In what way can the water behind the dam maintain the same salinity, so that it has as little impact as possible on the current ecosystem?

PROJECT DELTA

Project Delta

Sea level rise is a well-known problem all around the world. People are expecting that the sea will be raised by 3 meters by 2100. There are enough reasons to think about the consequences that the sea level rise will bring. This also applies to the Delta city of Rio de Janeiro in Brazil, which will largely be flooded without adjustments. A good reason to let the engineers of the future, brainstorm about possible solutions. Students from Rotterdam University of Applied Sciences in the Netherlands and Universidade Veiga de Almeida in Brazil have been thinking about this solution during the Preventing Delta Floods project in November 2021.

During the Delta Project, the student of Rotterdam University of Applied Sciences will continue to further develop a part of the solution from the Preventing Delta Floods project. The solution created during this project is to close the bay through a dam. As a result, a large part of Rio de Janeiro and the surrounding area are protected against the 3-meter sea-level rise. However, closing a bay has consequences. One of these consequences is the decreasing salinity in the water behind the dam, which will have an impact on the ecosystems, among other things. To avoid this, the following question will be answered during the Delta Project:

In what way can the water can the water behind the dam maintain the same salinity, so that it has as little impact as possible on the current ecosystem?

Preventing Delta Floods

Preventing
Delta Floods

Before thinking about the consequences that are created behind the dam, this dam was first conceived and elaborated during the Preventing Delta Floods project. During this project, there was weekly contact between Dutch and Brazilian students about the question "How can we protect Rio de Janeiro against a 3-meter rise in sea level?"

By closing off the bay near the Rio-Niterói bridge, 195 kilometers of the coast will be protected against the high water. This 9.5 kilometer long dam will replace the Rio-Niterói bridge when it reaches its 100-year lifespan. In addition, the dam will also facilitate a new metro connection, providing a better and faster connection between Rio de Janeiro and Niterói.

By choosing this location, the harbour and navy base remain available for ships. Two sluices will be installed to provide shipping to the part behind the dam. The water level inside the closed bay will be maintained by pumping stations. Furthermore, a fish passage will be placed to make it possible for the fish to enter and leave the closed bay.

In addition to the dam, there are several smaller solutions that together protect Rio de Janeiro. These are:

Raised Quay Walls
Raised Quay Constructions
Dunes
Oysterbanks with Mangroves

Sea level rise in 2100

9.5km

Lengte of the closure dam

sluices to enter the bay

Multiple

pumping stations

Possible Solutions

Artificial Tide

In order to fully imitate the current tide and create an artificial tide, a water level difference of 80 centimeters must be achieved over an area of 300 square kilometers in six hours. The water intake takes place under gravity. It is also possible to generate electricity through turbines. The water is lowered through pumps. This is done by pumps with a maximum pump capacity of 50 m3/s. To simulate the tide, 250 pumps are required, which together have a length of 2.5 kilometers. Pumping a large amount of water also requires a great deal of energy. The 250 pumps consume as much per day as 1000 Dutch households consume in a year. The estimated cost for the required energy is 56.5 million euros per year.

Inserting a calculated amout of salt water

In option two, the amount of water in the bay is determined by the required salinity. The graph above shows how in the course of time the salinity stagnates in the normative month of January. In order to realise this, 4500 m3/s must flow into the bay every other day and a half. In the other half day between the intake, 3280 m3/s must be pumped out of the bay. By generating electricity from turbines during the water intake, the annual costs for the electricity amount to 11 million euros.