the profile. The transports are calculated behind the breakwater using transmitted wave heights. In the second approach the breakwater is included in the profile and the transports are calculated using the normal wave climate.

Transmitted waves d’Angremond et al. (1996) derived a relationship to calculate transmission using Rc/Hi. The intent of this approach was to develop a design formula which may be used also for smooth structures for which Dn50 may not be defined. The relationship between Kt and the relative freeboard for permeable structures reads:

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 130

ANNEXES

0.31 R  B  c   0.5 Kt  0.4    (1 e )0.64 H i  H i  with: tan   H / L0 2 Lo  gT / 2

The equation is limited between Kt = 0.075 and Kt = 0.8. The formula appears to work well for structures with relative submergence between -0.75 and 0.5. For deeply submerged and relatively high structures, this equation is not recommended.

In table A9 the transmitted wave heights are shown. Table A9 H K H Transmitted w ave heights i t t 0.25 m 0.95 0.23 m 0.75 m 0.48 0.36 m 1.25 m 0.41 0.52 m 1.75 m 0.40 0.69 m 2.25 m 0.39 0.88 m 2.75 m 0.40 1.09 m 3.25 m 0.40 1.31 m 3.75 m 0.41 1.54 m 4.25 m 0.42 1.77 m 4.75 m 0.43 2.02 m 5.25 m 0.43 2.27 m 5.75 m 0.44 2.54 m 6.25 m 0.45 2.81 m

The wave heights in the wave occurrence tables are replaced by the corresponding transmitted wave heights. These new achieved tables are used for the calculations for the approach where the breakwater is not included in the profile. Calculations are made for 2 different perched beaches: Table A10 Characteristics perched Distance from waterline Crest height beach 1&2 Perched beach 1 ± 150 m -0.5 m Perched beach 2 ± 100 m -1.5 m

Perched Beach 1 In Figure A8 the input profiles for the approach where the breakwater is included in the profile. In Table A11 and Figure A9 the longshore transports for this approach are shown.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 131

ANNEXES

Figure A8 Input profile UNIBEST for location B_P04, B_P06 and B_P08 respectively (Perched beach 1)

Table A11 Location Net transport Longshore sediment Northern Southern Equilibrium transport transport orientation w.r.t. the transport and equilibrium coastal normal orientation; Perched beach B_P04 7,000 m3/y 1,000 m3/y 6,000 m3/y 13.88° 1, approach including B_P06 9,000 m3/y 1,000 m3/y 8,000 m3/y 16.71° breakw ater B_P08 9,000 m3/y 1,000 m3/y 7,000 m3/y 15.84°

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 132

ANNEXES

Figure A9 Longshore transport for location B_P04, B_P06 and B_P08 respectively; Perched beach 1, Approach including breakw ater

In Figure A10 the input profiles for the approach where the breakwater is not include d in the profile are shown. In Table A12 and Figure A11 the longshore transports for this approach are shown.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 133

ANNEXES

Figure A10 Input profile UNIBEST for location B_P04, B_P06 and B_P08 respectively; Perched beach 1, approach transmitted w aves

Table A12 Location Northern Southern Net transport Equilibrium Longshore sediment transport transport orientation w.r.t. the transport and equilibrium coastal normal orientation; Perched beach B_P04 12,000 m3/y 3,000 m3/y 9,000 m3/y 13.02° 1, approach transmitted B_P06 16,000 m3/y 3,000 m3/y 13,000 m3/y 14.92° w aves B_P08 16,000 m3/y 3,000 m3/y 13,000 m3/y 14.92°

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 134

ANNEXES

Figure A11 Longshore transport for location B_P04, B_P06 and B_P08 respectively; Perched beach 1, approach transmitted w aves

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 135

ANNEXES

In Table A13 the net transports and equilibrium orientations are presented for both approaches. Table A13 Longshore sediment Location Net transport Equilibrium orientation w.r.t. the coastal normal transport and equilibrium Incl. breakwater Transmitted Incl. breakwater Transmitted orientation; Perched beach w aves w aves 1 B_P04 6,000 m3/y 9,000 m3/y 13.88° 13.02°

B_P06 8,000 m3/y 13,000 m3/y 16.71° 14.92° B_P08 7,000 m3/y 13,000 m3/y 15.84° 14.92°

Perched Beach 2 In table A14 the results, the net transport and equilibrium angle, for the perched beach 2 are presented for the approach including the breakwater and in Figure A12 the transports are shown. Table A14 Location Net transport Longshore sediment Northern Southern Equilibrium transport transport orientation w.r.t. the transport and equilibrium coastal normal orientation; Perched beach B_P04 44,000 m3/y 7,000 m3/y 36,000 m3/y 14.76° 2, approach including B_P06 56,000 m3/y 7,000 m3/y 50,000 m3/y 17.48° breakw ater B_P08 52,000 m3/y 8,000 m3/y 44,000 m3/y 15.81°

Figure A12 Longshore transport for location B_P04, B_P06 and B_P08 respectively; Perched beach 2, Approach including the breakw ater

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 136

ANNEXES

In table A15 the results, the net transport and equilibrium angle, for the perched beach 2 are presented for the approach where the breakwater is not included in the profile are shown. In Figure A13 the longshore transports for this approach are shown.

