GUIDELINES
   
Coastal erosion

What is coastal erosion and when is it a problem?
 
What can be done?
Key concepts
Framework
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
   
LINKS
Relevant Web links

 

 

Danube Delta
 

Delta beach
Sf. Gheorghe dunes
Delta beach

Sulina jetties

 
 
Presentation Danube Pilot Site
 

 

 
The Black Sea coastal zone of the Danube Delta (Romania)
 

Problem setting
The pilot site is part of the Danube Delta Biosphere Reserve, a RAMSAR and UNDESCO nature protection site. Its northern and central part has been subject to historical erosion, due to the existing natural trend involving the Danube Delta evolution. Human interventions consisted of various works along the Danube (damming, embankments, meander cut-offs) as well as on the coastal zone (building and extension of jetties). These interventions have changed the trends of the coast`s natural evolution, meaning also an increase of the erosion intensity. For instance, the central part of the Sulina – Sf. Gheorghe coastal strip is subject to the most severe erosion along the entire Romanian Black Sea coast, with areas in retreat at a rate of about 20 m/yr. Coastal managers must now decide whether or not to protect the studied coastal strip from erosion, and, if yes, which is the most acceptable option.

Strategic objectives
The strategic objective for the Sulina – Sf. Gheorghe coastal strip (Danube Delta pilot site) is to ensure sustainable development of the area.

Operational objectives
Reduce coastal erosion to natural rates.

Coastal sediment cell
The littoral cell is confined by the Sulina jetties (north), Sahalin spit island (south), the closure depth (ranging from 6 to 11 m) offshore (east) and the dune system (west). The northern limit is an artificial structure, virtually impermeable to sediment transport while the southern limit is a natural feature. The sediment transport cycle contains: sources (central part of Sulina – Sf. Gheorghe area), pathways (from north to south) and sinks (Sahalin spit island).

The main process causing loss of sediments from the Sulina – Sf. Gheorghe beach sector is the wave-induced alongshore current. Due to human interventions the quantity of sediments reaching the coast has decreased dramatically. The sediments lost from the system are not replaced at a natural rate, resulting thus in severe erosion especially in the central part. Another cause of short term shoreline retreat (also contributing to the multannual erosion) is the sea level variation, mainly due to the storm surges and the variation of the storm system distribution over the Black Sea basin.

Strategic sediment reservoirs
The strategic sediment reservoir considered for this pilot site is situated at the northern extremity of the area, immediately north and in front of the Sulina jetties. As the jetties practically block all the north-south longshore transfer of sediments, Musura Bay (north of the jetties) has been subject to intense sedimentation, being virtually transformed into a lagoon. Sediments also accumulate in front of the jetties – and are consequently dredged to maintain the navigation depth along the Sulina channel. Therefore, in this strategic sediment reservoir two main sources of sediments were identified:

  1. sediment dredged for maintaining the navigation;
  2. sediment accumulated in the vicinity of the Sulina jetties.

Quantitative State Concept:
In order to restore the equilibrium of the coastal zone the volume of sand lost from the system every year has to be replaced. 

Update activities and recent research findings

  1. investigation of the hydrodynamics and sediment circulation in the Sulina – Sahalin area using state-of-the-art numerical model DELFT3D;
  2. conference paper presented at International Conference on Coastal Engineering, Hamburg, September 2008.

Favourable sediment status and coastal resilience
The sediment budget of the pilot site indicates a lack of approximately 1 million m³ of sand every year. When the Danube Delta coastal zone was not affected by human interventions, a large part of this volume was replaced by sediment discharged by the Danube River. Artificial nourishment of the beach can compensate partially or totally this loss, resulting in stability of the beach.