Portugal: Leirosa Coastal Dune Restoration

Project Stage:
Implementation

Start Date:
2000-03-27

End Date:
2007-12-27

Primary Causes of Degradation

Degradation Description

The Leirosa sand dune system was damaged as a result of construction on a submarine outfall pipeline for two nearby industries. Heavy machinery was used to excavate a channel for the new pipeline across 80 meters of dune area. This disturbance, along with continuing erosion caused by a breakwater 1 kilometer north of the site, necessitated the partial reconstruction and revegetation of the dunes in March 2000. In the winter of 2001, just months after the successful completion of this rehabilitation project, a severe storm completely destroyed the oceanic side of the newly rebuilt sand dune.

Project Goals

To restore and stabilize the Leirosa sand dune system

Monitoring

The project does not have a monitoring plan.

Stakeholders

The dune system is the natural protection for the deaeration and load chamber of the outfall pipe installed to channel effluent from operations at Celulose Beira Industrial (CELBI), S.A. and Portucel Soporcel, two local industries. Because the dunes play such an important role in the hydrologic system that allows for the proper discharge of effluents, these two industries are the primary stakeholders in this project.

Description of Project Activities:
PHASE 1 (2000) The rehabilitation of the Leirosa sand dunes began in March 2000 with the mechanical reconstruction of the dunes in a process known as AIDS--Artificially Inseminated Dune System (Carter, 1995). This process allows for the reconstruction of dunes to desired heights and slopes in a relatively short period of time. For three weeks, sand was brought from a close inland site, and the foredune of the Leirosa system was rebuilt in an extension of about 200 m. The sand used for the reconstruction was very similar in texture and nutrient content to the sand already found on the Leirosa dunes. In an attempt to help control erosion, a walkover with stairs was constructed on the dunes to allow people access to the beach. A fence made of pine planks was also constructed across the top of the dunes to help control human traffic. Planks were placed 8 cm apart to create the 50% porosity advised for projects such as this (Dewhurst, 1999). With the sand accretion phase complete, revegetation with transplants of Ammophila arenaria (L.) Link was conducted in order to help stabilize the dune system further. A. arenaria is widely used on the European coast for this type of revegetation, as it is easy to collect, transplant and propagate rapidly (van der Putten, 1990). Its complex root and rhizome system help stabilize loose sand and thereby protect against coastal erosion. Dune plants are not commercially available in Portugal, and therefore transplants for this project were taken from well-preserved dune systems at Osso da Baleia, a few kilometers south of Leirosa. Plants were collected manually, using vertical spades to gather as much root material as possible. A dispersed pattern was used, removing individual plants at intervals not closer than 50 cm in order to minimize the impact caused to the system. Plants were collected in the morning and stored in large plastic bags with wet sand in the bottom. Transplanting in the Leirosa dunes was done every afternoon, so that plants would not be stored overnight. With small shovels, holes of about 20cm-depth were made, and after adding a very small amount of fertilizer, one or two shoots of Ammophila arenaria were dibbled. Since the slope of the dune was rather steep, a close pattern of 50 cm in a diagonal grid was chosen for the revegetation. The transplants were only placed where no other vegetation previously existed. The slow-release grain fertilizer "Osmocote" was used, but no more than 100 Kg/ha was deployed (Seliskar, 1995). Revegetation began in the last week of April and lasted for approximately five weeks. Adjacent areas were also revegetated in an attempt to recover the complete system The Spring of 2000 was characterized by heavy rain in March and April, and this made for humid soil that proved a great advantage to the transplants' adaptation. Monitoring activities commenced in June 2000 and aimed to characterize and quantify the evolution of the dune system. The restored area was divided into continental and oceanic sides, in order to determine the efficiency of plant recovery in both sides of the foredune, and transects perpendicular to the coastline were established. All aspects related to the individual shoots of A. arenaria were documented, as was the appearance of any new species. Graduated wooden poles were also placed at intervals over the dune to measure sand mobility. PHASE 2 (2005) After a severe winter storm in 2001 destroyed the entire seaward side of the newly restored dune, the decision was made to install geotextiles as a means of providing more durable protection from future disturbances. Geotextiles were installed along a 120-meter extension of the coast. A defense was created on the front bottom of the dune, at the +2.0 level (hydrographic zero), with sand containers about 6.40 meters in length, 3.20 meters in width and 0.825 meters in height placed in a pyramidal position parallel to the coastline. The protection barrier was constructed to the height of 8 meters using several layers of sand involved in geotextiles, in a so called "wrap around technique", which encapsulates the sand and offers a high installation speed. The upper layer has a geotextile revetment in all the area, with about 8.60-meter length, 4.30-meter width and 1.10-meter height. On the top of the geotextiles, a 1-meter layer of sand was deposited, and Ammophila arenaria transplants were introduced into this layer. The revegetation procedure was similar in all respects to that which was conducted in 2001, except that transplants had to be watered this time. The revegetation work occurred in an area of 3000 m2, and it was conducted by four experienced gardeners over three weeks. It started in March/April to allow the complex root and rhizome system of A. arenaria to better develop before the beginning of the next winter period. Although it is not very common and necessary to water the dune systems when revegetation is performed, some irrigation was included this time due to the very dry winter of 2004/05. A container with a 4000-liter capacity was used to moisten the sand before transplantation, at the beginning of every working week. Monitoring activities associated with this phase of the restoration were similar to those conducted under the earlier phase. All aspects of the transplants' development were recorded, along with patterns of sand mobility, as indicated by the graduated wooden measuring poles.