Table A15 Location Net transport Longshore sediment Northern Southern Equilibrium transport transport orientation w.r.t. the transport and equilibrium coastal normal orientation; Perched beach B_P04 41,000 m3/y 7,000 m3/y 34,000 m3/y 14.76° 1, approach transmitted B_P06 53,000 m3/y 6,000 m3/y 47,000 m3/y 17.46° w aves B_P08 51,000 m3/y 8,000 m3/y 43,000 m3/y 15.64°

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 137

ANNEXES

Figure A13 Longshore transport for location B_P04, B_P06 and B_P08 respectively; Perched beach 2, Approach transmitted w aves

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 138

ANNEXES

In table A16 the net transports and equilibrium orientations are presented for both approaches.

Table A16 Longshore sediment Location Net transport Equilibrium orientation w.r.t. the coastal normal transport and equilibrium Incl. breakwater Transmitted Incl. breakwater Transmitted orientation; Perched beach w aves w aves 2 B_P04 36,000 m3/y 34,000 m3/y 14.76° 14.76°

B_P06 50,000 m3/y 47,000 m3/y 17.48° 17.46° B_P08 44,000 m3/y 43,000 m3/y 15.81° 15.64°

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 139

ANNEXES

ANNEX 5 XBeach 2D

Input XBeach 2D In the first instance, some calculations were made with XBeach 2D. In the following the set- up for 50 year storm conditions for a perched beach with a submerge breakwater with a distance from the boulevard of approximately 200 meter and a submergence of 0.5 meter is shown. Table A17 Characteristics perched Perched Beach 1 beach 1 Location sill into seaw ard direction ±200m Submergence sill 0.5m

Grid Table A18 2D XBeach grid, perched Number of grid cells in M-direction 88 beach 1 Number of grid cells in N-direction 52 Delta X [m] 20 Delta y [m] 50 Origin X [UTM] 718180°N Origin Y [UTM] 4613665°S Rotation left [°] 40

The grid is refined in N-direction as shown in Table A19. In Figure A14 the grid is shown. Table A19 Refined grid, perched Number of grid cells in N-direction beach 1 25 50 28 25 10 12.5 4 5 28 2.5 20 5 21 10 5 25

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 140

ANNEXES

Figure A14 2D XBeach grid

Grid including bathymetry The bathymetry is obtained from the bathymetrical survey of 2003. To this bathymetry the submerged breakwater and the artificial sandy beach profile is added. The result can be found in Figure A15. Figure A15 Bathymetry, input 2D XBeach

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 141

ANNEXES

Input

Water level The water levels for different scenarios as computed in the previous study are shown in Table A20. For this calculation the average scenario is used. Table A20 Sea level after 50 years for Contribution Minimum Average Maximum different scenarios Sea level rise 0.1 m 0.2 m 0.5 m Tide 0.1 m 0.1 m 0.1 m Atmospheric pressure 0.3 m 0.3 m 0.3 m Seasonal fluctuation 0.2 m 0.4 m 0.5 m Wind setup at MSL-5m 0.0 m 0.0 m 0.0 m Total 0.7 m 1.0 m 1.4 m

Calculations are made for a period of 30 hours in which the storm will build up and weaken. It is assumed that during a storm the water level will raise due to atmospheric pressure and after the storm the contribution to the water level by the atmospheric pressure will decrease again. Therefore the water level is simulated as a cosine square function as shown in Figure A16.

