Hamr na Jezeře

Application of ultrasound on Lake Hamr

  • Client: Municipality of Hamr na Jezeře
  • Location: Hamr na Jezeře
  • Duration: 2018
  • Total cost: 298,000 CZK

Hamr na Jezeře is a very popular tourist region, often called the Riviera of the North. The property of the municipality includes a local lake and an adjacent camp with a sandy beach. The surrounding flat countryside is inviting for cycling. Tourism is an important source of finance for the municipal authorities. The Mayor of Hamr na Jezeře is aware of this fact and is trying to fight against cyanobacteria in the long-term. This is done mainly by selecting and regulating fish stocks, applying physical methods to reduce the growth of cyanobacteria, and attempting to reduce nutrients flowing into the lake. Despite these measures, cyanobacteria have appeared in recent years mainly due to the shallow depth of the lake (2 m).

As a further measure, the Municipality of Hamr na Jezeře has chosen ultrasound. In May 2018, we installed two autonomous ultrasound floating units powered by a small solar power plant on the lake. Solar energy powers the ultrasonic transmitter not only during the day but also thanks to batteries at night. The ultrasound wavelength of each unit is 400 m in each direction. Each unit treats a radius of 800 m. Due to the positive results of ultrasonic application, the municipality plans to double the number of ultrasonic transmitters on the water surface in 2019.

In order to assess the effect of ultrasound on Lake Hamr, data from 2017 before the ultrasound application and from 2018 when the ultrasound was applied were compared. Compared to 2017, 2018 was characterized by lower total rainfall, a significantly higher degree of sunshine, and with it, higher average temperatures (e.g. April 2018 exhibited the same temperatures as May 2017). From a meteorological point of view, therefore, 2018 was significantly more favourable for the development of cyanobacteria than 2017.

Nevertheless, the occurrence of cyanobacteria was significantly reduced. The increasing trend of cyanobacterial concentrations was completely suppressed by the installation of the ultrasound technology. One single significant occurrence of cyanobacteria was recorded by a single round of sampling in mid-July. Even during this period, there was no the occurrence of water blooms on the surface of Lake Hamr, so the bathing season was not significantly affected by this increase. The water treated with ultrasound therefore was pleasantly cooling for visitors to Lake Hamr in the summer. The municipality’s satisfaction with the application made it possible to extend the contract to 2019 and increase the number of ultrasonic transmitters on the water surface. Water sampling and analyses were carried out by the independent laboratory of the Institute of Health, located in Ústí nad Labem.