Early warning of bathing water quality - an operational water forecast service

Faecal pollution of recreational water is a worldwide problem posing risk to human health. Therefore regional and district councils in New Zealand monitor the hygienic water quality at 350 coastal recreational sites every summer. Samples are typically collected once per week to test for the concentration of the indicator bacteria enterococci. These test results show that recreational waters are not always safe. In addition management is retrospective as the results of the testing are not available until after human exposure to the hazard. To overcome the latter problem operational modelling of the water quality today and in the coming days is now applied at several recreational sites in Denmark and Sweden. This Bathing Water Forecast supports the daily management of the sites and provides the authorities with a tool for timely warning of bathers when human health is at risk. Results are published on the internet, smartphones, Facebook and by direct emailing. Important inputs are actual data on loading and meteorological forecasts. The core of the system – a combined hydrodynamic and water quality model – is also a strong tool for assessment of cost-effective investments to reduce the risk of pollution, i.e. to improve sewer systems. This presentation will describe the Danish Bathing Water Forecast and discuss experiences.