Figure A16 Water level simulation

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 142

ANNEXES

Waves To determine the extreme waves the SWAN output at location A2, at a depth of 20m is used. With the use of the Weibull distribution the wave height for the return periods, 1, 2, 5, 10, 50 and 100 years are determined. The results can be found below. Figure A17 Weibull distribution

Figure A18

SWAN output location Weibull, A2

Method : Peak over treshold No. Of data points : 274 Data treshold : 7.50

Distribution : Weibull - Location parameter : 7.45 - Scale parameter : 0.30 - Shape parameter : 1.85

Goodness of fit - Rsquare : 0.996

Return Period Wave height (Years) (m) 1 8.00 5 8.14 10 8.20 50 8.31 100 8.36

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 143

ANNEXES

The wave height for a return period of 50 years is used. The storm is simulated as shown in Figure A19. The wave steepness is assumed to be 3.5 % and from the time series follows a wave direction of 325°. Figure A19

Storm simulation H1 = 2 fp1= 0.165 H2 = 3.67 fp2 = 0.122

H3 = 5.09 fp3 = 0.104 H4 = 6.25 fp4 = 0.094 H5 = 7.15 fp5 = 0.087 H6 = 7.79 fp6 = 0.084 H7 = 8.18 fp7 = 0.082

H8 = 8.31 fp8 = 0.081 H9 = 8.18 fp9 = 0.082 H10 =7.79 fp10 = 0.084 H11 = 7.15 fp11 = 0.087 H12 = 6.25 fp12 = 0.094 H13 = 5.09 fp13 = 0.104 H14 = 3.67 fp14 = 0.122 H15 = 2 fp15 = 0.165

Input file In the note below the main input file is given.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 144

ANNEXES

Parameters

%%% Flow boundary condition parameters front = abs_2d left = neumann right = neumann back = abs_2d epsi = -1

%%% Grid parameters depfile = depth_new.dep posdwn = 0 alfa = 0 vardx = 1 thetamin = -145 thetamax = 35 dtheta = 20 thetanaut = 1 gridform = delft3d xyfile = grid_new.grd

%%% Model time tstop = 108000

%%% Morphology parameters morfac = 10 morstart = 120 D50 = 0.0003 D90 = 0.0004 struct = 1 ne_layer = struct_new.dep

%%% Tide boundary conditions zs0file = wl.txt tideloc = 4

%%% Wave boundary condition parameters instat = jons

%%% Wave-spectrum boundary condition parameters bcfile = filelist.txt

%%% Output variables outputformat = netcdf CFL = 0.9 tintm = 3600 tintp = 3600 tintg = 600 tstart = 0

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 145

ANNEXES

Also calculations are made for perched beach 2, with a submerged breakwater which has a submergence of -1.5m and a distance from the boulevard of 150m. Table A21 Characteristics perched Perched Beach 2 beach 2 Location sill into seaw ard direction ± 150m Submergence sill 1.5 m

Results

Results perched beach 1 The sedimentation and erosion in the nearshore area is shown in Figure A20. The breakwater is indicated with an added pink line. Figure A20 Sedimentation and erosion, perched beach 1

In Figure A21 cross sections with the corresponding sediment transports and wave heights are given for different locations along the Old Boulevard. Cross section 15 is located at the northern part of the modelled coastal stretch, cross section 75 is located at the southern part of the modelled coastal stretch and cross-section 45 is located somewhere in the middle.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 146

ANNEXES

Figure A21 Cross section w ith corresponding sediment transports and w ave heights for different locations along the old boulevard, perched beach 1

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 147

ANNEXES

Results perched beach 2 The sedimentation and erosion in the nearshore area is shown in Figure A22. The

breakwater is indicated with an added pink line.

Figure A22 Sedimentation and erosion, perched beach 2

In Figure A22 cross sections with the corresponding sediment transports and wave heights are given for different locations along the Old Boulevard. Cross section 15 is located at the northern part of the modelled coastal stretch, cross section 75 is located at the southern part of the modelled coastal stretch and cross-section 45 is located somewhere in the middle.

Figure A23 Cross section w ith corresponding sediment transports and w ave heights for different locations along the old boulevard, perched beach 2

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 148

ANNEXES

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 149

ANNEXES

ANNEX 6 Cross-shore transport

Input XBeach 1D To estimate the yearly averaged amount of sand which will be lost in cross -shore direction over the submerged breakwater, the XBeach 1D model and the wave occurrence table of B_P08 are used. The occurrence table is converted to combinations of wave height and direction with a yearly occurrence in seconds. The medial of the directional bin and wave height bin are defined as values for these parameters, e.g. the value for the directional bin between 15 and 45 degrees is defined as 30 degrees. Each combination of wave height and direction (49 combinations) and corresponding duration is used separately as input for the 1D XBeach model. The loss of sediment over the breakwater for each condition is calculated by subtracting the initial profile at the beachside of the breakwater from the final profile at the beachside of the breakwater as calculated by XBeach. The sum of the sediment losses for each condition gives an estimate of the yearly sediment loss over the submerged breakwater. The 49 combinations of wave height direction and durations used as input for the XBeach models are presented in Table A22.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 150

