Rainfall and Runoff

The amount of water in the Tennessee River system and its reservoirs depends on rainfall and runoff. Runoff is the portion of rainfall that doesn’t soak into the ground but drains from the surrounding lands into streams and reservoirs.

In early spring, we need plenty of rain to fill the tributary reservoirs, and summer storms help keep reservoir levels up and adequate water flowing through the system. However, meeting flow requirements can be a challenge during the summer. Summer storms generally bring less rainfall than winter ones, and more rainfall is absorbed by the roots of green plants before it can drain into streams, rivers, and reservoirs.

Even in summer, however, flooding is still a concern. The higher reservoir levels that enhance summer recreation also mean that less flood-storage space is available.

In the winter, when more runoff reaches the river system, reservoir levels are kept lower so there’s room to store the water from heavy rains.