Normandy Reservoir

Ecological health rating

Normandy Reservoir rated poor in 2008, consistent with the poor to “low fair” ratings in previous years. Historically, the main issue has been low dissolved oxygen. In 1994, TVA installed aeration equipment to add oxygen to the deep water near the dam and to improve conditions in the Duck River downstream from the dam. A new, larger compressor and four new diffuser lines were added to the aeration system in 1997. Two of the new diffuser lines extended upstream near the sampling location.

Little variation in reservoir condition or individual indicators was observed from 1993 to 1996. However, three indicators exhibited a marked change between that period and the 1998-2008 period, which was presumably due to the added aeration in 1997. (Monitoring was changed to an every-other-year rotation after 1996). The results are discussed below.

TVA monitors one location on Normandy Reservoir — the deep, still water near the dam — usually on a two-year cycle.

Normandy Reservoir Ecological Health Ratings, 1994-2008

Click chart for raw data.

The table below shows the ratings for individual ecological health indicators at Normandy in 2006. These ratings are briefly explained in the paragraphs that follow.

Ecological Health Indicators for
Normandy Reservoir, 2008

Monitoring location

Dissolved oxygen

Chlorophyll

Fish

Bottom life

Sediment

Forebay

Dissolved oxygen

As in previous years, dissolved oxygen levels near Normandy Dam rated poor. However, the volume of water affected in 1998-2008 was significantly smaller than in previous years. This was the result of an aeration system that added oxygen to the water and also helped reduce the difference in temperature between the oxygen-rich water near the surface and the low dissolved oxygen water near the reservoir bottom, allowing the two layers to remain mixed for a longer period of time.

Chlorophyll

The good ratings for chlorophyll changed to poor in 1998-2008 due to a substantial increase in concentrations. It is plausible that the chlorophyll increase is due to an upwelling of nutrients from the lower water column caused by the aeration system.

Fish

The fish community rated good, as in all previous years.

Bottom life

Bottom life rated at the upper end of the poor range in 2008. The consistently poor rating for bottom life changed to fair in 1998-2006, probably because of improved dissolved oxygen conditions. Both the number and variety of organisms collected showed improvement. However, a shift in ratings from fair to poor between 1996-2006 and 2008 was the result of a slight decline in the variety of organisms collected, indicating that episodes of low dissolved oxygen on the reservoir bottom during much of the summer continue to impact the density and composition of the community of animals present.

Sediment

Sediment quality rated good during all monitoring periods except in 2002, when sediment samples contained low levels of chlordane, and arsenic concentrations were slightly higher than the expected background concentration. Chlordane is a pesticide previously used to control termites and crop pests.

See definitions of ecological health indicators and monitoring locations.

Fish consumption advisories

There are no fish consumption advisories on Normandy Reservoir. TVA collected channel catfish and largemouth bass from the reservoir for tissue analysis in the autumn of 2006. All contaminant levels were either below detectable levels or below the levels used by the state of Tennessee to issue fish consumption advisories. TVA will analyze fish from Normandy again in the autumn of 2010.