ANNEXES

Table A22 -1 Input XBeach 1D Case H (m) D (°) fp (s ) Duration (s) MORFAC 1 0.125 0 0.661 264910 45 2 0.50 0 0.331 213520 30 3 1.00 0 0.234 22077 3 4 1.50 0 0.191 3469 1 5 0.125 30.00 0.661 297730 50 6 0.50 30.00 0.331 23970 3 7 1.00 30.00 0.234 315 1 8 0.125 60.00 0.661 254521 40 9 0.125 90.00 0.661 508727 80 10 0.125 120.00 0.661 1703746 300 11 0.125 150.00 0.661 1616067 250 12 0.50 150.00 0.331 1262 1 13 0.125 180.00 0.661 1194704 190 14 0.50 180.00 0.331 148549 20 15 0.125 210.00 0.661 497373 80 16 0.50 210.00 0.331 237805 30 17 0.125 240.00 0.661 808034 130 18 0.50 240.00 0.331 583790 70 19 1.00 240.00 0.234 36901 5 20 0.125 270.00 0.661 1051516 170 21 0.50 270.00 0.331 2466048 290 22 1.00 270.00 0.234 701747 80 23 1.50 270.00 0.191 92094 11 24 2.00 270.00 0.165 17347 3 25 2.50 270.00 0.148 2208 1 26 0.125 300.00 0.661 3322652 570 27 0.50 300.00 0.331 4849779 580 28 1.00 300.00 0.234 2732238 320 29 1.50 300.00 0.191 1340099 160 30 2.00 300.00 0.165 600506 70 31 2.50 300.00 0.148 282276 35 32 3.00 300.00 0.135 139719 17 33 3.50 300.00 0.125 79163 10 34 4.00 300.00 0.117 44155 5 35 4.50 300.00 0.110 15770 2 36 5.00 300.00 0.105 4100 1 37 5.50 300.00 0.100 315 1 38 0.125 330.00 0.661 2188819 340 39 0.50 330.00 0.331 2048785 240 40 1.00 330.00 0.234 599875 70 41 1.50 330.00 0.191 308768 35 42 2.00 330.00 0.165 102187 12 43 2.50 330.00 0.148 56770 7 44 3.00 330.00 0.135 34062 4 45 3.50 330.00 0.125 15454 2 46 4.00 330.00 0.117 5362 1 47 4.50 330.00 0.110 10408 2 48 5.00 330.00 0.105 5046 1 49 5.50 330.00 0.100 1262 1

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 151

ANNEXES

Water level Water level variations, caused by tide and storm are assumed to be negligible for yearly conditions. The mean sea level is used as the water level throughout the computational domain. Additional variations by wave group effects and coastal set-up are calculated by XBeach.

Results XBeach 1D The loss of sediment over the breakwater for each condition is determined for the alternatives 4, 5, 6 and 7. For alternative 4 and 5 the cross -shore transport is determined at two locations, because the beach profile differs in longitudinal direction. A4a and A5a show the result from the calculations made at a cross section south of a groyne and A4b and A5b show the calculations made at a cross section north of a groyne. The cross-shore losses for each alternative for all the 49 combinations are shown in Table A23.

The crest of the breakwater consists of large rocks. In the XBeach model the breakwater is simulated as an impervious structure. However sand can easily move through the large stones at the crest of the breakwater. It can be concluded that the XBeach calculations underestimate the cross-shore losses over/through the submerged breakwater. The submerged breakwater will however somehow be made impermeable in a later stadium and therefore the calculations with an impermeable structure will be applicable.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 152

