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River Tay Water Temperature at Dams Project

In 1999 / 2000 the Tay Foundation supported an investigation into water temperatures in two dammed tributaries of the River Tay – the River Lyon and the Errochty Water.

Loggers which measured the water temperature every hour were installed.

Both the Lyon and the Errochty are maintained by compensation flows which are drawn from the lower levels of hydro reservoirs, the dams on the Errochty and the Lyon being the highest in the Tay system. The study showed that in spring and summers the temperature of the water close to the dam displayed a relatively low daily variation and was relatively cold. Natural temperatures would have been higher as evidenced by the fact that going progressively downstream temperatures did warm up because of warming by the sun and the inflow of natural tributaries. In winter, however, the dam water was relatively warm.

In the spring the temperature of the water issuing from the dams tended to rise over time in a stepped manner. The temperature might remain relatively constant for days or weeks then suddenly rise. The steady periods tended to coincide with warm weather and the jumps with cooler weather. This shows that during warm weather these reservoirs become stratified, i.e. warm water basically floats on top of cold water, but when a depression passes over the waters become mixed so the bottom water temperature increases.

The unnatural temperature regime below these dams will have ecological impacts.

termp data


Daily water temperature readings on the Errochty Water, mid March 2000 to mid June 2001. Dark green line represents average daily temperature near the dam at Trinafour (light green line represents hourly temperature readings) and the red line represents average daily temperatures at a location approximately four miles downstream from Trinafour (orange represents hourly readings).



Hourly temperature readings at three sites on the River Lyon April / early May 2000. Lubreoch Dam is the source of the flow, Kenknock is approximately six kilometres downstream and Invervar is approximately 25 kilometres downstream. The Fillan Water is a neighbouring unregulated catchment used as a control. Comparing the Fillan with Invervar, Lyon temperatures have more of less naturalised by that distance, but in the upper Lyon there was a significant impact on temperature at this biologically important time of year.