Coastal lagoons, encompassing nearly 13% of the world's coastline, represent a vital ecosystem for a considerable variety of flora and fauna. The appealing environment of coastal lagoons has resulted in the establishment of numerous communities around them. The intensification of extreme events due to climate change, the expansion of urban systems, and the release of more pollutants into surface water have altered the natural dynamics of the system. These alterations increase the challenges regarding water safety and quality. Therefore, it is genuinely important to ensure the long-term survival of coastal lagoons. Coastal lagoons are shallow waterbodies parallel to the coast, separated by a small barrier and connected to the sea or ocean by one or multiple inlets. Their behaviour is influenced by the tides, freshwater discharges, wind, geometry, and bathymetry. In a well-functioning lagoon, the water is of sufficient quality, and the surrounding area lives harmoniously with the lagoons, meaning fishing activities are balanced with the lagoon, and the surroundings can cope with floods and droughts.

The Ciénaga de la Virgen in Cartagena, Colombia, is a prime example of a coastal lagoon that faces problems such as pollution, contamination, floods, and droughts, which are common in the area. The consortium ConAgua had proposed multiple measures to enhance the natural dynamics of the Ciénaga, commissioned by the Dutch governmental organisation Rijksdienst voor Ondernemend Nederland.

This report analysed the influence of those measures on the water safety and quality of the Ciénaga.
As part of this, the lagoon and its behaviour were simulated using the numerical hydrodynamic model Delft3D. The measures were implemented in this program, and by altering the boundary conditions, the effects of each measure under different circumstances were evaluated.
The implemented baseline model represents a dry month, normal tides and current bathymetry. Modifications were adapted to evaluate the effect of the limited data and observe the impact of extreme rainfall, sea level rise and wind forcing. Combinations of measures and their behaviour were also simulated.
For the water quality, the flushing time was considered by means of a tracer. Inserting a passive tracer, which either indicated polluted water (1) or clean water (0) into the model, made it possible to analyse the reduction and/or mixing of the pollution. For water safety, the rise in water level at any observation point within the Ciénaga was compared to the baseline model without measures, and the maximum water levels within the month were considered.

The simulations showed a significant impact of tides, wind, and sea level rise on the behaviour of the lagoon. Incorporating wind showed an improved refreshment rate due to the enhanced mixing and altered the plume formation into the Caribbean Sea. However, there are windless days on which the advantage of wind may not be taken into account.
Other simulations, such as the simulation of the combined measures, showed that combinations are not merely the sum of the individual measures and their effect, but the total hydraulic behaviour is altered.
Furthermore, the importance of a clean discharge from the urban and rural side into the Ciénaga was demonstrated. Due to the low refreshment rate, polluted water lingers inside the Ciénaga for a long time, affecting the ecology and the health of the surrounding residents.

In short, the rate of improvement of the water quality by the measures is limited, because the effects remain local. Therefore, achieving water of proper quality is a challenge. The measures did not negatively influence the water levels inside the Ciénaga. For flood risk, it is important to prioritise other effects since it remains a problem in the area.


The report shows that preserving healthy lagoons worldwide is important. To maintain proper water quality, the input of clean freshwater and sufficient mixing due to tidal (ensured by inlets) and/or wind forcing is important. Likewise, the effect of floods and droughts should be limited since many people live near the lagoon. However, water safety cannot be assessed solely by the water levels inside the lagoon. Models can help to assess challenging problems regarding water quality and safety in complex lagoon systems. In future steps, it is recommended that more data be gathered through measurements and observations to assess the quality of the lagoon with more certainty.

Playa Unión and Puerto Rawson are facing severe coastal erosion and increasingly the negative effects. Since the first half of the 20th century there have been signs of erosion, but also of sedimentation. However, the coastline in the project area is retreating over the years. The situation has recently been declared an emergency. Furthermore, there are several expansion plans for the port consisting of new quay walls and dredging. It is unsure if these plans will influence the erosion. In this report, the following research question is formed: ”What are valued, preferably nature-based, interventions that can mitigate the coastal erosion in Playa Unión and Puerto Rawson considering the planned expansion of the port?” Due to the limited information and data available, assumptions have been made during the research. A site analysis and a CoastSat analysis are conducted to research the morphology of the coastline and its drivers. The coast has been shaped into a steep upper section of coarse granular material and a gentle lower slope with finer material. The main driver of longshore sediment transport in the area are swell waves, with predominant directions SSE and E. This transport is directed from south to north, resulting in the inflow and outflow of sediments. Furthermore, there is a sediment flow from the Chubut river. Due to the construction of the port’s breakwaters, the longshore sediment transport is interrupted, which causes an imbalance in the sediment flow in the system. More sediment flows out of the system than enters, causing coastal erosion. The development of the port contains public as well as private expansion plans and maintenance dredging. The expansion plans will have little effect on its surroundings. The private plan include a parallel breakwater, which alters the natural balance in the area and dredging works, for which the stability of the existing breakwaters has to be figured out. A stakeholder analysis was done to get insights in the opinions and visions of the stakeholders. This was done by interviewing stakeholders and by doing a questionnaire, resulting in a power-interest grid and overview of interests and attitudes. The boundary conditions for the interventions and criteria for the multi-criteria analysis are partly formulated as a result of the stakeholder analysis. The following interventions were considered in this report: • Permeable pile groynes and low crested groynes
• Opening the northern breakwater: opening and reshaping with a curve, constructing tunnels underneath the breakwater and a sediment bypass
• Port expansion and a sediment bypass with power supply southern of the port
• Dredging and moving sediment
• Sediment trap
• Plant vegetation with beach nourishment
• Gravel engine
• Temporary longitudinal flood barrier as a short term intervention.
A conceptual multi-criteria analysis in combination with a nature-based assessment has been conducted to distinguish the most promising interventions in the conceptual design phase. The criteria formulated were effectiveness, easiness of implementation, maintenance, environmental impact and the benefits for recreation. From this, it can be concluded that the gravel engine and the plant vegetation with beach nourishment score the best.