Project To Improve Water Quality At Brno Dam Enters New Phase

The project to clean the reservoir began in 2010. Credit: Zdenek Kolarik, Brno City Municipality.

Brno, Aug 31 (BD) – A new phase has begun in the project to improve the water quality at the Brno Dam, known locally as přehrada.

The main problem of the Brno Reservoir for a long time was green cyanobacteria, caused primarily by the high amount of human-produced nutrients flowing into the reservoir, and also high eutrophication of the reservoir. These cyanobacteria polluted the entire water area and made recreational use of the area impossible, especially during the summer season. Since 2010, a joint project of the South Moravian Region, the City of Brno and Povodí Moravy has been working to improve the water quality of the reservoir, and make it safer for swimming. This project entered its fourth phase this year.

The system used to clean the dam’s water is based on two key elements: ferric sulphate dosing, and the operation of mixing and aeration towers. Monitoring of the water quality in the reservoir has confirmed that these measures are effective. The Ferric sulphate dosing, which limits the spread of phosphorus into the water reservoir, will continue. “Phosphorus precipitation works very well, and it is clear from the detailed data that most of the dissolved phosphorus is captured by the coagulant and does not enter the tank as a major nutrient for cyanobacteria development,” said the general director of Povodí Moravy, Václav Gargulák.

Adjusting the aeration system and increasing the number of mixing towers will lead to more efficient mixing of the water column, which will make it even more difficult for cyanobacteria to multiply. In the first phase of the intensification of the aeration system, five existing aeration towers will be gradually replaced by mixing towers, and one new mixing tower will be added in Rakovecká Bay. The water managers are preparing the new tower for installation below the level of the Brno reservoir at the end of August. 

“High temperatures, low inflow into the tank and high transparency for a long time encourage the development of cyanobacteria,” said Gargulák. “The aim of increasing the number of mixing towers is to mix the warm and oxygenated water near the level where the cyanobacteria thrive with the colder water, which slows down the development of cyanobacteria and at the same time positively oxygenates the lower oxygen-free layers of the tank.”

The phase started this year is intended to adjust and strengthen the functioning of these measures, which began in 2010, when the aeration system and precipitation of phosphorus were started for the first time. “The results from previous years show that the system is working,” said Deputy Mayor of Brno Jaroslav Suchý. “However, we are continuously working on improving it and making it more efficient. Before we started this project at the Brno dam, it was usually only possible to swim in the reservoir until the beginning of July, after which the Regional Hygiene Station announced a ban on swimming, mainly because of the overgrowth of cyanobacteria and the massive occurrence of water bloom. Since 2010, we have managed to maintain the water quality in the reservoir at good values ​​throughout the bathing season.”

The fourth stage of the project to maintain water quality and equilibrium was launched in May this year. Despite the high temperatures and low water inflow into the reservoir, it was possible to maintain the water quality in the reservoir at levels one (water suitable for bathing) and two (water suitable for bathing with impaired sensory properties) on the five-point scale. It was not until the end of August that the Regional Hygiene Station rated the water in the Brno Dam as level three (deteriorated water quality).

Approximately CZK 16 million is set aside for each year of the project, with the costs shared equally by the City of Brno and the South Moravian Region. The operation of the measures and the regular, detailed monitoring of water quality is carried out by Povodí Moravy, sp. 

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