Ecological Outcomes Achieved

Eliminate existing threats to the ecosystem:
The initial restoration and revegetation (2000) resulted in a total of 23,250 A. arenaria transplants,17,200 on the continental side and the remainder on the oceanic side. After 4 months, a survival rate of 40% was observed, which is considered a significantly high rate of success (Dewurhst, 1999). During the summer months immediately following plantation, a decrease in the number of green plants was documented. However, this decrease was most likely due to hot weather, as the number of green plants began to rise again in September, indicating that plants had not actually died but were just subjected to stress from transplanting and weather conditions. The reconstruction of the foredune allowed a stabilized ecosystem in the back, aided by almost nonexistent sand mobility. A similar situation did not occur in the oceanic side, where significant sand accumulation was found during the first phase of the monitoring program. With the passing of the winter storm in 2001 and the near-total destruction of the oceanic side of the dune, monitoring activities continued on the continental side. While intensified erosion from the loss of sand and plant cover was observed on the oceanic side, results on the continental side were encouraging. A stable dune was formed in little more than one year, and 13 plant species were identified in March 2001, including Ammophila arenaria. In March 2002, the number of species had more than doubled, totaling 32. Plant cover during this monitoring period was estimated at an average of 42.8% in the established plots. This figure is significantly high when one takes into consideration that revegetation was concluded only one year prior, and that the storm destroyed part of the rehabilitated dune. After the installation of the geotextiles in 2005, monitoring activities resumed, employing the same methodology as those already mentioned. In only six months, eleven plant species had colonized an area where only Ammophila arenaria was planted: Artemisia maritima, Calystegia soldanella, Crucianella maritime, Pancratium maritimum, Elymus farctus, Medicago marina, Silene littorea, Eryngium maritimum, Polygonum maritimum and Euphorbia paralias. Sand mobility was again evaluated using graduated wooden poles arrayed along tansects on the top back, top front and base of the dune. After six months, some distinctions were noted between the three defined zones, namely that little or no mobility occurred on the top of the dune while accumulations of about 4 to 6 cm of sand were observed at the base of the dune.

Factors limiting recovery of the ecosystem:
The first and most notable factor limiting the recovery of the dune system is the winter storm of February 2001 that completely destroyed the oceanic side of the newly rehabilitated dunes and rendered that earlier project futile. More recently, problems have arisen with some of the geotextile units. In March 2006, several units in the bottom three layers of the dune came open after high tides and the resulting hydrodynamic pressure. The opened areas allowed an outflow of the sand fill material, which precipitated a partial collapse of the dune structure and a settling of geotextiles from the top five layers. The cause of this breach is thought to be inappropriate sealing of the geotextile layers, which was done partly in conditions of high humidity.

Socio-Economic & Community Outcomes Achieved

Key Lessons Learned

It has been shown that the use of geotextiles can be as effective as any so called “hard engineering protection,” with the added advantage of being adaptable to the morphology of the dune system and using locally available sand (Bleck et al., 2003). Furthermore, this method saves time and money, and its visual impact is considerably less than other coastal protection measures such as stone revetments and seawalls. This was the first project in Portugal to use geotextiles for dune protection, and the technique was found to be complementary to revegetation efforts and potentially useful in other dune systems with similar erosion problems.

Long-Term Management

The next step will be the rehabilitation of the geotextile-reinforced sand dune in the areas where the encapsulated sand layers have partially opened up. A proposal is currently being considered for rehabilitation with large geotextile tubes (which are prefabricated to avoid failure of the joints) filled with a suspension of sand and water and placed at the bottom of the existing structure as toe protection.

Sources and Amounts of Funding

191,370 Euros Funding for project activities was provided by Celulose Beira Industrial (CELBI), S.A. and Portucel Soporcel, Figueira Mill, two industries with production facilities in Leirosa.

Other Resources

João Rebola
Celulose Beira Industrial, S.A. (CELBI)
Leirosa
3081-853 Figueira da Foz
PORTUGAL
Telephone: + 351 233 955 600
Fax: + 351 233 955 648
E-Mail: joao.rebola@celbi.pt
Website: www.celbi.pt (under construction)

Instituto do Mar (IMAR)
http://www.imar.pt/

Primary Contact

Organizational Contact