Nosara, Nature

“The possibility is always going to exist that an event will exceed the capacity of the dike in Nosara,” says the engineer in charge of the work

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Translator: Arianna Hernandez

The government began the final reconstruction of the Nosara dike a month ago. The work became necessary because the original infrastructure’s hydraulic capacity failed due to lack of maintenance, which made it completely ineffective.

Although the Office of the Comptroller General of the Republic approved the budget back in 2019, the National Emergency Commission (CNE) together with the National Irrigation and Drainage Service (SENARA) didn’t start the work until now due to budget errors that weren’t resolved until April 2020, at the beginning of the pandemic and the end of the dry season. That’s what the president of the Nosara Integral Development Association (ADIN), Marco Avila, explained to The Voice in 2020.

The CNE estimates that the new infrastructure will be completed this year in May, just before the first rains of the season. In total, the institutions will invest ¢1,161 billion (about $1,935,000) in rebuilding the dike.

In 2020, The Voice published an investigative report on a hydrological study by the National Meteorological Institute (IMN) that argued that the dike was not effective and that, even in areas where the structure exists, the river can flood with much less rain than what was projected by SENARA.

We discussed this issue and the new infrastructure’s details with the engineer in charge of the work, David Barrantes, who is a member of the CNE. Barrantes affirmed that it’s worth the investment even though the dike isn’t a definitive solution to the floods because “the idea is that it protects the community and improves its conditions.”

This is an excerpt from the interview with the expert:

What does repairing the Nosara dike involve?

The project consists of restoring approximately 2.2 kilometers (1.4 miles) of the dike, mainly in the vicinity of the airport and Santa Marta. In the airport area, there are 1,000 meters (0.6 miles) [of work] that includes cleaning, moving dirt, restructuring the riverbed and building a series of deflectors, stone structures that basically work by gravity, which are intended to protect one of the most vulnerable faces of the dike. There are a couple of minor intervention projects, and the condition of some sewer exits will be improved to prevent tributariesstreams or secondary riversthat fill the sewers from generating any potential damage to the dike.

In the Santa Marta sector, it would be 1.2 kilometers (0.75 miles) of intervention and that is where there is perhaps a slightly more complex task in terms of restoration work. It’s a challenge because since it’s an area where there are more houses near the dike, conserving those houses requires a level of technical complexity to implement it. Likewise, we’ll clean the river, improve the banks of the dike and build two walls, which are gravity retaining walls that will be made of stone. They are going to be retained by a concrete mixture to secure the blocks and protect the houses.

How was the dike when you started reconstruction?

The Nosara River is a river that fills up quite a bit in the rainy season. It carries sediments and those sediments accumulate. As sediments accumulate, the function of the dike is reduced from year to year, and the accumulation of materials wasn’t being removed. That was increasing the flow of the river. That was because the Municipality of Nicoya didn’t maintain the river flow. In other words, what has happened here is that there has been an accumulation of several cubic meters of material that has been reducing the dike’s capacity.

In general, let’s say the dike was being functional, at least in its structural capacity, but the hydraulic capacity had problems and that caused it to overflow. In conclusion, it was not 100% damaged but it did need very severe maintenance.

Will the dike be a definitive solution to the problem of flooding in Nosara?

I’d love to give you an answer to that. I’d love to say that there will never be problems again and that it’s a solution forever, but that’s not the reality. First, the climate elements that we’ve seen in recent years are going to continue to happen. For example, like Eta. They are events that are reaching very high return periodsthe hydraulic design term to measure the magnitude of natural events. They are events with return periods of 100, 50 years, longer each time.

It is important for the community to know that the idea of ​​the work is obviously to minimize their risk of flooding. The possibility is always going to exist that an event exceeds the normal conditions that the dikecan withstand. The idea is to safeguard as much as possible the integrity of not just the dike, but also the neighbors and the area that is constantly hit.

Construction started on February 15 after a year’s delay due to budget errors | Roberto CruzPhoto: Roberto Cruz

How do you plan to maintain the integrity of the levee?

We are talking with the Municipality of Nicoya so they can look after it after this work, so they include an annual maintenance plan for the dike, so these works guarantee precisely that integrity and the proper functioning of the work. From now on, it’s a work that includes multiple factors and people involved, and all of them need to be collaborating on these solutions. I can’t guarantee that this is a definitive solution, but the point is to collaborate as much as possible to reduce those events.

Which environmental studies support this repair?

This is a project supported by Law 8488. This law supports non-ordinary projects that are done in response to an emergency. Therefore, by law, there are studies that are not required for this type of project. In this case, the environmental impact that the current project would have, I understand that it’s the same one consulted in the original project.

Where were the most critical points shown on the dike?

Right in Santa Marta, under the bridge. Let’s say the previous structure had quite a bit of damage. In fact, the structure there needed many design adjustments. We made modifications to the original design because a part of the dike there had been almost completely affected as it was closer to the houses. At the moment, there isn’t greater risk of a natural event happening in that place, but that point was definitely very affected.

What can we expect from the dike when the work is finished?

The idea is basicall to build a structure that protects the community from the effects typical of the rainy season, knowing that there are constantly natural disasters in these sectors. For those events that happen regularly in the area, the idea is for [the dike] to protect the community, to improve living conditions and to last over time.

The thinking in the repair of the dike is that it won’t be affected again like it was, that it will last a long time with the new maintenance that we agreed on with the people involved. We have to remember that without maintenance, the [dike] isn’t going to work. Our plans are designed to last, but maintenance is necessary.

Are there plans to intervene on the dike again in the future?

Not in this case, because the dike is under the protection of law 8488, which talks about emergency interventions. In other words, we continue to repair it due to the project approved by the event of Hurricane Nate. So in theory, this would be a final intervention. The only thing I would say there is that for that reason we need the support of the Municipality for future maintenance, but after this there are no more plans to intervene.