ANNEXES

3 Table A23 Cross-shore losses (m /m/yr) Case Results A4a A4b A5a A5b A6 A7 1 0.00 0.00 0.00 0.00 0.00 0.00

2 0.00 0.00 0.00 0.00 0.00 0.00 3 -0.06 0.00 0.00 0.00 0.00 -0.12 4 -0.06 -0.06 0.00 0.00 0.00 -0.06 5 0.00 0.00 0.00 0.00 0.00 0.00 6 0.00 0.00 0.00 0.00 0.00 0.06 7 0.00 0.00 0.00 0.00 0.00 0.00 8 0.00 0.00 0.00 0.00 0.00 0.00 9 0.00 0.00 0.00 0.00 0.00 0.00 10 0.00 0.00 0.00 0.00 0.00 0.00 11 0.00 0.00 0.00 0.00 0.00 0.00 12 0.00 0.00 0.00 0.00 0.00 0.00 13 0.00 0.00 0.00 0.00 0.00 0.00 14 0.00 0.00 0.00 0.00 0.00 0.00 15 0.00 0.00 0.00 0.00 0.00 0.00 16 0.00 0.00 0.00 0.00 0.00 0.00 17 0.00 0.00 0.00 0.00 0.00 0.00 18 0.06 0.00 0.00 0.00 0.00 0.00 19 -0.12 -0.06 -0.06 -0.06 -0.06 0.04 20 0.00 0.00 0.00 0.00 0.00 0.00 21 0.12 0.04 -0.08 0.02 -0.14 -0.06 22 0.09 0.06 0.02 0.00 0.00 -0.04 23 0.18 -0.04 -0.14 0.07 -0.11 0.08 24 0.13 -0.10 -0.12 -0.12 -0.06 0.30 25 0.11 -0.18 -0.18 0.10 0.10 0.00 26 0.00 0.00 0.00 0.00 0.00 0.00 27 0.13 -0.02 -0.06 0.04 -0.02 0.06 28 0.14 0.05 -0.09 0.07 -0.13 0.51 29 0.92 0.05 0.08 0.14 -0.02 13.65 30 2.19 0.20 0.23 0.21 0.46 33.96 31 2.51 0.24 0.33 0.31 0.43 39.90 32 3.49 -0.39 0.21 0.20 0.40 39.93 33 3.94 0.05 0.42 0.30 0.41 38.67 34 4.60 0.19 0.34 0.41 0.81 35.10 35 2.61 0.15 0.24 0.46 0.52 20.84 36 0.88 0.12 0.04 0.04 0.14 7.05 37 -0.04 0.00 -0.06 -0.12 -0.12 0.18 38 0.00 0.00 0.00 0.00 0.00 0.00 39 -0.06 -0.02 0.14 -0.04 0.08 -0.11 40 0.01 -0.03 -0.02 -0.11 0.01 0.16 41 0.47 0.15 -0.03 0.01 0.21 2.08 42 0.80 -0.15 -0.08 0.04 0.00 5.94 43 1.18 -0.08 -0.06 0.04 0.14 10.17 44 1.88 0.00 0.13 0.41 0.18 13.28 45 1.18 -0.02 0.00 -0.13 0.06 10.96 46 0.42 0.08 0.01 0.06 -0.02 5.77 47 1.60 0.57 0.12 0.19 0.01 13.95 48 0.91 0.08 0.11 0.11 0.05 9.17 49 0.19 -0.18 -0.19 -0.01 -0.06 2.84

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 153

ANNEXES

Cross sections of the calculated cross-shore transports for an arbitrary case (case 29) are as an example given below:

Figure A24 Cross section A4a, case 29

Figure A25 Cross section A4b, case 29

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 154

ANNEXES

Figure A26 Cross section A5a, case 29

Figure A27 Cross section A5b, case 29

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 155

ANNEXES

Figure A28 Cross section A6, case 29

Figure A29 Cross section A7, case 29

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 156

ANNEXES

The sum of the losses for all the 49 results in an estimation for the annual cross-shore losses per running meter. The estimated total annual cross-shore losses over the entire artificial beach for each alternative is presented in Table A24. Table A24 Alternative Cross section Annual cross-shore Annual cross-shore Average annual cross- loss (m3/yr/m) loss (m3/yr) shore losses for A4 A4a 30.43 27,000 alternative 4, 5, 6 and 7 A4b 0.73

A5 A5a 1.28 4,000 A5b 2.68 A6 3.27 6,000 A7 304.25 532,000

The annual cross-shore losses for A7 is much higher than for the other alternatives. The breakwater crest of alternative 7 is one meter lower than of the other alternatives, resulting in the enormous losses. The table also shows that the losses for A4a are much higher than for A4b, A5a, A5b and A6. This can be explained by the following characteristics or a combinations of these: . The distance between the submerged breakwater and the waterline for A4a is 60 meter, where the distance between the submerged structure and the waterline for alternative A5a, A5b and A6 is approximately 150 meter and for A4b 200 meter. . The height between the sandy profile at the breakwater and the breakwater crest is smaller for A4a than for A4b, A5a, A5b and A6.

These characteristics also play a role in the high cross-shore losses for A7 and clarifies as well the differences between A4b, A5a, A5b and A6.

This approach is however rather conservative. To be able to estimate to what extent the approach is conservative the results are to be further analysed.

Analysis of the cross-shore transport The XBeach model is not developed to simulate processes behind submerged structures and this raises the question whether the model is applicable for this study. In order to get some insight into the simulation of these processes by the XBeach model, the relation between the erosion at the beachside of the breakwater and loss of sand over the breakwater are compared. A relation can be found between the percentage of sand lost over the breakwater and the height difference between the crest of the breakwater and the sandy profile at the beachside of the breakwater. The results can be found in Table A25. There seems to be a logarithmic relation as shown in Figure A30.

