Impacts of Coastal Developments on Existing Coastal Morphology: A Case Study of Developing Marinas a...

M. Salauddin, R.M.R.M Jayathilaka, C.A. Rey Velasco

American Journal of Civil Engineering and Architecture

Impacts of Coastal Developments on Existing Coastal Morphology: A Case Study of Developing Marinas along the coast of Netherlands

M. Salauddin1,, R.M.R.M Jayathilaka2, C.A. Rey Velasco3

1Department of Civil Engineering, Chittagong University of Engineering & Technology, Chittagong-4349, Bangladesh

2National aquatic resources research and development agency, Colombo, Sri Lanka

3UNESCO-IHE Institute for water Education, Delft, Netherlands

Abstract

This study aimed to investigate the impacts of coastal developments like marinas on coastal morphology, a practical case study of developing a marina along the coast of Netherlands was selected in this research. A marina needs to be constructed along the coast of Netherlands in the best possible location minimizing the effects of the marina on the coastline. The focus was to keep the coastline of Netherlands intact by strongly focusing on the accretion and erosion areas before choosing a location for the marina. The present research shows the morphological effects of the marina located along the coast of Netherlands. The design vessel, marina layout, location of the marina and effects of constructing hard structures along the coast are also discussed. In this research, regarding to morphological (erosion/accretion) and economical (hinterland) aspects, the best possible location was chosen to construct marina. The model results obtained in this study were expected. It was observed that after constructing the breakwaters, the wave climate at southern side is shielding from northerly waves and on the northern side shielding from southerly waves. As a consequence, the equilibrium of coastline orientation was also affected on both sides leading to very strong accretion on both sides of the marina. Further away from the breakwaters considerable erosion has been taken place, especially in the south of the breakwater.

Cite this article:

  • M. Salauddin, R.M.R.M Jayathilaka, C.A. Rey Velasco. Impacts of Coastal Developments on Existing Coastal Morphology: A Case Study of Developing Marinas along the coast of Netherlands. American Journal of Civil Engineering and Architecture. Vol. 3, No. 3, 2015, pp 71-79. http://pubs.sciepub.com/ajcea/3/3/3
  • Salauddin, M., R.M.R.M Jayathilaka, and C.A. Rey Velasco. "Impacts of Coastal Developments on Existing Coastal Morphology: A Case Study of Developing Marinas along the coast of Netherlands." American Journal of Civil Engineering and Architecture 3.3 (2015): 71-79.
  • Salauddin, M. , Jayathilaka, R. , & Velasco, C. R. (2015). Impacts of Coastal Developments on Existing Coastal Morphology: A Case Study of Developing Marinas along the coast of Netherlands. American Journal of Civil Engineering and Architecture, 3(3), 71-79.
  • Salauddin, M., R.M.R.M Jayathilaka, and C.A. Rey Velasco. "Impacts of Coastal Developments on Existing Coastal Morphology: A Case Study of Developing Marinas along the coast of Netherlands." American Journal of Civil Engineering and Architecture 3, no. 3 (2015): 71-79.

Import into BibTeX Import into EndNote Import into RefMan Import into RefWorks

At a glance: Figures

1. Introduction

To Coastal environments are exceedingly popular as they used for various purposes such as tourism, recreational activities (water sports), transportation hubs (i.e. ports, marinas), residential areas (beach houses), economical use (waterfront mall) and these are just a few to mention. The impacts of these developments are rapidly increasing around the world. Even though these developments produce a significant amount of profit, it is not certain whether these developments are as beneficial for the environment. Structures constructed offshore often contribute to erosion/accretion problems along the coast. Therefore, before doing any coastal development like Marinas in a coastal area impact of that particular structure on the coastal environment should be considered and investigated.

In this research, a case study of designing and developing a marina along the coast of Netherlands was chosen. A marina needs to be constructed along the coast of Netherlands which has a significant amount of aesthetic value, is functional, safe, and contributes to the economic sector of the country. All factors should be considered during the design process including location, expected traffic, design boat, wave conditions, etc. The objective of this research is to choose a location to design a marina which is safe, functional, has aesthetic value, and contributes to the economic sector. The designated location of the marina should be chosen in such a manner that the marina has the least impact on the environment. Therefore, the accretion and erosion impact should be analysed in detail during the decision making process.

