Coastal erosion

What is coastal erosion and when is it a problem?
What can be done?
Key concepts
Indicators and monitoring
Potential interventions
Setback lines
Use of models
EU policies and Directives
The way forward
How to do it?
Systematic approach
Decision loop
Relevant Web links


Costa Brava
Presentation Costa Brava


Costa Brava Bays, Mediterranean coast (Spain)

Problem setting
Urban beaches are representative of a large percentage of the Mediterranean coastline, being one of (if not the most) most important resources for coastal tourism. They can be represented by beaches with the following profile: (i) they are mostly relatively narrow beaches and are backed by waterfronts and (ii) they are heavily used only during the bathing season and, in consequence, they support (or have) services for beach users. The typical length scale of these beaches varies from 100s m to few kms with one or two lateral obstacles (semi-enclosed and pocket beaches respectively). Due to these characteristics, these beaches play two main functions: protection and recreation. Protection refers to the function played by the beach to protect the hinterland (usually occupied by a promenade or any other infrastructure) from wave action and, recreation makes reference to the function played by the beach to properly offer an environment for leisure (e.g. beach surface to accommodate users).

The appearance of erosion associated to medium/long-term processes (imbalance in the sediment budget) and episodic events (impact of storms) determine fluctuations of the beach width (in some cases of periodic nature and, in some cases, systematic) that affect to the above mentioned beach functions. As a result of this, beach problems are becoming frequent during the last years: damages in existing infrastructures such as promenades during winter and, insufficient emerged beach to allocate users during summer.

Description of the coastline
The Costa Brava is located on the NE Spanish Mediterranean coast. It is a highly indented coast with most of the coastline composed of cliffs, especially in the northernmost area. Bayed and pocket beaches are the dominant beach type, with most of them composed of coarse sands. This area is represented in this project by s’Abanell and Lloret de Mar beaches. s’Abanell is a 2.5 km long sandy semi-enclosed beach located in Blanes. The North part of the beach is based on sa Palomera, a small rocky headland whereas its South end is open being supported by the Tordera delta. The beach can be zoned into two areas in function of its urban development of the hinterland: (i) a N urban area, about 1.5 km long, with a promenade running along the back of the beach and (ii) a S semi-urban area, about 1 km long, where the hinterland is occupied by camping areas with the southernmost 500 m without any infrastructure in the backbeach. This spatial variation in the hinterland is also reflected in the degree of beach use, with the N area being intensively used whereas the S one presents a much lower density of use. The subaerial beach has a 32 m average width and it is composed by a sediment size of about 1.2 mm. Lloret de Mar is a 1.3 km long and 50 m wide sandy bay beach embedded between two low cliffs. The shoreline is almost linear with the exception of the areas in the surrounding of the two ends where it adopts a curved form due to the effects of wave diffraction at the cliffs. The beach is backed by a promenade placed at approximately 4.5 m above the sea level which is protected at the ends by a revetment of quarry stones. A total of 6 short groins, of about 30 m long, are placed along the beach at regular distances and are partially or totally covered during “typical” conditions. The emerged area is characterized by a sediment size of 0.95 mm.

Beach processes

S’Abanell beach
s’Abanell beach presents two different evolutive periods from 1957 until present: (i) an original accretive behavior during the period 1957- 1973 and (ii) an actual erosive one since the end of 70s until present. During the first period the beach was accreting due to the supplies of the Tordera river. Although most of sediments were transported towards the South by the net longshore sediment transport pattern, part of the sediment was redistributed towards the beach by diffusion and by the action of secondary southern waves. At the end of this period the beach reached its maximum width. During the second period, the beach presented an erosive behavior that can be related to the sharp decrease in river sediment supplies due to the dredging of several millions of m3 of sediment from the river bed mainly from the end of the 60s to the end of the 70s. This affected the balance between sediment sources and removal due to littoral dynamics and it determined the Tordera delta to be reshaped and eroded. Since the delta front was acting as a dynamical support for the beach (at its S end), the beach started to be eroded. The beach shows two differentiated parts in terms of shoreline evolution: (i) a N part where the beach is almost stable and, (ii) a S one extending along 1 km, where the beach is erosive with shoreline recession rates increasing towards the S. The average annual sediment loss in the beach has been calculated to be 30,000 m3/yr which should be removed from the coastal cell (the beach) by the southwards directed net longshore sediment transport.