Table A25 Relation betw een the Cross section Erosion at the Loss of sand Percentage of Height difference beachside of over the sand lost over the between the crest percentage of sand lost the breakwater breakwater breakwater and the sandy 3 3 over the breakw ater and (m /m/yr) (m /m/yr) profile (m) the height difference A4a 105.3 30.4 28.9% 1.32 betw een the crest and the A4b 58.6 0.7 1.2% 3.54 sandy profile A5a 81.9 1.3 1.6% 2.83 A5b 95.6 2.7 2.8% 2.76 A6 93.6 3.3 3.5% 2.77 A7 411.4 304.3 73.9% 0.87

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 157

ANNEXES

Figure A30 Relation loss of sand over 4 breakw ater and height difference between crest 3.5 breakw ater and sandy profile 3

2.5

1.5

1 Height difference between crest difference Height between sand (m) profile and

0.5 0 10 20 30 40 50 60 70 80 90 100 Loss of sand over the breakwater (%)

This relation between the percentage of sand lost over the submerged breakwater and the height difference between the crest of the structure and the sand profile at the structure seems to be likely and the calculated losses over the submerged breakwater seems to be plausible. It is therefore assumed that the processes are approached reasonable and can be used to get a rough estimate of the losses of sand over the submerged breakwater and the behaviour of the beach profile in front of the breakwater.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 158

ANNEXES

ANNEX 7 Storm conditions

To determine the robustness and to determine whether the boulevard is save during a storm, calculation are made for different storm conditions. The input can be found in Table A26. Table A26 Return period Wave height Storm duration Water level Storm conditions 1 yr 8.00 m 10 hrs 0.4 m 5 yr 8.14 m 20 hrs 0.6 m 50 yr 8.31 m 30 hrs 1.0 m

The output of the calculations for each alternative are treated in the following.

Alternative 1 Alternative 1 is a sandy beach placed under the equilibrium angle. A cross section in the north, differs a lot from a cross section in the south. Therefore calculations are made for the most southern part of the beach and for the most northern part of the beach. The results are presented in the figures below.

Most southern location:

Figure A31 Cross section A1a, return period 1 year

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 159

ANNEXES

Figure A32 Cross section A1a, return period 5 years

The output for a 1/50 year storm is unstable. The boulevard is eroded and because the erosion reaches the boundary of the model, the output errors. A seaward shift of the beach with 20 meter results in:

Figure A33 Cross section A1a, return period 50 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 160

ANNEXES

Most northern location:

Figure A34 Cross section A1b, return period 1 year

Figure A35 Cross section A1b, return period 5 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 161

ANNEXES

Figure A36 Cross section A1b, return period 50 years

Conclusion It can be concluded that in order to keep the boulevard safe for a 1/50 year storm condition the beach should be shifted in seaward direction with approximately 20 meter.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 162

ANNEXES

Alternative 2 Alternative 2 is a segmented sandy beach. A cross section north of a groyne is very different from a cross section south of a groyne. Therefore calculations are made for a cross section north of a groyne as well as for a cross section south of a groyne. The results are presented in the figures below.

South of groyne:

Figure A37 Cross section A2a, return period 1 year

Figure A38 Cross section A2a, return period 5 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 163

ANNEXES

Figure A39 Cross section A2a, return period 50 years

North of groyne:

Figure A40 Cross section A2b, return period 1 year

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 164

ANNEXES

Figure A41 Cross section A2b, return period 5 years

Figure A42 Cross section A2b, return period 50 years

Conclusion North of the groyne where the beach width is only 60 meter the boulevard gets in danger in case of a 1/50 year storm. Therefore it is recommended to shift the beach in seaward direction.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 165

ANNEXES

Alternative 3 Alternative 3 is a sandy beach parallel to the boulevard. The figures below show the behaviour of the profile under storm conditions.

Figure A43 Cross section A3, return period 1 year

Figure A44 Cross section A3, return period 5 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 166

ANNEXES

Figure A45 Cross section A3, return period 50 years

Conclusion For this alternative the boulevard seems to be safe for the calculated storm conditions.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 167

ANNEXES

Alternative 4 Alternative 4 is a segmented perched beach. The beach profile south of a groyne differs from the beach profile north of a groyne. Therefore calculations are made for a cross section north of the groyne and a cross section south of the groyne. The results are presented in the figures below.