2. Case Study

To investigate the impacts of coastal developments like marinas on coastal morphology, a practical case study of developing a marina along the coast of Netherlands was selected in this research. The study area of present research is Bergen town, situated along the Netherland coastline, see Figure 1. The red boundaries in Figure 1, shows the area under investigation. Furthermore, the red stars show the wave stations situated nearby the allocated area from which the wave data could be obtained. It is to note that some areas along the coastline are facing severe erosion which is combated with regular nourishments. Other areas do not meet the Dutch safety standards and required improvement. It is already mentioned that one of the main objective of this study is to determine a location where a marina could possibly be constructed in line with nature and economy.

3. Methodology

The various steps were taken to achieve the research goal. Firstly, the design vessel has been determined which contributes to designing the marina layout. The marina layout was designed according to the design criterions obtained from PIANC reports. The design layout includes the marina, channel approach, turning circle, and breakwater design. The next step was to determine the marina location. Together with the marina layout and location, the numerical modelling approach has been introduced. To determine the morphological effects, matlab programme was used. Further wave climate was also introduced during this phase of the methodology which includes the distribution of significant wave heights and dominant wave directions. By using matlab code profile model was introduced used to determine the wave transformation, flow velocities and sediment transport along the coast. Then, a coastline model has been created to determine the morphological effects (accretion and erosion) of the marina at a certain location. Afterwards, the validation of the model has been done to ensure that used model is a good representation of the reality. The results obtained from the numerical modelling process are used to evaluate the processes occurring at the specific location. Finally, after the validation of the model, coastline trend over the years was monitored using the model in order to find a suitable location for the marina.

4. Results and Discussions

4.1. Design Vessel

Throughout the Netherlands various marinas can be found. The number of ships accommodated in marinas depends on the local demand as well as size of the marina. Figure 2 represents the number of boats located in several marinas across the Netherlands. The red line in Figure 2 shows the average number of vessel accommodated by the marinas across the Netherlands. The resulting average number of ships has been used in further analysis in order to determine the size of the marina.

Figure 2. Number of vessels accommodated by marinas across Netherlands

In general, two types of ships are observed in marinas namely; motor yachts and sail boats. By observing the sizes of the ships berthed at marinas in the Netherlands, an educated estimate can be made concerning the design vessel. It is important to consider the availability of ships in the industry whilst making this decision. The design vessel used for the purpose of this study is printed in Table 1.

4.2. Marina Layout

Regarding to the guidelines provided in Layout and Design Guidelines for Marina Berthing Facilities [1], the channel dimensions were calculated and summarised in Table 2.

Furthermore, the design of fairway, design of berth (number, length and width) and walkway have been also done using the guidelines of "Layout and Design Guidelines for Marina Berthing Facilities". It is noted that the complete design of a marina is not a prime concern of the present research therefore it is not discussed here in details. In Figure 3, the layout of the marina is presented.

4.3. Location of Marina

The location of Marina has been fixed depending on economical/commercial aspects (Hinterlands connection) and morphological aspects (erosion/accretion). The term economical/commercial aspect indicates good hinterland connections in order to get financial profits. If marina is placed close to local infrastructure with available hinterland connections than it would be more feasible in economic point of view since no need to build infrastructure. On the other hand, coastline has been changing over the years with erosion in some place and accretion in others. The construction of a hard structure like Breakwater or Groin has a great impact on occurrence of erosion and accretion close to the structure.

Figure 4 illustrates the sediment transport along the coast from 2006 until 2013. The graph is interpreted by observing the accretion (values of y>=0) and erosion (values y<0) patterns. Certain pattern shows how the accretion decreases or increases over the years and even describes how it moves along the coastline, either northward or southward. Ideally, the marina should be placed in areas of accretion. If the marina is placed in an area of erosion, it might worsen the state of the beach. The focus would be to place the marina in an area least affecting the coastline and even contribute to coastline accretion.

Initially, three alternative locations have been selected and observed in relation to which alternative is more promising in economical/commercial aspects and morphological aspects. Based on the observation on coastline trend over the last eight years, it appears that the same process occurs at alternative 1 and alternative 3. A significant amount of erosion occurred at one side compared to small accretion on the other side. However, alternative 2 produces accretion at both sides.

If hard structures like breakwater or groin is constructed at alternative 1 and 3, it will promote accretion on the both side of the structure due to the dominant waves from NW and SW direction, see Figure 4. Moreover, the construction of a breakwater or groin at alternative 2 will also increase the accretion on both sides. Thus in morphological and environmental point of view, marina should be placed either alternative 1 or 3 to minimize the erosion.

Figure 4. Erosion and accretion patterns observed along the coast

By observing the hinterland connections between alternative 1 and 3, it is clear that construction of marina at alternative 3 will be more beneficial in economic point of view. Thus, alternative 3 has been decided as the final location for building our marina. Figure 5 shows the allocated alternatives along the Netherland coastline.