Lloret de Mar
Lloret de Mar is a pocket beach with two headlands delimiting a closed sediment cell. Due to this, shoreline changes are limited to coastline fluctuations around an equilibrium shape depending on the direction of the incoming waves. The most frequent configuration corresponds to a shoreline orientated towards the SSE which corresponds to the direction of the integrated energy flux of effective waves in the area and it will correspond to the equilibrium shape. The other two configurations correspond to: (i) a situation generated by the cumulative action of Eastern storms during a long time without the action of secondary S waves resulting in an extreme reorientation towards the South (e.g. May 2004) and; (ii) a situation generated by the cumulative action of Southern storms without the action of E waves resulting in an extreme reorientation towards the North (e.g. May 2001). It has to be noted that this last configuration is not very frequent in the area due to the dominance of E waves. An analysis of beach shoreline changes from 1986 until present has demonstrated that sediment losses from the beach are negligible and, in consequence, it can be considered as a closed sediment cell.

Beach problems
Different problems related to beach malfunction regarding the protection of the hinterland have been detected in both beaches. These problems vary in intensity depending on the balance between storm characteristics and beach morphology at the time of the storm impact. Minor problems occur when the beaches are overtopped by waves during the storm and the promenade and the area behind the beach is overwashed by water and sediment removed from the beach. These events usually occur when total water level during the storm exceeds the beach crest level and promenade height.

When waves impact directly on the promenade, failure of the infrastructure usually occurs. In most of the cases, the failure is due to the fact that most of the existing beach promenades along the Spanish Mediterranean coast were built in the 70s during the tourist boom. At that time, beaches were wide and promenades were not generally built taking into account that waves could impact on the structure. As a consequence they were not designed as coastal structures but as architectural elements. As erosion becomes dominant in our coasts, beaches protecting these infrastructures get progressively narrower and storm waves were able to directly impact on them. If other infrastructures are present in the beach, they will be also affected. An example in the s’Abanell beach are the existing facilities of a desalinization plant (wells and a pumping station). Because these facilities were built in the most erosive stretch, few years after their construction were severely affected by storm impacts.

Protection problems in s’Abanell beach

In the case of pocket beaches without background erosion, this problem can also be present although the average beach width exceeds the storm-induced erosion. This will occur when the storm impacts on a beach showing an extreme reorientation. Under these conditions, although the beach has the same subaerial surface, this is “badly distributed” because there will be a part of the beach very wide and another part very narrow.


Protection problems in Lloret de Mar beach

Application of the Frame of Reference approach
The Frame of reference approach provides a systematic framework for the development and implementation of a policy for coastal management. The application of the Frame of Reference to Costa Brava beaches is illustrated in the figure below.

Application of the Frame-of-Reference for protection (P) and recreation (R) oriented beach management.

The strategic objective is the Sustainable erosion management in Costa Brava beaches. This has to be done in such a way that the beach has to properly play both targeted functions: protection during winter and recreation during summer.

To achieve this objective we can make use of the concept of favourable sediment status, that due to the characteristics of these beaches will be time-dependent:

  • winter (stormy period) – Protecting infrastructures: Volume of sediment required to generate a beach wider than the one to be eroded by storms (Tr to be selected ).
  • summer (calm period) – Recreational carrying capacity: Volume of sediment required to generate a beach wide enough to accommodate users (~ 30 m ).

Present erosion management in s’Abanell

At present, erosion management in s’Abanell beach is reactive. Thus, actions limit to:

  • promenade reinforcement
  • emergency beach nourishments [170,000 m3 (11/07) + 165,000 m3 (05/08) + 250,000 m3 (07/09)]
  • relocation of camp site limits – retreat –
  • desalinization plant protection

Emergency beach nourishment at South s’Abanell beach at December 2007.