Impingement is the general term used for the collision of organisms with the filter screens protecting the water intakes. Typical fine screens have a mesh size of about 1 cm, and will retain most adult fish and crustaceans. In many power stations impinged animals are killed in large numbers. Fish kills are typically in the hundreds of thousands to millions per year, while shrimps, prawns and other crustaceans are impinged in millions of individuals per year.
Problems & examples
The principal environmental concern relates to the loss of fish and the resulting damage to the local populations. Such problems are likely to be particularly marked in small lakes or estuaries, and in coastal regions where direct-cooled power plants are concentrated. Read our feature Are coastal power stations affecting Northern European inshore fish populations? which analyses the issue in British and Northern European waters. See also our reports on Hinkley Point, where Pisces staff studied impingement every month for 39 years.
Pisces have acted as advisors to a variety of organisations on impingement including Riverkeeper in the USA and EDF/British Energy in the UK. For information on how Pisces could help you, please contact us.
We produce the commercially available PISCES expert system (see Prediction, below) to predict impingement rates.
Solutions
A variety of technologies have been tried to reduce impingement. Wedgewire screens can be placed at intakes to prevent impingement mortality. When properly designed they can be highly effective.
However, they have not been used on the largest intakes and are unsuitable for marine and estuarine environments where biofouling is a problem.
Sound deterrent systems for fish have also been used, but are rarely sufficiently effective.
The most effective way of managing impingement is to reduce the volume of water pumped, and if necessary to arrange partial or complete shutdowns at times of the year when large numbers of fish are regularly impinged.
Prediction
The PISCES expert system to predict fish impingement in cooling water intakes in N. European waters was developed by Pisces Conservation, based on decades of data on actual catches. Our software is based on our unrivalled database on power station impingement plus the extensive experience of our staff.
The PISCES expert system is available for lease or purchase - please contact us.
Planning: We have provided computer predictions of levels of fish impingement at proposed power station sites around the UK, using our own software.
Ongoing monitoring programs: We are carrying out monitoring of fish impingement (including salmon/trout smolts), entrainment, water quality, and the causes and impacts of CW discharge foaming, at a number of UK power stations.
Intensive impingement studies: We have completed 4 years of intensive 24-hour impingement samples at 2 UK nuclear power plants, in connection with the proposals for new-build nuclear stations, providing an unparalleled volume of data on fish impingement.
Pisces is internationally recognised as expert in the prediction and minimisation of impingement effects from both environmental and operational causes.
Pisces can provide advice and expertise on the full range of environmental and operational issues - please contact us for further information and assistance.