4.4. Morphology
4.4.1. Measured Coastline Trend

In Figure 6, the coastline trend obtained from Deltares together with the coastal lines is presented. The green area represents the mean high water mark while the blue strip indicates the mean low water mark. Further the red strip represents the dune line, where the dunes are situated along the coastline.

Figure 7. Coastline trend during 2006-2013 at JarkusKB121-2726 (measured data: Deltares 2001 ref. line)
Figure 8. Coastline trend during 2007-2013 at JarkusKB121-2726 (measured data: Deltares)

Coastline trend at JarkusKB121-2726 was studied using the measured data from Deltares (Figure 7) which is calculated referenced to 2001 coastline. Furthermore, Figure 8 shows the coastline trend from 2007 to 2013 referenced from the 2007 coastline.


4.4.2. Wave Climate

The modelling was carried out assuming the wave climate is constant along the coast. Two wave climates were investigated; waves approaching from the southern and northern direction. These directions were chosen as they contribute significantly to long shore sediment transport. For modelling purposes, these wave climates are presented as wave windows. Wave windows only consider wave directions within a specified window which impacts each location. Thus, the wave windows are interpolated to all grid points. In each grid point, an S - ϕ curve is constructed within the time loop as in [2].

Figure 9. Wave height distribution (20 degree wave direction classes)

Figure 9 shows the percentage of occurrence of significant wave height and wave direction classes. From Figure 8, it is clear that two dominant wave directions are present; southwest (210-240 degrees) and northwest (330-360 degrees).


4.4.3. Wave Breaking

Depth-limited wave breaking is a prerequisite to generate near shore currents and secondary wave conditions. Seaward of the surf zone, wave energy losses primarily occur due to white capping and friction against the sea bed. Depth-limited breaking occurs when orbital velocities increases and exceeds the wave phase speed as the waves propagates towards the coastline. When this happens, the wave speed decreases in the landward direction [3].

Reference [4] re-analysed wave data for a number of laboratory and field experiments concerning various type of bathymetries. Values for the breaker index γ were determined. These values were found to be between 0.6 and 0.83 and a calculated average of 0.73 was determined. Later, through extensive complicated data sets and experiments, Reference [5] observed values in the range of 0.6–1.59 with an average of 0.78. Thus, γ is not a universal constant. Reference [6] showed that less than 10% of the breakers can be predicted to break solely on the basis of a constant wave-height-to-depth ratio. Its value seems to depend on bottom slope and incident wave steepness and even on the wind [3].

The maximum wave height Hmax under is generally expressed as a fraction γ of the local water depth (including wave-induced set-up):

(1)

In which,

Further, the root mean square wave height Hrms is expressed as:

(2)

Where,


4.4.4. Profile Model

By using Matlab profile modelling has been done in the present research. Profile model was used to calculate the wave transformation, flow velocities and sediment transport in order to understand the phase shift between the bed elevation and the current sediment transport. Soulsby-Van Rijn formula was used to calculate wave height, water level, alongshore transport, and velocities across the profile considering over all wave conditions, see Figure 10. The result is exported as a function of coast angle and wave direction) which is further used in coastline model.

Figure 10. Profile model: prediction of wave transformation, hydrodynamics and sediment transport

4.4.5. Coastline Model

The coastline model computation was split up into two parts. First, a profile model was run where the alongshore transport rate was computed as a function of the coast angle and wave climate. Second the coastline model has been run. Here, the alongshore transport has been computed as a function of the coast angle by looking up the transport computed in the profile model. Thereafter, the coastline positions can be updated. Finally, the coast angle can be recomputed. Gross positive, gross negative and net long shore transport rates have been plotted as function of coast angle and wave direction.

The breakwater has been designed with the aim to protect the ship inside the port. The length of the breakwater is about 750 m from the shoreline. In the model, the breakwater has been simulated as a straight line perpendicular to the shoreline. The effect of the breakwater was simulated by blocking the transport rate in proportion to the part of the cross shore distribution of the alongshore transport that they cover, and by selectively shielding certain wave conditions. The coastline model uses an initial coastline position, additional information about structures, and alongshore transport curve (S-phi) to predict the future coastline position. In Figure 11, alongshore transport curve (S-phi) observed from coastline modelling is shown.