South of groyne:

Figure A46 Cross section A4a, return period 1 year

Figure A47 Cross section A4a, return period 5 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 168

ANNEXES

Figure A48 Cross section A4a, return period 50 years

North of groyne:

Figure A49 Cross section A4b, return period 1 year

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 169

ANNEXES

Figure A50 Cross section A4b, return period 5 years

Figure A51 Cross section A4b, return period 50 years

Conclusion North of the groyne where the beach width is only 60 meter the boulevard gets in danger in case of a 1/50 year storm. Therefore it is recommended to shift the beach in seaward direction.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 170

ANNEXES

Alternative 5 Alternative 5 is also a segmented perched beach, this time however the breakwater is also placed under the equilibrium angle. Calculations are made for a cross section south of a groyne as well as for a cross section north of a groyne. The results are presented in the figures below.

South of groyne:

Figure A52 Cross section A5a, return period 1 year

Figure A53 Cross section A5a, return period 5 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 171

ANNEXES

Figure A54 Cross section A5a, return period 50 years

North of groyne:

Figure A55 Cross section A5b, return period 1 year

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 172

ANNEXES

Figure A56 Cross section A5b, return period 5 years

Figure A57 Cross section A5b, return period 50 years

Conclusion North of the groyne where the beach width is only 60 meter the boulevard gets in dange r in case of a 1/50 year storm. Therefore it is recommended to shift the beach in seaward direction.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 173

ANNEXES

Alternative 6 Alternative 6 is a perched beach with a sandy beach parallel to the boulevard. The behaviour of the beach profile under storm conditions are presented in the following figures.

Figure A58 Cross section A6, return period 1 year

Figure A59 Cross section A6, return period 5 years

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 174

ANNEXES

Figure A60 Cross section A6, return period 50 years

Conclusion For this alternative the boulevard seems to be safe for the calculated storm conditions.

Alternative 7 Alternative 7 is also a perched beach parallel tot het boulevard, the breakwater is however lowered with 1 meter and located more shoreward. The results are presented in the figures below. Figure A61 Cross section A7, return period 1 year

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 175

ANNEXES

Figure A62 Cross section A7, return period 5 years

Figure A63 Cross section A7, return period 50 years

Conclusion For this alternative the boulevard seems to be safe for the calculated storm conditions.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 176

ANNEXES

Final conclusion To be proofed against 1/50 year storm conditions a beach width of 60 meter is not sufficient. It is recommended that the designs of alternative1, 2, 4 and 5 are shifted in seaward direction.

Result The amounts of cross-shore losses can be found for a 1/1 yr, 1/5 yrs and 1/50 yrs storm for each cross section presented in Table 27. Table A27 Alternative 1 yr 5 yrs 50 yrs Cross-shore losses for 3 3 3 different return periods at A1a 2.0 m /m 4.8 m /m 7.6 m /m 3 3 3 the different cross sections A1b 28.1 m /m 71.9 m /m 125.4 m /m 3 3 3 A2a 3.5 m /m 5.4 m /m 7.0 m /m A2b 2.6 m3/m 4.6 m3/m 7.1 m3/m A3 2.6 m3/m 4.1 m3/m 7.1 m3/m A4a 41.9 m3/m 92.6 m3/m 157.5 m3/m A4b 3.3 m3/m 10.2 m3/m 22.4 m3/m A5a 8.2 m3/m 28.7 m3/m 61.4 m3/m A5b 8.1 m3/m 23.9 m3/m 46.5 m3/m A6 9.5 m3/m 25.4 m3/m 51.6 m3/m A7 53.5 m3/m 93.3 m3/m 161.7 m3/m

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 177

ANNEXES

ANNEX 8 Calculations alternatives

Design sandy beach Minimal distance breakwater – waterline In the alternatives a minimal distance between the breakwater and the waterline is applied in order to limit the cross-shore losses and dangerous currents. This minimal distance is specified by 1 á 2 times the wavelength, resulting in 60 meter.

Minimal beach width The minimal beach width is determined to be 60 m, because a certain length is needed for the course of the profile from +3.5m to 0m. This length has to be at least 60 meters.

Required amount of sand The volume of required sand is calculate for certain cross sections along the coastline and mediation of these volumes result in the final total volume. The volumes at certain points and the total volume are for each alternative given in the Table A28 below. Table A28 3 Required amount sand Alternatives Volume [m /m] Total volume

Southern B_P08 B_P06 Northern boundary boundary A1 960 2740 6710 18650 11 Mm3

Southern South of North of South of North of Northern boundary 1st 1st 2nd 2nd boundary groyne groyne groyne groyne

A2 960 2800 960 3870 1340 6840 4.9 Mm3

Southern B_P08 B_P06 Northern boundary boundary

A3 1272 1275 1770 3955 3.3 Mm3

Southern South of North of South of North of South of North of Northern boundary 1st 1st 2nd 2nd 3rd 3rd boundary groyne groyne groyne groyne groyne groyne

