Upper Bear Creek Operating Guide

Chart

What is an operating guide?

TVA uses operating guides for each reservoir to make decisions about moving water through its dams. These guides are based on many decades of operating experience. They are built around the idea of allowing seasonal variations in the use of flood storage space.

Operating guides take into consideration all the features that influence a reservoir’s ability to store and release water—the size and shape of the surrounding watershed, the reservoir’s surface area and the average rainfall and runoff—as well as historical demands for water use and flood storage space at different times of the year.

Observed midnight elevation

Observed midnight elevations are shown for two years: last year and the current year to date. These are the actual elevations of the reservoir immediately upstream of the dam, measured at midnight of each day. The previous night’s elevation is added to the graph by 6 a.m. the next morning.

Low notch

This is a small area cut out of the top of the spillway (a structure designed to discharge surplus water from a reservoir) that allows a small amount of water to flow over the spillway when the reservoir elevation reaches the notch.

Spillway crest

The spillway crest is the elevation at which water can flow across the entire spillway (a structure designed to discharge surplus water from a reservoir). For most of the year, Upper Bear Creek is self-regulated by the spillway crest at elevation 799. Pool levels vary depending on the amount of water flowing through the reservoir and over the spillway crest.

Caution

If you compare the operating guides for different reservoirs, please note that the scale for the vertical “Elevation” axis varies. To keep the size of the charts consistent, a larger scale is used for reservoirs that fluctuate significantly; a smaller scale is used for reservoirs that typically fluctuate only a few feet.