4.4.6. Validation of Coastline Model

Validation is the process of verifying that a model meets the specifications to represent reality. The model should therefore be a good representation of the actual system. In other words, the model should reproduce the same expected behaviour as the prototype with enough reliability to satisfy analysis objectives. After validation of coastline model, the following parameters were found in this research

Gamma=0.63; % Breaker parameter index

Beta =0.025; % Roller slope parameter

hmin =0.5; % Cut-off water depth


4.4.7. Coastline Trend Using Model

The 2007 coastline was used as the base reference line for calculating the coastline trend during 2007-2013, see Figure 12. After the model was validated (see section 4.4.6), the potential coastline trend from 2013 (2013 used as base reference line) to 2019 was predicted using the validated breaker index, see Figure 13. The results were used to find a suitable location for the marina.

Figure 14, Figure 15 and Figure 16 show that the development of the coastline position, gross and net transport rate in time (lines plotted annually) with the presence of structure. From the graphs it can be observed that after constructing the breakwaters, the wave climate at southern side is shielding from northerly waves and on the northern side shielding from southerly waves. As a consequence, the equilibrium of coastline orientation has been modified on both sides leading to very strong accretion on both sides. Further away from the breakwaters considerable erosion has been taken place, especially in the south.

Figure 12. Coastline trend during 2007-2013 at JarkusKB121-2726 (prediction without marina for data validation)
Figure 13. Coastline trend prediction for 2013-2019 Period at JarkusKB121-2726 (without marina)
Figure 14. Coastline trend prediction for 2014-2019 at JarkusKB121-2726 (with marina)
Figure 15. Coastline trend prediction for 2014-2022 at JarkusKB121-2726 (with marina)
Figure 16. Gross northward (green), gross southward (red) and net alongshore transport (blue), at JarkusKB121-2726 area, the Netherlands

This is due to the reduction of the gross southward transport at southern side, which leads to a strong increase in the net transport. Likewise, the net transport in northern side is determined by the reduction of the northward gross transport respectively.

5. Conclusions

This paper has attempted to observe the impacts of marinas on coastal morphology. Based on the model results and discussions following conclusions can be drawn from the present research:

In the present research, regarding to morphological (erosion/accretion) and economical (hinterland) aspects, the best possible location was chosen to construct marina. Construction of coastal structures at offshore often lead to accretion in some areas and erosion in other areas along the coast depending on the direction of dominant waves. The model results obtained in this study are expected. It was found that due to the construction of breakwaters, equilibrium of coastline orientation has been modified on both sides (north and south) leading to very strong accretion on both sides. The model results showed that strong accretion occurs at northern and southern side of the marina. Further away from the breakwaters considerable erosion has been taking place, especially in the south. For this reason, preventive actions should be taken. This can be done by hard or soft engineering solutions. Groins are recommended to counteract the erosion. Soft engineering solutions could be also being considered. For instance, beach nourishment or shore-face nourishment are good soft engineering solutions but are more expensive than hard solutions. To keep the coastline as it is, it would be best to inform Authority in advance that constructing marinas will enhance accretion in certain areas and erosion in others. Thereby effective planning may prevent enormous coastal erosion to keep the coastline intact.

Acknowledgement

The technical support of Prof. Dano Roelvink and Dr. Ali Dastgheib (UNESCO- IHE Institute of Water Education) is gratefully acknowledged.

References

[1]  Schwarzenegger, A., Chrisman, M., & Tsuneyoshi, R. (2005). Layout and Design Guidelines for Marina Berthing Facilities.
In article      
 
[2]  Roelvink, D., & Reniers, A. (2011). A Guide to Modelling Coastal Morphology, Advances in Coastal and Ocean Engineering, Volume 12, World Scientific.
In article      
 
[3]  Holthuijsen LH (2007). Waves in oceanic and coastal waters
In article      
 
[4]  Battjes JA & Stive MJF (1985). Calibration and verification of a dissipation model for random breaking waves. Proceedings of nineteenth international conference on coastal engineering (Houston, USA: sep 3-7, 1984), bl edge (ed), 1, New York, U.S.A., Am. Soc. Civ. Engrs., 1985, Part I, Chapter 44, p.649-660.
In article      View Article
 
[5]  Kraus NC & Kaminsky GM (1994). Evaluation of depth-limited wave breaking criteria. Proceedings of the 2nd International Symposium on Ocean Wave Measurement and Analysis, ASCE, New York, NY, United States.
In article      
 
[6]  Babanin AV, Young IR & Banner ML (2001). Breaking probabilities for dominant surface waves on water of finite constant depth. Journal of Geophysical Research: Oceans, 106: pp. 11659-11676.
In article      View Article
 
  • CiteULikeCiteULike
  • MendeleyMendeley
  • StumbleUponStumbleUpon
  • Add to DeliciousDelicious
  • FacebookFacebook
  • TwitterTwitter
  • LinkedInLinkedIn