A4 440 930 410 1130 460 1260 590 1130 1.0 Mm3

A5 340 1940 340 1940 340 1250 400 1770 1.4 Mm3

Southern B_P08 B_P06 Northern boundary boundary

A6 530 470 720 800 1.0 Mm3

A7 370 330 380 700 0.7 Mm3

Required volume groynes The groynes in alternative 1, 2 and 3 extend till a depth of -10m, because it is expected that this is where the dynamical zone ends and the transports are almost zero deeper than 10m. the groynes in the other alternatives extend till the breakwaters. The slope of the groynes are defined 1:3. The crest height of the groyne is 2 meter above the sand profile. The crest height at the northern boundary is higher and is an extension of the revetment in the north. At the southern boundary the groyne of the designed groyne system along the southern part of the coast will be extended. The calculated volumes for each groyne and each alternative are given in Table A29.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 178

ANNEXES

Table A29

Southernmost Groyne 2 Groyne 3 Groyne 4 Northernmost Total Required volumes for Alternative construction groynes groyne groyne 3 3 21,100 m - - - 1,043,600 m 1,065,000 m3 Alternative 1 Sand, equilibrium angle

3 3 3 3 3 Alternative 2 21,100 m 79,600 m 123,700 m - 283,400 m 508,000 m Sand, segments

3 3 3 Alternative 3 29,400 m - - - 142,500 m 172,000 m Sand, parallel

3 3 3 3 3 3 Alternative 4 5,500 m 21,200 m 26,700 m 31,600 m 35,600 m 121,000 m Perched beach, equilibrium angle

3 3 3 3 3 Alternative 5 2,500 m 52,800 m 52,000 m 33,500 m 81,200 m 222,000 m3 Perched beach, oblique breakwaters

3 3 Alternative 6 5,500 m - - - 35,600 m 41,000 m3 Perched beach, parallel

3 3 Alternative 7 2,200 m - - - 33,400 m 36,000 m3 Perched beach 2, parallel

Required volume breakwater Alternative 4, 5, 6 and 7 contain a breakwater as sill for the perched beach. The width of the breakwater crest is determined to be 5 meter and the slope of the breakwater is determined to be 1:3. The volume of required material for the breakwater is calculate at certain points along the breakwater and mediation of these volumes result in the final total volume. The volumes at certain points and the total volume are for each alternative given in the tables below, Table A30 and Table A31. Table A30 Total Required volumes for Alternative Volume at Volume at Volume at B_P08 B_P06 B_P04 construction breakwaters Alternative 4 154 m3/m 218 m3/m 236 m3/m 321,000 m 3

Perched beach, equilibrium angle Alternative 6 154 m3/m 218 m3/m 236 m3/m 321,000 m 3 Perched beach, parallel Alternative 7 55 m3/m 104 m3/m 177 m3/m 148,000 m 3 Perched beach 2, parallel Table A31 Required volumes for Southern- South of North of South of North of South of North of Northern- Total Alternative most groyne 2 groyne 2 groyne 3 groyne 3 groyne 4 groyne 4 most construction breakwaters, 3 3 3 3 3 3 3 3 alternative 5 Alternative 5 146 m /m 245 m /m 124 m /m 259 m /m 91 m /m 262 m /m 138 m /m 324 m /m 323,000 3 Perched m

beach, oblique breakwaters

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 179

ANNEXES

NPV The net present value is a central tool in discounted cash flow analysis, and is a standard method for using the time value of money to appraise long-term projects. Each cash flow is discounted back to its present value after which they are s ummed. This results in the following formula: N CFn NPV   n1 n1 (1 r) In which n = the time of the cash flow r = the discount rate

CFn = the net cash flow

In this study the NPV is calculated for 50 years with a discount rate of 5% and the net cash flow is equal to the maintenance costs for each year.

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 180

ANNEXES

ANNEX 9 Maintenance costs preliminary design

Longshore sediment transport The results of the UNIBEST-LT calculations for the beach profile as designed in the preliminary design are presented in Table A32. Table A32 Net longshore sediment Location Net longshore sediment transport transport Incl. breakwater Transmitted waves 3 3 B_P04 7,000 m /y 9,000 m /y B_P06 10,000 m3/y 14,000 m3/y B_P08 10,000 m3/y 13,800 m3/y

Cross-shore sediment transport From the yearly average cross-shore sediment transport calculations for the preliminary design follows that the total yearly loss of sediment over the submerged breakwater along the entire artificial sandy beach is approximately 9,000 m 3/yr. A cross section of the calculated cross-shore transports for an arbitrary case (case 29) is as an example given in Figure A64.

Figure A64 Cross section preliminary design, case 29

MSc thesis report Feasibility study of an artificial sandy beach at Batumi, Georgia 181